

Citation: Fernández-Galván, L.M.;
Prieto-González, P.; Sánchez-Infante,
J.; Jiménez-Reyes, P.; Casado, A. The
Post-Activation Potentiation Effects
on Sprinting Abilities in Junior
Tennis Players. Int. J. Environ. Res.
Public Health 2022, 19, 2080. https://
doi.org/10.3390/ijerph19042080
Academic Editor: Paul B. Tchounwou
Received: 28 December 2021
Accepted: 8 February 2022
Published: 13 February 2022
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International  Journal  of
Environmental Research
and Public Health
Article
The Post-Activation Potentiation Effects on Sprinting Abilities
in Junior Tennis Players
Luis Miguel Fernández-Galván 1
, Pablo Prieto-González 2,*
, Jorge Sánchez-Infante 3
, Pedro Jiménez-Reyes 4
and Arturo Casado 4
1
Department of Physical Education, Sport, and Human Movement, Autonomous University of Madrid,
28049 Madrid, Spain; luisdepucela@gmail.com
2
Health and Physical Education Department, Prince Sultan University, Riyadh 11586, Saudi Arabia
3
Performance and Sport Rehabilitation Laboratory, Faculty of Sport Sciences, University of Castilla-La Mancha,
45071 Toledo, Spain; jorge.ﬁsio.uclm@gmail.com
4
Center for Sport Studies, Rey Juan Carlos University, 28032 Madrid, Spain; peterjr49@hotmail.com (P.J.-R.);
arturo.casado@urjc.es (A.C.)
*
Correspondence: pprieto@psu.edu.sa; Tel.: +966-114-948-661; Fax: +966-114-548-317
Abstract: Objective: This study aimed to compare the acute effects of a full squat (SQ) or hip thrust
(HT) with two different loading intensities (60% and 85% 1 RM) on sprint ability in junior male tennis
players. Methods: Nineteen tennis players were included in this research. They underwent four
different experimental conditions: HT at 60% 1 RM, HT at 85% 1 RM, SQ at 60% 1 RM, or SQ at 85%.
The force–velocity (F–V) proﬁle was used to assess tennis players’ sprint acceleration ability before
and after applying the conditioning stimulus. The variables registered were as follows: 5 m test
(5 m), 10 m test (10 m), maximum theoretical force (F0), maximum power (Pmax), and the maximal
ratio of horizontal-to-resultant force (RFpeak). Results: Signiﬁcant improvements in 5 m, Pmax, and
RFpeak were observed when the conditioning stimulus was performing one set of seven reps of HT at
60% 1 RM. When the activation protocol was one set of seven reps of SQ at 60% 1 RM, signiﬁcant
improvements in 5 m, 10 m, F0, Pmax (N), and RFpeak were detected. Additionally, performing one
set of three reps of SQ at 85% 1 RM as an activation protocol provided signiﬁcant improvements
in F0. Conclusion: The use of HT and SQ with a load of 60% 1 RM improved the sprint F–V proﬁle
components related to the acceleration phase of the sprint in junior tennis players. Using intensity
loads of 85% 1 RM is not adequate to increase acute sprint performance in this population. HT
presents a higher transferability to sprinting in the ﬁrst 5 m of sprinting, whereas SQ provides acute
improvements in different sprinting phases.
Keywords: post-activation potentiation; tennis; sprinting; acute performance; force-velocity proﬁle
1. Introduction
Tennis is a complex racquet sport played by two opposing players or pairs that
perform intermittent efforts. In tennis, players compete against one opponent in singles
or two opponents in doubles who condition the motor actions of each player [1]. Tennis
has signiﬁcantly evolved during the last decades [2,3]. In addition to the well-known
technical and tactical requirements, physical ﬁtness is now also a relevant performance
factor [3]. During the effective playing time, among all the technical skills and movements
performed by the tennis players, serving, accelerations, and changes of directions are the
key performance actions. Therefore, performance in this sport is largely conditioned by
power, agility, and speed abilities [2–5].
In youth tennis, the internal and external loads slightly differ with respect to elite
tennis [6]. Even so, it has been determined that explosive and ballistic actions are also key
performance aspects in youth tennis [7]. Thus, junior tennis players, coaches, and physical
trainers should aim to improve strength, power, and sprinting abilities. Additionally, as
Int. J. Environ. Res. Public Health 2022, 19, 2080. https://doi.org/10.3390/ijerph19042080
https://www.mdpi.com/journal/ijerph
Int. J. Environ. Res. Public Health 2022, 19, 2080
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young athletes acquire a higher level of sports maturity, physical ﬁtness training becomes
increasingly relevant [8].
