Citation: Prieto-González, P.;
Sedlacek, J. Effects of
Running-Speciﬁc Strength Training,
Endurance Training, and Concurrent
Training on Recreational Endurance
Athletes’ Performance and Selected
Anthropometric Parameters. Int. J.
Environ. Res. Public Health 2022, 19,
10773. https://doi.org/10.3390/
ijerph191710773
Academic Editors: Jesús Siquier Coll,
Ignacio Bartolomé and María
Concepción Robles-Gil
Received: 29 June 2022
Accepted: 26 August 2022
Published: 29 August 2022
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International  Journal  of
Environmental Research
and Public Health
Article
Effects of Running-Speciﬁc Strength Training, Endurance
Training, and Concurrent Training on Recreational Endurance
Athletes’ Performance and Selected Anthropometric Parameters
Pablo Prieto-González 1,*
and Jaromir Sedlacek 2
1
Health and Physical Education Department, Prince Sultan University, Riyadh 11586, Saudi Arabia
2
Department of Sport Kinanthropology, Faculty of Sports, University of Prešov, 080 01 Prešov, Slovakia
*
Correspondence: pprieto@psu.edu.sa
Abstract: Objective: The present study aimed to verify the effects of running-speciﬁc strength
training alone, endurance training alone, and concurrent training on recreational endurance athletes’
performance and selected anthropometric parameters. Method: Thirty male recreational endurance
runners were randomly assigned using a blocking technique to either a running-speciﬁc strength
training group (RSSTG), an endurance training group (ETG), or a concurrent training group (CTG).
RSSTG performed three strength-training sessions per week orientated to running, ETG underwent
three endurance sessions per week, and CTG underwent a 3-day-per-week concurrent training
program performed on non-consecutive days, alternating the strength and endurance training
sessions applied to RSSTG and ETG. The training protocol lasted 12 weeks and was designed using
the ATR (Accumulation, Transmutation, Realization) block periodization system. The following
assessments were conducted before and after the training protocol: body mass (BM), body mass
index (BMI), body fat percentage (BFP), lean mass (LM), countermovement jump (CMJ), 1RM (one-
repetition maximum) squat, running economy at 12 and 14 km/h (RE12 and RE14), maximum oxygen
consumption (VO2max), and anaerobic threshold (AnT). Results: RSSTG signiﬁcantly improved the
results in CMJ, 1RM squat, RE12, and RE14. ETG signiﬁcantly improved in RE12, RE14, VO2max,
and AnT. Finally, CTG, obtained signiﬁcant improvements in BFP, LM, CMJ, 1RM squat, RE12,
RE14, VO2max, and AnT. RSSTG obtained improvements signiﬁcantly higher than ETG in CMJ,
1RM squat, and RE14. ETG results were signiﬁcantly better than those attained by RSSTG in AnT.
Moreover, CTG marks were signiﬁcantly higher than those obtained by ETG in CMJ and RE14.
Conclusion: Performing a 12-week concurrent training program integrated into the ATR periodization
system effectively improves body composition and performance variables that can be obtained with
exclusive running-speciﬁc strength and endurance training in recreational runners aged 30 to 40.
Running-speciﬁc strength training enhances maximum and explosive strength and RE, whereas
exclusive endurance training improves VO2max, AnT, and RE. Performing concurrent training on
non-consecutive days effectively prevents the strength and endurance adaptations attained with
single-mode exercise from being attenuated. The ATR periodization system is useful in improving
recreational endurance athletes’ performance parameters, especially when performing concurrent
training programs.
Keywords: concurrent training; endurance training; running-speciﬁc strength training; periodization;
recreational runner
1. Introduction
Several sports require an adequate levels of strength and endurance to perform at
optimum level in competitive events. However, successfully combining endurance and
strength training represents the highest complexity in exercise prescription [1]. It has often
Int. J. Environ. Res. Public Health 2022, 19, 10773. https://doi.org/10.3390/ijerph191710773
https://www.mdpi.com/journal/ijerph
Int. J. Environ. Res. Public Health 2022, 19, 10773
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been speculated that concurrent training does not generate the same adaptations as single-
mode exercise [1]. Even so, the possible mechanisms whereby concurrent training of both
ﬁtness components can attenuate strength and endurance adaptations remain unclear [2].
In endurance sports, it has traditionally been thought that cardiovascular capacity is
the main limiting factor in sports performance [3]. Therefore, maximum oxygen consump-
tion (VO2max) and anaerobic threshold (AnT) have been considered the best indicators to
predict athletes’ performance [4]. Nevertheless, in reality, endurance athletes with similar
VO2max may perform differently in sports competitions. Hence, VO2max could not be the
best indicator to predict their racing performance. Nowadays, running economy (RE) and
the evaluations that imply assessing the muscular power exerted or the speed reached by
an athlete during the VO2max are considered better sports performance indicators [5–7]. In
this way, speciﬁc scientiﬁc evidence indicates that combining endurance and strength train-
ing generates additional beneﬁts in terms of athletic performance improvement and injury
prevention [8]. These improvements could be related to the following mechanisms [8–13]:
(a)
Musculotendinous factors: Improved muscle-tendinous stiffness and stretch-shortening
cycle properties, conversion of fast-twitch type IIx into more fatigue-resistant type IIa
ﬁbers, and delayed activation of less-efﬁcient type II ﬁbers.
(b)
Neuromuscular factors: Improved neuromuscular function and efﬁciency, improved
intramuscular coordination, motor unit recruitment, and ﬁring frequency.
(c)
Physical ﬁtness components: Improved levels of strength. This allows athletes to
apply a lower relative percentage of force, which reduces the contribution of the
anaerobic energy system and results in reduced fatigue, maintenance of the required
application of strength over a longer period, or appliance of more strength per unit
of time. Additionally, peak velocity, speed, maximum aerobic speed, and anaerobic
capacity are enhanced.
All these enhancements would result in an improved RE.
Nevertheless, there are arguments against using concurrent training programs in
endurance runners. Vikmoen et al. (2016) and Berryman et al. (2018) [14,15] state that
sports requiring high strength levels are opposite in nature to endurance sports in terms of
energy metabolism and effort duration. Therefore, developing both ﬁtness components
simultaneously would result in potential combative adaptations [14–16]. Actually, the main
adaptations produced by endurance and strength training are not only different but also
opposed: Endurance training adaptations include oxidative enzyme activity increment,
mitochondrial and capillary density increment, maintenance or reduction of ﬁber size, and
possibly also ﬁber type transformations (Type II into I), modifying the model of recruitment
and reducing the muscle contractile capacity [17]. In contrast, strength training is associated
with reduced capillary density, oxidative enzymes, and mitochondrial density, reducing
the oxidative muscle capacity [10,15].
