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The Effects of 4 and 10 Repetition Maximum Weight-Training Protocols on Neuromuscular Adaptations in Untrained Men

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The purpose of this study was to identify and compare the strength, cross-sectional area, specific tension, and anthropometric changes elicited by 4 repetition maximum (RM) and 10RM weight-training protocols in untrained subjects. Twenty-four men (24.17 +/- 1.76 years) volunteered to participate and were randomly assigned to either the 4RM group or the 10RM group. Training was performed 3 times per week for 10 weeks; free weights were used to exercise the forearm extensors and flexors. The 4RM group performed 6 sets of 4 repetitions to failure and the 10RM group performed 3 sets of 10 repetitions to failure. Strength (1RM) was measured at 0, 6, and 10 weeks, and muscle cross-sectional area (determined through magnetic resonance imagery), specific tension (kilograms per square centimeter), and relaxed-and flexed-arm girth (corrected for skinfolds) were measured at 0 and 10 weeks. Significant (p < 0.05) increases in both forearm extensor and flexor 1RM strength, muscle cross-sectional area, specific tension, and flexed-arm girth occurred in both groups. The 4RM and 10RM loading intensities elicited significant and equal increases in strength, cross-sectional area, specific tension, and flexed girth. These results suggest that 4RM and 10RM weight-training protocols equated for volume produce similar neuromuscular adaptations over 10 weeks in previously untrained subjects. (C) 1999 National Strength and Conditioning Association
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353
Journal of Strength and Conditioning Research, 1999, 13(4), 353–359
q1999 National Strength & Conditioning Association
The Effects of 4 and 10 Repetition Maximum
Weight-Training Protocols on Neuromuscular
Adaptations in Untrained Men
JAMES L. CHESTNUT
AND
DAVID DOCHERTY
School of Physical Education, University of Victoria, Victoria, British Columbia, Canada.
ABSTRACT
The purpose of this study was to identify and compare the
strength, cross-sectional area, specific tension, and anthro-
pometric changes elicited by 4 repetition maximum (RM)
and 10RM weight-training protocols in untrained subjects.
Twenty-four men (24.17 61.76 years) volunteered to partic-
ipate and were randomly assigned to either the 4RM group
or the 10RM group. Training was performed 3 times per
week for 10 weeks; free weights were used to exercise the
forearm extensors and flexors. The 4RM group performed 6
sets of 4 repetitions to failure and the 10RM group per-
formed 3 sets of 10 repetitions to failure. Strength (1RM) was
measured at 0, 6, and 10 weeks, and muscle cross-sectional
area (determined through magnetic resonance imagery),
specific tension (kilograms per square centimeter), and re-
laxed- and flexed-arm girth (corrected for skinfolds) were
measured at 0 and 10 weeks. Significant (p,0.05) increases
in both forearm extensor and flexor 1RM strength, muscle
cross-sectional area, specific tension, and flexed-arm girth
occurred in both groups. The 4RM and 10RM loading inten-
sities elicited significant and equal increases in strength,
cross-sectional area, specific tension, and flexed girth. These
results suggest that 4RM and 10RM weight-training proto-
cols equated for volume produce similar neuromuscular ad-
aptations over 10 weeks in previously untrained subjects.
Key words: strength training, hypertrophy, neural ad-
aptation
Reference Data: Chestnut, J.L., and D. Docherty. The
effects of 4 and 10 repetition maximum weight-train-
ing protocols on neuromuscular adaptations in un-
trained men. J. Strength Cond. Res. 13(4):353–359. 1999.
Introduction
T
he neuromuscular adaptations to resistance train-
ing include muscle hypertrophy and increased
neural activation, both of which are associated with
increases in muscular strength (9, 13, 14, 18, 25). Mus-
cle hypertrophy is the result of an increase in the
cross-sectional area (CSA) of individual muscle fibers
and a concomitant increase in whole-muscle CSA (4,
10). It has been proposed that increased neural acti-
vation is the result of greater recruitment of motor
units, quicker firing frequency of the motor units, and
improved synchronization of motor unit firing (18). It
has also been suggested that there is a decrease in in-
hibitory or protective neural mechanisms (18, 26).
