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Maximal and explosive strength training elicit distinct neuromuscular adaptations, specific to the training stimulus

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To compare the effects of short-term maximal (MST) vs. explosive (EST) strength training on maximal and explosive force production, and assess the neural adaptations underpinning any training-specific functional changes. Male participants completed either MST (n = 9) or EST (n = 10) for 4 weeks. In training participants were instructed to: contract as fast and hard as possible for ~1 s (EST); or contract progressively up to 75 % maximal voluntary force (MVF) and hold for 3 s (MST). Pre- and post-training measurements included recording MVF during maximal voluntary contractions and explosive force at 50-ms intervals from force onset during explosive contractions. Neuromuscular activation was assessed by recording EMG RMS amplitude, normalised to a maximal M-wave and averaged across the three superficial heads of the quadriceps, at MVF and between 0-50, 0-100 and 0-150 ms during the explosive contractions. Improvements in MVF were significantly greater (P < 0.001) following MST (+21 ± 12 %) than EST (+11 ± 7 %), which appeared due to a twofold greater increase in EMG at MVF following MST. In contrast, early phase explosive force (at 100 ms) increased following EST (+16 ± 14 %), but not MST, resulting in a time × group interaction effect (P = 0.03), which appeared due to a greater increase in EMG during the early phase (first 50 ms) of explosive contractions following EST (P = 0.052). These results provide evidence for distinct neuromuscular adaptations after MST vs. EST that are specific to the training stimulus, and demonstrate the independent adaptability of maximal and explosive strength.
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Eur J Appl Physiol (2014) 114:365–374
DOI 10.1007/s00421-013-2781-x
ORIGINAL ARTICLE
Maximal and explosive strength training elicit distinct
neuromuscular adaptations, specific to the training stimulus
Neale A. Tillin · Jonathan P. Folland
Received: 3 July 2013 / Accepted: 20 November 2013 / Published online: 1 December 2013
© Springer-Verlag Berlin Heidelberg 2013
interaction effect (P = 0.03), which appeared due to a
greater increase in EMG during the early phase (first 50 ms)
of explosive contractions following EST (P = 0.052).
Conclusions These results provide evidence for distinct
neuromuscular adaptations after MST vs. EST that are
specific to the training stimulus, and demonstrate the inde-
pendent adaptability of maximal and explosive strength.
Keywords Resistance training · Rate of force
development · Neural activation · Specificity
Abbreviations
ANOVA Analysis of variance
EMG0–50 Electromyography recorded during explosive
contractions over a time period denoted in
subscript
EMGMVF Electromyography recorded at MVF
EST Explosive strength training
F50 Explosive force recorded at a discrete time
point from force onset denoted in subscript
Mmax Maximal M-wave
MST Maximal strength training
MVC Maximal voluntary contraction
MVF Maximal voluntary force
M-wave Compound muscle action potential
RF Rectus femoris
RMS Root mean square
VL Vastus lateralis
VM Vastus medialis
Introduction
Skeletal muscles apply force to the skeleton to move and/
or stabilise the body, and thus their capacity for volitional
Abstract
Purpose To compare the effects of short-term maximal
(MST) vs. explosive (EST) strength training on maxi-
mal and explosive force production, and assess the neural
adaptations underpinning any training-specific functional
changes.
Methods Male participants completed either MST
(n = 9) or EST (n = 10) for 4 weeks. In training partici-
pants were instructed to: contract as fast and hard as pos-
sible for ~1 s (EST); or contract progressively up to 75 %
maximal voluntary force (MVF) and hold for 3 s (MST).
Pre- and post-training measurements included recording
MVF during maximal voluntary contractions and explosive
force at 50-ms intervals from force onset during explosive
contractions. Neuromuscular activation was assessed by
recording EMG RMS amplitude, normalised to a maximal
M-wave and averaged across the three superficial heads
of the quadriceps, at MVF and between 0–50, 0–100 and
0–150 ms during the explosive contractions.