In this regard, one of the strategies currently implemented to attain acute increases in
athletes’ functional performance in explosive and ballistic exercise is post-activation poten-
tiation (PAP). PAP has been deﬁned by Tillin and Bishop as the situation in which muscle
performance is acutely improved as a result of a prior voluntary contraction [9]. Similarly,
Goła´s et al. deﬁne PAP as an acute enhancement of performance or an enhancement of
factors determining an explosive sports activity following a preload stimulus [10]. PAP
enhances sports performance through the following mechanisms: (a) increased number
of active motor units (motor unit recruitment), enhanced motor unit synchronization, de-
creased presynaptic inhibition, and increased number of nerve impulses transmitted [9,11];
(b) modiﬁcations in pennation angle; and (c) phosphorylation of myosin regulatory light
chains [9,11]. After receiving the appropriate conditioning stimulus, performance opti-
mization depends on the balance between fatigue and potentiation [12]. PAP depends
on athletes’ training level, muscle ﬁber type, muscle contraction type and duration, and
stimulus volume and intensity [13]. Thus, it has been veriﬁed that well-trained athletes
respond better to PAP than recreational athletes. Subjects with a higher percentage of type
II muscle ﬁbers also obtain better PAP responses. Likewise, voluntary contractions provide
better responses than electrostimulation. Additionally, it must be taken into account that
there is a consistent and signiﬁcant inter-individual variability in the responses obtained
by the athletes after the implementation of PAP strategies. For this reason, it is not possible
to establish the optimal PAP conditioning protocol for each group of athletes [10,14].
Moreover, substantial differences have been observed in the PAP interventions imple-
mented in different studies. This great variability could explain the discrepancies observed
in the degree of improvement attained by the athletes. In this respect, conﬂicting results
have been found, including improvements in some studies and no effects or decreases in
sports performance in other research [13]. Consequently, further research is required to
determine which is the optimal PAP protocol for different groups of athletes and different
sports disciplines because each type of exercise induces different effects, and the stimuli
applied to young athletes differ from those of professional athletes [13,14].
As a result, it is necessary to clarify the effect of certain aspects that still remain
unclear, such as the appropriate conditioning activity intensity, the number of sets to be
performed, type of exercise used, and rest period between the conditioning stimulus and
the activity [15,16]. The adequate dosage of these parameters has not been standardized
in previous research [9]. In this regard, Seitz and Haff indicate that stronger athletes
show greater PAP responses with shorter rest periods between the PAP stimulus and
the activity, whereas weaker athletes would need a longer rest. They also stated that
maximum loads induce better PAP responses in stronger athletes and submaximal loads in
weaker athletes [13]. Weaker individuals obtain better PAP effects with multiple sets [13,17].
However, this could increase fatigue [10]. As for the type of exercise included in the
conditioning activities, the squat (SQ) is commonly used to improve jumping ability since
athletes have to apply strength in the vertical vector [13,17]. The SQ also has a greater
range of motion than the hip thrust (HT), which can result in greater muscle tension [18].
However, in the case of running, the hip thrust (HT) exercise (which involves greater
activation of the hip extensor muscles) has higher speciﬁcity and transferability to activities
that require applying strength on a horizontal vector, such as sprinting [19–21]. In tennis,
to our knowledge, only one recent study conducted by Terraza-Rebollo and Baiget has
analyzed the effects of PAP [22]. This study veriﬁed that a PAP intervention did not
affect serve velocity and accuracy in young competition tennis players. Likewise, no
studies analyzing the inﬂuence of PAP on sprint performance in tennis players have been
conducted. This ability, as previously mentioned, is a key performance factor in tennis.
Additionally, since stronger athletes obtained greater PAP effects than weaker subjects in
previous studies, it is necessary to ﬁnd suitable protocols for the weaker athletes to attain
Int. J. Environ. Res. Public Health 2022, 19, 2080
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acute performance improvements. Therefore, further research is warranted to verify the
effects of PAP on key performance skills and abilities in tennis.
