Neuromuscular Differences Between Endurance Trained, Power Trained and Sedentary Subjects

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514
Journal of Strength and Conditioning Research, 2003, 17(3), 514–521
q 2003 National Strength & Conditioning Association
Neuromuscular Differences Between Endurance-
Trained, Power-Trained, and Sedentary Subjects
GREGORY LATTIER, GUILLAUME Y. MILLET, NICOLA A. MAFFIULETTI,
NICOLAS BABAULT, AND ROMUALD LEPERS
INSERM/ERIT-M 0207 Motricite´-Plasticite´, Universite´ de Bourgogne, Unite´ de Formation et de Recherche
Sciences Techniques des Activite´ Physiques et Sportives, Dijon, France.
ABSTRACT
This study tested the hypothesis that neuromuscular char-
acteristics of plantar flexor (PF) and knee extensor (KE) mus-
cles explain differences of both performance in vertical jump
and maximal voluntary isometric contraction (MVC) be-
tween endurance-trained (END, n 5 9), power-trained (POW,
n 5 8), and sedentary subjects (SED, n 5 8). Evoked twitch
characteristics of PF and KE were measured. MVC, maximal
voluntary activation (%VA) of KE, and performance in ver-
tical jump were also measured. POW have higher maximal
rate of twitch force development (MRFD) than SED and END
for both PF (p , 0.05) and KE (p , 0.01); %VA and MVC
were higher for POW and END than SED (p , 0.01). Higher
performances were measured in vertical jump for POW com-
pared with END and SED. Significant relationships were
found between the squat jump performance and MRFD for
both KE and PF (R 5 0.71, p , 0.0001 and R 5 0.55, p ,
0.01, respectively). These findings show that low MRFD on
lower limbs extensors does not limit expression of MVC on
subjects with high levels of activation, whereas intrinsic mus-
cular qualities have a direct influence on performance during
the vertical jump.
Key Words: maximal voluntary isometric contraction,
vertical jump, twitch contractile properties, voluntary
activation
Reference Data: Lattier, G., G.Y. Millet, N.A. Maffiulet-
ti, N. Babault, and R. Lepers. Neuromuscular differ-
ences between endurance-trained, power-trained, and
sedentary subjects. J. Strength Cond. Res. 17(3):514–521.
2003.
Introduction
Longitudinal studies have shown that training caninduce neural adaptations (29) as well as structural
modifications such as changes in muscle fiber type (19,
33) and muscle cross-sectional area (17, 26, 33). To
study long-term training adaptations, cross-sectional
experiments have illustrated histochemical differences
between endurance and power athletes. For example,
Sleivert et al. (31) have shown that the proportion of
type II fibers in the vastus lateralis was higher in vol-
leyball players than in middle-distance runners. Tesch
and Karlsson (32) have observed a higher percentage
of slow fibers in the vastus lateralis in endurance run-
ners compared with wrestlers, kayakers, lifters, and
physical education students. These studies have also
shown muscle cross-sectional area differences between
endurance-trained athletes and sprinters or strength
athletes (12, 31).
Cross-sectional experiments have also been used to
quantify differences between endurance-trained ath-
letes, power-trained athletes, and untrained people in
terms of physical capacity. For instance, it is well
known that explosive force, explored through the per-
formance in the vertical jump, is greater in power ath-
letes such as volleyball players than in endurance ath-
letes or untrained men (6). Several authors have shown
that power athletes demonstrate higher maximal vol-
untary force than endurance-trained counterparts for
the quadriceps (12, 20) and the triceps surae muscle
(2, 28). However, muscular mass has not always been
taken into account to explain differences in maximal
strength between subjects.
