ARTICLE
OPEN
Rethinking aerobic exercise intensity prescription in adults with
spinal cord injury: time to end the use of “moderate to
vigorous” intensity?
Michael J. Hutchinson
1 and Victoria L. Goosey-Tolfrey
1✉
© The Author(s) 2021
STUDY DESIGN: Cohort study.
OBJECTIVES: To investigate and critique different methods for aerobic exercise intensity prescription in adults with spinal cord
injury (SCI).
SETTING: University laboratory in Loughborough, UK.
METHODS: Trained athletes were split into those with paraplegia (PARA; n = 47), tetraplegia (TETRA; n = 20) or alternate health
condition (NON-SCI; n = 67). Participants completed a submaximal step test with 3 min stages, followed by graded exercise test to
exhaustion. Handcycling, arm crank ergometry or wheelchair propulsion were performed depending on the sport of the participant.
Oxygen uptake (V̇O2), heart rate (HR), blood lactate concentration ([BLa]) and ratings of perceived exertion (RPE) on Borg’s RPE scale
were measured throughout. Lactate thresholds were identiﬁed according to log-V̇O2 plotted against log-[BLa] (LT1) and 1.5 mmol
L−1 greater than LT1 (LT2). These were used to demarcate moderate (<LT1), heavy (>LT1, < LT2) and severe (>LT2) exercise intensity
domains.
RESULTS: Associations between percentage of peak V̇O2 (%V̇O2peak) and HR (%HRpeak) with RPE differed between PARA and TETRA.
At LT1 and LT2, %V̇O2peak and %HRpeak were signiﬁcantly greater in TETRA compared to PARA and NON-SCI (P < 0.05). The variation
in %V̇O2peak and %HRpeak at lactate thresholds resulted in large variability in the domain distribution at ﬁxed %V̇O2peak and %HRpeak.
CONCLUSIONS: Fixed %V̇O2peak and %HRpeak should not be used for aerobic exercise intensity prescription in adults with SCI as the
method does not lead to uniform exercise intensity domain distribution.
Spinal Cord (2022) 60:484–490; https://doi.org/10.1038/s41393-021-00733-2
INTRODUCTION
For adults with spinal cord injury (SCI), aerobic exercise is
beneﬁcial for improving indices of physical [1] and mental [2]
health. On this theme, scientiﬁc guidelines published in 2018
describe the dose of aerobic exercise required to improve
cardiorespiratory ﬁtness and cardiometabolic health in adults
with SCI [3]. Central to the guidelines is information on the
frequency (e.g., 3 times per week) and duration (e.g., 30 min) of
the exercise, both of which are simple to deﬁne and monitor. The
ﬁnal important aspect of the guidelines is the exercise intensity. If
aerobic exercise is performed at too low an intensity, without
sufﬁcient exercise volume, it will not lead to beneﬁcial physiolo-
gical adaptations [4]. Despite this, the guidelines provide no clear
prescription of the exercise intensity, other than to say that
aerobic exercise should be of a “moderate to vigorous” intensity
[3]. The lack of clarity with the exercise intensity terminology is a
hindrance to adults with SCI using the guidelines to inform their
exercise habits; practitioners actively prescribing exercise training;
and researchers investigating the effects of exercise training
interventions on markers of health in adults with SCI. There is,
therefore, an urgent need to better understand aerobic exercise
intensity prescription in adults with SCI.
Guidelines for non-disabled adults deﬁne thresholds for ﬁve
intensity zones (very light, light, moderate, vigorous, near-
maximal/maximal) according to many physiological variables [5].
These variables include percentage maximum oxygen uptake (%
V̇O2max) and heart rate (%HRmax), oxygen uptake and heart rate
reserve (%V̇O2R, %HRR), and ratings of perceived exertion (RPE)
[5]. However, despite the SCI guidelines adopting the “moderate”
and “vigorous” descriptives, there is no equivalent resource
published for adults with SCI regarding the physiological thresh-
olds coinciding with these descriptors. Furthermore, given the
physiological consequences of SCI on cardiovascular and respira-
tory responses to exercise [6], there is no justiﬁcation for simply
adopting the percentage thresholds utilised for non-disabled
adults.