Moreover, it is essential to use quality assessment instruments to assess the improve-
ments obtained in sprinting. For this purpose, the force–velocity (F–V) proﬁle provides
valuable information about the relationship between the force applied by one athlete and
the speed at which his or her neuromuscular system generates it in ballistic or explosive
movements (i.e., sprinting and running) performed with his or her lower limbs [23,24]. The
F–V is calculated by a linear regression over a distance of 30 m [25], and it has proven to be
reliable in youth athletes [26]. The proﬁle is composed of different variables, some of them
related to the sprint acceleration ability, such as maximum theoretical force (F0), maximum
power (Pmax), and the maximal ratio of horizontal-to-resultant force (RFpeak) [23,27].
In this context, the objective of the present study was to compare the acute effects of
performing a full SQ and HT using two different loads (60% and 85% 1 RM) on sprinting
ability in 19 junior male tennis players. The F–V was used to estimate the potential
improvements obtained through the PAP. We hypothesized that both SQ and HT would
effectively improve the sprint F–V proﬁle and that more signiﬁcant improvements would
be obtained with loads of 60% 1 RM rather than 85% 1 RM.
2. Materials and Methods
2.1. Participants
Nineteen male tennis players of Benicarló Tennis Club (Castellón, Spain), with a
minimum of three years of tennis training experience (4.47 ± 1.54) but without resistance
training experience participated in the present study. Subjects´ characteristics are shown
in Table 1. All study participants underwent an annual medical examination in the health
services of the Valencian Tennis Federation, and none of them presented any injury or
health condition that could prevent them from participating in this research. Study par-
ticipants and their parents or guardians received detailed verbal and written information
about the experimental protocol and the potential risks and beneﬁts of participating in
it. They were also allowed to withdraw from the study at any stage without penalty. All
participants´ parents or guardians gave their written informed consent to be included
in this research. The present study was conducted in accordance with the Declaration of
Helsinki Ethical Principles. It was also approved by the Institutional Review Board of the
Bio-ethics Committee at Prince Sultan University (Riyadh, Saudi Arabia) (ethical clearance
number: PSU IRB-2021-02-0070).
Table 1. Participants descriptive information.
Experimental Group (n = 19)
Age (years)
15.61 (1.35)
Height (cm)
173.89 (8.24)
Weight (kg)
68.31 (13.34)
Tennis training experience (years)
4.47 (1.54)
Note: Data is presented as mean (standard deviation).
2.2. Procedures
Before proceeding with data collection, anthropometric variables were recorded in the
laboratory. Height and body mass were measured to the nearest 0.1 cm and 0.1 kg, respec-
tively. Both height and body mass were measured with a digital measuring station—Seca
284, Hamburg (Germany). The experimental sessions were carried out always at the same
time of the day (between 4.00 and 6.00 p.m.) to avoid the possible effect of circadian rhythm,
and also because the participants´ training sessions were usually conducted at that time.
The sessions were separated by a minimum of 72 h of rest time to avoid the impact of
fatigue on speed test results. The tests were preceded by a 20 min warm-up consisting of
seven minutes of jogging at a self-selected pace, eight minutes of dynamic stretching, and
ﬁve minutes of progressive sprint bouts, with and without change of direction (60%, 70%,
Int. J. Environ. Res. Public Health 2022, 19, 2080
4 of 11
and 85% of perceived maximum). The participants performed maximal-effort 30 m linear
sprints on a synthetic outdoor track. A smartphone application (My Sprint, Apple Inc.,
Cupertino, CA, USA) was used to record and analyze the trials’ split times (5, 10, 15, 20,
25, and 30 m). The recording was conducted with an iPhone 7 (iOS 10.0.2), mounted on
a tripod, and located 10 m perpendicular to the sprint direction, just in front of the 15 m
marker. The system is based on high-speed video analysis (240 frames per second), and it
has proven to be valid and reliable to assess linear sprint performance in relation to two
different reference systems: timing photocells and radar gun [25]. Subjects started from a
crouching position (staggered-stance) with their right hand on the track. The beginning of
the sprint was set when the right thumb of the athlete left the ground (this was detected
by visual inspection with MySprint). Two independent observers were asked to select
the ﬁrst frame in which participants’ right thumb left the ground (i.e., the start of the
sprint) and, subsequently, the frame in which the pelvis was aligned with each of the three
different markers for each of the recorded sprints [23]. Split times, participants’ body mass,
and height were used by the MySprint app to calculate F0, Pmax, and RFpeak following
previously validated formulas [23–25].