Increases in strength have been found without a
corresponding increase in muscle CSA and have been
attributed to neural adaptations (8, 14, 15). Neural ad-
aptations occur in the form of increased integrated
electromyographic (iEMG) activity or increased force
generated per unit of muscle (specific tension) (7). The
greater specific tension of power lifters (compared
with that of endurance athletes) has also been pro-
posed in support of neural adaptation (7). Ha¨kkinen
(8) found that elite power lifters using loading inten-
sities of 1–3 repetition maximums (RM) demonstrated
increases in strength and iEMG activity without sig-
nificant changes in CSA. A loading intensity of ap-
proximately 10RM did not increase strength or iEMG
activity. Consequently, it has been recommended that
resistance-training programs consisting of relatively
high loads (85–90% of 1RM) and few repetitions (that
is, 1–4 repetitions) are effective in increasing strength
without concomitant increases in CSA (21).
Significant improvements in strength have resulted
from significant increases in muscle fiber or whole-
muscle CSA (5, 11, 15). The greater CSA of muscle
found in strength-trained individuals (compared with
CSA of muscle in untrained individuals) has also been
proposed as evidence of a hypertrophic response to
resistance training (10). As a result of these and other
studies, training programs consisting of moderate
loads (70–75% of 1RM) and a moderate number of rep-
etitions (that is, 10–12 repetitions) have been recom-
mended to maximize muscle CSA or hypertrophy (20,
24).
However, there has not been any direct attempt to
compare the recommended training protocols with re-
gard to the specific hypertrophic and neural adapta-
tions. In addition, studies that have compared different
354 Chestnut and Docherty
loading intensities have generally not equated for dif-
ferences in training volume. Consequently, the purpose
of this study was to compare the effects of 2 training
protocols designed to elicit either a hypertrophic re-
sponse (10RM) or neural adaptation (4RM) and equat-
ed for relative training volume, on muscular strength,
CSA, specific tension, and muscle circumference.
Methods
Subjects
Twenty-four men aged 24.2 61.76 years and weighing
80.4 613.9 kg completed the study. Five subjects
served as controls, and the remaining 19 subjects were
randomly assigned to a high-intensity strength-train-
ing group (4RM; n510) or a medium-intensity hy-
pertrophy-training group (10RM; n59). All subjects
were informed of the testing and training protocols,
which were approved by the University of Victoria
Ethics Committee, and signed the consent form for
participation. Subjects were familiar with strength
training but had not followed a regimented weight-
training program or participated in weight training for
at least 1 year. They were required to refrain from any
other form of training during the study.
Resistance Training
Training was performed 3 times per week for 10
weeks, with at least 48 hours between sessions. Core
exercises consisted of triceps bench press, triceps pul-
ley press-downs, standing biceps barbell curls, and
standing simultaneous dumbbell curls. Supplemental
exercises were added for other major upper-body mus-
cle groups and included bench press, bench pulls, and
shoulder press. The 4RM group performed 6 sets of 4
repetitions (;85% of 1RM) to failure for the core ex-
ercises and 2 sets to failure for the supplemental ex-
ercises (also ;85% of 1RM). The 10RM group per-
formed 3 sets of 10 repetitions (;70% of 1RM) to
failure for the core exercises and 1 set for the supple-
mental exercises (;70% of 1RM). The initial loads
were established as a percentage of 1RM and subse-
quently adjusted to produce either 4RM or 10RM, ac-
cording to the training group. Both training groups
were therefore approximately equated for relative
training volume (repetitions 3sets 3percentage of
1RM, as calculated by O’Hagan et al. [16]). There were
3-minute and 2-minute rest periods between sets for
the 4RM and 10RM groups, respectively. The training
loads were monitored and increased when necessary
to produce failure at the desired number of repetitions.
The control group refrained from training during the
study.
