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Ki ne siology 51(2019)1:78- 82Grgic, J. and Schoenfeld, B.J.: A CASE FOR CONSIDERING AGE AND SEX W HEN...
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A CASE FOR CONSIDERING AGE AND SEX WHEN
PRESCRIBING REST INTERVALS IN RESISTANCE TRAINING
Jozo Grgic1 and Brad J. Schoenfeld2
1Institute for Health and Sport (IHES), Victoria University, Melbourne, Australia
2Health Sciences Department, CUNY Lehman College, Bronx, NY
Commentary
Abstract:
Current resistance training position stands recommend that rest interval duration in resistance training
should be prescribed based on the training goal and exercise selection. However, these recommendations
are mostly extrapolated from studies that included young men as participants. Therefore, they cannot be
generalized to all age groups and all resistance training programs. Herein, two overlooked, but possibly
important factors for rest interval prescription are discussed: (1) age, and (2) sex of the individual. Acute
studies indicate that older adults, as compared to young adults, require a shorter duration rest interval to
achieve recovery between sets. Due to the sex differences in fatigability, it can be speculated that men need
a longer duration rest interval than women to maintain high levels of performance. Both sex and age may be
relevant variables when determining rest interval duration in resistance exercise and should not be overlooked
by exercise practitioners in program design.
Key words: intensity; skeletal muscle; repetition maximum; exercise; training; intervals
Introduction
Rest intervals are most commonly dened as the
time dedicated to recovery between sets and exer-
cises (Baechle & Earle, 2000). The current Amer-
ican College of Sports Medicine position stand
(ACSM, 2009) suggests employing longer dura-
tion rest intervals (>three minutes) when training
for muscular strength gains, moderate rest intervals
(60-90 seconds) when training for muscular hyper-
trophy, and short rest intervals (<60 seconds) when
training for muscular endurance. In addition to the
training goal, the position stand suggests that rest
intervals might depend on exercise selection. Longer
rest intervals are recommended for multi-joint
exercises, while shorter rest intervals are deemed
sufcient for single joint exercises (ACSM, 2009).
These guidelines are mostly inferred from studies
that included young men as participants and thus
cannot necessarily be generalized to performance
in women (Ahtiainen, Pakarinen, Alen, Kraemer, &
Häkkinen, 2005; Pincivero, Lephart, & Karunakara,
1997; Robinson, et al., 1995; Willardson & Burkett,
2008). In addition to sex, the age of an individual
might be a consideration when designing training
programs. Specically, some studies suggest that
older individuals might require different resist-
ance exercise prescription when compared to the
young (Bickel, Cross, & Bamman, 2011). There-
fore, current recommendations cannot universally
be generalized to all age groups and all resistance
training programs as several variables need to be
considered when prescribing rest interval duration.
Herein, two overlooked, but likely important factors
for rest interval prescription are discussed: (i) age,
and (ii) sex of the individual.
Age
Age is commonly classied as follows: (i) chil-
dren (0-10 years), (ii) adolescents (10-18 years), (iii)
young adults (19-39 years), (iv) middle-aged adults
(40-64 years), and (v), older adults (≥65 years)
(Grgic, Mikulic, Podnar, & Pedisic, 2017). Acute
studies indicate that rest interval duration needed to
achieve recovery in resistance training might differ
based on the age of the individual. Theou, Gareth,
and Brown (2008) observed that older women (71±4
years), compared to younger women (22±2 years),
required a shorter rest interval duration to obtain full
muscular strength recovery between sets of eight
repetitions (i.e., 30 vs. 60 seconds, respectively).
These ndings are further supported by Bottaro,
Russo, and de Oliveira (2005) who demonstrated
that untrained older men (66±4 years) achieved full
recovery after four repetitions of unilateral knee
Grgic, J. and Schoenfeld, B.J.: A CASE FOR CONSIDERING AGE AND SEX W HEN... Ki ne siology 51(2019)1:78- 82
79
extension exercise by employing a brief rest interval
of 30 seconds, although there was no comparison
with recovery in younger individuals in this study.