2.3. Familiarization and Maximal Dynamic Strength Test
During the four weeks prior to the study commencement, 12 familiarization sessions
were carried out to ensure the proper technique in the full SQ and HT exercises. These
familiarization sessions consisted of four sets of seven, ﬁve, and three repetitions with loads
of 60%, 70%, and 85% 1 RM, respectively, for the full SQ and HT exercises. The encoder
Speed4Lifts (v2.0., Speed4Lifts, Madrid, Spain) was used to calculate the peak dynamic
force, which uses the load–velocity relationship evaluation method, which involves measur-
ing concentric velocity with two different weight loads, and then, through linear regression
equations, it predicts the load (1 RM percentage) from velocity data [28,29]. All reported
repetition velocities in this study correspond to the mean propulsive velocity (MPV) of
the concentric phase [29]. The MPV was used in the present study for the following two
reasons: (i) it has been proven to have a very high intra-and inter-participant reliability,
similar to mean and peak velocity [30]; (ii) regarding the mean values of the propulsive
phase (i.e., MPV), when assessing the velocity with which a load is lifted in a concentric
action, it avoids underestimating individuals´ neuromuscular ability, especially when
lifting light and medium loads [31].
2.4. Full Squat and Hip Thrust
The full SQ was performed starting from the upright position with the knees and hips
fully extended. Each participant descended in a continuous movement until his upper
thighs were below the horizontal plane and then immediately ascended back to the upright
position. Participants were always required to execute the concentric phase of full SQ
at maximal velocity. An SQ rack Fitness Line (Collado-Villalba, Spain) and a standard
Olympic bar and weight plates (Eleiko, Halmstad, Sweden) were used for all sessions. To
perform the HT, subjects were instructed to start by sitting on the ground with their legs
ﬂat on the ﬂoor, feet shoulder-width apart, and their upper back against a padded exercise
bench. Using the same Olympic bar and disks utilized in the previous exercise, the bar
was covered with a pad for comfort, and it was placed above the participants´ lower legs,
slightly below their knees [32]. Once the subjects positioned the barbell above their pelvis,
they assumed the starting position of the exercise by bringing their heels toward the bench
and bending their knees. Then, subjects lifted their hips until their knee joints formed a 90◦
angle with their tibias.
2.5. Methodology
The activities carried out during the intervention process are shown in Figure 1. In
session 1, the 1 RM full SQ test was performed, and one week later, in session 2, the
1 RM HT test was conducted. A random selection of the participants was used. Thus,
Int. J. Environ. Res. Public Health 2022, 19, 2080
5 of 11
subjects were assigned to four groups, so that on each day, one group performed one type
of exercise with a different load to avoid the learning effect, which could represent a threat
to internal validity. All tests were performed at an outdoor facility maintained at standard
environmental conditions. To simulate an “active” athletic setting, instead of seating during
the rest period, the tennis players were instructed to perform an active recovery with short
displacements in different directions at low intensity. Thirty seconds before testing, athletes
were notiﬁed to be prepared. Session 3 began with the warm-up explained in Section 2.2.
Subsequently, the 30 m sprint test was performed. Then, study participants rested for four
minutes and performed three repetitions at 85% 1 RM of a full SQ, and after resting for
four minutes, they performed the 30 m sprint test again. The session structure used in
session 3 was applied in sessions 4, 5, and 6, but using a different conditioning stimulus.
Thus, session 4 began 72 h later than session 3, and the activation protocol consisted of
performing one set of seven repetitions of a full SQ at 60% of 1 RM. Session 5 started 96 h
later, and the conditioning stimulus was one set of three repetitions of an HT at 85% of
1 RM. Finally, session 6 was performed 72 h later, and the activation protocol was one set of
seven repetitions of an HT at 60% 1 RM. Moreover, the MySprint application was used to
measure the F–V proﬁle when the 30 m tests were performed.
 
The activities carried out during the intervention process are shown in Figure 1. In
session 1, the 1 RM full SQ test was performed, and one week later, in session 2, the 1 RM
HT test was conducted. A random selection of the participants was used. Thus, subjects
were assigned to four groups, so that on each day, one group performed one type of ex-
ercise with a different load to avoid the learning effect, which could represent a threat to
internal validity. All tests were performed at an outdoor facility maintained at standard
environmental conditions. To simulate an “active” athletic setting, instead of seating dur-
ing the rest period, the tennis players were instructed to perform an active recovery with
short displacements in different directions at low intensity. Thirty seconds before testing,
athletes were notified to be prepared. Session 3 began with the warm-up explained in
Section 2.2. Subsequently, the 30 m sprint test was performed. Then, study participants
rested for four minutes and performed three repetitions at 85% 1 RM of a full SQ, and after
resting for four minutes, they performed the 30 m sprint test again. The session structure
used in session 3 was applied in sessions 4, 5, and 6, but using a different conditioning
stimulus. Thus, session 4 began 72 h later than session 3, and the activation protocol con-
sisted of performing one set of seven repetitions of a full SQ at 60% of 1 RM. Session 5
started 96 h later, and the conditioning stimulus was one set of three repetitions of an HT
at 85% of 1 RM. Finally, session 6 was performed 72 h later, and the activation protocol
was one set of seven repetitions of an HT at 60% 1 RM. Moreover, the MySprint applica-
tion was used to measure the F–V profile when the 30 m tests were performed. 
