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Review
The strength-endurance continuum revisited:
a critical commentary of the recommendation of
different loading ranges for different muscular adaptations.
James P. Fisher, James Steele, Patroklos Androulakis-Korakakis, Dave Smith, Paulo Gentil, Jürgen Giessing
Objectives: The accepted wisdom within resistance training is that differing loads and corresponding repetition maximum (RM)
ranges are optimal for inducing specific adaptations. For example, prominent organizations and their respective publications
have typically prescribed heavy loads for maximal strength increases ( ≥ 85% 1RM/ ≤ 6RM), more moderate loads for
hypertrophy (67-85% 1RM/6-12RM) and lighter loads for local muscular endurance (LME; ≤ 67% 1RM/ ≥ 12RM). Since we
believe these recommendations originate from a misunderstanding and misinterpretation of DeLorme’s strength-endurance
continuum, the aim of this narrative review is to discuss the preponderance of research surrounding training load and
strength and LME adaptations.
Design & Methods: Narrative Review
Results: The current body of literature fails to support recommendations for the use of specific loads for specific strength,
hypertrophy or LME adaptations. Furthermore, that the strength-endurance continuum originally presented by DeLorme was
never intended to compare the use of heavier- and lighter-load resistance training, but rather to consider the adaptations to
strength training and aerobically based endurance exercise. Finally, a lack of clarity considering absolute- and relative- LME
has confounded understanding of this adaptation.
Conclusions: The body of research supports that absolute LME appears to adapt as a result of maximal strength increases.
However, relative LME shows minimal response to strength training with either heavier- or lighter-loads. We present the lim-
itations of the current body of research and promote specif ically detailed recent research as well as the importance of gener-
ality of strength and LME in both sporting and real-world settings.
(Journal of Trainology 2020;9:1-8)
Key words: strength local muscular endurance load intensity repetitions, resistance training
INTRODUCTION
Traditionally, resistance training has been prescribed based
upon knowledge of the maximal load a person can lift for a
single repetition (i.e., 1-repetition maximum; 1RM) and then
training performed using a predetermined percentage of this
load based on the desired outcome (e.g. increased strength,
hypertrophy, or local muscular endurance; LME). The promi-
nent organisations within strength training (the National
Strength and Conditioning Association [NSCA] and
American College of Sports Medicine [ACSM], have typically
prescribed training loads as follows: ~ 60-70% 1RM for nov-
ice or intermediate trainees, or ~80-100% 1RM for advanced
individuals for strength; ~70-85% 1RM for novice or interme-
diate, or ~70-100% 1RM for advanced individuals for hyper-
trophy; and ≤ 67% 1RM for local muscular endurance
(LME;1,2). This is often referred to as the repetition maximum
continuum or the strength-endurance continuum; the idea that
heavier loads optimise strength adaptations and lighter loads
optimise LME adaptations. We propose that this is the gener-
ally accepted wisdom amongst personal trainers and strength
and conditioning coaches based on these long-standing
beliefs.
However, cu rrent literature3,4 supports the view that heavy-
and light-loads produce equivalent increases in strength
(when measured by impartial methods to parse-out improve-
ments in skill due to familiarity of the testing mode) when
exercise is continued to momentary failure. For instance,
improving maximal strength (as measured by 1RM in a spe-
cific exercise) might best be achieved by practicing heavy/
maximal repetitions of that specific exercise (e.g., to improve
a bench press 1RM a person might be best advised to practice
a bench press 1RM3-6). Certainly, evidence has supported the
notion that motor schemata are both highly movement specif-
ic as well as load/force specif ic7. As such, this appears domi-
nantly a product of rehearsing the synchronous motor unit
recruitment required for maximal lifts (e.g., bench press), as
well as their coordinated recruitment patterning for the tech-
nical elements of more complex exercises (e.g., clean and
jerk). However, evidence suggests that the apparent superiori-
ty of heavy/maximal loading might be absent when using
impartial testing methods. For example, Mitchell et al.8
reported greater increases in 1RM for groups training with
1
Received December 16, 2019; accepted January 18, 2020
From the Solent University, East Park Terrace, Southampton, UK (J.P.F., J.S., P.A.K.), Manchester Metropolitan University, Crewe, UK (D.S.),
Faculdade de Educação Física e Dança, Universidade Federal de Goiás, Goiânia, Brazil (P.G.), and University of Koblenz-Landau, Germany (J.G.)