An alternative approach to exercise intensity prescription is to
consider whether different methods result in participants exercis-
ing in the same of three exercise domains (moderate, heavy,
severe) [7]. This is because of the similar V̇O2 and blood lactate
responses between individuals exercising in these domains [7].
Speciﬁcally, the moderate intensity domain (below lactate thresh-
old (LT)) is characterised by steady state responses for V̇O2 and
blood lactate concentration ([BLa]) [8]. In the heavy intensity
Received: 26 July 2021 Revised: 19 November 2021 Accepted: 23 November 2021
Published online: 8 December 2021
1Peter Harrison Centre for Disability Sport, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK. ✉email: V.L.Tolfrey@lboro.ac.uk
www.nature.com/sc
1234567890();,:
domain (between LT and critical power/speed (CP/CS)) there is a
delayed steady state response due to the V̇O2 “slow component”,
whilst in the severe domain (above CP/CS) no steady state
response is observed [8].
To satisfy the aim of producing a homogenous exercise
intensity, the ﬁxed percentage approach is only valid if it is
demonstrated that equal relative intensities result in individuals
exercising in the same intensity domain [7]. However, in a recent
study of non-disabled participants, no ﬁxed %V̇O2max or %HRmax,
typically used for exercise prescription, resulted in all participants
being in the same intensity domain [9]. This has led to assertions
that using ﬁxed %V̇O2max or %HRmax for prescribing exercise
intensity is inaccurate and will lead to signiﬁcant inter-individual
physiological responses, precluding homogenous exercise inten-
sity prescription [7, 9]. Furthermore, with evidence that individual
participant %V̇O2R:%HRR relationships diverges from the assumed
linear trajectory, there are also questions over how appropriate %
V̇O2R and %HRR are for prescribing exercise intensity at the
individual level [10].
For adults with SCI there is currently nothing more to inform
aerobic exercise intensity prescription than the arbitrary use of
“moderate to vigorous” intensity [3]. Furthermore, evidence in
non-disabled adults would suggest a need to rethink the
traditional use of ﬁxed percentages [7, 9, 10]. Therefore, this
study aimed to investigate and critique potential methods for
prescribing aerobic exercise intensity in adults with SCI.
METHODS
This study was performed via a retrospective analysis of athlete data
collected in the author’s laboratory. All procedures were approved by the
Human participants ethical sub-committee at Loughborough University,
and participants provided written, informed consent.
Participants
Data were available for 134 individuals (male: 98; female: 36). Participants
were split into those with paraplegia (PARA), tetraplegia (TETRA), or
alternate health condition (NON-SCI), see Table 1. Examples of health
conditions for NON-SCI included spina biﬁda, limb deﬁciency, cerebral
palsy, and arthrogryposis. Participants were competitive athletes, compet-
ing at a national or international level, from one of the following sports:
handcycling, para-alpine ski, paratriathlon, wheelchair basketball, wheel-
chair rugby or wheelchair tennis.
Exercise testing
Participants completed a submaximal step test followed by graded
exercise test (GXT) to exhaustion. Handcycle (HC) tests were performed
in the participants own handcycle attached to a Cyclus 2 ergometer
(Avantronic Richter, Leipzig, Germany). For some Paratriathlon, and all
para-alpine ski athletes, arm crank ergometry (ACE) was used (Lode Angio,
Lode B. V., Groningen, the Netherlands). The ergometer was positioned
vertically so the crank axis centre was level with the shoulder, and
horizontally to allow slight elbow ﬂexion at the furthest point of the crank
cycle. Wheelchair basketball, rugby and tennis players performed a
wheelchair propulsion (WCP) test using a motorised treadmill (HP Cosmos,
Traunstein, Germany) and their own custom sports wheelchair.