In this regard, some studies have revealed a certain degree of incompatibility between
endurance and strength training [9,18,19]. Thus, maximum voluntary contraction, rate of
force development and some adaptations such as maximal strength and VO2max can be
attenuated [20]. Similarly, time to exhaustion and mitochondrial density can be reduced [14].
This phenomenon is known as the interference effect or concurrent training effect [11], and
the potential interferences can be chronic and acute [2,11].
The reasons why the interference effect occurs are [1,2,11] the mechanism of muscle
ﬁber recruitment used, the transformation of fast twitch muscle ﬁbers into slow twitch
muscle ﬁbers, and the functioning of the endocrine system. From the molecular point of
view, the simultaneous activation of cellular biomarkers that elicit optimal anabolic and
endurance responses is also not possible [11]. Moreover, muscle hypertrophy implies the
cross-sectional area increment of muscle ﬁbers, which may increase the distance between
the capillaries inside the muscle and could negatively impact performance. Even so, in
untrained individuals, there is an increase in (or at least a maintenance of) the number
of capillaries surrounding each muscle ﬁber, and the capillaries per ﬁber area do not
experience modiﬁcations. However, since performing concurrent strength and endurance
Int. J. Environ. Res. Public Health 2022, 19, 10773
3 of 17
training can mitigate the hypertrophic response, and endurance-trained athletes have a
greater number of capillaries than untrained athletes, these ﬁndings may not apply to
experienced endurance athletes [14].
In line with the existence of arguments for and against the use of concurrent train-
ing, some studies have found improvements in sports performance after using strength
training in endurance athletes [6,11], whereas no beneﬁcial effect was observed in other
research [14,21]. The discrepancies between studies may be due to the development of
different types of strength, external variables not directly related to the intervention, the
use of different training methods [12,22], or the application of training methods lacking
scientiﬁc rigor [23].
As a result, it is essential to continue searching for better strategies to improve athletic
performance by implementing strength training sessions on endurance training programs
and preventing the interference between both ﬁtness components [11,16]. Future studies
should focus on minimizing the interference effect when concurrent training is applied,
and training load organization, type, order, and optimal application are crucial to attain
this goal. Further research is also needed to understand better the relationship between
strength training, anaerobic metabolism, and endurance sports performance. New studies
must be longer in duration, since the greatest increases in RE occur after implementing
training protocols of more than 24 sessions, and most of the existing studies are shorter [15].
Moreover, valid strength assessments through a range of different velocities must be used,
implementing adequate strength training programs over a long-term intervention period,
and using multi-joint strength, explosive-strength, or reactive-strength exercises due to
their superior functionally [6].
Future studies must also integrate the intervention design into a suitable periodization
system and apply sports training principles to synchronize all training contents [20]. In this
respect, to the best of our knowledge, at present, only one investigation has been conducted
to verify the effect of strength training on endurance runners by using a periodization
system [21]. Additionally, athletes’ training programs must be adapted to their personal
needs and abilities. Thus, according to the law of diminishing returns, individuals’ ability
to attain speciﬁc adaptations will depend on their training level. Less-trained subjects are
likely to obtain greater adaptations since they have a greater adaptation reserve. In contrast,
well-trained individuals need more demanding training stimuli to attain improvements
throughout the training process [22].
Importantly, most existing studies related to concurrent training have focused on
verifying the compatibility of simultaneous strength and endurance training. However,
very few of them have examined the inﬂuence of strength, and particularly of running-
speciﬁc strength training, on endurance performance [24]. Most studies examined the
interference of endurance on maximal strength and hypertrophy, but not the opposite [11].
In this context, the utility of strength training remains to be clariﬁed for endurance athletes,
and research ﬁndings are often inconclusive [22]. For this reason, it is necessary to continue
investigating this topic [17]. In fact, sports scientists have studied new ways to enhance
biomechanics, technique, energy production, sports equipment, injury prevention, and
recovery. However, concurrent training and the effect of strength training in endurance
athletes is a very complex phenomenon that requires new research.
2. Objective
The main objective of the present study was to verify the effect of running-speciﬁc
strength training, endurance training alone, and concurrent training on physiological
performance and selected anthropometric variables in recreational runners. We also aimed
to ascertain if 3-day-per-week concurrent training performed on non-consecutive days
attenuates the strength, endurance, and anthropometric adaptations compared to strength
and endurance training in isolation.
Int. J. Environ. Res. Public Health 2022, 19, 10773
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3. Materials and Methods
A quasi-experimental randomized study was conducted.
3.1. Subjects
Thirty male recreational endurance runners participated in the present research. They
were assigned into three different groups: a running-speciﬁc strength training group
(RSSTG) [age: 34.7 (2.36); height: 1.77 (0.04); weight: 67.05 (5.37); BMI: 21.27 (1.87)], an
endurance training group (ETG) [age: 35.1 (2.77); height: 1.78 (0.05); weight: 65.80 (4.38);
BMI: 20.68 (1.31)], or a concurrent training group (CTG) [age: 34.3 (2.37); height: 1.76 (0.03);
weight: 66.96 (4.48); BMI: 21.48 (1.03)]. RSSTG performed thrice-per-week strength training
program orientated to running on non-consecutive days. ETG performed thrice-per-week
endurance training on non-consecutive days. Finally, CTG underwent 3-days-per-week
concurrent training performed on non-consecutive days. CTG alternated the running-
speciﬁc strength training sessions performed by RSSTG and the endurance training sessions
underwent by ETG. The inclusion criteria were (a) be an active recreational runner; (b) able
to run one km in less than 4:30 min; (c) have practiced running at a recreational level for at
least the past ﬁve years before participating in the current research; (d) perform endurance
training regularly, with a weekly frequency of not less than three times a week, but no more
than ﬁve times a week; (e) have not performed endurance or strength systematic training
for the last year leading up to the research’s commencement; (f) non-smoker; (g) do not use
nutritional supplementation; (h) do not suffer from chronic diseases or ongoing injuries;
(i) aged between 30 and 40 years old.
Participants were asked not to modify their dietary habits or lifestyle during the
intervention process, and attendance was recorded. Subjects were required to attend
at least 90% of the training sessions to be included in the study. Similarly, participants
were informed that they could voluntarily withdraw from the study at any time. The
research was conducted according to the ethical principles of the Declaration of Helsinki. It
was approved by the Ethics Commission of Prešov University (Prešov, Slovakia) (ethical
clearance number: 2/2021). Similarly, all subjects who participated in this study were
required to submit written informed consent. Previously, they received a verbal and
written explanation about the experimental design and the potential risks and beneﬁts of
participating in this research.
3.2. Randomization
A blocking design was used to avoid any possible bias when the subjects were allocated
into three different experimental groups and to ensure the trial’s proper randomization.
The blocking factor was the VO2max value obtained through the incremental load test.