Communicated by Takashi Abe, PhD
Correspondence to: Dr. James P. Fisher, Solent University, East Park Terrace, Southampton, UK.
Email: James.Fisher@solent.ac.uk
Journal of Trainology 2020;9:1-8 ©2012 The Active Aging Research Center http://trainology.org/
Journal of Trainology 2020;9:1-82
80% of 1RM compared to those training with 30% 1RM.
However, when tested using isometric torque (an impartial
testing method since neither group had trained using isomet-
ric contractions) there were no between group differences in
strength increases. Fisher, Ironside and Steele9 reported simi-
lar f indings; that dynamic knee extension exercise at either
80% or 50% of maximum torque produced similar increases
in maximal isometric strength. This is further supported by a
recent systematic review and meta-analysis considering high-
( > 60% 1RM) and low- ( ≤ 60% 1RM) load training.4 The
authors reported statistically significant differences in favour
of heavy loads when considering 1RM, yet no signif icant dif-
ference when considering impartial (isometric) strength test-
ing.
Furthermore, evidence suggests that hypertrophic adapta-
tions can be equally attained almost irrespective of training
load used.4,8 For example, the aforementioned study by
Mitchell et al.8 repor ted similar increases in quadriceps mus-
cle volume between groups training at 30% and 80% 1RM. In
addition, a comprehensive review comparing loads > 60%
1RM to those ≤ 60% 1RM concluded “muscle hypertrophy
can be equally achieved across a spectrum of loading rang-
es”4. The caveat to these similar increases in muscle size irre-
spective of load appears to be intensity of effort, that is; that
similar adaptations are attained so long as participants train
to momentar y failure.
In view of these publications it is interesting that there have
been no recent reviews of the strength-endurance continuum
in consideration of the relationship between maximal strength
(e.g., 1RM) and LME adaptations. As such, we believe the
area warrants a narrative discussion of the origins of this con-
tinuum as well as to discuss often cited articles supposedly
supporting a continuum and perhaps attempt to explain why
differing adaptations might occur. With this in mind, the aim
of this commentary is to discuss the limitations of the notion
of the repetition maximum /strength-endurance continuum
and provide more evidence-based recommendations for prac-
titioners.
Absolute- and Relative- Muscular Endurance
A notable problem with any recommendations pertaining to
strength and LME adaptation is the failure to differentiate
between absolute and relative LME. Absolute LME should be
considered the number of repetitions possible at a given abso-
lute load, whereas relative LME is the number of repetitions
possible at a given %1RM.10 In testing, these would be repre-
sented by use of either an absolute load (that does not change
in relation to strength or following any strength training inter-
vention), or, in contrast, a relative load (that is always mea-
sured as a percentage of maximal strength. e.g. %1RM). The
ACSM 2 (page 697) stated:
“RT has been shown to increase absolute LME (i.e., the
maximal number of repetitions performed with a specific
pre-training load), but limited effects are observed in rel-
ative LME (i.e., endurance assessed at a specific relative
intensity or %1RM)…
…A relationship exists between increases in strength and
LME such that strength training alone may improve
endurance to a certain extent.”
This statement appears to conflict with the guidance based
on loading and repetition ranges.1,2 As such we should ques-
tion why, if absolute LME improves with maximal strength
and relative LME shows limited effects, would we recom-
mend that individuals use different training loads or repeti-
tion ranges to target strength or LME.
Clarity regarding the work of DeLorme
The above guidelines by the ACSM2 and NSCA1 cite the
work of Anderson and Kearney11, Stone and Coulter10, and
Campos et al.12; each of which will be discussed later herein,
in support of what has become the accepted “wisdom” in
strength and conditioning; the strength-endurance continuum.
Each of these studies cites, in turn, the seminal work of
DeLorme13 where he discusses the use of heavy resistance
exercise rather than endurance exercise for restoration of
muscular strength and power in injured veterans. However,
each of these studies, and many others, appear to have misin-
terpreted, and as such misrepresented, DeLorme’s hypothesis
and f indings. For example, DeLorme clarifies “By ‘power-
building’ exercises we mean exercises in which a heavy resis-
tance is used for a low number of repetitions. ‘Endurance-
building’ exercises are those in which a low-resistance is used
for a large number of repetitions” (page 650).