Submaximal tests were individualised based on the sport, sex, training
status and level of impairment of the participant, with the goal of
completing 6-8 stages (average: 6; range: 4–10). HC and ACE tests started
at 15–60 W, with 10–20 W increments every 3 min. WCP tests started at
0.7–2.8 m s−1 and were increased by 0.2-0–4 m s−1 every 3 min. V̇O2
(Metalyzer 3B, Cortex, Leipzig, Germany) and HR (RS400, Polar, Kempele,
Finland) were continually monitored throughout. The Metalyzer was
calibrated before each participant against ambient air and a mix of 15% O2,
5% CO2, with the volume calibrated using a 3 L syringe. RPE was verbally
reported in the ﬁnal minute of each stage using Borg’s 6–20 RPE scale [11].
A capillary blood sample from the ear lobe was collected at the end of
each stage for measurement of [BLa] (Biosen C-line, EKF Diagnostics,
Barleben, Germany). HC and ACE tests were continuous, however,
WCP tests were discontinuous as the treadmill needed to be slowed
between stages to facilitate blood sampling. For discontinuous tests, the
typical interval between stages was 45–60 s. Submaximal tests continued
until [BLa] exceeded 4 mmol L−1 or RPE was rated as 17. The RPE criteria
was used in TETRA where there may have been blunted lactate responses
[12].
Following the submaximal test, participants received 15 min of active
recovery or rest before performing a GXT to exhaustion. The starting
workload was set to that from the preceding test when [BLa] increased by
0.5 mmol L−1 above rest. Participants performed 1 min at this load, before
the exercise intensity were increased in a stepwise manner by 10–20 W
min−1 (HC/ACE) or 0.1 m s−1 min−1 (WCP) until participants reached
volitional exhaustion. This was deﬁned as an inability to maintain
their preferred cadence at the required PO for HC/ACE, or the required
speed of the treadmill, despite verbal encouragement. V̇O2 and HR were
again monitored throughout, with RPE and [BLa] measured at the end of
the test.
Data processing
V̇O2 and HR data were subjected to a 30 s rolling average, with the greatest
of these from the GXT recorded as peak values (V̇O2peak, HRpeak). V̇O2 and
HR in the ﬁnal 30 s of each submaximal stage were extracted and
calculated as percentages of peak (%V̇O2peak, %HRpeak). Using the
submaximal data, the lactate thresholds were identiﬁed as the intersection
of the horizontal and ascending sections of the plot of log-[BLa] against
log-V̇O2 (LT1) [13], and at [BLa] equal to LT1 plus 1.5 mmol L−1 (LT2) [14].
The inverse of the log-V̇O2 at these points were calculated to give the V̇O2
at LT1 and LT2. HR at LT1 and LT2 was identiﬁed by interpolation of the
linear V̇O2:HR relationship for each participant. RPE was modelled against
[BLa] using a quadratic function for each participant, with the resultant
coefﬁcients used to calculate the RPE at LT1 and LT2 [15]. Exercise intensity
domains were deﬁned as moderate (<LT1), heavy (between LT1 and LT2)
and severe (>LT2).
Statistical analyses
Analyses were performed using IBM SPSS Statistics Version 23.0 (IBM
Corp., Armonk, NY) and MLWiN Version 3.05 [16]. Data are presented
as mean (standard deviation) with statistical signiﬁcance accepted at P <
0.05. Data were checked for normal distribution using the Shapiro Wilk
statistic.
All individual RPE data points were modelled against the corresponding
%V̇O2peak and %HRpeak using dynamic multilevel models with lagged
independent variable, whilst accounting for the initial condition. Separate
models were created for %V̇O2peak and %HRpeak, which served as the
independent variable, with RPE as the dependent variable. Models were
multilevel to adjust for the repeated stages performed by each participant
and were used due to their ability to characterise group- and individual-
level effects [17]. Stage was deﬁned as the ﬁrst, and participant as the
second level. Models accounted for the initial condition (e.g., stage (i) = 1)
as it was thought that RPE would depend on the %V̇O2peak and %HRpeak
when i = 1. The need for them to be dynamic and incorporate a lagged
independent variable was required as it was thought RPE at subsequent
measurement occasions (when i > 1) would be dependent on %V̇O2peak
and %HRpeak for that, as well as the previous, measurement occasion (i.e.,
i–1). Potential confounding variables were added to the models to assess
whether they improved the model ﬁt with ﬁxed effects, or random effects
for between- and within-individual variation. Confounding variables were
sex (male/female), group (PARA/TETRA/NON-SCI) and exercise mode (ACE/
HC/WCP). The resultant models were used to calculate the %V̇O2peak and %
HRpeak corresponding to each value on Borg’s RPE scale.