 
Figure 1. Description of the intervention process and the activities performed in each session. 
2.6. Statistical Analysis 
Data are presented using the format of the mean SD (standard deviation). The
Shapiro–Wilk test was used to contrast the normality of the variables. To determine the
consistency between the measurements made in the pre- and post-test, the interclass cor-
relation coefficient (ICC) was calculated for all the assessed 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 (Koo and Li, 2016). To verify whether there were differences between
groups in the baseline, a one-way ANOVA test was conducted. Furthermore, to assess the
effects of PAP on the three different conditions (time: pre- vs. post-test; load: 85% vs. 60%;
and exercise: HT vs. SQ), a factorial repeated measures ANOVA (2 × 2 × 2) was conducted.
When statistically significant p values were found (interaction effects or significant main
effects), a post hoc pairwise comparison was conducted with Sidak correction to identify
those differences. The effect size was calculated using the partial eta squared (η2p). Values
of η2p = 0.01, η2p = 0.06, and η2p = 0.14 were considered as small, medium, and large effect
sizes, respectively [33]. The level of significance established was p = 0.05. The statistical
Figure 1. Description of the intervention process and the activities performed in each session.
2.6. Statistical Analysis
Data are presented using the format of the mean SD (standard deviation). The Shapiro–
Wilk test was used to contrast the normality of the variables. To determine the consistency
between the measurements made in the pre- and post-test, the interclass correlation coefﬁ-
cient (ICC) was calculated for all the assessed 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 (Koo and Li, 2016). To verify whether there were differences between groups in
the baseline, a one-way ANOVA test was conducted. Furthermore, to assess the effects
of PAP on the three different conditions (time: pre- vs. post-test; load: 85% vs. 60%; and
exercise: HT vs. SQ), a factorial repeated measures ANOVA (2 × 2 × 2) was conducted.
When statistically signiﬁcant p values were found (interaction effects or signiﬁcant main
effects), a post hoc pairwise comparison was conducted with Sidak correction to identify
those differences. The effect size was calculated using the partial eta squared (η2p). Values
of η2p = 0.01, η2p = 0.06, and η2p = 0.14 were considered as small, medium, and large effect
sizes, respectively [33]. 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).
Int. J. Environ. Res. Public Health 2022, 19, 2080
6 of 11
3. Results
The results obtained by the subjects in the 1 RM tests are shown in Table 2, and the
assessed F–V variables are presented in Table 3. The ICC values between test and retest
were higher in all cases than 0.9, which reﬂects excellent reliability. In addition, the one-
way ANOVA conﬁrmed the absence of signiﬁcant differences between the four different
measurements conducted at the baseline.
Table 2. Results obtained by the study participants in the 1 RM tests.
Exercise
1 RM Test Result (kg)
Hip thrust
53.11 (15.71)
Squat
66.89 (17.16)
Table 3. Results obtained by the study participants in the force–velocity variables assessed before
(pre-) and after (post-) applying the post-activation potentiation.