Strength Testing
Strength was measured as 1RM for the tricep bench
press and the standing bicep curl. Prior to testing, sub-
jects warmed up by completing 1 set of 15 repetitions
at approximately 25RM, 1 set of 10 repetitions at ap-
proximately 15RM, and 1 set of 5 repetitions at ap-
proximately 10RM. There were 4-minute rest periods
between the warm-up and testing sets. 1RM values
were determined by having subjects attempt succes-
sive lifts of single repetitions with increasing load.
When the maximum value had been reached, the load
was taken to a beam scale and weighed. The tricep
bench press was performed with the subject lying on
the bench, keeping head, shoulders, and buttocks in
contact with the bench and feet flat on the floor. Ini-
tially, the curling bar was held apart the distance be-
tween the nipples, resting on the subjects chest at nip-
ple level. The bar was then pressed to a position in
which the elbows were locked. The barbell curl testing
was performed with the subject standing with shoul-
ders and buttocks against a wall, knees slightly flexed,
and feet shoulder-width apart. With the bar resting on
the thighs, the arms fully extended, and hands held
shoulder-width apart, the bar was lifted to full flexion
of the elbows. Strength was measured at the beginning
of the first week, the end of week 6, and the end of
week 10. The loads at training repetitions, either 4RM
or 10RM, were also recorded at the pre-, mid-, and
posttraining periods. At the end of a training session,
the loads used for the tricep bench press and the bar-
bell curl test were weighed on a beam scale. Subse-
quently, the increases in the load from pre- to mid-
training and mid- to posttraining were calculated as
percentage of change and used as additional depen-
dent measures.
Muscle CSA
Muscle CSA was measured by magnetic resonance im-
aging (MRI; Siemens Magnetom 1.5 T). Repetition
time and echo time were set at 200 and 20 ms, respec-
tively, and slice thickness was set at 10 mm. All scans
and measurements were of the right arm. Coronal
scans were used to establish humeral length and mid-
point. After the midpoint of the humerus was mea-
sured, 3 axial scans were taken: 1 at midpoint, 1 at
15% of the total humeral length proximal to the mid-
point, and 1 at 15% of the total humeral length distal
to the midpoint. The proximal midpoint scan was sub-
sequently not used because of the difficulty in differ-
entiating between the shoulder and arm musculature.
Two measures of CSA were included to determine if
the training regimen produced any selective hypertro-
phy along the muscle length. CSA consisted of the
combined forearm flexor and extensor muscle groups
and included the triceps brachii, biceps brachii, and the
brachialis. CSA was measured by using the area func-
tion of the MRI computer program. Each image was
displayed on the computer screen, and the outlines of
the forearm extensor and flexor muscles were traced
(Figure 1). The area of the bone was calculated and
subtracted from the total area to provide the CSA for
Weight-Training Protocols and Neuromuscular Adaptations
355
Figure 1. Magnetic resonance image showing the fore-
arm extensor and flexor muscles. Figure 2. Mean (6SD) pretraining and posttraining mid-
point cross-sectional area values for control (n55), 4 rep-
etition maximum (n510), and 10 repetition maximum (n
59) groups. An asterisk represents significant difference
between pretraining and posttraining values.
Figure 3. Mean (6SD) pretraining and posttraining distal
cross-sectional area values for control
(n55), 4 repetition maximum (n510), and 10 repetition
maximum (n59) groups. An asterisk represents signifi-
cant difference between pretraining and posttraining val-
ues.
the combined muscle groups. The test reliability for
repeated measures of muscle CSA was 0.998. CSA was
only obtained at the beginning of the first week and
at the end of week 10. CSA was not recorded at mid-
training because of the cost and availability of the
MRI.
Specific Tension
Specific tension was measured by dividing the com-
bined 1RM tricep press and barbell curl scores (kilo-
grams) by the CSA (square centimeters) at both mid-
point and distal axial scans.