Differences in V̇O2 (L min−1, ml kg−1 min−1, %V̇O2peak), HR (beats·min−1,
%HRpeak) and RPE between groups at LT1 and LT2 were assessed via one-
way analysis of variance with Bonferroni post-hoc correction for multiple
comparisons. Standardised effect sizes (ES) were calculated to describe the
magnitude of differences and categorised as trivial (< 0.2), small (0.2–0.6),
moderate (0.6–1.2), large (1.2–2.0) and very large (> 2.0) [18]. For each
group, the percentage of participants in each intensity domain (moderate,
heavy, severe) were calculated at 5% intervals from 35 to 95% V̇O2peak and
%HRpeak.
RESULTS
The associations between RPE and both %V̇O2peak and %HRpeak
were not signiﬁcantly affected by sex or exercise mode, so
stratiﬁcation based on these variables was not needed. The %
M.J. Hutchinson and V.L. Goosey-Tolfrey
485
Spinal Cord (2022) 60:484 – 490
V̇O2peak and %HRpeak coinciding with each rating on Borg’s RPE
scale for PARA and TETRA can be found in Table 2. The full RPE
models
against
%V̇O2peak
and
%HRpeak
can
be
found
in
the Supplementary Material.
RPE and %V̇O2peak model
RPE was signiﬁcantly affected by the initial %V̇O2peak (i = 1) (P <
0.01), by %V̇O2peak at subsequent occasions when i > 1 (P < 0.01),
as well as by the lagged %V̇O2peak (i.e., i–1) (P < 0.01). Each of these
variables also showed signiﬁcant between-individual variation,
which was incorporated into the model. There was also an effect
of Group at occasions when i > 1 (P = 0.01). TETRA showing
signiﬁcantly greater within-individual variation for the effect of %
V̇O2peak on RPE compared to PARA and NON-SCI. As such, PARA
and NON-SCI remained grouped, as there was no difference
between these groups.
RPE and %HRpeak model
RPE was signiﬁcantly affected by the initial %HRpeak (i = 1) (P <
0.01), by %HRpeak at subsequent occasions when i > 1 (P < 0.01), as
well as by the lagged %HRpeak (i.e., i–1) (P < 0.01). These effects
were ﬁxed and showed no signiﬁcant between- or within-
individual variation. There was a ﬁxed effect for Group, with the
association between RPE and %HRpeak being signiﬁcantly different
for PARA (P = 0.03). There was no difference between TETRA and
NON-SCI, so these remained grouped in this model.
Responses at LT1 and LT2
The V̇O2, HR and RPE at LT1 and LT2 are shown in Fig. 1. At LT1
there was a signiﬁcant group effect for absolute (F2 = 7.11, P <
0.01; Fig. 1a) and relative V̇O2 (F2 = 17.65, P < 0.01; Fig. 1c), %
V̇O2peak (F2 = 9.86, P < 0.01; Fig. 1e), HR (F2 = 42.79, P < 0.01; Fig. 1i)
and %HRpeak (F2 = 7.94, P < 0.01; Fig. 1k). LT1 occurred at a
signiﬁcantly smaller absolute and relative V̇O2 in TETRA compared
to PARA (ES = 0.86, 1.00) and NON-SCI (ES = 1.00, 1.62). However,
%V̇O2peak at LT1 was signiﬁcantly greater in TETRA compared to
PARA (ES = 0.96) and NON-SCI (ES = 0.94). Similarly, HR at LT1 was
smaller in TETRA compared to PARA (ES = 2.33) and NON-SCI
(ES = 2.74), whereas %HRpeak was greater in TETRA compared to
PARA
(ES = 1.00)
and
NON-SCI
(ES = 0.69).
There
was
no
signiﬁcant difference between groups for RPE (F2 = 0.48, P =
0.62) at LT1 (Fig. 1g).