Results Improvements in MVF were significantly greater
(P < 0.001) following MST (+21 ± 12 %) than EST
(+11 ± 7 %), which appeared due to a twofold greater
increase in EMG at MVF following MST. In contrast, early
phase explosive force (at 100 ms) increased following EST
(+16 ± 14 %), but not MST, resulting in a time × group
Communicated by Alain Martin.
N. A. Tillin (*)
Department of Life Sciences, Whitelands College, University
of Roehampton, Holybourne Avenue, London SW15 4JD, UK
e-mail: neale.tillin@roehampton.ac.uk
J. P. Folland
School of Sport, Exercise and Health Sciences, Loughborough
University, Leicestershire, UK
366 Eur J Appl Physiol (2014) 114:365–374
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force production (skeletal muscle strength) limits function.
Two components of skeletal muscle strength include: maxi-
mal strength, measured as the maximal voluntary force
(MVF) the muscles can produce; and explosive strength, the
ability of the muscles to increase force rapidly from a low
force or resting state (Tillin et al. 2012b). Maximal strength
sets the upper functional limit of the musculoskeletal sys-
tem and is important for relatively slow movement tasks
[e.g. ambulation/locomotion of older individuals (Faulkner
et al. 2007) and neuromuscular patients (Ada et al. 2000),
or sports activities such as rugby scrummaging (Quar-
rie and Wilson. 2000) and wrestling (Garcia-Pallares et al.
2011)]. However, it takes time to develop MVF [>100 ms
in concentric contractions (Tillin et al. 2012a) and >250 ms
in isometric and eccentric contractions (Thorstensson et al.
1976; Tillin et al. 2012a)], and thus explosive strength is
considered more important where time available to develop
force is limited [e.g. restabilising the body following a loss
of balance (Domire et al. 2011; Pijnappels et al. 2008) and
sports activities such as sprinting and jumping (de Ruiter
et al. 2006; Tillin et al. 2013a)]. Understanding how these
components of strength are affected by different strength
training modalities has important practical implications for
improving health and sports performance.
Time under tension and magnitude of the training load
are considered important stimuli for developing maximal
strength (Crewther et al. 2005), and thus maximal strength
training typically involves sustained (>2 s) contractions
against loads 70 % MVF (Del Balso and Cafarelli 2007;
Jones and Rutherford 1987; Kubo et al. 2001). In contrast,
training for explosive strength is typically characterised by
a series of short (1 s) contractions performed as rapidly as
possible (Barry et al. 2005; de Ruiter et al. 2012) to prac-
tise and improve the rate of force development. Based on
the training principle of specificity, it is conceivable that
these different training stimuli induce distinct functional
adaptations, e.g. with greater gains in the explosive strength
after explosive training. On the other hand, maximal and
explosive strength are determined by similar physiological
mechanisms [e.g. muscle size and neural drive; (Andersen
and Aagaard 2006; Duchateau et al. 2006; Hakkinen and
Keskinen 1989; Schantz et al. 1983; Tillin et al. 2010)], and
might be expected to exhibit similar changes in response to
training.
Evidence in support of distinct training stimuli for
improvements in maximal and explosive strength is equiv-
ocal. Individual studies have examined the functional
responses to either maximal strength training, explosive
strength training, or a combination of both, with some
investigations observing distinct effects on maximal and
explosive strength (Andersen et al. 2010; Gruber et al.
2007; Rich and Cafarelli 2000; Tillin et al. 2011) and oth-
ers reporting improvements in both attributes (Barry et al.
2005; de Ruiter et al. 2012; Del Balso and Cafarelli 2007;
Kubo et al. 2001; Suetta et al. 2004; Tillin et al. 2012b).
Methodological differences (e.g. training duration, inten-
sity and volume; instructions to the participants during the
training; and the type of training contractions performed)
preclude meaningful comparisons of functional responses
between separate studies. Therefore a direct comparison
of maximal and explosive strength training is required to
establish whether there are distinct functional responses to
these different training stimuli.