According to the results obtained in this test, participants were allocated to one of the ten
blocks created. Athletes who obtained the best three marks were assigned to block one.
Athletes who obtained the fourth, ﬁfth, and sixth-best marks were assigned to block two,
and so on. Afterward, each block’s three members were randomly assigned to one of the
three different experimental groups. Therefore, there was one member of each block in
each experimental group.
3.3. Training Protocol
The intervention lasted 12 weeks, and study participants performed three sessions
per week on non-consecutive days. The training protocol was designed using the ATR
block periodization system. The training intervention was divided into three mesocycles:
accumulation (ﬁrst six weeks), transmutation (from week seven to week 10), and realization
(weeks 11 and 12). The duration of the training protocol was the minimum necessary to
attain the planned adaptations in accordance with the abilities developed in each mesocycle,
the sports discipline, and the characteristics of the athletes. The training methods applied
to RSSTG are shown in Table 1, and the training methods that ETG underwent are shown
in Table 2.
Int. J. Environ. Res. Public Health 2022, 19, 10773
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Table 1. Training methodology that will be used with RSSTG.
Week
Training Parameters
1
I: 64% 1RM; S: 4; R: 14; RT: 2”; Ex: Squat, leg curl, calf raise
2
I: 69% 1RM; S: 4; R: 12; RT: 2′; Ex: Squat, leg curl, calf raise
3
I: 69% 1RM; S: 5; R: 12; RTS: 2′; Ex: Squat, leg curl, calf raise
4
I: 69%–69%–75%–75%–80% 1RM; S: 5; R: 12-12-10-10-8; RTS: 3′; Ex: Squat, leg curl,
calf raise
5
I: 69%–75%–80%–85% 1RM; S: 4; R: 12-10-8-6; RTS: 3′; Ex: Squat, leg curl, calf raise
6
I: 80% 1RM; S: 4; R: 8; RTS: 3′; Ex: Squat, leg curl, calf raise
7
6S of: Squat (6R at 80% 1RM) + hurdle hops (10R) + 2′30′′ running at 100% of MAS;
RTS: 5′
8
6S of: Squat (5R at 82% 1RM) + hurdle hops (10R) + 2′30′′ running at 100% of MAS;
RTS: 5′
9
6S of: Squat (4R at 84% 1RM) + extended bounds (cover 50 m alternating legs by doing
the lowest possible number of strides) + 2′15′′ running at 105% of MAS; RTS: 5′
10
6S of: = Squat (3R at 86% 1RM) + extended bounds (cover 50 m alternating legs by
doing the lowest possible number of strides) + 2′ running at 110% of MAS; RTS: 5′
11
Uphill running. Di: 200 m; I: 115% of MAS; Incl: 6%; S: 3; R: 5; RTR: 3′; RTS: 10′
12
Uphill running. Di: 200 m; I: 120% of MAS; Incl: 6%; S: 2; R: 5; RTR: 3′; RTS: 10′
I: intensity; S: sets; R: repetitions; RTS: resting time between sets; RTR: resting time between reps; 1RM: one-
repetition maximum; MAS: maximum aerobic speed; Di: distance; Incl: inclination.
Table 2. Training methodology that will be used with ETG.
Week
Training Parameters
1
Fartlek training. Du: 50′; I: 117–162 b.p.m.
2
Fartlek training. Du: 55′; I: 117–162 b.p.m.
3
Fartlek training. Du: 60′; I: 117–162 b.p.m.
4
Continuous training; Du: 55′; I: 135–139 b.p.m.
5
Continuous training; Du: 50′; I: 139–144 b.p.m.
6
Continuous training; Du: 45′; I: 144–149 b.p.m.
7
Extensive interval training (long intervals); I: 159–162 b.p.m.; 10S of 3′; RT: 2′
8
Extensive interval training (long intervals); I: 162–165 b.p.m.; 10S of 2′30′′; RT: 2′
9
Extensive interval training (medium intervals). I: 165–168 b.p.m.; 14S of 1′30′′; RT: 2′
10
Extensive interval training (medium intervals). I: 168–171 b.p.m.; 16S of 1′; RT: 2′
11
Repetition training. I: 180 b.p.m.; 5R of 3′. RT: 8′
12
Competition method. I: 100% of competition running pace; 1R; Di: 3.5 km
Du: duration; I: intensity; R: repetitions; RT: resting time; b.p.m.: beats per minute; Di: distance.
Likewise, CTG underwent 3-day-per-week concurrent training performed on non-
consecutive days, alternating the strength and endurance sessions carried out by RSSTG
and ETG. All training sessions were supervised by the same researcher: a One Physical
Education Bachelor’s Degree holder, expert in sports training, and with more than 20 years
of working experience in the sports ﬁeld. Likewise, all training sessions were conducted in
the same ﬁtness center to minimize external variables’ inﬂuence avoid compromising the
results’ validity and.
Int. J. Environ. Res. Public Health 2022, 19, 10773
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3.4. Assessments
Physiological and selected anthropometric parameters were measured before (pre-
test) and after (post-test) applying the 12-week training protocol. The assessments were
conducted after a rest period of 48 h, between 5:00 p.m. and 7:00 p.m. The study participants
were asked to refrain from ingesting food or beverages three hours before testing. To avoid
the learning effect, a theoretical–practical training session was conducted one week before
the pre-test. The main researcher explained the testing protocols in detail. Thereupon, the
participants practiced the proper technique of execution of all tests to verify the correct
functioning of the equipment and procedures used in the assessment. The following
two-phase warm-up was performed before conducting the physical and physiological tests:
General warm-up: 10 min running at 60% of their theoretical maximum heart rate plus ﬁve
minutes of joint mobilization exercises. Speciﬁc warm-up: 2 × 10 vertical jumps, three sets
of squats (10 reps at 50% of their estimated 1RM, ﬁve reps at their estimated 70% 1RM, and
three reps at their estimated 80% 1RM), and one set of 20 m acceleration. The theoretical
1RM was estimated based on the information collected during the theoretical–practical
training session conducted one week before the pre-test. In addition, the subject’s BM, age,
and strength training experience were also taken into account.
Assessments included in the pre-test and post-test are detailed below:
•
Body mass (BM) and body mass index (BMI): Both were measured using a Seca digital
column scale, model 769 (Hamburg, Germany). Height was measured to the nearest
0.1 cm and body mass to the nearest 0.1 kg. Body mass and body mass index were
assessed by the same investigator, and the subjects were in bare feet.
•
Body fat percentage (BFP): BFP was obtained through the following equation [25]:
BFP = [(Σ of abdominal, subscapular, triceps, suprailiac, abdominal, thigh, calf)0.143]
+ 4.56. The plicometer used to measure the fat folds was a Harpenden Skinfold Caliper,
model FG1056 (Sussex, UK).