Whilst DeLorme states endurance exercise to be low-resis-
tance/high-repetition, he further clarifies examples as “stair-
climbing, walking, bicycling and similar low-resistance exer-
cises” (651). He continues: “How illogical it would be for a
track man to train for long-distance running events solely by
doing knee bends with heavy weights on his shoulder, or a pro-
fessional weight-lifter to train for heavy lifts solely by running
several miles a day” (page 651). In fact, within his 1945 arti-
cle he provides guidance that “the workout must begin with a
weight considerably less than the 10RM, so that when the
10RM has been reached, seventy to 100 repetitions have been
performed” (page 648). Notably this number of repetitions
was completed across 7-10 sets of 10 repetitions. Furthermore,
DeLorme does not use the term muscular endurance through-
out this article, in contrast to what other authors have stat-
ed10-12. Instead, DeLorme was making reference to what is
now considered aerobically based endurance exercise modali-
ties (e.g., “stairclimbing, walking, bicycling” and “running
several miles a day”). In this discussion of the work of
DeLorme it is important to clarify that he developed these
ideas in later publications, and in 1948 DeLorme and
Wat k i n s14 clarified that “it has become apparent that the term
‘heavy resistance exercises’ bears false implications, and the
term ‘progressive resistance exercises’ was suggested as being
far more appropriate” (page 263). It is, thus, evident that
DeLorme did not intend to differentiate between heavy- and
light-load resistance training per se, but rather to determine
the disparity in adaptations between progressive resistance
exercise and aerobically based endurance exercise. It is per-
Fisher et al. The strength-endurance continuum revisited 3
haps also noteworthy that in this article DeLorme and
Wat k i n s14 suggested a decreased training volume, from 7-10
sets to, the now commonly accepted, 3 sets of 10 repetitions.
Perhaps notably though, this was described in the following
format;
First set of 10 repetitions - use ½ of 10 repetition maximum
Second set of 10 repetitions - use ¾ of 10 repetition maxi-
mum
Third set of 10 repetitions - use 10 repetition maximum
In this case DeLorme appears to be suggesting 2 submaxi-
mal sets and then a single set to repetition maximum, with the
technical advice that:
“The movements are done smoothly, rhythmically, and
without haste, but not so slowly that the mere holding of
the weight will tire the patient. Quick or sudden motions
while exercising are to be avoided.” (page 646).
It is unclear as to whether DeLorme was suggesting to train
to momentary failure, or to a repetition maximum, as have
been recently more clearly defined.15 Nevertheless, it is clear
that the final set in this protocol was intended to require at
least a near maximal effort. It is perhaps also worth mention-
ing that DeLorme13 (page 649) describes the principles of
double-progression; that, when performing a given exercise,
as the number of repetitions increases beyond a target range
(e.g., 8-12) a person should increase the load being used,
which has the subsequent effect of reducing the repetitions
possible, and so the trainee repeats the process as he or she
becomes stronger. Whilst DeLorme does not provide a cita-
tion for this concept our research suggests that this originates
from Allan Calvert in his text “The First Course in
BodyBuilding and Muscle Developing Exercises”.16 As an
example of double progression; a person who could initially
only perform 8 repetitions with a load of 100kg progresses
over time to be able to perform 12 repetitions with 100kg
(with all other exercise factors being equal; repetition dura-
tion, range of motion, exercise technique, etc.). He or she then
increases the load to 105kg and the number of repetitions
which can be performed decreases to 8 repetitions. If we
accept that an 8RM is a measure of strength, then the necessi-
ty of this principle to increase strength is something of a para-
dox; it is built on a premise that as we increase the number of
repetitions we perform we increase strength sufficiently to
increase the training load. But that increasing the load is
important to continue increasing strength. Ultimately, this
principle is anecdotally used to support the strength-endur-
ance continuum and that of specificity: lifting heavier weights
increases maximal strength, whilst performing a greater num-
ber of repetitions with a lighter weight increases local muscu-
lar endurance. However, it seems far more likely that double
progression in this sense represents a more time-efficient, but
not essential, method of training. For example, if performed at
a repetition duration of 2s concentric: 2s eccentric, perform-
ing 8-12 repetitions represents a time of 32-48 seconds. If a
person were to continue increasing strength with an absolute
load, and thus continue increasing the number of repetitions
they could perform, then this time under load might become
impractical, and other sensations such as discomfort might
become a factor for exercise cessation (see later section on
effort and discomfort).