Moment
Results Obtained before Applying the Post-Activation Potentiation
5 m
10 m
30 m
F0 (N)
Pmax (N)
RFpeak
Pre-85%1 RM-HIP THRUST
1.62 (0.11)
2.4 3(0.15)
5.45 (0.39)
429.90 (128.82)
791.20 (274.11)
44.50 (4.13)
Pre-PAP-60%1 RM-HIP
THRUST
1.60 (0.12)
2.41 (0.14)
5.40 (0.37)
441.90 (114.83)
818.20 (245.02)
45.23 (3.90)
Pre-PAP-85%1 RM-SQUAT
1.55 (0.12)
2.33 (0.16)
5.23 (0.41)
467.66 (120.11)
895.69 (268.72)
47.16 (4.33)
Pre-PAP-60%1 RM-SQUAT
1.60 (0.17)
2.42 (0.20)
5.42 (0.44)
430.47 (132.40)
797.86 (288.61
45.14 (5.65)
Results obtained after applying the post-activation potentiation
5 m
10 m
30 m
F 0(N)
Pmax (N)
RFpeak
Post-PAP-85%1 RM-HIP
THRUST
1.59 (0.11)
2.40 (0.16)
5.42 (0.39)
448.90 (128.36)
824.79 (276.91)
45.44 (4.08)
Post-PAP-60%1 RM-HIP
THRUST
1.55 (0.11) *
2.36 (0.17)
5.38 (0.45)
475.95 (124.44)
873.73 (285.38) *
46.97 (4.28) *
Post-PAP-85%1 RM-SQUAT
1.55 (0.12)
2.32 (0.15)
5.26 (0.39)
479.18 (127.05) *
904.35 (274.73)
47.53 (4.38)
Post-PAP-60%1 RM-SQUAT
1.55 (0.15) *
2.35 (0.20) *
5.32 (0.45) *
473.17 (147.74)
885.14 (329.37) *
46.94 (5.37) *
5 m: 5 m split sprint time; 10 m: 10 m split sprint time; 30 m: 30 m split sprint time; F0(N): maximal theoretical
velocity; Pmax (N): maximal power; RFPeak (%): maximal ratio of horizontal-to-resultant force; PAP: post-activation
potentiation; 1 RM: 1 maximum repetition; *: signiﬁcant effect found (p < 0.05).
The 2 × 2 × 2 ANOVA conﬁrmed the absence of interaction effects for all the assessed
variables. However, a main effect of time was found for the following parameters: 5 m
(F1–18 = 7.35; p = 0.014; 268 η2p = 0.290), 10 m (F1–18 = 8.62; p = 0.009; η2p = 0.324), Pmax
(F1–18 = 7.22; p = 0.015; η2p = 0.286), and RFpeak (F1–18 = 8.36; p = 0.010; η2p = 0.317). A
main effect of exercise was also found for F0 (N) (F1–18 = 7.71; p = 0.035; η2p = 0.223). The
results of the pairwise comparisons are shown below:
3.1. 5 m
Signiﬁcant differences were observed after applying the PAP load of seven reps at 60%
1 RM in HP (p = 0.018; 95%CI = 0.010 to 0.090), and in SQ (p = 0.006; 95%CI = 0.015 to 0.78).
3.2. 10 m
A signiﬁcant difference was found in the SQ (p = 0.003; 95%CI = 0.023 to 0.101) after
applying the PAP load of seven reps at 60% 1 RM.
Int. J. Environ. Res. Public Health 2022, 19, 2080
7 of 11
3.3. F0 (N)
A signiﬁcant difference was observed between the HT and SQ in favor of the latter
condition (p = 0.024; 95%CI = −0.415 to −0.033) after applying the PAP load of three
repetitions at 85% 1 RM.
3.4. Pmax (Wkg-1)
Signiﬁcant differences in the HT (p = 0.013; 95%CI = −98.05 to −13.01) and in SQ
(p = 0.037; 95%CI = −205.92 to −7.06) were found after applying the PAP load of seven
reps at 60% 1 RM.
3.5. RFpeak
Signiﬁcant differences were observed in HP (p = 0.016; 95%CI = −3.10 to −0.36), and
in SQ (p = 0.007; 95%CI = −3.04 to −0.54) after applying the PAP load of seven reps at 60%
1 RM.
4. Discussion
The main ﬁnding of the present study was that the PAP protocol applied was effective
in improving the 5 m time with 60% 1 RM using both an HT and SQ with an ES of 0.43 and
0.31, respectively. The PAP was also effective in improving 10 m times when the SQ was
applied with a load of 60% 1 RM (ES = 0.34), conﬁrming our hypothesis that moderate loads
are sufﬁcient to produce performance improvements in young athletes without previous
strength training experience.