There was also a signiﬁcant group effect at LT2 for absolute
(F2 = 9.96, P < 0.01; Fig. 1b) and relative V̇O2 (F2 = 19.75, P < 0.01;
Table 1.
Participant characteristics by group.
PARA
TETRA
NON-SCI
Sample size (n)
47
20
67
Sex (M/F)
30/17
18/2
50/17
Age (years)
33 ± 8a
32 ± 7a
27 ± 7
Body mass (kg)
70.9 ± 14.1a
70.8 ± 12.9
64.5 ± 12.8
Neurological level of injury
T4-L2
C3-C7
-
Injury completeness
Complete: 21
Complete: 8
-
Incomplete: 23
Incomplete: 4
Unavailable: 3
Unavailable: 8
Time since injury (years)
12 ± 9
12 ± 6
-
Peak oxygen uptake
(L·min−1)
2.5 ± 0.6b
1.7 ± 0.5
2.6 ± 0.7b
(ml·kg−1·min−1)
35.1 ± 8.2b
23.4 ± 5.8
39.9 ± 8.3b
Peak heart rate
(beats·min−1)
188 ± 9b
134 ± 20
187 ± 10 b
Sport (n)
Handcycling
8
0
3
Paratriathlon
11
0
8
Para alpine ski
2
1
2
Wheelchair basketball
20
1
31
Wheelchair rugby
0
15
13
Wheelchair tennis
6
3
10
Test mode (n)
Arm crank ergometry
11
1
7
Handcycling
10
0
6
Wheelchair propulsion
26
19
54
a: signiﬁcantly greater than NON-SCI; b: signiﬁcantly greater than TETRA, P < 0.05.
Table 2.
Resultant calculations of percentage peak oxygen uptake
and heart rate by group based on multilevel modelling.
RPE
%V̇O2peak
%HRpeak
PARA
TETRA
PARA
TETRA
6
16
22
40
43
7
22
28
44
48
8
28
34
49
52
9
34
40
54
57
10
40
46
58
62
11
46
52
63
66
12
52
58
68
71
13
58
64
73
76
14
64
70
77
81
15
70
76
82
85
16
76
82
87
90
17
82
88
91
95
18
88
94
96
99
19
94
100
100
20
100
M.J. Hutchinson and V.L. Goosey-Tolfrey
486
Spinal Cord (2022) 60:484 – 490
Fig. 1d), %V̇O2peak (F2 = 14.80, P < 0.01; Fig. 1f), HR (F2 = 58.99, P <
0.01; Fig. 1i) and %HRpeak (F2 = 6.10, P < 0.01; Fig. 1l). Absolute and
relative V̇O2 at LT2 were signiﬁcantly smaller in TETRA compared
to PARA (ES = 0.83, 0.97) and NON-SCI (ES = 1.03, 1.72). However,
%V̇O2peak at LT2 was signiﬁcantly greater in TETRA compared to
PARA (ES = 1.26) and NON-SCI (ES = 1.06). Furthermore, HR at LT2
was signiﬁcantly smaller in TETRA than in PARA (ES = 3.00) and
NON-SCI (ES = 3.55), while %HRpeak was signiﬁcantly greater in
TETRA compared to PARA (ES = 0.93) and NON-SCI (ES = 0.62).
There was no signiﬁcant difference between groups in RPE (F2 =
2.18, P = 0.19) at LT2 (Fig. 1h).
Intensity classiﬁcation
Thresholds for %V̇O2peak and %HRpeak corresponding with
intensity classiﬁcations used in non-disabled exercise guidelines
are shown in Table 3. These data suggest there are differences
between non-disabled individuals, PARA and TETRA in the
thresholds for intensity classiﬁcations. Frequency distribution of
individuals
within
moderate,
heavy
and
severe
intensity
domains for discrete percentages of %V̇O2peak and %HRpeak
are shown in Figs. 2 and 3, respectively. These show that no %
V̇O2peak or %HRpeak typically used for exercise prescription
purposes leads to all participants being in the same domain,
with many %V̇O2peak including participants spread across all
three domains.