Repetition Maximum Continuum
Within the fourth edition of “Essentials of Strength Training
and Conditioning”, Haff and Triplett1 provide a table (17.9,
page 458) clarifying loads/repetition ranges for optimizing
specific strength (≥ 85% 1RM/ ≤ 6RM), hypertrophy (67-85%
1RM/6-12RM), and muscular endurance (≤ 67% 1RM/ ≥
12RM) adaptations. However, the references cited do not
wholly support these recommendations. For example, two of
the eight citations are textbooks17,18, and a third citation is a
chapter from a book.19 The fourth and fifth citations are a
commentary/review article20, and an ar ticle aimed at provid-
ing strength training recommendations by Kraemer and
Koziris21. None of these citations are empirical studies pre-
senting data. Of the remaining three citations, the first empir-
ical study, that of Berger22, considered bench press strength
increases for 199 male college students following a 12-week
intervention. Berger22 reported more favorable strength
increases for 8RM training compared to both higher- (10RM
and 12RM) and lower- (2RM) repetition maximum training.
The second empirical study, that of Herrick and Stone23, com-
pared previously untrained females divided into one of two
groups; either progressive resistance exercise (PRE; 3 sets of
6RM for 15 weeks) or periodized resistance exercise (PER; 8
weeks of 3 sets using 10RM, 2 weeks of 3 sets using 4RM and
2 weeks of 3 sets using 2RM, with 1 week of active rest
between each cycle). The authors measured bench press and
back squat pre- and post-inter vention as well as every 3
weeks (totaling 6 testing time points) finding significant with-
in-group strength increases for both groups with no between-
groups differences. The third empirical study, by Tesch and
Larsson24, took biopsies from the vastus lateralis and medial
deltoid muscles from 3 competitive bodybuilders, as well as
measuring strength of the quadriceps using isokinetic dyna-
mometry. They compared this data to reference groups of
physical education students and national elite power- and
weight-lifters. They did not conduct an intervention that com-
pared training adaptations following the proposed differing
repetition ranges. Interestingly, the authors reported similar
muscle morphology between the bodybuilders and the physi-
cal education students (% fast twitch muscle fibres, % fast
twitch muscle area, fast twitch: slow twitch ratio, as well as
fast twitch-, slow twitch- and mean- fibre area), stating:
“We did not observe any sign of individual muscle fiber
enlargement in either thigh or shoulder muscles of suc-
cessful bodybuilders. Thus, despite the considerably
greater body weight per height and less body fat in body-
builders compared to habitually trained and age matched
men, mean fiber area did not differ.” (page 305).
It can only be assumed that this study was cited based on
the comments in the discussion that bodybuilders typically
perform 3 or more sets of 6-12 repetitions to concentric fail-
Journal of Trainology 2020;9:1-84
ure, interspersed with short recovery periods - which is
aligned to the NSCA recommendation cited above.1 However,
based on this as well as the previous citations it is not clear
how Haff and Triplett1, nor the organization (NSCA), are able
to justifiably endorse such recommendations.
Support for a Repetition-Maximum Continuum
Since we have clarified that the strength-endurance continu-
um was never proposed to present disparate training adapta-
tions to heavier- and lighter-loads in resistance training, we
shall use the term repetition-maximum continuum in fur ther
discussion of this concept. The three often cited empirical
studies used (by the ACSM/NSCA) to support the repetition
maximum continuum shall now be considered chronological-
ly.
Anderson and Kearney11
The publication by Anderson and Kearney11 is a common
citation in favor of the repetition maximum continuum and as
such, it is worth discussing in detail the research design.
Forty-three untrained males were divided into heavy-load
(HL, n = 15; 3sets of 6-8RM), moderate load (ML, n = 16; 2
sets of 30-40RM), and light-load (LL, n = 12; 1 set of 100-
150RM) training groups. Participants trained using the bench
press exercise 3 x / week for 9 weeks. The authors reported
pre- and post-intervention 1RM, repetitions for absolute-LME
using 27.23kg, and repetitions for relative-LME using 40% of
pre- and post-intervention 1RM. Analysis of variance
revealed significant increases in 1RM for all groups
(HL = 13.7kg, ML = 5.4kg, and LL = 3.2kg) with a significant
group x time interaction. The authors found significant pre- to
post-intervention increases for absolute-LME (p < 0.0001;
HL = 9.5, ML = 14.4, and LL = 14.6 repetitions), but between-
group differences were not statistically significant (p < 0.13).