Muscle Girth
Girth of the right arm was obtained in relaxed and
flexed positions. For relaxed-arm girth measurement,
the subject stood with arms relaxed at the side of the
body. Measurements were taken at a distance midway
between the tip of the acromion and olecranon pro-
cess. Flexed-arm girth was the largest muscle circum-
ference of the arm with the arm flexed at 908and the
wrist also flexed. Both girth measurements were cor-
rected for skinfolds as described in the Canadian Stan-
dardized Test of Fitness Operations Manual (1).
Statistical Analysis
There were no initial differences among the 3 groups,
so a repeated 3 32 analysis of variance (ANOVA;
group by time) was used to compare the posttraining
values for strength (1RM), CSA, and specific tension,
and a repeated 2 33 ANOVA (group by time) was
used to assess the time effect for each training group.
Independent t-tests and t-tests for paired samples were
subsequently conducted when significant differences
in the 3 32 ANOVA were found to identify differences
within and between group means. Statistical signifi-
cance was accepted at p#0.05.
Results
There was no initial difference in any of the dependent
variables between the 3 groups. The control group did
not change in any of the dependent variables during
the 10-week period of the study.
Cross-sectional Area
CSA data for midpoint and distal MRI scans are
shown in Figures 2 and 3, respectively. Significant in-
creases occurred at the midpoint and distal CSA for
both the 4RM and 10RM groups. There was no differ-
ence in the magnitude of CSA changes between the
4RM and 10RM groups.
Strength
Figures 4 and 5 show the data for forearm extension
and flexion strength as measured by 1RM. No signif-
icant change occurred for the control group. Signifi-
cant increases in forearm extensor strength and flexed-
356 Chestnut and Docherty
Figure 4. Mean (6SE) 1 repetition maximum pretraining
and posttraining forearm extensor strength values for the
control (n55) group and pretraining, midtraining, and
posttraining values for 4 repetition maximum (n510) and
10 repetition maximum (n59) groups. An asterisk repre-
sents significant differences from previous value.
Figure 5. Mean (6SE) 1 repetition maximum pretraining
and posttraining forearm flexor strength values for the con-
trol group (n55) and pretraining, midtraining, and post-
training values for 4 repetition maximum (n510) and 10
repetition maximum (n59) groups. An asterisk represents
significant difference from previous value.
Figure 6. Mean (6SE) pretraining to midtraining and
midtraining to posttraining percentage increases for fore-
arm extensor strength of 4 repetition maximum (4 repeti-
tions; n510) and 10 repetition maximum (10 repetitions;
n59) groups. An asterisk represents significant within-
group difference (p,0.05); a dagger represents a signifi-
cant difference between pretraining–midtraining and mid-
training–posttraining values.
Figure 7. Mean (6SE) pretraining to midtraining and
midtraining to posttraining percentage increases for fore-
arm extensor strength of 4 repetition maximum (4 repeti-
tions; n510) and 10 repetition maximum (10 repetitions;
n59) groups. An asterisk represents significant within-
group difference (p,0.05); † represents a significant dif-
ference between pretraining–midtraining and midtraining–
posttraining values.
forearm strength occurred between pre- and midtrain-
ing and mid- and posttraining for both the 4RM and
10RM groups. There was no significant difference in
the magnitude of strength changes between the 2
training periods, and there was no difference between
the 4RM and 10RM groups. The percentage of change
in forearm extensor and flexor strength (load) related
to training repetition number (4RM or 10RM) are
shown in Figures 6 and 7. Both training groups (4RM
and 10RM) showed significant increases in the per-
centage of change in forearm extensor and flexor
strength at the respective training loads. Significant
percentages of change occurred from pretraining;
there was no significant difference in the percentage
of strength changes between the 2 groups. For the
4RM group, a significantly greater percentage increase
in forearm extensor strength related to training repe-
tition number occurred from the pre- to midtraining
periods compared with the mid- to posttraining pe-
riods. Both groups showed a significantly greater per-
centage increase in forearm flexor strength at training
load during the pre- to midtraining period compared
with the mid- to posttraining period.