Subsequently, Bottaro et al. (2010) carried out a
study that compared differences in recovery rates
between older (80±11 years) and younger untrained
men (24±3 years), and noted that the younger indi-
viduals did not recover fully after one- and two-
minute rest periods when performing three sets of
10 repetitions with an associated decline in peak
torque. However, older men achieved full quadri-
ceps recovery within two minutes of rest. When
comparing fatigability between young (24±2 years)
and older adults (70±5 years), Ditor and Hicks
(2000) reported that older adults were signicantly
less fatigable, as assessed by the voluntary fatigue
index (i.e., the percentage of force reduction from
baseline). Recovery of force might be important
from a muscular strength standpoint as it allows
training with higher loads, which might translate
to higher strength gains due to the principle of
specicity (Mattocks, et al., 2017). Based on these
acute results, it can be surmised that older individ-
uals may require shorter rest intervals to achieve
recovery. Such ndings might in part be explained
by the shift towards an increase in type I bers
and atrophy of type II muscle bers, both reported
to occur with ageing; an event that is occurring
due to a mixture of factors (Charette, et al., 1991).
Type I muscle bers are known to be less fatigable
than type II muscle bers, which might reduce the
recovery needs between sets in resistance training
for older adults (Schiafno & Reggiani, 2011).
The only two longitudinal studies performed in
older adults that compared adaptations to different
rest intervals support the notion that older adults
might benet from shorter rest intervals. Villanueva,
Lane, and Schroeder (2015) used a resistance
training protocol comprised of four to six exercises
per session, performed in two to three sets with four
to six repetitions per set (not performed to muscular
failure). The authors’ observed that training with a
one-minute rest between sets is superior to resting
for four minutes for gains in muscular strength,
body composition, and functional performance.
In resistance-trained older women (66±4 years),
Jambassi Filho et al. (2017) reported no signi-
cant differences in muscle activity, isometric, or
dynamic muscle strength between groups that
rested for one minute and three minutes following
an eight-week resistance training intervention. In
other words, equal effects were observed for both
groups; however, the one-minute rest interval group
had a shorter total training time, thus providing
greater training efciency. While future longitu-
dinal studies comparing adaptations to rest inter-
vals between age groups are warranted, these
initial ndings indicate that older adults might ef-
ciently recover during shorter rest intervals. Shorter
rest intervals will reduce the duration of training
sessions and might facilitate long-term adherence
to resistance training in older adults as lack of time
is commonly cited as the reason for poor exercise
adherence (Heesch & Masse, 2004). However, it
should also be noted that reducing the rest interval
duration can lead to acute increases in the rating
of perceived exertion (Farah, et al., 2012), which
should be taken into account, especially when
working with resistance training naïve individuals.
Sex
In addition to age, sex can also be a modifying
variable in the determination of rest interval dura-
tion. Men and women have different rates of fati-
gability and neuromuscular performance that are
likely due to sex differences in anatomy and physi-
ology (Hunter, 2014). Although based on a limited
sample size, there is evidence that, when compared
to women, men have larger muscles and greater
proportional area of type II muscle bers (Staron,
et al., 2000). These muscle bers are reported to
have a two-fold larger calcium uptake than type I
muscle bers (Li, et al., 2002). There is a signicant
relationship between the proportional area of type II
muscle bers and calcium activity, which together
might be related to muscle mechanics (Gollnick,
Körge, Karpakka, & Saltin, 1991; Hunter, et al.,
1999; Madsen, Franch, & Clausen, 1994). This
could be signicant from a fatigue standpoint, as
some evidence indicates that women have slower
calcium kinetics from the sarcoplasmic reticulum
than men; possibly explaining the sex differences
in fatigability (Hunter, 2014). In addition, for some
muscle groups, women may have greater muscle
perfusion, which can increase blood supply to the
activated muscle during exercise, thus delaying
fatigue and facilitating training with shorter rest
intervals (Hunter, 2014). These physiological differ-
ences, besides the possible differences in lipid
source utilization between sexes (Roepstorff, et al.,
2002), might be the primary reasons why women
are less fatigable than men during both isometric
and dynamic exercise of a similar intensity (Hunter,
2014). Taken together, it could be suggested that sex
is an important variable in exercise prescription.
Acute resistance training studies support this
notion as they indicate that women require shorter
rest intervals between sets to maintain performance
compared to men. This concept is best illustrated
by the work of Ratamess et al. (2012), who reported
that, during an upper-body resistance exercise with
a rest interval of one minute, women were able to
perform 10, nine and eight repetitions during sets
one, two and three, respectively. Men, also resting
for one minute, performed 10, seven and four repe-
titions during the three sets of bench press (Figure
1). Celes et al. (2010) observed similar differences
between men and women for lower body exercise
Ki ne siology 51(2019)1:78- 82Grgic, J. and Schoenfeld, B.J.: A CASE FOR CONSIDERING AGE AND SEX W HEN...