For relative-LME the authors reported significant pre- to
post-intervention changes (p < 0.0001) as well as group x test
interaction (p < 0.0001). Follow up analyses revealed signifi-
cant increases in the number of repetitions for ML and LL
groups which were also statistically significantly greater than
the change in repetitions for the HL group. There were no sig-
nificant differences for the change in the repetitions between
the ML and LL groups. The values for change in repetitions
from pre- to post-intervention for relative-LME were HL =
-2.86 repetitions/-6.99%, ML = 8.81 repetitions/+22.45%, and
LL = 10.67 repetitions/+28.45%. The authors reported a
tempo of 40 repetitions per minute, for muscular endurance
testing as well as training for the ML and LL groups.
It is interesting that whilst the HL group increased their
1RM by 13.7 kg (compared to only 5.4 kg and 3.2 kg for ML
and LL groups, respectively), the number of repetitions they
were able to perform at the absolute load of 27.23 kg (equiva-
lent to 40% of their pre-intervention 1RM, and only 33% of
their post-intervention 1RM) increased to a lesser degree
(although not significantly so) than the ML and LL groups
(14.4 and 14.6 repetitions, respectively). Furthermore, that
when performing repetitions assessed for relative-LME at
40% 1RM, the ML and LL groups achieved increases in the
number of repetitions with an increased load (8.8 and 10.7
repetitions, respectively). In considering the data in more
detail and by group, the LL group increased their 1RM by 3.2
kg, which resulted in an increase to their load at relative-LME
(40%) of only 1.3 kg, whilst the ML group increased their
1RM by 5.4 kg, which resulted in an increase to their load at
relative-LME (40%) of only 2 kg. It seems reasonable to sug-
gest that the increased number of repetitions for relative-LME
for the ML and LL groups might be a result of such small
changes in the loads used (i.e. < 2 kg). In this sense, the rela-
tive-LME test might have been closer to an absolute-LME
test.
It is interesting that, in the introduction, Anderson and
Kearney11 rationalize their own research by citing three stud-
ies25-27 which they claim challenge the observations of
DeLorme13. However, these studies, as well as their own,
compare heavy-load, low-repetition vs. light load, high-repeti-
tion resistance training. As clarified, this study design does
not resemble, and thus does not challenge, DeLorme’s obser-
vations regarding progressive resistance exercise compared
with aerobically based endurance modalities. Furthermore,
each of these three studies supported that both heavy- and
light-loads produce similar enhancement of muscular strength
and LME. Indeed, Anderson and Kearney11 stated that the
findings of Delateur et al.26 revealed that “choice of weights is
not of prime importance as long as the repetitions are contin-
ued to the point of fatigue” (page 248). They continue
“Strength and endurance thus appear to be two closely related
attributes of the well-trained muscle” (page 248).
Stone and Coulter10
A further study considering heavy-, moderate- and lighter-
loads in relation to increases in 1RM, absolute-LME and rela-
tive-LME is that of Stone and Coulter10. The authors divided
fifty untrained females into heavy-load (HL, n = 17; 3sets of
6-8RM), moderate load (ML, n = 16; 2 sets of 15-20RM), and
light-load (LL, n = 17; 1 set of 30-40RM) training groups.
Testing was performed for bench press (BP) and back squat
(BS) exercises with maximal strength measured using 1RM,
absolute-LME measured as repetitions at 15.9kg (BP) and
25kg (BS), and relative-LME measured using repetitions at
45%1RM (BP) and 55% 1RM (BS). The authors stated that
relative-LME was tested at two loads; load 1 involved pre-
and post-testing repetitions at a given percentage of the pre-
intervention 1RM. However, re-testing muscular endurance
post intervention using the same pre-intervention %1RM is
absolute- not relative-LME. Thus, the authors performed two
absolute-LME tests; for bench press they used 15.9kg and
45% of pre-intervention 1RM, and for back squat they used
25kg and 55% of pre-intervention 1RM. The second relative-
LME test using load 2 was a true relative-LME test where the
pre-test used a % of the pre-intervention 1RM, and the post-
test used the same percentage of the post-intervention 1RM.