Specific Tension
Figures 8 and 9 show specific tension data for mid-
point and distal measurements, respectively. Signifi-
Weight-Training Protocols and Neuromuscular Adaptations
357
Figure 8. Mean (SE) pretraining and posttraining midpoint
specific tension values of control (n55), 4 repetition maxi-
mum (n510), and 10 repetition maximum (n59)
groups. An asterisk represents significant difference be-
tween pre- and posttraining values (p,0.05).
Figure 9. Mean (SE) pretraining and posttraining distal
specific tension values of control (n55), 4 repetition maxi-
mum (n510), and 10 repetition maximum (n59)
groups. An asterisk represents significant difference be-
tween pre- and posttraining values (p,0.05).
Table 1. Pretraining and posttraining relaxed-arm girth,
flexed-arm girth, and sum of skinfolds (SOS) values for con-
trol (n55), 4RM (n510), and 10RM (n59) groups (mean
6SE).
Group
Relaxed-Arm
Girth (cm)
Flexed-Arm
Girth (cm) SOS (cm)
Control
pretraining
posttraining
28.5 61.9
28.5 62.1
30.3 61.6
30.6 61.7
1.3 60.3
1.3 60.3
4RM
pretraining
posttraining
31.2 60.9
31.5 61.0
33.2 61.0
33.9 61.1*
1.4 60.1
1.3 60.2
10RM
pretraining
posttraining
31.1 61.0
31.8 60.9
32.8 60.9
33.6 60.9*
1.3 60.2
1.3 60.2
* Significant difference between pretraining and posttrain-
ing values (p,0.05).
cant increases in specific tension were found for mid-
point and distal CSA for both the 4RM and 10RM
groups, but there was no difference between the 2
training groups.
Anthropometric Girth Measurement
Data for relaxed-arm girth, flexed-arm girth, and sum
of skinfolds are shown in Table 1. Significant increases
in flexed-arm girth (corrected) occurred for the 4RM
and 10RM groups; there was no difference between
the 2 training groups. There were no differences be-
tween the pre- and posttraining values for relaxed
girth or sum of skinfolds in any group.
Discussion
In the present study, the 4RM and 10RM training pro-
tocols elicited similar increases in strength, CSA, spe-
cific tension, and muscular circumference. These re-
sults are in agreement with Sale et al. (19), who used
3RM and 10RM training protocols. Unfortunately,
these results were only reported in abstract form, and
it is difficult to compare the studies without detail in
regard to design, especially regarding the equating of
training volume.
Several studies have reported increases in strength
and hypertrophy using training loads from 6–8RM to
loads of 15–20RM (2, 11, 20, 23). However, none of the
studies compared the specificity of different training
loads within their designs or equated training vol-
umes. In addition, a variety of training loads have con-
sistently elicited significant increases in CSA.
The magnitude of the increase in strength was the
same in the present study for both the 4RM and 10RM
training groups. Schmidtbleicher and Haralambie (22)
also found a similar increase in strength for groups
that trained at either 90–100% or 30% of their maxi-
mum voluntary strength. Stone et al. (24) compared 2
high-intensity training programs and reported that in-
creasing intensity from 10RM to 2RM significantly in-
creased strength gains in previously untrained sub-
jects. However, 1 group performed 3 sets at 6RM for
the entire study, whereas the other group performed
5 sets at 10RM for the first 3 weeks, 5 sets at 5RM for
the fourth week, 3 sets at 3RM for the fifth week, and
3 sets of 2RM for the final week. The volume of train-
ing differed between the groups, and the second
group had the possible stimulus of varying intensity
over the training cycle. It has been proposed that ad-
aptation to a training stimulus can deteriorate within
2 weeks of exposure, and that adding variety can op-
timize the training response (3, 8, 17).
The proposed advantage in varying the training
stimulus could partly account for the differences in the
358 Chestnut and Docherty
percentage increases in strength from pre- to mid-
training compared with mid- to posttraining. A sig-
nificantly greater increase in percentage change in
strength occurred during pre- to midtraining com-
pared with mid- to posttraining for forearm and flexor
strength in both the 4RM and 10RM training groups.