80
(i.e., isokinetic knee extensions), demonstrating
that both males and females required two minutes
of rest between sets to fully recover quadriceps
strength. However, for muscular strength observed
at 180°/s, a re st interval of one minute allowed suf-
cient recovery in women but not in men. Based on
these acute ndings, it can be hypothesized that
women, compared to men, might benet from a
shorter duration rest intervals.
short, and may hinder gains in strength. Nonethe-
less, rest of 80 seconds (which is still shorter than
the three minutes of rest between sets recommended
by the ACSM, 2009) between sets was sufcient to
achieve robust gains in muscular strength.
For men, the opposite seems to be the case. Both
Schoenfeld et al. (2016) and de Salles et al. (2010)
reported that training with a longer rest interval
duration (i.e., three and ve minutes, respec-
tively) was superior for gains in muscular strength
compared to a one-minute rest interval. The nd-
ings for strength are likely explained by more “prac-
tice” with heavier loads in the longer duration rest
interval groups, because, when training with shorter
rest intervals, the load needs to be reduced to main-
tain the desired repetition range. Besides strength,
Schoenfeld et al. (2016) observed greater muscular
hypertrophy (in some, but not all muscle groups) in
the three-minute vs. one-minute rest interval group;
a nding that also contradicts current resistance
training guidelines (ACSM, 2009). These nd-
ings on hypertrophy could be related to a greater
muscle protein synthesis response that occurs
when training with longer duration rest inter-
vals (McKendry, et al., 2016). While the area of
the importance of sex in prescribing rest interval
duration is an interesting one, at present, there
have been no published longitudinal studies that
would directly compare the effects of rest inter-
vals of varying duration on muscular adaptations
between sexes. Thus, this area remains speculative
and should be explored in future studies given the
current paucity of evidence. Future studies might
investigate this issue by including two mixed-sex
groups that would train with different rest intervals,
and sex difference could be explored by plotting the
results separately for men and women.
As the body of evidence continues to increase,
it is essential to revisit and reanalyze current resist-
ance exercise recommendations. It seems that
prescribing rest intervals merely on the training
goal and exercise selection could be too simplistic,
as other factors also need to be taken into account.
While the evidence is still emerging, both age and
sex might be relevant variables that should be consid-
ered in program design. Despite a logical rationale,
longitudinal studies directly exploring this topic
are needed to provide clarity on the topic. Given
the gaps in literature, future research should seek
to compare the effects of rest intervals of varying
duration on muscular adaptations between young
and older individuals. Furthermore, future studies
should endeavor to elucidate how the acute differ-
ences in fatigability between sexes might impact
long-term adaptations to rest intervals of different
durations.
Fig ure 1. Number of completed repetitions by women and men
in the three sets of the bench press exercise with a rest inter val
duration of one minute as presented by Ratamess, et al. (2012).
An unpublished 12-week intervention in 23
untrained women conducted by Reed-Hardison
(1998) showed that the group that trained with
30-second rest intervals increased lower body
strength to a greater extent compared to the group
that trained with 90-second rest intervals. More-
over, upper body strength in the 30-second rest
interval group increased by 40% compared to 30%
in the 90-second rest interval group; albeit, the
differences between the groups for the upper body
did not reach statistical signicance. Although the
study was not published, its methodological aspects
were deemed to be of good quality and similar, or
even of higher quality as compared to the other
peer-reviewed studies on the topic of rest intervals
(Grgic, Schoenfeld, Skrepnik, Davies, & Mikulic,
2018). While women may benet from shorter rest
intervals, it also should be noted that limiting rest
intervals to 20 seconds during a lower-body resist-
ance training program has been shown to produce
inferior muscular strength adaptations compared
to 80-second rest intervals. In a ve-week inter-
vention, Hill-Haas, Bishop, Dawson, Goodman,
and Edge (2007) reported that women who rested
for 20 seconds increased strength by 9%, whereas
those that rested for 80 seconds increased muscular
strength by 46%, even when matched for total
training volume. These ndings suggest that at a
certain point the rest interval duration can be too
Grgic, J. and Schoenfeld, B.J.: A CASE FOR CONSIDERING AGE AND SEX W HEN... Ki ne siology 51(2019)1:78- 82
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Submitted: September 21, 2017
Accepted: March 13, 2018
Published Online First: March 25, 2019
Correspondence to:
Jozo Grgic, M.Sc.
Institute for Health and Sport (IHES)
Victoria University, Melbourne, Australia
PO Box 14428, Victoria 8001, Australia
Email: jozo.grgic@live.vu.edu.au