Tempo was described as 40 and 30 repetitions per minute for
the bench press and back squat, respectively. The authors
reported no significant differences between the three proto-
cols for improvements in 1RM, or absolute-LME, and report-
ed no significant increases in relative-LME. It is, therefore,
surprising that the NSCA1/ACS M 2 cited this paper for the use
Fisher et al. The strength-endurance continuum revisited 5
of higher repetition ranges for improving muscular endurance
when the results do not support this claim.
Campos et al.12
Perhaps the most notable research cited to support a repeti-
tion-maximum continuum is that of Campos et al.12. Thirty-
two physically active but previously untrained young males
were divided into low repetition (Low Rep; 3-5RM, n = 9),
intermediate repetition (Int Rep; 9-11RM, n = 11), high repeti-
tion (High Rep; 20-28RM, n = 7), and non-exercising control
(CON; n = 5) groups. The exercising groups performed leg
press, squat and knee extension exercises 2x/week for the f irst
4 weeks and 3x/week for the last 4 weeks. Par ticipants were
tested pre- and post-intervention for 1RM and, after a 4-5
minute recovery, they completed as many repetitions as possi-
ble with 60% 1RM (the authors do not clarify whether this
was relative- or absolute- LME in the article, but this descrip-
tion and personal correspondence have confirmed this to be a
test of relative LME). The Low Rep group showed signifi-
cantly greater 1RM increases in leg press and squat exercises
compared to the other groups, but the increase in k nee exten-
sion 1RM was signif icantly greater than the High Rep group
only. The authors reported that the three training groups sig-
nificantly improved in the number of repetitions performed
with 60% 1RM in the squat exercise, but neither the Int Rep
group nor the Low Rep group showed a significant improve-
ment in the leg press or knee extension exercises. In fact, the
number of repetitions significantly decreased in the Low Rep
group for the leg press. The authors did not report a tempo or
repetition duration for testing or training.
The authors provide data in the form of figures, rather than
specific numerical values, and as such these cannot be dis-
cussed in detail. Indeed, in private correspondence we have
been advised that the raw data is no longer available for con-
sideration/analyses. However, in an attempt to better consider
this study, we have used a digitization program to calculate
the values from Figure 3 in the article12 (WebPlotDigitizer,
v3.12; Ankit Rohgati; http://arohatgi.info/WebPlotDigitizer/
index.html). We estimate pre-intervention 1RM values for the
leg press to be ~310kg for Low Rep, ~294kg for Int Rep, and
~300kg for High Rep (reported as not significantly different
between groups). The post-intervention 1RM values are esti-
mated as ~498kg for Low Rep (reported as 61% improve-
ment), ~398kg for Int Rep (reported as 36% improvement) and
~364kg for High Rep (reported as 32% improvement,
although using the values extracted using the digitization
software we calculate a 21% improvement). With a similar
method using the authors’ Figure 4, the local muscular endur-
ance testing appears to have produced estimated pre-interven-
tion values for the leg press of ~40 repetitions for Low Rep,
~39 repetition for Int Rep, and ~35 repetitions for High Rep.
The corresponding estimated post-testing repetitions were
~32 repetitions for Low Rep (reported as -20% change), ~43
repetitions for Int Rep (reported as 10% improvement), and 68
repetitions for High Rep (reported as 94% improvement).
It is, therefore, sur prising that the low rep group, increasing
their 1R M strength by ~188kg/61% decreased their relative
muscular endurance from 40 repetitions with ~186kg to 32
repetitions with ~298kg. In contrast, and more surprisingly,
the high rep group increased their 1RM strength by
~64kg/21% but also increased their relative muscular endur-
ance from 35 repetitions with ~180kg to 68 repetitions with
~218kg. Aside from the possibility that low rep training truly
does produce greater maximal strength increases but dimin-
ish relative muscular endurance performance whilst high rep
training produces (albeit lesser) strength increases and far
superior relative muscular endurance improvements (com-
pared to low rep training), we have hypothesized other factors
which might have confounded these results. For example (and
while we believe this to be highly improbable), though partici-
pants were randomized the relatively small sample size per
group may have resulted in heterogeneous groupings regard-
ing genetic predisposition to either maximal strength increas-
es or muscular endurance increases for low- and high-rep
groups respectively. Indeed, the wide heterogeneity in
response variation to resistance training is well known28 and,
though it is difficult to differentiate true intervention
response variation from other random variation29, it is well
evidenced that some individuals can show considerable
improvements in some outcomes but not others and vice
versa30,31. Another factor, might be that the strength increase
for the low rep group could be partially a result of improved
motor schema in the practice of synchronous recruitment3,
and the skill of the exercise itself par ticularly as the testing
resembled the training (although we might expect lower skill
increases in a leg press exercise, whether plate loaded or
selectorized compared to a more complex movement such as a
squat). Finally, and as discussed later, we might consider that
the high rep group became acclimatized to the discomfort of
performing a greater number of repetitions than the low rep
group (20-28RM compared to 3-5RM, respectively) through-
out the 8-week training intervention.