•
Lean mass (LM): LM was calculated by using the following formula: LM = Body Mass (kg)
− (Fat Mass (Kg) × BFP).
•
Countermovement jump (CMJ): CMJ was used to assess jumping ability and lower
body power due to its high reliability and validity [26]. The test was performed in
one indoor gymnasium on a dry and non-slippery surface. The device used was an
Optojump-next (Bolzano, Italy) connected to one laptop via USB, and the Microgate
software (Optojump software, version 3.01.0001) was also utilized. Participants were
not allowed to use the arm swing. Instead, they were required to keep their hands on
their hips while performing the test. The test started with a quick countermovement
action. When the knees were bent 90◦, athletes initiated the take-off and ﬂight. During
the ﬂight, they had to maintain their hips, knees, and ankles extended. Participants
were also required to jump vertically. Movements forward, backward, or sideways
were not allowed [27]. Each subject had two attempts, with three minutes rest between
each jump.
•
One-repetition maximum (1RM) squat: This test was used to measure lower body
maximum strength due to its validity, reliability, and applicability [28,29]. To conduct
the test properly, participants kept their trunks naturally upright. The bar was grasped
ﬁrmly with both hands, and it was also supported on the shoulders. The test started
with knees bent at 90◦ until the performer’s thighs were parallel with the ground.
Then, subjects regained the upright position, with the legs fully extended. The number
of attempts required to determine the 1RM of each subject was between two and four.
Only the attempts correctly performed were registered. The resting time between
attempts was three minutes.
•
Incremental load test: This laboratory test was used to assess the Anaerobic Threshold
(AnT), maximal oxygen consumption (VO2max), and running economy (RE). The
following protocols were implemented:
–
Protocol I: The objective was to determine the RE by using one treadmill (Cy-
bex 625T, Rosemont, IL, USA), one metabolic gas analyzer (Cosmed Srl, Albano
Int. J. Environ. Res. Public Health 2022, 19, 10773
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Laziale, Rome, Italy), and one heart rate monitor (Polar H9 BLE Kempele, Finland).
The protocol comprised an 8 min submaximal test consisting of two, four-minute
stages. That is to say, each stage was four minutes in length to allow for oxy-
gen consumption and steady-state heart rate. The ﬁrst stage was performed at
12 km/h, and the second at 14 km/h. These two speeds are within the intensity
range established by Barnes and Kilding (2015) to measure RE in recreational
athletes [30]. Then, to determine the RE values, the VO2 mean value of the last
minute of each stage was recorded [31].
–
Protocol II: This test was used to estimate the VO2max and AnT. The treadmill’s
initial velocity was set at 2 km/h slower than the subjects’ estimated 4 mmol
when the test started. Then, the speed was increased by 0.5 km/h every 30 s until
exhaustion [32].
3.5. Statistical Analysis
Data is presented using the format mean SD (standard deviation). The Shapiro–Wilk
test was used to contrast the normality of the variables and Levene’s test to verify the
homogeneity of variances. Sphericity assumptions were assessed using Mauchly’s test.
When those sphericity assumptions were violated, the Greenhouse Gessier correction was
applied. To determine the concordance between the pre-test and post-test measurements,
the interclass correlation coefﬁcient (ICC) was calculated for all the assessed anthropometric
and performance parameters. ICC values were interpreted as follows: ICC ≤ 0.49, poor;
0.50 ≤ ICC < 0.75, moderate; 0.75 ≤ ICC < 0.9, good; ICC ≥ 0.9, excellent [33]. To verify
whether there were differences between groups in the baseline, a one-way ANOVA (analysis
of variance) test was conducted. To assess the training effects between groups (ETG vs.
RSSTG vs. CTG) and within groups (pre-test vs. post-test) on the anthropometric and
performance variables, a two-way repeated-measure ANOVA was performed. When
statistically signiﬁcant p values were found (group by time interaction effect or signiﬁcant
main effects of time or group), a post hoc pairwise comparison was conducted with
Bonferroni correction to identify those differences. The effect size was calculated using
Cohen’s d. Values of d < 0.2, d = 0.2, d = 0.5, and d = 0.8 were considered as trivial, small,
medium, and large effect sizes, respectively [34]. The level of signiﬁcance established was
p < 0.05. The statistical analysis of the data was performed using the program IBM SPSS
V.26® computing (IBM Corp., Armonk, NY, USA).
4. Results
Once the normality and homoscedasticity of the data were veriﬁed, the one-way
ANOVA conﬁrmed the absence of signiﬁcant differences between the three experimental
groups at the baseline for all the anthropometric and performance variables. Likewise, the
ICC values obtained between the pre-test and the post-test in all assessed parameters were
higher than 0.9 for the three groups, which indicates an excellent reliability. Then, the two-
way repeated-measure ANOVA showed that there was no interaction effect, main effect of
time, or group for BM and BMI (see Table 3). Furthermore, the two-way repeated-measure
ANOVA revealed the existence of a group-by-time interaction effect for CMJ, 1RM squat,
RE12, RE14, VO2max, and AnT. A main effect of time was observed for the BFP, LM, CMJ,
1RM squat, RE12, RE14, VO2max, and AnT. Finally, a main effect of group was found for
CMJ and RE14 (see Table 3).
Subsequently, the Bonferroni post hoc comparison showed that ST obtained im-
provements signiﬁcantly higher than ET enhancements in the following variables: CMJ
(p = 0.003; CI95 = 1.81–7.51), 1RM squat (p = 0.035; CI95 = 1.33–9.86), and RE14 (p = 0.046;
CI95 = 46.69–5036.38). ET results were signiﬁcantly better than those obtained by ST in AnT
(p = 0.04; CI95 = 0.04–1.95). Finally, the improvements obtained by CT were signiﬁcantly
higher than those attained by ET in CMJ (p = 0.002; CI95 = 1.21–4.26), and RE14 (p = 0.046;
IC95 = 47.47–5035.51).
Int. J. Environ. Res. Public Health 2022, 19, 10773
8 of 17
Table 3. Between-subjects comparisons of all the variables assessed: main effect of time, main effect
of group, and interaction effect.