PAP has proven to be an effective warm-up to enhance maximal strength and speed of
strength development [9,34]. In the present study, signiﬁcant differences with a small effect
size were found when the study participants performed the PAP with loads of 60% 1 RM
using both the HT and SQ. These ﬁndings indicate that moderate loads may sufﬁce in this
population to enhance motor unit recruitment and synchronization, which are the main
mechanisms associated with improved performance when applying PAP protocols [9]. The
mentioned results were somewhat expected. Indeed, in previous studies, light stimuli ap-
plied to young athletes with little or no strength training experience signiﬁcantly enhanced
sprint performance by eliciting lower fatigue [13]. In this regard, a recent meta-analysis
that included 32 primary studies showed greater effects (ES = 1.06) with moderate loads
(60 to 84% 1 RM) than with high loads (ES = 0.31) (>85% 1 RM) [35] in 141 subjects aged
20 ± 5 years [20]. Likewise, it was observed that an HT is effective in 5 m, but its effect
declines in 10 m. We consider that the HT is more effective in improving sprinting ability
over shorter distances due to the nature of this exercise because, because unlike SQ, it
mainly activates the hip extensor muscles [20]. Some authors also attributed the effective-
ness of an HT in the ﬁrst sprinting meters to the application of strength in the horizontal
vector [20,21]. However, Fitzpatrick et al. state that this theory is ﬂawed [36]. They argue
that, according to the principle of dynamic correspondence, the forces applied by an athlete
must be considered in relation to the coordinate system set by the athlete. While it is true
that during accelerations, athletes apply force basically in the horizontal plane, that is
because their bodies lean forward, meaning that the direction of the force applied both
in accelerations and high-speed running is basically the same [36]. By contrast, SQ was
effective both in 5 m, 10 m, and 30 m. In this case, the improvement could be attributed
to the enhanced intramuscular coordination by increasing eccentric strength in extensor
muscles, which results in a decreased ground contact time and consequently improves
their stride frequency (i.e., V0) [19]. Based on the results, we interpret that SQ presents
great levels of transferability to all sprinting phases.
The study results revealed the absence of signiﬁcant differences in sprinting perfor-
mance after applying the PAP using both the HT and SQ with a load of 85% 1 RM. One
possible explanation is that the accumulated fatigue could have overridden the PAP ef-
fect [9]. It is plausible that applying heavy loads to subjects without previous strength
training experience produces a degree of fatigue that prevents them from optimizing sprint
Int. J. Environ. Res. Public Health 2022, 19, 2080
8 of 11
performance. However, it must be taken into account that fatigue can result from using
high-intensity conditioning stimuli but could also be due to factors such as excessive vol-
ume, short recovery, strenuous warm-up, or personal characteristics of each subject. In
this regard, it should be noted that greater beneﬁts have been observed after applying PAP
protocols in trained subjects [13,35,37]. Another possible explanation of these results could
be that the age of the subjects (15.61 ± 1.35) coincides with the mid-PHV (peak height
velocity) [37]. At this stage, the natural growth of the adolescents can lead to poorer training
results due to the temporary disruption in basic motor skills caused by the accelerated
growth of long bones [38]. This stage is known as adolescent awkwardness [39] and impacts
neuromuscular function and physical performance [38].
In the present study, the deep SQ was performed as it generates greater motor unit
activation and synchronization [13]. In this regard, the study results also show that the
subjects improved the F0 and Pmax variables, which coincides with other studies where a
deep SQ was also performed [14,17]. However, Seitz et.al. [13] obtained greater performance
improvements using a half SQ (ES = 0.58) than full SQ (ES = 0.25). This discrepancy suggests
that a deep SQ produces higher levels of acute fatigue [19] and therefore PAP become less
effective. Even so, certain discrepancies have been found in this regard in the scientiﬁc
literature since some authors did not observe signiﬁcant differences in sprint performance
after using either a half SQ or full SQ [20–22]. Therefore, it is not possible to determine
the effect of PAP by performing a half SQ instead of full SQ. In this sense, it should be
noted that the acute performance improvements that can be obtained depending on SQ
depth vary according to the athlete’s level. Stronger subjects perform better with shallow
SQs, whereas subjects with lower strength levels obtain greater improvements with deep
SQs [3]. For this reason, the full SQ exercise was selected in the training protocol of the
current research.
As for the F–V proﬁle components, a signiﬁcant increase in F0 after performing a SQ
with a load of 85% was observed. Additionally, the Pmax and RFpeak were also signiﬁcantly
increased after performing a SQ and HT with a load of 60% 1 RM. Improving the last
two variables is crucial, since acceleration in short distances is a key performance factor
in tennis. These results again suggest that both HT and SQ are effective in improving
various F–V proﬁle components, and the most appropriate intensity for both exercises is
60%, rather than 85%. Therefore, this reinforces the idea that in youth athletes without
previous strength training experience, moderate loads should be used in the PAP protocols.