It has been proposed in the coaching literature that the
training stimulus (such as load) should be changed ev-
ery 2 to 3 weeks to maximize neuromuscular adapta-
tions (17). The present program used a relative con-
stant load, so the optimal training response probably
occurred between the pre- and midtraining period.
Specific tension in the present study was used to
reflect changes in strength attributable to neural ad-
aptations (2, 8, 15). Both the 4RM and 10RM training
protocols produced significant increases in specific
tension, suggesting that both intensities evoked in-
creases in neural drive. There was no significant dif-
ference between the specific tension of the training
groups. Garfinkel and Cafarelli (2) found that a 10RM
loading intensity did not significantly increase specific
tension in previously untrained subjects. However,
they did not do a statistical within-group comparison;
if they had, it may have revealed a significant training
effect based on their reported findings.
The results related to the measure of specific ten-
sion should be interpreted within the limitations of the
measurement techniques. Muscle CSA was calculated
from the combination of the forearm flexors and ex-
tensors, and the force was the combined scores of the
1RM tricep press and barbell curl. In addition, the tri-
cep press may not have been the optimal measure of
the strength of the forearm extensors. Specific tension
was also calculated from bilateral exercises, but the
CSA of the limb was measured from the MRI scan.
Separation of the CSA of the forearm flexors and ex-
tensors (not possible from the MRI scan), inclusion of
unilateral exercises, and use of triceps push-down
would have provided more specific information in re-
gard to the neural adaptations that were considered to
be reflected by the measure of specific tension. How-
ever, because specific tension was compared between
the pre- and posttest results using the same method
of calculation, changes in the value would reflect some
form of neural adaptation. It is also possible that
changes in fiber type and protein expression could
have contributed to the increases in strength that were
found for both training groups.
Significant and equal increases in flexed-arm girth
were demonstrated by the 4RM and 10RM training
loads in this study. Similar results were reported by
Moritani and DeVries (14), who used a 10RM training
load for forearm flexors, and MacDougall et al. (12),
who reported significant increases in arm girth using
a 8–10RM loading intensity for forearm extensors.
These results suggest that corrected flexed-arm girth
measurement can be used to reflect training-induced
changes in muscle hypertrophy.
Discrepancies between the results of this and pre-
vious studies and the lack of specificity in the neuro-
muscular adaptations to the different training loads
may be partly attributable to the training age of the
subjects. Although the subjects were familiar with
weight training, they were regarded as untrained. Un-
trained subjects may have a more generic response to
resistance training than trained subjects. It has been
suggested that, with untrained subjects, initial
strength gains from resistance training programs are
primarily the results of neural adaptations; whereas
after 6 weeks, muscle hypertrophy contributes more to
the increases in strength (14, 15, 18). Unfortunately, it
was not possible to describe the time line of the neural
and hypertrophic adaptations within the design of the
present study. In addition, it has been suggested that
high loads are critical factors in maintaining or elicit-
ing strength and neural adaptations in trained indi-
viduals (6, 8). It is possible that trained subjects would
have responded differently than the untrained subjects
in this study in their response to the 4RM and 10RM
training loads.
Practical Applications
For relatively untrained males, a 10-week training reg-
imen of either 4RM or 10RM will produce both an
increase in strength and some degree of muscular hy-
pertrophy. Both programs were performed 3 times per
week, and each set was done to muscle failure. For
untrained individuals, it may be beneficial to use a
lighter training load to reduce the risk of injury and
to help them acquire good exercise techniques while
realizing improvements in strength and size. However,
the lack of specificity in the response to training at
different loads may not hold for individuals with a
resistance-training background. It has been previously
proposed that individuals with several years of resis-
tance training may require high loads (4–6RM) to elicit
significant neuromuscular adaptations. The relation-
ship between training age and the specificity of neu-
romuscular response to different training loads and
protocols is an area requiring further research.