DISCUSSION
This study aimed to investigate potential methods of aerobic
exercise intensity
prescription in adults with SCI.
Findings
demonstrate that there are differences between PARA and TETRA
for
the
%V̇O2peak
and
%HRpeak
corresponding
with
the
Fig. 1
Group physiological responses at lactate thresholds. a Absolute V̇O2 at LT1. b Absolute V̇O2 at LT2. c Relative V̇O2 at LT1. d Relative
V̇O2 at LT2. e %V̇O2peak at LT1. f %V̇O2peak at LT2. g RPE at LT1. h RPE at LT2. i HR at LT1. j HR at LT2. k %HRpeak at LT1. l %HRpeak at LT2.
Data are presented at mean (SD) with individual points overlaid. Within each group, numbers refer to the same participant in each ﬁgure.
Asterisk (*) indicates signiﬁcantly greater than the identiﬁed group, P < 0.05.
Table 3.
Classiﬁcation of exercise intensity for individuals with paraplegia and tetraplegia, compared to non-disabled guidelines.
Very light (RPE ≤
8)a
Light (RPE 9–11)a
Moderate (RPE
12–13)a
Vigorous (RPE
14–17)a
Near maximal-maximal (RPE ≥
18)a
%V̇O2peak
Non-disableda
≤36% V̇O2peak
37–45% V̇O2peak
46–63% V̇O2peak
64–90% V̇O2peak
≥91% V̇O2peak
Paraplegia
≤31% V̇O2peak
32–49% V̇O2peak
50–61% V̇O2peak
62–85% V̇O2peak
≥86% V̇O2peak
Tetraplegia
≤37% V̇O2peak
38-55% V̇O2peak
56–67% V̇O2peak
68–91% V̇O2peak
≥92% V̇O2peak
%HRpeak
Non-disableda
≤56% HRpeak
57–63% HRpeak
64-76% HRpeak
77–95% HRpeak
≥96% HRpeak
Paraplegia
≤51% HRpeak
52–65% HRpeak
66-75% HRpeak
76–93% HRpeak
≥94% HRpeak
Tetraplegia
≤54% HRpeak
55–68% HRpeak
69–78% HRpeak
79–97% HRpeak
≥98% HRpeak
a data from Riebe et al. [5].
M.J. Hutchinson and V.L. Goosey-Tolfrey
487
Spinal Cord (2022) 60:484 – 490
descriptions of “moderate” and “vigorous” exercise intensity, as
used by the exercise guidelines for adults with SCI [1, 3]. However,
the ﬁndings also show that using ﬁxed %V̇O2peak or %HRpeak
cannot guarantee a homogenous domain-speciﬁc exercise inten-
sity prescription for adults with SCI.
Fixed percentages and intensity domains for exercise
intensity prescription
The ﬁnding of adults with SCI being in different intensity domains,
as deﬁned in this study according to LT1 and LT2, despite being at
the same %V̇O2peak or %HRpeak supports similar evidence in non-
disabled participants [9]. The domain-speciﬁc distribution is also
arguably more variable in adults with SCI. For V̇O2peak, Iannetta
et al. [9]. report participants in moderate, heavy, and severe
domains only at 70% V̇O2peak, whereas in this study this was
shown at several ﬁxed percentages, 55-70% V̇O2peak in PARA and
60-70% V̇O2peak in TETRA. It would, therefore, given recent calls to
stop using ﬁxed percentages for exercise intensity prescription in
non-disabled participants [7, 9, 10], seem appropriate that this is
expanded to apply to adults with SCI performing aerobic exercise.
This would apply to all adults with SCI, and not just the athletic
population utilised in this study. Inter-individual variation will exist
in sedentary or low-active participants as much, if not more, than
in athletic groups, further limiting the use of ﬁxed percentages for
exercise intensity prescription.