The twitch interpolation method has been used to
measure the level of voluntary activation of motor
units (1). With this method, it is possible to quantify
a ’’nervous deficit’’ (i.e., the subject’s failure to mobilize
all the motor units of a given muscle). Although in-
vestigations studying neural adaptations associated
with strength training (16, 26, 29) have been conduct-
ed, a few experiments have used the twitch interpo-
lation method to study the effects of different types of
training on nervous deficit (16). Electrically evoked
twitches of skeletal muscles have been used to char-
acterize muscular property changes with exercise
training (8). As a consequence, much is known about
adaptations induced by training in terms of neural and
structural aspects, but few studies have been designed
to explain intergroup differences in explosive and iso-
Training Effects on Neuromuscular Characteristics 515
Table 1. Selected characteristics of the subjects.†
Power Sedentary Endurance
Age (y)
[range]
Training exposure (y)
Height (cm)
Weight (kg)
Lean body mass (kg)
24.0 (2.9)
[21–28]
11.4 (1.8)
182.1 (5.1)
80.3 (8.2)***
69.5 (4.0)***
25.8 (5.3)
[21–33]
—
175.2 (4.5)
61.3 (6.7)
54.0 (5.2)
41.6 (5.9)***§
[31–48]
13.7 (8.4)
177.3 (10.5)
69.4 (6.7)*‡
61.7 (6.6)**‡
† Values are means (SD).
*, **, *** Significantly different from sedentary (p , 0.05, p , 0.01, and p , 0.001, respectively).
‡, § Significantly different from power (p , 0.01 and p , 0.001, respectively).
metric strength by determining factors such as neural
recruitment or contractile characteristics. Therefore,
the aim of this study was to test the hypothesis that
neuromuscular characteristics of lower limb extensors
can explain the performance in maximal voluntary iso-
metric strength of these muscles and in vertical jump
by subjects with different training backgrounds.
Methods
Experimental Approach to the Problem
To test our hypothesis, we conducted a cross-sectional
experiment that compared the explosive and isometric
strength of endurance-trained, power-trained, and
sedentary subjects. Explosive and isometric strength
(dependent variables) were tested using performance
in the vertical jump and the force reached during knee
extensors (KE) maximal voluntary isometric contrac-
tion, respectively. Neuromuscular characteristics (in-
dependent variables) were the level of maximal vol-
untary activation and the contractile properties of both
KE and PE muscles, which were evaluated using the
electrically evoked twitch.
Subjects
Twenty-five healthy men, divided into 3 groups, com-
pleted the study. The first group (endurance [END])
was composed of 9 athletes regularly participating in
ultramarathons and triathlons. The second group
(power [POW]) was composed of 4 volleyball players,
1 basketball player, 2 sprinters (track and field), and 1
weightlifter who were playing in regional or national
championships. The third group was composed of 8
sedentary subjects (SED) who did not engage in phys-
ical activity more than once a week. The subject char-
acteristics are presented in Table 1. After being in-
formed of the nature of the experiment, written in-
formed consent forms were obtained from the sub-
jects. The study was conducted according to the
Declaration of Helsinki and approval for the project
was obtained from the local committee on human re-
search.
Experimental Protocol
Muscle Contractile Properties. All muscle contractile
measurements were conducted on both KE and plan-
tar flexor (PF) muscles. Electrical stimulations were
given using a high-voltage stimulator (Model DS-7,
Digitimer Stimulator, Herthfordshire, England). The
amperage of a 400 V rectangular pulse (1 ms) was pro-
gressively raised (increment 10 mA) until the increase
of intensity did not induce a higher twitch mechanical
response and a higher amplitude of the EMG signals
(M-wave; see below). This was considered the optimal
intensity (i.e., the stimulus allowing the recruitment of
all motor units of the muscular group considered).
Three stimuli were given over a 15-s period, and the
electromechanical response was averaged.