Variable
Main Effect of Time
Main Effect of Group
Group per Time
Interaction Effect
F (1–9)
p
F (2–18)
p
F (2–18)
p
BM
0.31
0.591
0.24
0.785
0.55
0.584
BMI
0.30
0.596
0.86
0.440
0.47
0.632
BFP
13.24
0.005 *
0.42
0.662
3.92
0.055
LM
4.35
0.006 *
0.25
0.780
0.92
0.413
CMJ
42.93
<0.001*
7.48
0.004 *
18.62
<0.001 *
1RMsquat
216.38
<0.001 *
1.92
0.175
27.62
<0.001 *
RE12
194.51
<0.001 *
0.127
0.882
23.08
<0.001 *
RE14
85.14
<0.001 *
20.86
<0.001 *
23.95
<0.001 *
VO2max
52.59
<0.001 *
0.12
0.891
8,72
0.002 *
AnT
109.84
<0.001 *
1.39
0.275
37.31
<0.001 *
Legend: BM: Body mass; BMI: Body mass index; BFP: Body fat percentage; LM: Lean mass; CMJ: Counter-
movement jump; 1RM squat: One-repetition maximum squat; AnT: Anaerobic threshold; VO2max: Maximum
oxygen consumption; RE: Running economy; p: Level of statistical signiﬁcance; F: Variation between sample
means/variation within the samples; *: Signiﬁcant improvement between the pre-test and post-test.
As for the within-subject comparisons (see Table 4), RSSTG signiﬁcantly improved
between the pre- and post-tests in CMJ (p < 0.001; IC95 = 3.42–4.13), 1RM squat (p < 0.001;
IC = 5.66–8.73), RE12 (p < 0.001; 5.66–8.73) and RE14 (p = 0.007; F: 0.23–1.11). The effect
size of these improvements was small in the case of RE12 and RE14, and large for CMJ and
1RM squat. ETG signiﬁcantly improved between the pre- and post-tests in the following
parameters: RE12 (p < 0.001; IC95 = 1.93–2.59), RE14 (p = 0.015; F = 620.65–4464.61), VO2max
(p < 0.001; CI95 = 0.51–0.77), and AnT (p < 0.001; CI95 = 262–738). The effect size of these
improvements was small in the case of RE14, medium for VO2max, and large for RE12
and AnT. Additionally, CTG signiﬁcantly improved its results between the pre- and the
post-tests in the following variables: BFP (p < 0.001; CI95 = 0.354–0.590), LM (p = 0.035;
CI95 = 0.5–1.12), CMJ (p < 0.001; CI95 = 1.72–2.47), 1RM squat (p < 0.001; CI95 = 3.10–4.10),
RE12 (p = 0.035; CI95 = 1.62–2.56), RE14 (p < 0.001; CI95 = 0.80–1.84), VO2max (p < 0.001;
CI95 = 1.57–3.02), and AnT (p < 0.001; 0.84–1.15). The effect size of these improvements was
small in the case of RE14, medium for BFP and RE12, and large for the CMJ, 1RM squat,
and AnT variables.
Table 4. Results obtained by the three experimental groups in the pre- and post-test in all the
variables assessed.
Variable
Group
Pre-Test
Post-Test
Cohen’s d
p
X
SD
X
SD
BM
RSSTG
67.11
5.37
67.49
5.32
0.076
0.159
ETG
65.80
4.38
65.62
4.30
0.037
0.330
CTG
66.96
4.48
67.10
4.31
0.066
0.172
BMI
RSSTG
21.27
1.87
21.38
1.76
0.066
0.190
ETG
20.68
1.31
20.63
1.34
0.051
0.645
CTG
21.47
1.03
21.52
1.08
0.098
0.171
BFP
RSSTG
15.28
1.03
15.04
1.16
0.199
0.152
ETG
15.09
0.95
14.86
0.87
0.233
0.051
CTG
15.18
1.07
14.32
1.15
0.721
<0.001 *
LM
RSSTG
56.77
4.58
57.31
4.71
0.115
0.110
ETG
55.84
3.59
55.81
3.73
0.006
0.108
CTG
56.73
4.29
57.50
4.21
0.141
0.018 *
Int. J. Environ. Res. Public Health 2022, 19, 10773
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Table 4. Cont.
Variable
Group
Pre-Test
Post-Test
Cohen’s d
p
X
SD
X
SD
CMJ
RSSTG
33.29
1.71
37.07
1.81
2.141
<0.001 *
ETG
32.86
1.73
32.42
2.33
0.210
0.446
CTG
33.06
1.41
35.16
1.29
1.551
<0.001 *
1RM squat
RSSTG
83.10
4.51
90.30
4.57
1.571
<0.001 *
ETG
83.61
2.27
84.71
3.37
0.348
0.168
CTG
82.70
2.75
86.30
2.66
1.321
<0.001 *
RE12
RSSTG
41.63
3.07
42.41
3.01
0.272
<0.001 *
ETG
40.49
2.65
42.76
2.75
0.838
<0.001 *
CTG
41.61
3.08
42.55
2.71
0.783
<0.001 *
RE14
RSSTG
49.44
3.41
50.28
3.17
0.253
<0.001 *
ETG
48.92
3.13
50.08
3.33
0.346
<0.001 *
CTG
48.58
3.12
50.18
3.01
0.431
<0.001 *
VO2max
RSSTG
60.29
4.18
60.91
4.51
0.138
0.097
ETG
59.02
3.01
60.91
4.27
0.581
<0.001 *
CTG
58.67
3.25
60.98
3.36
0.207
<0.001 *
AnT
RSSTG
14.95
0.68
15.05
0.83
0.131
0.172
ETG
14.90
0.51
16.05
0.83
0.845
<0.001 *
CTG
14.65
0.58
15.70
0.42
2.749
<0.001 *
Legend: BM: body mass; BMI: body mass index; BFP: body fat percentage; LM: lean mass; CMJ: countermovement
jump; 1RM squat: one-repetition maximum squat; AnT: anaerobic threshold; VO2max: maximum oxygen
consumption; RE: running economy; p: level of statistical signiﬁcance; *: signiﬁcant improvement between the
pre-test and post-test.
5. Discussion
5.1. Anthropometric Parameters
None of the three experimental groups presented modiﬁcations to their BM in the
present study. Furthermore, the effect sizes of the modiﬁcations produced in this parameter
between the baseline and the post-test were trivial in all three cases. These results are
consistent with previous recent studies [12,32,35]. Thus, on the one hand, it can be expected
that the exclusive practice of endurance training may promote muscular catabolism and
increase mitochondrial density and activity. Therefore, these adaptations could reduce body
mass and body fat percentage [36]. On the other hand, strength training can potentially
increase lean tissue by increasing the release of anabolic hormones such as testosterone and
growth hormone [37,38]. However, in the present study, we understand that the absence of
signiﬁcant modiﬁcations in BM may be due to the following reasons: Firstly, the duration
of the intervention period (12 weeks) could not be long enough to generate signiﬁcant
variations in this parameter. Secondly, in RSSTG and CTG, the potential or expected
decrease in BM of the participants derived from the slight reduction in fat mass has been
hindered by the slight increase in LM. Thus, the net result would be a non-signiﬁcant
alteration of athletes’ BM. Likewise, since the study participants were recreational athletes
who perform endurance training sessions regularly, to be able to attain signiﬁcant decreases
in their body weight, it is plausible that they require not only more extended intervention
periods, but also signiﬁcant increases in their weekly training frequency, volume, density,
and intensity.