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... Holm and colleagues (Holm et al., 2008) reported that high-load (~70% 1RM) versus very low-load (~15.5% 1RM) leg extensor training increased quadriceps CSA; however, the change in the high-load condition was greater than the change in the low-load condition. Chestnut and Docherty (1999) reported similar increases in muscle CSA of the upper arm following 10 weeks of upper body resistance training using ~85% of 1RM for 6 sets of 4 repetitions versus ~70% for 3 sets of 10 repetitions. Mitchell and colleagues reported that performing three sets of knee-extensor training to fatigue at 30% or 80% of 1RM resulted in similar increases in quadriceps volume measured by MRI (Mitchell et al., 2012). ...
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The effects of a 1 year training period on 13 elite weight-lifters were investigated by periodical tests of electromyographic, muscle fibre and force production characteristics. A statistically non-significant increase of 3.5% in maximal isometric strength of the leg extensors, from 48411104 to 50101012 N, occured over the year. Individual changes in the high force portions of the force-velocity curve correlated (p<0.05–0.01) with changes in weight-lifting performance. Training months 5–8 were characterized by the lowest average training intensity (77.1+2.0%), and this resulted in a significant (p<0.05) decrease in maximal neural activation (IEMG) of the muscles, while the last four month period, with only a slightly higher average training intensity (79.13.0%), led to a significant (p<0.01) increase in maximum IEMG. Individual increases in training intensity between these two training periods correlated with individual increases both in muscular strength (p<0.05) and in the weight lifted in the clean & jerk (p<0.05). A non-significant increase of 3.9% in total mean muscle fibre area occurred over the year. The present findings demonstrate the limited potential for strength development in elite strength athletes, and suggest that the magnitudes and time courses of neural and hypertrophic adaptations in the neuromuscular system during their training may differ from those reported for previously untrained subjects. The findings additionally indicate the importance of training intensity for modifying training responses in elite strength athletes.
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The purpose of this experiment was to determine whether training-induced increases in maximal voluntary contraction (MVC) can be completely accounted for by increases in muscle cross-sectional area. Fifteen female university students were randomly divided into a control (N = 7) and an experimental (N = 8) group. The experimental group underwent 8 wk of isometric resistance training of the knee extensors of one leg; the other leg was the untrained control. Training consisted of 30 MVC.d-1 x 3 d.wk-1 x 8 wk. Extensor cross-sectional area (CSA), assessed by computerized tomographic (CT) scanning of a cross-sectional slice at mid-thigh, was used as a measure of muscle hypertrophy. After 8 wk of training, MVC increased by 28% (P < 0.05), CSA increased by 14.6% (P < 0.05), and the amplitude of the electromyogram at MVC (EMGmax) was unchanged in the trained leg of the experimental subjects. The same measures in the untrained legs of the experimental subjects and in both legs of the control subjects were not changed after training. Although there was an apparent discrepancy between the increase in MCV (28%) and CSA (14.6%), the ratio between the two, the specific tension (N.cm-2), was not significantly different after training. As a result of these findings, we conclude that in these subjects there is no evidence of nonhypertrophic adaptations to resistance training of this type and magnitude, and that the increase in force-generating capacity of the muscle is due to the synthesis of additional contractile proteins.
Eight men (20-23 years) weight trained 3 days.week-1 for 19 weeks. Training sessions consisted of six sets of a leg press exercise (simultaneous hip and knee extension and ankle plantar flexion) on a weight machine, the last three sets with the heaviest weight that could be used for 7-20 repetitions. In comparison to a control group (n = 6) only the trained group increased (P less than 0.01) weight lifting performance (heaviest weight lifted for one repetition, 29%), and left and right knee extensor cross-sectional area (CAT scanning and computerized planimetry, 11%, P less than 0.05). In contrast, training caused no increase in maximal voluntary isometric knee extension strength, electrically evoked knee extensor peak twitch torque, and knee extensor motor unit activation (interpolated twitch method). These data indicate that a moderate but significant amount of hypertrophy induced by weight training does not necessarily increase performance in an isometric strength task different from the training task but involving the same muscle group. The failure of evoked twitch torque to increase despite hypertrophy may further indicate that moderate hypertrophy in the early stage of strength training may not necessarily cause an increase in intrinsic muscle force generating capacity.