For stimulations designed to study contractile
properties ofKE, the subject lay prone on a strength
training device with the hip and knee angles fixed at
908. The mechanical response was recorded by a strain
gauge (SBB 200 kg, Tempo Technologies Co., Taipei,
Taiwan), securely strapped around the ankle. The fem-
oral nerve was stimulated using a monopolar cathodal
electrode (0.5 cm diameter) pressed in the femoral tri-
angle. The anode was a 10 3 5-cm rectangular elec-
trode (Medicompex SA, Ecublens, Switzerland) locat-
ed in the gluteal fold opposite the cathode. For stim-
ulations designed to study contractile properties of PF,
the subject was seated with the knee and ankle angles
fixed at 908 of flexion. The posterior tibial nerve was
stimulated with the cathodal electrode pressed in the
popliteal fossa and the anode located on the anterior
surface of the knee. The mechanical response was re-
corded by a pedal equipped with strain gauges and
specifically developed for the study by the local engi-
neering school. The following parameters were ob-
tained from the mechanical response of the evoked
contraction: (a) peak twitch force (Pt; i.e., the highest
value of twitch torque production); (b) twitch contrac-
tion time (CT; i.e., the time from the origin of the me-
chanical signal to twitch maximal force); (c) maximal
rate of twitch tension development (MRFD; i.e., max-
516 Lattier, Millet, Maffiuletti, Babault, and Lepers
imal value of the first derivative of the force signal);
(d) half relaxation time (HRT; i.e., the time to obtain
half of the decline in twitch maximal force); and (e)
maximal rate of twitch tension relaxation (MRFR; i.e.,
lowest value of the first derivative of the force signal).
Maximal Voluntary Contraction and Activation. Maxi-
mal voluntary isometric contraction (MVC) was deter-
mined for KE. MVC involved 2 maximum isometric
contractions of KE with a 1-minute rest in the same
position as for the evoked twitch between trials. The
highest value obtained was used for analysis purposes.
Maximal voluntary muscle activation of KE was car-
ried out by using the technique of twitch interpolation
(1). An electrically evoked twitch was superimposed
to the plateau reached during the determination of
MVC. The ratio of the amplitude of the superimposed
twitch over the size of the twitch at rest was then used
to calculate the level of voluntary activation (%VA) as
follows: %VA 5 (1 2 superimposed twitch·mean con-
trol twitch21)·100. The force corresponding to the com-
plete activation of the muscle was calculated as fol-
lows: MVC at 100% VA 5 MVC·%VA21. These 2 pa-
rameters were then normalized with respect to lean
body mass as follows Lean body mass 5 body weight
2 (body weight·percentage of body fat). Percentage of
body fat was calculated using skinfold thickness at 4
sites (triceps, biceps, subscapular, and supra-iliac) ac-
cording to the method of Durnin and Rahaman (9).
EMG Recording. Two EMG signals per muscular
group studied were recorded using a bipolar arrange-
ment of silver chloride surface electrodes during trans-
cutaneous electrical stimulation: vastus lateralis (VL)
and vastus medialis (VM) for KE, soleus (Sol) and gas-
trocnemius medialis (GM) for PF. The recording elec-
trodes were fixed lengthwise over the middle of the
muscle belly with an interelectrode distance of 20 mm.
The reference electrode was attached to the wrist of
the opposite arm. Low impedance at the skin-electrode
surface was obtained (Z , 2 kV) by abrading the skin
with emery paper and cleaning with alcohol. Myo-
electrical signals were amplified with a bandwidth fre-
quency ranging from 1.5 and 2 kHz and simultaneous-
ly digitized on-line (sampling frequency 1,000 Hz).
Peak-to-peak amplitude and duration of electrically
evoked compound action potentials (M-wave) were
determined for the 4 muscles during twitches. In ad-
dition, the root mean square (RMS) of the whole signal
was analyzed during the determination of the MVC
for both VM and VL muscles over a 0.5 s period after
the torque had reached a plateau. All mechanical and
EMG data were stored with commercially available
software (Tida, Heka Elektronik, Lambrecht/Pfalz,
Germany).
Vertical Jumps. The subjects performed 2 squat
jumps (SJ) and 2 counter movement jumps (CMJ) on
a contact mat (Ergo Test, Globus, Codogne, Italy) in a
randomized way. In order to minimize trunk move-
ments, the position of the upper body was standard-
ized and controlled by the main experimenter. The
subjects were asked to jump as high as possible, and
the best SJ and CMJ performances were used in the
subsequent statistical analysis. One-minute rest was al-
lowed between the 4 jumps. During jumps, the sub-
jects were instructed to keep their hands on their hips.