Instead, more attention should be given to methods that can
lead to participants exercising within the same exercise intensity
domain, each of which are characterised by distinct V̇O2 kinetic
and blood lactate proﬁles [19, 20]. This study utilised LT1 to
identify the transition between moderate and heavy intensity
domains, in accordance with the literature [19, 20]. However, a
limitation within the current study was the use of LT2 to identify
the heavy-severe domain transition, due to a lack of evidence
supporting this, as well as the number of different methods used
to measure and identify LT2 [7, 21]. As such, ﬁrm conclusions
cannot be made regarding the heavy-severe domain transition
from this study. It would have been more appropriate to measure
CP/CS for this purpose [19–21], however, only data from a GXT
were available in this study.
This highlights an important limitation to the widespread
implementation of intensity domain-related exercise prescription.
Speciﬁcally, the suitability of different testing protocols for
identifying different threshold concepts, as well as data collection
and threshold identiﬁcation methods used [21]. This poses the
challenge of how to simply prescribe domain-speciﬁc exercise
intensity. Data from the present study may support the use of RPE
for this purpose, as no difference in RPE was found between
groups at LT1 (Fig. 1g) and LT2 (Fig. 1h), in support of previous
ﬁndings [15]. Mean RPE at LT1 and LT2 in this study were found to
be 11 and 15, respectively, suggesting that these values could be
Fig. 2
Distribution of individuals in moderate, heavy, and severe
intensity domains at ﬁxed %V̇O2peak. a PARA group. b TETRA
group. c NON-SCI group.
Fig. 3
Distribution of individuals in moderate, heavy and severe
intensity domains at ﬁxed %HRpeak. a PARA group. b TETRA
group. c NON-SCI group.
M.J. Hutchinson and V.L. Goosey-Tolfrey
488
Spinal Cord (2022) 60:484 – 490
used to guide exercise prescription using a simple and easy to
implement method. However, the SD for these values ranged from
1 to 2 units dependent on group. This inter-individual variation
serves, therefore, as a limitation to the use of ﬁxed RPE values for
exercise intensity prescription and highlights the importance of
individualisation in this context. Individualisation, though, poses a
further challenge, due to the trade-off between the precision
required for research purposes versus the simple messaging for
population-level exercise guidelines.
Implications for research
Our results highlight the need to prescribe exercise intensity in a
way that ensures a homogenous intensity domain distribution
between participants within both acute and longitudinal study
designs. Previously, studies have conducted training interventions
with an intensity of either a target range, or ﬁxed value, using
variables such as %V̇O2peak, %HRpeak and RPE, e.g. [22–26]., which
will have led to signiﬁcant domain heterogeneity. This means the
dose of exercise stimulus would not have been controlled
between
participants.
Moving
forwards,
researchers
should
identify the domain transitions and prescribe intensity in relation
to these. That being said, the authors are not aware of any
investigations into CP/CS using participants with SCI, so initial
studies
need
to
investigate
the
validity
and
reliability
of
identifying domain transitions in participants in SCI. Furthermore,
V̇O2 kinetic responses to exercise in each domain should be
investigated in participants with SCI, due to potential differences
in V̇O2 kinetics between non-disabled participants and those with
SCI [27]. Finally, these investigations must also account for any
differences based on the mode of exercise [28].
Our ﬁndings also emphasise the need to individualise the
exercise
intensity
prescription.
In
non-disabled
participants,
standardised intensity prescription (e.g., 55–75% V̇O2peak), has
been shown to lead to signiﬁcant heterogeneity in responsiveness
[29] leading to participants being described as either “responders”
or “non-responders” to the intervention. However, an individua-
lised exercise prescription (relative to ventilatory threshold) in
non-disabled
participants
resulted
in
100%
responsiveness,
compared to 60% in the standardised intervention [30]. Subse-
quently, future exercise research in participants with SCI should
individualise the intensity prescription according to intensity
domains, whilst also report individual responsiveness to an
intervention. This will improve methodological control while also
increasing conﬁdence in conclusions made based on the data.
Implications for exercise guidelines using “moderate to
vigorous” exercise intensity
Exercise guidelines must balance the precision required for a
speciﬁc intensity prescription, against the need for a simple
population-level recommendation. Furthermore, scientiﬁc guide-
lines must undergo a knowledge translation process to ensure
that the scientiﬁc integrity of the guidelines are maintained, whilst
also incorporating the varied needs of all potential end-users [31].