Interestingly despite each of these studies being used to
support a repetition maximum continuum of ≤ 6RM for
strength, 6-12RM for hypertrophy, and ≥ 12RM for LME
adaptations (NSCA1, page 458), only the study by Campos et
al.12 study tested these repetition ranges (e.g. strength [low
rep] 3-5RM, hypertrophy [int rep] 9-11RM, and LME [high
rep] 20-28RM). Furthermore, only Campos et al.12 took any
measurement of muscle hypertrophy. The authors reported
that a hypertrophic effect was observed in type I, IIA and IIB
muscle fibre types in the low- and inter mediate-RM training
groups only. There were no significant differences between
the low- and intermediate- RM groups for muscle fibre hyper-
trophy (low RM = 12.4, 22.9, 25.3% and inter mediate
RM = 13.1, 16.3, 27.2%, for type I, IIA, and IIB fibre types,
respectively).
Effort and Discomfort
When we consider heavier- and lighter-load RT, a factor
that might become important when trying to exercise to
momentary failure is that of discomfort compared to effort.
There is a growing body of research supporting that discom-
fort (defined as the physiological and unpleasant sensations
associated with exercise32,33) is greater when performing exer-
Journal of Trainology 2020;9:1-86
cise to momentary failure using a lighter- (50% MVC) com-
pared to a heavier- (80% MVC) load in both males and
females9,34. This is potentially a result of increased blood lac-
tate and cortisol accumulation35 and primarily thought to
result from afferent feedback mechanisms33. As such, it seems
likely that the ability to reach momentary failure with lighter
loads could be impaired by the discomfort during resistance
exercise36. This, in turn, might negatively impact the chronic
muscular adaptations across the duration of an intervention
when compared to a heavier-load group, who can reach
momentary failure and attain the desired effort with far less
discomfort. An example might be the Anderson and
Kearney11 study where participants in the HL group per-
formed 3 sets of 6-8 repetitions to momentary failure, where-
as the ML and LL group performed 30-40 and 100-150 repeti-
tions respectively. At the rate of 40 repetitions per minute this
equates to ≤ 12 seconds per set for the HL group (performing
3 sets = 36 seconds under load), 60 seconds per set for the ML
group (performing 2 sets = 2 minutes under load) and 3 min-
utes 40 seconds per set for the LL group.
Furthermore, the changes to LME testing for lighter-load/
higher repetition groups might be a potential adaptation to
discomfort as a result of the training intervention, i.e., per-
forming very high-repetition sets; e.g. 20-28RM12, 30-4010,11
and 100-150RM11. A test of LME will likely stimulate consid-
erable discomfort as a person nears maximal effort and task
failure and as such training at lighter loads/higher repetitions
might not incur neuromuscular or morphological adaptations
that improve LME but rather accommodate familiarisation
and increased tolerance of the discomfort associated with a
test of LME. Certainly, recent work has shown that repeated
exposure to exercise conditions known to cause discomfort,
such as high intensity interval training, increases pain toler-
ance and this might partly explain improvements in time to
task failure37. Indeed, there might be mechanisms beyond
muscular adaptations by which the repetition maximum con-
tinuum applies. For example, by training at heavier/maximal
loads a person might improve strength more than at lighter
loads as a result of enhanced skill, along with practicing high
synchronous motor unit recruitment, and by training at lighter
loads a person might improve LME as a result of the familiar-
isation and tolerance to the discomfort of lighter-load exer-
cise.