Statistical Analyses
Comparisons of the study variables were performed
between groups by 1-way analysis of variance (ANO-
VA). By first using a multivariate ANOVA, it was ver-
ified that the 1-way ANOVA did not increase the risk
of committing the Type I error for variables that can
potentially co-vary (e.g., Pt and MFRD). Since the re-
sults were not affected, the 1-way ANOVA was used.
Individual comparisons were made with the Newman-
Keuls post-hoc test when F values were significant. Re-
lationships between strength performance parameters
and neuromuscular characteristics of lower limb exten-
sors were examined using Pearson product correla-
tions. A p value of #0.05 was accepted as the level of
statistical significance for all analyses.
Results
Muscle Contractile Properties
Mean values of Pt, MRFD, and MRFR of the 2 muscle
groups were higher for POW than for the 2 other
groups (Table 2). On the contrary, there were no sig-
nificant differences in CT among the 3 groups for both
muscles studied. The same tendency was found for the
relaxation time since the only difference was a longer
HRT of KE for POW to compare with SED (Table 2).
Peak-to-peak amplitude and duration of the surface
action potential (M-wave) were not significantly dif-
ferent among the 3 groups (Figure 1). Significant linear
relationships between Pt of PF and Pt of KE (R 5 0.49,
p , 0.05, n 5 24) and between MRFD of PF and MRFD
of KE (R 5 0.56, p , 0.01, n 5 24) were observed.
Maximal Voluntary Contraction and Activation
MVC and %VA were significantly higher in POW and
END compared with the untrained subjects (Figure 2).
Similar differences existed when MVC was expressed
relative to lean body mass (MVC·LBM21; Figure 3).
However, intergroup difference in MVC disappeared
when a simulation with 100% VA was calculated (Fig-
ure 3). A significant linear relationship was found be-
tween voluntary activation and MVC (R 5 0.46, p ,
0.01, n 5 22). Also, the RMS values measured during
MVC were not significantly different between groups
for both the VL and the VM muscles.
Vertical Jumps
SJ and CMJ performance were higher for POW than
END and SED, whereas no differences were found be-
tween END and SED (Figure 4). For both KE and PF,
Training Effects on Neuromuscular Characteristics 517
Table 2. Selected parameters of twitch mechanical response for both muscular groups studied.†
Knee extensors
Power Sedentary Endurance
Plantar flexors
Power Sedentary Endurance
Pt (N or N·m)
CT (ms)
HRT (ms)
MRFD
(N·ms21 or N·m·ms21)
MRFR
(N·ms21 or N·m·ms21)
217.9
(63.12)
61.3
(14.1)
77.7
(22.8)
6.89
(2.45)
2.84
(1.40)
139.9***
(10.7)
56.9
(5.9)
53.4*
(9.5)
4.50***
(0.54)
1.94**
(0.27)
131.9***
(21.2)
65.7
(6.6)
68.9
(13.5)
3.70**
(0.89)
1.36*
(0.32)
24.6
(8.1)
122.4
(10.6)
87.7
(5.2)
0.36
(0.12)
0.20
(0.04)
14.8*
(3.0)
118.4
(14.6)
93.8
(9.3)
0.22**
(0.05)
0.13**
(0.02)
15.8**
(7.0)
130.8
(13.6)
93.8
(19.5)
0.22*
(0.08)
0.14*
(0.05)
† Values are means (SD). Pt 5 Peak twitch force; CT 5 twitch contraction time; HRT 5 half relaxationtime; MRFD 5 maximal
rate of twitch tension development; MRFR 5 maximal rate of twitch tension relaxation.
*, **, *** Significantly different from power (p , 0.05, p , 0.01, and p , 0.001, respectively).
a significant relationship was found between MRFD
and the SJ performance (R 5 0.71, p , 0.0001, n 5 25
for KE, and R 5 0.55, p , 0.01, n 5 24 for PF; Figure
5). Similar relationships were observed between
MRFD and CMJ performance (R 5 0.62, p , 0.01, n
5 25 for KE, and R 5 0.50, p , 0.05, n 5 24 for PF).