Regarding ETG, the absence of a signiﬁcant weight reduction might be related to the
participants’ regular practice of endurance training. Therefore, this group may need more
intense or prolonged workouts to signiﬁcantly decreases BM. Importantly, there was no
increase in lean tissue in ETG but a slight reduction. This means that the slight decrease in
lean tissue of the participants included in this group, together with their slight reduction in
BFP, was of such small magnitude that it did not cause a signiﬁcant reduction in BM. This
is in line with the trivial effect sizes observed in ETG in its reduction of BFP and LM.
Int. J. Environ. Res. Public Health 2022, 19, 10773
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As for the BMI, there were no signiﬁcant variations in any of the three experimental
groups. In the case of RSSTG and CTG, a certain increase in their BMI might be expected
due to the strength training practice and its potential anabolic effect. However, the effect
size of the BMI increase in both groups was trivial. These results are somewhat surprising,
since none of the study participants had previous experience in strength training. Moreover,
it must be taken into account that, although the objective of the strength training protocol
used in the present research was not designed to produce muscle hypertrophy (see Table 1),
strength training is likely to generate certain amount of hypertrophy, particularly in subjects
without previous strength training experience [39]. These results are more surprising in the
case of RSSTG, since they did not perform endurance training. Thus, the trivial increase
in RSSTG suggests that for strength training to generate signiﬁcant increases in BMI, it is
necessary to use training methods speciﬁcally aimed at achieving this goal and, probably, a
longer intervention period. In ETG, as expected, the BMI did not increase but decreased.
However, the reduction was trivial. We understand this slight decrease is in line with
the training principle of speciﬁcity since endurance training is more likely to generate
reductions in BM and BMI rather than increases [36].
As far as the BFP is concerned, signiﬁcant reductions were only observed in CTG.
These results coincide with the study carried out by Eklund et al. (2016) [40]. In con-
trast, the BFP remained unaffected in some studies after applying a concurrent training
protocol [12,32]. Furthermore, Blagrove et al. (2018c) conducted a systematic review to ana-
lyze the effects of adding strength training to the endurance training programs of medium-
and long-distance athletes. They observed that BFP is commonly unaffected [41]. In the
present study, we understand that only CTG signiﬁcantly improved its BFP due to the
strength and endurance training combination. This could be because strength training can
increase basal metabolism [39,42], and endurance training may produce a signiﬁcant caloric
expenditure [39,42,43]. Regarding ETG, despite the fact that endurance training effectively
reduced BFP in some previous studies [38,44], we understand that subjects included in this
group did not improve their BFP due to the absence of strength training, which implied
that they could not beneﬁt from its potential capacity to increase basal metabolism. On
the contrary, we interpret that RSSTG could not signiﬁcantly decrease their BFP since
they did not practice endurance training and could not beneﬁt from the signiﬁcant caloric
expenditure that endurance training produces.
Concerning the LM, only CTG signiﬁcantly increased this parameter after undertaking
the 12-week-training protocol. This increase could be related to the following reasons. First,
a greater training variability was applied to this group. Second, only CTG signiﬁcantly
decreased BFP. Therefore, even though CTG and RSSTG reduced their LM in absolute terms
at similar levels and with similar effect sizes, the increase in CTG in relative terms was
higher due to its greater reduction in BFP. Third, according to Coffey and Hawley (2017) and
Fyfe and Loenneke (2018), the practice of divergent exercise (i.e., strength and endurance) by
untrained or recreationally active individuals induced similar increased anabolic signaling
in skeletal muscle during the ﬁrst weeks of training [1,22]. Not surprisingly, ETG did not
increase the LM. Unlike CTG and RSSTG, this group decreased its LM, but not signiﬁcantly.
We consider that this could be related to the potential catabolic effect of aerobic exercise [36].
The LM results of the present study are consistent with those attained by Eklund et al. (2016)
and Vikmoen et al. (2020) [40,45]. However, our results only partially coincide with those
obtained by Vikmoen et al. (2017) since they observed that both concurrent strength–
endurance training and running-speciﬁc strength training are useful for increasing LM [46].
Furthermore, Beattie et al. (2017) did not observe any changes in LM in competitive distance
runners, probably because it is more difﬁcult for well-trained subjects to attain adaptations
due to their lower reserve of adaptation [32].
5.2. Performance Variables
As expected, ETG did not improve the results in CMJ. This conﬁrms that endurance
training does not signiﬁcantly modify the marks obtained by recreational endurance ath-
Int. J. Environ. Res. Public Health 2022, 19, 10773
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letes in CMJ. In contrast, RSSTG and CTG signiﬁcantly improved their performance in CMJ.
In the ﬁrst case, it was expected since RSSTG only performed running-speciﬁc strength
training sessions, and the subjects included in the present study had no previous strength
training experience. As for CTG, it has been veriﬁed that their improvements in CMJ
produced by the strength training performed were not attenuated despite the concomitant
strength and endurance training. Additionally, RSSTG and CTG obtained signiﬁcantly
better results than ETG in CMJ. This proves that the interference effect does not occur with
the weekly training frequency used in the training protocol. The results of the present study
are consistent with the ﬁndings obtained by Fyfe, Bishop and Stepto (2014) [47]. These
authors state that there is no evidence supporting the interference effect theory. In this
regard, Coffey and Hawley (2017) add that despite chronic studies indicating that there is
robust evidence supporting that endurance training attenuates strength adaptations when
concurrent training protocols are applied, the underlying mechanisms of the mentioned in-
terference are unknown. Nevertheless, some studies have veriﬁed that endurance training
attenuates improvements in power, speciﬁcally in CMJ when concurrent training protocols
are implemented [45,48].
As for 1RM squat, as expected, RSSTG and CTG improved their marks between pre-
and post-test, probably because the study participants had no previous strength training
experience. Only the marks obtained by RSSTG were signiﬁcantly higher than those
attained by ETG in the post-test. This could indicate that a higher frequency of strength
training provides additional beneﬁts, since the number of strength sessions performed by
RSSTG was higher than the sessions performed by CTG. However, we understand that
the interference effect did not occur in CTG, because no signiﬁcant differences between
RSSTG and CTG were observed in the post-test in 1RM squat. The present research results
are consistent with those obtained by Vikmoen et al. (2016), Vikmoen et al. (2017), and
Sousa et al. (2017) [14,46,49]. In all three cases, the utility of concurrent training to improve
the 1RM squat was veriﬁed.