Hypertrophic adaptations
Whilst this narrative review has primarily been focused
upon the concurrent adaptations in maximal strength and
absolute muscular endurance across a range of training loads,
hypertrophy has often been considered in context of the few
respective studies which have tested the “hypertrophy-zone”
of the repetition maximum continuum (e.g. 67-85% 1RM/6-
12RM1). With a dearth of research, both the NSCA1 and
ACSM 2 have failed to provided support for the claims that
this loading range is optimal for muscular growth. As dis-
cussed earlier, the repetition maximum continuum, displayed
as table 17.9 (page 458) in “Essentials of Strength Training and
Conditioning”1 cites only 3 empirical studies. Those of
Berger22 and Herrick and Stone23 did not take any measure-
ment of muscle size. The final study, that of Tesch and
Larsson24, was observational in comparing intramuscular
properties following biopsy between elite bodybuilders and
reference groups of physical education students. The authors
did not perform pre- or post-intervention measurements and
did not consider different loads/repetition ranges to scientifi-
cally test the repetition maximum continuum. More so, whilst
the authors suggest that bodybuilders typically train using 3
sets of 6-12 repetitions, the data presented does not support
that this is optimal for muscle growth. In fact, as stated above,
the authors report similar muscle morphology when compar-
ing the elite bodybuilders to the physical education reference
group.
Of the other often cited studies, neither Anderson and
Kearney11, nor Stone and Coulter10 took measurements of
muscle size. Campos et al.12 considered hypertrophic adapta-
tions measured by muscle biopsy in assessment of the repeti-
tion maximum continuum, reporting similar increases in type
I, IIA and IIB muscle fibres between the groups which
trained using low reps (3-5RM) and intermediate reps
(9 -11R M).
More recent publications provide conf licting evidence to a
repetition maximum continuum. Mitchell et al.8 reported sim-
ilar increases in quadriceps muscle volume between groups
training using 30% and 80% 1RM, and a meta-analysis and
systematic review supported that hypertrophic adaptations
are similar between loads > 60% 1RM and loads < 60%
1RM4.
CONCLUSIONS
The aim of this piece was to review and challenge the com-
monly accepted wisdom of the repetition-maximum continu-
um as well as to clarify the work of Thomas DeLorme and the
strength-endurance continuum. The data and discussions pre-
sented suggest that the guidance of specific loads/repetition
ranges for strength, hypertrophy, or LME are not supported
by the evidence. When reviewing the data it appears that
strength increases are not only attainable, but effectively the
same, at both very heavy (maximal/near maximal) loads and
more moderate loads of 8-12RM. Furthermore, that as
strength increases so too does absolute-LME. Finally, that
hypertrophic adaptations appear similar across a spectrum of
loading ranges where exercise is performed to momentar y
failure.
Whilst many persons train for maximal strength, and as
such might practice heavy/maximal resistance training under
the guidance of “practicing the test”, we should not underval-
ue the importance of adaptations in absolute LME in both
sports and real-world activities. The reality is that a person
seldom performs single maximal efforts, but rather repeated
muscle actions. A prime example in a sporting environment
might be the 225lb bench press for as many repetitions as pos-
sible in the NFL Combine test. Prospective athletes are not
asked to perform a 1RM test but rather a test of absolute LME
(e.g. the load is set at 225lbs irrespective of player position or
weight). A lay example might be the movement of our own
Fisher et al. The strength-endurance continuum revisited 7
bodyweight, which, whilst it might f luctuate to a degree, is
generally relatively constant; as such tests of press-ups, pull-
ups, or dips, as well as more functional tasks such as rising
from a chair, climbing a flight of stairs, etc. are effectively
tests of absolute LME.
Practical Applications
With the above in mind, and since training specifically for
strength, hypertrophy or LME is often performed as part of a
periodised resistance training programme we caution strength
and conditioning coaches, personal trainers and trainees in
the use of specific loads/repetition ranges for specific out-
comes (e.g. strength, hypertrophy, LME). It is our view that
the preponderance of research does not support a repetition-
maximum continuum, but rather we suggest that resistance
training be performed to a high degree of effort and that loads
are self-selected based on convenience, safety, and psycho-
physiological factors such as discomfort, etc. The data sug-
gests that following this guidance similar strength adaptations
will occur irrespective of load, and that absolute LME
increases with maximal strength, whereas relative LME
shows little response to strength increases. Persons training
specifically for muscle hypertrophy are able to self-select a
load based on personal preference, accessibility, etc.
Compliance with ethical standards
Funding
No sources of funding were used to assist in the preparation
of this article.
Conflicts of Interest
James Fisher, James Steele, Patroklos Androulakis-
Korakakis, Dave Smith, Jürgen Giessing, and Paulo Gentil
declare that they have no conflicts of interest relevant to the
content of this article.
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