When considering each group separately, the only sig-
nificant relationships were found for the POW group
between KE MFRD and SJ (R 5 0.90, p , 0.01, n 5 8)
and between KE MFRD and CMJ (R 5 0.74, p , 0.05,
n 5 8).
Discussion
Large differences in both explosive strength and con-
tractile properties have been previously observed in
subjects with different training backgrounds (2, 6, 12,
20, 28, 31). To our knowledge, the present study is the
first one to connect muscle characteristics to explosive
strength and to show that, in a heterogeneous group,
performance in vertical jump can be explained by the
maximal rate of twitch force development of both KE
and PF muscles. Two other interesting results of this
study are that (a) both endurance- and power-trained
athletes have higher maximal voluntary activation and
maximal isometric force of KE muscles than sedentary
subjects, and (b) while large differences in vertical
jump heights were found between endurance- and
power-trained subjects, these 2 groups have similar
maximal isometric strength.
Twitch contraction times for KE and PF are similar
to those measured in previous studies. For instance,
CT for PF was reported to be from 103.3 6 7.1 to 139.3
6 7.3 ms (11, 32) vs. 123.9 6 13.6 ms in the present
experiment. In our study, CT was the only parameter
of the mechanical response similar for all groups of
subjects and the 2 muscles studied. There is a paucity
of information on the effects of training on this param-
eter in the literature. Pa¨a¨suke et al. (28) have found
that both endurance and power athletes had shorter
triceps surae CT compared with untrained men,
whereas CT has been found to be longer in the triceps
surae of elite bodybuilders and untrained men com-
pared with endurance athletes (2). This discrepancy
could be due to the type of contraction performed dur-
ing training. Indeed, Duchateau and Hainaut (8) have
found that dynamic strength training induced a re-
duction of CT, whereas CT was unchanged after an
isometric maximal training.
In the present study, peak twitch (Pt) was higher
in POW than in SED and END. In the absence of dif-
ference of CT between the groups of subjects, the
greater value of Pt for POW is explained by their high-
er twitch rate of force development that could be a
result of greater activity of the myosin ATPase, which
could reflect a difference in myotypology between ath-
letes trained in sports requiring explosive actions and
the 2 other groups (24). It is worthy to note that mus-
cular characteristics such as high MRFD found in POW
are not necessarily entirely due to training. In fact,
part of these contractile properties can probably be at-
tributed to genetic predispositions of POW athletes for
explosive sports.
With the exception of the half-relaxation time, the
differences between the groups of subjects observed
for KE were also found for PF for all mechanical and
electrophysiological parameters associated with the
twitch. Also, a linear relationship between the values
of the 2 muscular groups considered was observed for
Pt and MRFD. This suggests that the contractile prop-
erties of the 2 lower limb extensors studied are mod-
ified in a comparable way by training. This similarity
is interesting to note even if the genetic predisposi-
tions in self-selecting a sport cannot be completely ex-
cluded.
518 Lattier, Millet, Maffiuletti, Babault, and Lepers
Figure 1. Mean values of duration (upper panel) and am-
plitude (lower panel) of the M-wave for the 3 groups of
subjects and for the 4 muscles studied. GM 5 gastrocnemi-
us mediallis; Sol 5 soleus; VM 5 vastus medialis; VL 5
vastus lateralis. Brackets represent 1 SD.
Figure 2. Mean values of maximal voluntary contraction
(MVC, upper panel) and voluntary activation (lower panel)
of the KE for the 3 groups of subjects. **, *** indicate signif-
icant differences between the groups at p , 0.01 and p ,
0.001, respectively. Brackets represent 1 SD.