In adults with SCI, the scientiﬁc guidelines [1, 3] recommend
performing aerobic exercise at a “moderate to vigorous” intensity,
without providing any speciﬁc details on what this means. The same
intensity prescription is also used in a community and clinical-
practice version of the guidelines [31]. Results from the current study
would
suggest
the
scientiﬁc
integrity
of
such
an
intensity
prescription is questionable. Table 3 shows equivalent thresholds
for PARA and TETRA for “moderate” and “vigorous” intensity, based
on the guidelines for non-disabled adults [5]. Combining these with
the intensity domain distributions in Fig. 2, shows participants were
spread across moderate, heavy, and severe domains at both
“moderate” and “vigorous” intensities. It should also be noted that
participants in the present study were competitive athletes, and that
responses would likely be even more variable for sedentary or low-
active populations. This shows how the use of “moderate” to
“vigorous” intensity will not lead to anything close to resembling a
uniform exercise intensity prescription between individuals. It also
shows how someone expecting to perform “moderate” intensity
exercise may actually be much closer to their maximum capacity.
This will likely decrease the pleasure the person feels during the
exercise, which could ultimately impact on whether they decide to
continue doing it [32].
As it is operationally more difﬁcult to deﬁne compared to
frequency (e.g., 3 times a week) and duration (e.g., 30 min), it is
possible that exercise intensity becomes an ignored piece of
exercise guidelines. Perhaps research could seek to understand
end-user
perceptions
of
“exercise
intensity”,
or
needs
for
interpreting and monitoring intensity, before using that informa-
tion alongside physiological principles to underpin an evidence-
informed intensity prescription. Alternatively, maybe the focus for
exercise guidelines should shift from exercise intensity to also
acknowledge factors that might help individuals become and stay
active, such as their pleasure when performing exercise [32].
CONCLUSION
Prescribing a “moderate to vigorous” exercise intensity will not
lead to a uniform intensity domain distribution in adults with SCI.
Neither will the use of ﬁxed percentages of V̇O2peak or HRpeak, or
generic values of RPE, due to inter-individual variation. Such
methods of exercise intensity prescription should not be used in
this population. Future research should individualise the intensity
prescription to ensure a homogenous inter-individual domain
distribution. However, the accurate testing required to ensure an
individualised intensity prescription poses a challenge to exercise
guidelines aimed at informing behaviour at the population-level.
Data archiving
The datasets generated and analysed during the current study are
available from the corresponding author on reasonable request.
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ACKNOWLEDGEMENTS
We would like to thank the various members of the Peter Harrison Centre for
Disability Sport who were involved in the collection of data used in this study. These
include Dr John Lenton, Dr Christof Leicht, Dr Tom Paulson, Dr Terri Paulson, Dr Katy
Griggs, Dr Ben Stephenson, Dr Ben Stone, Tom O’Brien, and Conor Murphy.
AUTHOR CONTRIBUTIONS
MJH and VLGT were both responsible for developing the concept of the study and
were both involved in the data collection. MJH performed the data analysis, with MJH
and VLGT involved in the interpretation of the data. MJH drafted the original version
of the manuscript, with VLGT providing comments. MJH and VLGT were both
responsible for reviewing and approving the ﬁnal version of the manuscript.
FUNDING
This work was supported by funding from the Peter Harrison Foundation.
STATEMENT OF ETHICS
We certify that all applicable institutional regulations concerning the ethical use of
human volunteers were followed during the course of this research.
COMPETING INTERESTS
The authors declare no competing interests.
ADDITIONAL INFORMATION
Supplementary information The online version contains supplementary material
available at https://doi.org/10.1038/s41393-021-00733-2.
Correspondence and requests for materials should be addressed to Victoria L.
Goosey-Tolfrey.
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© The Author(s) 2021
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Spinal Cord (2022) 60:484 – 490

Rethinking aerobic exercise intensity prescription in adults with spinal cord injury: time to end the use of "moderate to vigorous" intensity?
Hutchinson, Michael J,Goosey-Tolfrey, Victoria L