As far as RE is concerned, the three groups signiﬁcantly improved this parameter at 12
and 14 km/h. The improvements obtained in RE14 by CTG and RSSTG were signiﬁcantly
higher than those achieved by ETG. In RSSTG, the improvements in RE could be related
to the attainment of certain adaptations [9,10,32,50]: (a) improved musculotendinous
stiffness of the lower extremities; (b) improved motor unit recruitment and synchronization
patterns; (c) improved intermuscular coordination and neural inhibition; (d) delayed
activation of less-efﬁcient type II muscle ﬁbers; (e) conversion of type IIx ﬁbers into fatigue-
resistant IIa ﬁbers; (f) facilitation of the optimal application of strength throughout the
entire training or competition; (g) reduction of the relative intensity that each particular
cycle of effort or sports technique represents for one athlete when overcoming the same
resistance; (g) improved ability to perform the same effort with lower oxygen consumption;
(h) improved ability to apply the same strength with less muscle mass; (i) improved reuse
of elastic energy in each stride. Therefore, attaining all of these physiological adaptations
could be the reason why RSSTG obtained signiﬁcant improvements over ETG in RE14.
Regarding the results obtained by ETG in RE12 and RE14, we interpreted that the
improvements were the result of attaining certain adaptations [51]: (a) improved oxidative
capacity, which in turn is associated with better mitochondrial functioning, and leads to
a reduction in the use of the oxygen required to perform submaximal intensity efforts;
(b) improved buffering capacity of the skeletal muscles and hematological system. As for
CTG, we considered they simultaneously beneﬁted from the adaptations that both strength
and endurance training provide to improve RE. This circumstance would explain why
CTG obtained signiﬁcantly better results than ETG in RE14. Likewise, it is also under-
standable that the results obtained by ETG were signiﬁcantly lower than those attained
by RSSTG and CTG in RE14 but not in RE12, since runners show greater RE values at
race pace [12]. In this regard, considering the characteristics of the athletes included in the
present research and their results in AnT (see Table 3), it is understood that their compe-
tition race velocity is close to 14 km/h. The results of the present research are consistent
Int. J. Environ. Res. Public Health 2022, 19, 10773
12 of 17
with the studies of Beattie et al. (2017), Blagrove et al. (2018b), Giovanelli et al. (2017), and
Li et al. (2019) [12,31,32,52]. In all four cases, the practice of concurrent training was effec-
tive in improving RE. Additionally, recent systematic reviews and meta-analyses conﬁrmed
the efﬁcacy of strength training in improving RE [6,15,41]. In contrast, some studies veriﬁed
that the implementation of concurrent training programs was not effective in enhancing
RE [14,53].
Regarding the VO2max, although the trainability of this variable could be conditioned
by genetic factors [54], ETG and CTG obtained signiﬁcant improvements. Therefore, it
can be assumed that these improvements are training-speciﬁc adaptations. Likewise,
the fact that the improvements attained by ETG were not signiﬁcantly higher than those
achieved by CTG suggests that no interference effect has occurred. The present study
results coincide with the research conducted by Patoz et al. (2021) [53]. However, in a
systematic review, Blagrove et al. (2018c) veriﬁed that VO2max is typically unaffected
after the application of concurrent training programs [41]. Therefore, the discrepancies
between studies could occur because the possibility of improving VO2max is genetically
conditioned [54]. Moreover, as expected, RSSTG did not improve the VO2max, probably
because this group did not perform endurance training sessions. In fact, few studies found
signiﬁcant improvements in VO2max after the exclusive practice of strength training. In
this regard, Ozaki et al. (2013) conducted a review study to verify the effects of strength
training on increasing VO2max, and in only three out of the 17 studies analyzed were
signiﬁcant improvements in VO2max registered. They also ascertained that the higher the
training level, the more difﬁcult it is to improve the VO2max [55].
Finally, regarding AnT, both ETG and CTG improved this variable. We understand
that this improvement resulted from the training methods speciﬁcally designed to enhance
the AnT (see Table 2). Likewise, the results attained by ETG were signiﬁcantly better than
those achieved by RSSTG. However, the absence of signiﬁcant differences between ETG
and CTG reveals that no interference effect has occurred in CTG. Furthermore, as expected,
RSSTG did not signiﬁcantly improve the AnT. In this case, we consider that the absence of
endurance training explains the non-achievement of signiﬁcant improvements. Moreover,
few studies have examined the effects on AnT. Ferrauti et al. (2010) veriﬁed the absence of
signiﬁcant differences in AnT between a concurrent and endurance training program in
isolation [35]. Likewise, Cragnulini (2016), after conducting one review article, concluded
that adding strength training to endurance athletes’ training programs does not have a
negative impact on AnT [17].
5.3. Overall Interpretation of the Results
The improvements attained by the three experimental groups are speciﬁc exercise
mode adaptations. Thus, RSSTG improved all strength parameters, ETG all the endurance
parameters, and CTG strength and endurance parameters, and only the concurrent training
program effectively improved body composition in 12 weeks. Additionally, the interference
effect did not occur for the strength, endurance, or anthropometric variables. This suggests
that the weekly frequency used in the training protocol of the present study prevents the
attenuation of adaptations in concurrent training protocols with respect to single-mode
strength or endurance exercise. In this regard, Pattison et al. (2020) point out that CMJ
is useful for analyzing the interference effect on neuromuscular improvements when
performing concurrent training programs [48], and the results obtained in the present
research by RSSTG in CMJ were not signiﬁcantly better than those attained by CTG.
Furthermore, based on the improvements attained by RSSTG and CTG in 1RM squat
and CMJ, and also considering the large effect sizes obtained by both groups, it can be
inferred that athletes without previous strength training experience can obtain signiﬁcant
improvements in key performance parameters due to their greater reserve of adaptation.
In this sense, Fyfe and Loenneke (2018) consider that untrained individuals have a greater
capacity to adapt to training stimuli than trained individuals, although their individual
genetic potential could also limit the possibility of obtaining improvements [22]. For this
Int. J. Environ. Res. Public Health 2022, 19, 10773
13 of 17
reason, Beattie et al. (2014) indicate that, for endurance athletes with lower levels of strength,
a general strength training program may be sufﬁcient to improve their maximum strength,
explosive strength, and reactive strength [6]. However, athletes with higher strength
levels should perform explosive and reactive strength training programs to improve their
performance [6,56].
It is also noteworthy that, based on the improvements achieved by the three experi-
mental groups after the 12-week training program, the ATR periodization system seems to
be adequate to improve the performance of recreational endurance runners, mainly when
concurrent training programs are applied. However, it is also possible that intervention
periods longer than 12 weeks can be required to attain signiﬁcant improvements in body
composition, mainly when a single-mode exercise is used. Regrettably, few studies used
concurrent training protocols integrated into periodization systems such as the ATR block
periodization system. In this regard, García-Manso et al. (2017) conducted one research
with recreational college-age subjects, using one block periodization for nine weeks. They
veriﬁed that concurrent and exclusive endurance training effectively improves sports
performance. However, no signiﬁcant differences were found between both training proto-
cols [21].