The %VA found in the present experiment may
seem low compared with other studies (4, 5, 7, 27),
especially for the SED subjects. This can be explained
by 2 reasons. First, when the reference twitch is a po-
tentiated one (i.e., measured immediately following a
maximal contraction), a higher degree of maximal ac-
tivation is found. This was not the case here. Also, in
the present study the subject laid prone on a strength
training device with the hip and knee angles fixed at
908. This unusual position may have reduced the neu-
ral input to the KE, and this can partly explain the low
degree of maximal activation found in the present
study. However, since all subjects were tested in the
same position, this factor does not affect the inter-
group comparison.
The results of the experiments studying the train-
ing effects on the level of maximal voluntary activation
are contradictory. Herbert et al. (16) did not find any
change in maximal voluntary activation after isometric
training. Similarly, Narici et al. (25) did not observe
any modification of quadriceps integrated EMG
(IEMG) measured during a maximal contraction after
6 months of strength training. However, Ha¨kkinen and
Komi (13) have observed an increase in IEMG after
strength training. These contradictory results could be
explained by the discrepancy between studies in terms
of recording conditions, type of training, physical sta-
tus of subjects at the beginning of the training period,
and type of muscle studied. An increase in IEMG is
generally interpreted as a higher number of motor
units recruited and/or a higher firing rate (30). In this
context, it is worthy to note that Van Cutsem et al. (34)
found that dynamic training of the ankle dorsiflexor
muscles only induced an increase in motor units dis-
charge frequency without variation of their spatial re-
cruitment. An interesting result of the present study
Training Effects on Neuromuscular Characteristics 519
Figure 3. Mean values of maximal voluntary contraction
divided per lean body mass (MVC·LBM21, upper panel)
and maximal voluntary contraction at 100% of voluntary
contraction divided per lean body mass (MVC [100%
VA]·LBM21, lower panel) for the 3 groups of subjects.
Brackets represent 1 SD.
Figure 4. Mean values of performance in squat jump (SJ)
and in counter-movement jump (CMJ) for the 3 groups of
subjects. **, *** Indicate significant difference between the
groups at p , 0.01 and p , 0.001, respectively. Brackets
represent 1 SD.
is that maximal activation was significantly higher in
POW and END than in SED. Despite the lack of sig-
nificant difference in IEMG measured during MVC,
probably due to a large variability, this result is an
argument in favor of nervous adaptations due to train-
ing. It also suggests that the intensity of training stim-
ulus does not influence the adaptation in terms of
maximal voluntary activation measured in isometric
conditions.
The intergroup %VA differences in activation were
similar to those found in voluntary maximal force.
This result, emphasized by the linear relationship be-
tween %VA and MVC, suggests that isometric strength
is primarily dependent on the level of activation. In-
deed, a simulation of the MVC with an activation of
100% cancels the differences between the groups.
However, under these conditions a tendency exists for
MVC to be higher for POW than for the 2 othergroups
(p 5 0.051). This could be related to the higher lean
mass in POW since the effect of the muscular mass on
MVC has been extensively discussed in the literature
(17). In this context, it is worthy to note that the 3
groups of subjects had very similar MVC per kilogram
of lean mass at 100% of simulated activation (see Fig-
ure 3, lower panel). In the present study, only isometric
force was evaluated, and results from dynamic mea-
surements would probably have been different, partic-
ularly at high speeds. It can be speculated that at high
contraction velocity, differences between endurance-
and power-trained athletes would be similar to those
observed during the vertical jump.
The higher performances in SJ and CMJ measured
in POW compared with the 2 other groups are in
agreement with the results of Bosco (6). It is well es-
tablished that athletes trained in power sports (e.g.,
sprint, volleyball, basketball) have higher performanc-
es in vertical jumps when compared with endurance
runners. Longitudinal studies have also showed an in-
crease in jump height after maximal or explosive
strength training (14, 33). However, to our knowledge
the present study is the first to show a direct relation-
ship between the twitch rate of force development and
the performance in vertical jump for both knee and
ankle extensors. The twitch MRFD was used in this
study as a measure of muscle maximal velocity con-
traction. It can be argued that MRFD of a tetanic con-
traction would be a better witness of muscle contractile
properties than MFRD of a twitch. However, an un-
published recent study from our laboratory showed a
strong linear relationship (R 5 0.88) between MRFD
of a twitch and MRFD of a tetanic contraction at 80
Hz. Therefore, the use of twitch parameters to char-
acterize the muscle contractile properties was probably
520 Lattier, Millet, Maffiuletti, Babault, and Lepers
Figure 5. Relationships between performance in squat
jump (SJ) and maximal rate of twitch tension development
(MRFD) of the knee extensors (upper panel) and of the
plantar flexors (lower panel).