Importantly, Seitz et al. [13] veriﬁed that resting time duration used after the condition-
ing activity should be set depending on the subject’s maximal strength. Thus, the PAP effect
is greater in stronger subjects when short recovery times are used (i.e., 2–3 min), whereas
longer rest intervals produce greater improvements in individuals with lower strength
levels. This is because of the ratio of type II muscle ﬁbers [40,41], which in turn is associated
with a higher myosin light chain phosphorylation and represents the peripheral factor on
which the PAP effects are based [42]. In our study, the resting time was four minutes. This
selection is justiﬁed based on the results of previous studies [43–45]. However, it cannot
be ruled out that a more extended recovery period could have produced lower fatigue to
study participants, and consequently, they could have obtained better results. In this sense,
Wilson et al. [35], after conducting a meta-analysis, veriﬁed that long rest periods (i.e., 7 to
10 m) could be more effective than short periods (3 to 7 min) (ES = 0.54 vs. 0.14).
Finally, only one set of HTs or SQs was undertaken in the conditioning protocol.
However, some studies found greater effects of PAP when more than one set was performed
(ES = 0.69 vs. ES = 0.24) [13,35,37], particularly in stronger athletes. Therefore, it is also
possible that further PAP enhancements could have been attained if more than one set had
been performed. However, it should also be considered that the study participants had no
previous strength training experience. That means that performing more sets could have
caused them great fatigue, as Wilson et al. state [35].
This study has some limitations that must be mentioned. The muscle activity was
not measured. Thus, the results and conclusions are exclusively based on the PAP effects.
Int. J. Environ. Res. Public Health 2022, 19, 2080
9 of 11
Moreover, we must consider that, since the study participants knew the study’s objective,
the occurrence of a placebo effect cannot be excluded. Future research should include
control groups and verify the effect of performing full vs. half SQs and the results of using
a different number of sets and different rest periods between the conditioning activity and
the task.
5. Conclusions
The PAP protocols applied to junior tennis players without previous strength training
experience effectively improved the F–V proﬁle when the loading intensity used in the
conditioning activity was 60% 1 RM and the exercises performed were either an HT or SQ.
However, 85% 1 RM loads were not adequate to increase acute sprinting performance in
this population group. In addition, HT presented a higher level of transferability in the ﬁrst
5 m of sprinting, whereas SQ provided acute improvements in different sprinting phases.
Practical Applications
Both the HT and the SQ are used in sports training to improve sprinting speed or
other sport skills and ﬁtness components. The present study veriﬁed that both exercises
could be useful in PAP protocols aiming to enhance sprinting ability. Practitioners and
trainers can use them as a suitable PAP stimulus to induce acute effects on subsequent
ballistic or explosive activities. However, the greatest effect occurs when moderate loads
are applied in youth tennis players without previous strength training experience (60%
1 RM). Therefore, heavy loads may reduce their adaptative reserve prematurely and limit
future performance improvements.
Author Contributions: Conceptualization, A.C., P.J.-R. and L.M.F.-G.; Methodology, A.C. and
L.M.F.-G.; Soft-ware, L.M.F.-G.; Validation, L.M.F.-G. and A.C.; Investigation, L.M.F.-G. and J.S.-I.;
Resources, L.M.F.-G.; Data Curation, L.M.F.-G. and P.P.-G.; Writing—Original Draft Preparation,
L.M.F.-G. and P.P.-G.; Writing—Review and Editing, J.S.-I.; Supervision, J.S.-I., P.J.-R. and A.C.; Fund-
ing Acquisition, P.P.-G. All authors have read and agreed to the published version of the manuscript.
Funding: The authors would like to recognize the efforts made by Prince Sultan University (Riyadh,
Saudi Arabia), for its support in funding the research either with fees, incentives, or seed grants.
Institutional Review Board Statement: The present study was conducted according to the principles
set out in the Helsinki Declaration, and it was also approved by the Institutional Review Board of
the Bioethics Committee at Prince Sultan University (Riyadh, Saudi Arabia) (approval no. PSU
IRB-2021-02-0070).
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Data Availability Statement: Not applicable.
Conﬂicts of Interest: The authors declare no conﬂict of interest.
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The Post-Activation Potentiation Effects on Sprinting Abilities in Junior Tennis Players.
Fernández-Galván, Luis Miguel,Prieto-González, Pablo,Sánchez-Infante, Jorge,Jiménez-Reyes, Pedro,Casado, Arturo