Importantly, we must mention future lines of research. Despite several studies exam-
ining concurrent training programs’ effects on endurance athletes, many aspects remain
unclear. This circumstance is further aggravated by the important methodological differ-
ences that exist between studies and their limitations. Thus, future studies might consider
the following aspects:
(a)
The use of concurrent training programs might be oriented to ensure that neuro-
muscular adaptations positively impact athlete’s biomechanical and performance
parameters [57].
(b)
It could be interesting to investigate the effect of different running volumes combined
with explosive strength training [58].
(c)
Since an eight-week concurrent training program could not be long enough to improve
certain performance variables [35], long-term intervention periods might be applied.
Li et al. (2019) propose the use of training protocols longer than 16 weeks [31], and
Beattie et al. (2014) longer than six months [6].
(d)
Although Berryman et al. (2018) found that the beneﬁcial effects of strength training
on endurance performance occur regardless of athletes’ level [15], some authors
propose conducting studies with different populations. Low et al. (2019) recommend
conducting research with women and people with different training status [59], and
Li et al. (2019) with groups of senior citizens and women [31].
(e)
Future training protocols might be integrated into periodization systems such as the
ATR model. In this vein, Berryman et al. (2018) point out that the use of periodization
strategies could help clarify the optimal moment to implement strength training
activities within the annual training plan [15].
(f)
Future studies might include training protocols combining different endurance train-
ing methods (i.e., fartlek, continuous training, interval training) [23].
(g)
Appropriate training methods and tests to develop and assess strength levels must be
used [6].
(h)
The number of strength training sessions per week might be between two and
three [41].
(i)
The training protocols used might be designed in accordance with the sports
training principles.
Finally, it is necessary to mention the study’s strengths and limitations. As for the
strengths, there are two noteworthy aspects. First, as well as including one concurrent
and one single-mode endurance training group, one running-speciﬁc strength training
group was incorporated. This circumstance (which is not usual in studies conducted
with endurance athletes) was useful to verify the adaptations that endurance runners
can attain with running-speciﬁc strength training and determine the possible existence of
Int. J. Environ. Res. Public Health 2022, 19, 10773
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interference effects in CTG. Second, the number of weekly training sessions applied to the
three experimental groups was equated. In this regard, it should be noted that in several
previous studies, the concurrent group performed two or three additional weekly strength
sessions with respect to the endurance training group, which implies using a distinctive
number of sessions.
As for the limitations, ﬁrst, the sample size was small. A larger sample would have
ensured greater representativity. Second, no time-trial test was conducted in the present
research since the study participants were not specialized in any speciﬁc distance. Finally,
we consider that if the intervention period had been longer, it would have been possible
that the three experimental groups had obtained additional improvements, particularly
in body composition. Furthermore, signiﬁcant differences between groups could have
occurred in more anthropometric and performance variables at the post-test.
6. Conclusions
A concurrent training program of 12 weeks integrated into the ATR periodization
system is effective in enhancing body composition and selected sports performance param-
eters associated with the exclusive practice of strength training (maximum and explosive
strength) and endurance training (VO2max and AnT), in addition to RE in recreational
runners aged 30–40. The exclusive practice of running-speciﬁc strength training during
the same period also using the ATR design improves maximum and explosive strength
and RE, while the exclusive practice of endurance training using the ATR model improves
endurance parameters (VO2max and AnT) and RE. Thus, concurrent training is the most
time-efﬁcient method to attain anthropometric and performance adaptations. Addition-
ally, a concurrent training program performed on non-consecutive days did not attenuate
the endurance and strength adaptations that can be attained with single-mode exercise.
However, it cannot be ruled out that a higher weekly training frequency may generate
interference effects.
The ATR periodization system improves the performance parameters of recreational
endurance athletes, especially when performing concurrent training. Likewise, in recre-
ational athletes without previous strength training experience, due to their greater reserve
of adaptation, concomitant running-speciﬁc strength and endurance training—in addition
to enhancing their body composition and relevant performance variables—produce large
improvements in maximum and explosive strength and further enhance RE.
7. Practical Applications
•
Performing exclusive strength or endurance training allows athletes only to attain
speciﬁc exercise mode adaptations.
•
Undertaking concurrent training programs allows athletes to obtain strength and
endurance adaptations. However, to this end, separating the training sessions by at
least nine hours is necessary to avoid signiﬁcant interferences, or 24 h to guarantee to
a greater extent that the adaptations will not be attenuated [60].
•
Concurrent training programs should be integrated into a periodization model to attain
greater effectiveness. In this sense, the ATR block periodization system effectively im-
proves anthropometric and performance variables in recreational endurance athletes.
•
Long-term interventions of more than 12 weeks might be used. Intervention periods of
12 weeks are insufﬁcient to attain improvements in anthropometric parameters when
single-mode exercise training is used.
•
Regarding the training load and the type of strength that must be developed, it is nec-
essary to adapt the strength training program to the athlete’s objectives, training level,
and previous training experience. Thus, a general strength training program might
improve sports performance in subjects without previous strength training experience.
However, in subjects who did not previously develop their maximum strength, it can
be leapfrogging using inappropriate workloads or developing types of strength with
lower residual effect (i.e., explosive strength, muscular endurance, reactive strength).
Int. J. Environ. Res. Public Health 2022, 19, 10773
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It may also reduce their adaptation reserve unnecessarily and limit future improve-
ments. By contrast, endurance athletes with previous strength training experience
should develop explosive and reactive strength to enhance their performance.
Author Contributions: Conceptualization, P.P.-G.; methodology, P.P.-G.; validation, P.P.-G. and J.S.;
formal analysis, P.P.-G.; investigation, P.P.-G.; resources, P.P.-G.; data curation, P.P.-G.; writing—
original draft preparation, P.P.-G.; writing—review and editing, P.P.-G. and J.S.; supervision, J.S. All
authors have read and agreed to the published version of the manuscript.
Funding: The authors would like to thank Prince Sultan University, Riyadh, Saudi Arabia, for
supporting the article processing charges.
Institutional Review Board Statement: The research was conducted according to the ethical princi-
ples of the Declaration of Helsinki. It was approved by the Ethics Commission of Prešov University
(Slovakia) (ethical clearance number: 2/2021).
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Data Availability Statement: The data presented in this study are available on request from the
corresponding author.
Acknowledgments: The authors would like to thank Prince Sultan University, Riyadh, Saudi Arabia,
for their support in research.
Conﬂicts of Interest: The authors declare no conﬂict of interest.
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Effects of Running-Specific Strength Training, Endurance Training, and Concurrent Training on Recreational Endurance Athletes' Performance and Selected Anthropometric Parameters.
Prieto-González, Pablo,Sedlacek, Jaromir