adequate. In the present study, the coefficient of deter-
mination of the relationship between MRFD and the
SJ (R2 5 0.50 for KE, R2 5 0.30 for PF) showed that
while contractile properties are a determining factor
of vertical jump performance, other parameters are of
importance in explaining interindividual differences
in explosive force. In this context, other studies have
shown that the pattern of activation influences the per-
formance during explosive movements (3, 15). In our
study, the fact that %VA between END and POW was
not different while SJ performance was lower for END
is not in contradiction with this role of neural factors
during vertical jump performance. In fact, %VA was
measured in isometric conditions, not during high-ve-
locity contraction. The influence of MRFD on the ex-
plosive force is confirmed by the fact that (a) despite
a similar level of voluntary activation and MVC, the
performances in vertical jump were significantly lower
in END compared with POW; and (b) in spite of high-
er MVC and level of voluntary activation, the SJ per-
formances of END were not significantly different
from SED.
One can consider that the age differences between
the END group and the 2 other groups have affected
the conclusions of this study. However, the majority of
studies have shown that neuromuscular alterations
start in the fifth or the sixth decade (e.g., 21, 22, 36).
For instance, Vandervoort (35) established in a recent
review that a steady decline of 1 to 2% per year oc-
curred for voluntary or stimulated muscle strength
only after the sixth decade. Similar conclusions can be
made for the peak twitch tension of ankle PF muscles
(36). Moreover, there were no significant differences on
PF contractile properties between the present study
and a previous experiment carried out in our labora-
tory on young endurance-trained subjects (23). It must
be noted that 1 study has shown differences in maxi-
mal isometric force and squat jump height between the
age group of 20 and 40 years (18). Nevertheless, this
study was not in accordance with the results of Ferretti
et al. (10), which have shown that peak muscle power
decreased markedly only above the age of 50 years.
Thus the age factor has probably no influence on the
present results.
In conclusion, the results of the present study show
that (a) low speeds of contraction do not compromise
the development of maximal isometric force in subjects
(i.e., the END athletes) with a high level of activation,
but (b) intrinsic muscular qualities have a direct influ-
ence on performance in the vertical jump. Also, with
the exception of the parameters linked to the twitch
relaxation time, electrophysiological and mechanical
differences between groups are similar for KE and PF
muscles.
Practical Applications
The practical application of this study is that the as-
sociation of 2 simple tests (vertical jump and maximal
isometric strength of KE) and 2 anthropomorphic mea-
sures (body mass and percent body fat in order to
calculate lean body mass) may be of interest to explore
the neuromuscular capacities of a subject within a
group. In fact, 4 types can be characterized: (a) high
performance in the vertical jump and high
MVC·LBM21; (b) high performance in the vertical
jump and low MVC·LBM21; (c) low performance in the
vertical jump and high MVC·LBM21; (d) low perfor-
mance in the vertical jump and low MVC·LBM21. Ac-
cording to the results of the present study, this can be
associated with the following profiles: (a) contractile
properties suitable for explosive activities and a high
level of maximal activation, (b) contractile properties
suitable for explosive activities but a low level of max-
imal activation, (c) contractile properties suitable for
endurance activities but a high level of maximal acti-
vation, and (d) contractile properties suitable for en-
Training Effects on Neuromuscular Characteristics 521
durance activities and a low level of maximal activa-
tion.
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Address correspondence to Gregory Lattier, Gregory.
Lattier@u-bourgogne.fr.