Whilst maximal and explosive strength training might
be expected to elicit distinct functional responses, the
physiological bases of this specificity are unknown. The
changes in function with any type of strength training
are underpinned by neural and/or morphological adapta-
tions (Folland and Williams 2007), with neural adapta-
tions widely thought to dominate the adaptive response
to short-term training (within 4 weeks; Folland and Wil-
liams 2007; Sale 2003). Increased maximal strength has
been associated with increased neuromuscular activation
at MVF (Del Balso and Cafarelli 2007; Tillin et al. 2011),
whilst increased explosive strength has been accompanied
by greater activation during the explosive phase of contrac-
tion (Barry et al. 2005; de Ruiter et al. 2012; Tillin et al.
2012b). However, the degree of specificity and/or transfer-
ability of these neural changes between the explosive and
maximal phases of contraction, and vice versa, are unclear.
Neuromuscular activation can be assessed by EMG ampli-
tude normalised to a maximum evoked compound muscle
action potential (M-wave), as a non-volitional reference,
to reduce the between-subject variability and increase the
sensitivity of the experiment to detect changes in activa-
tion (Buckthorpe et al. 2012). In addition, the proportional
changes in neuromuscular activation during the explosive
and maximum phases of contraction can be examined by
assessing EMG during the explosive phase of contraction
relative to EMG at MVF.
The purpose of this study was to compare the effects of
short-term maximal vs. explosive strength training on max-
imal and explosive force production, and assess the neural
adaptations underpinning any training-specific functional
changes. We hypothesised that the two types of training
would elicit distinct functional and neural changes specific
to the training stimulus.
Methods
Participants
Nineteen male participants who were recreationally active
(moderate exercise 4 times per week), but had not been
involved in any form of lower-body strength training for
367Eur J Appl Physiol (2014) 114:365–374
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>6 months prior to the start of the study, were recruited and
completed either maximal strength training (MST group;
n = 9) or explosive strength training (EST group; n = 10).
All participants were healthy, injury free and provided
written informed consent prior to their involvement in this
study, which was approved by the Loughborough Univer-
sity Ethical Advisory Committee. At baseline the groups
were of similar age and height, and whilst they differed in
body mass and MVF, there were no differences in MVF
relative to body mass (Table 1).
Overview
Participants completed a familiarisation session and a meas-
urement session (separated by 2–3 days) before, and one
measurement session after, 4 weeks of unilateral isometric
strength training of the knee extensors. The pre-training
measurement session took place within 10 days prior to
the start of training, whilst the post-training measurement
session took place 2–3 days after the last training session.
During the familiarisation session, participants practised the
range of measurement tasks without data recording. Pre-
and post-training measurement sessions involved recording
external knee extension force and surface EMG of the super-
ficial knee extensors during a series of explosive voluntary
and maximal voluntary (MVCs) isometric contractions of
the knee extensors. EMG responses (M-waves) to electrical
stimulation of the femoral nerve with single, supramaximal
impulses were also recorded for normalisation of the EMG
signal recorded in the voluntary efforts. Training was of
one leg chosen at random and involved isometric contrac-
tions of the knee extensors (either EST or MST) performed
four times a week for 4 weeks with the same apparatus as
the measurement sessions. Some within-group compari-
sons of the trained vs. untrained leg after maximal (Tillin
et al. 2011) and explosive (Tillin et al. 2012b) strength train-
ing have previously been reported separately. Participants
were instructed to maintain their normal physical activities
throughout the period of the study.
Whilst dynamic contractions might be considered more
relevant to functional human movement, we chose an iso-
metric contraction model to assess the effects of MST and
EST on these two components of strength as it provides a
more experimentally controlled situation in which to assess
the mechanisms underpinning the changes in function.
Training
Each training session consisted of a brief warm-up of sub-
maximal isometric knee extensions, followed by four sets
(separated by 2 min) of ten isometric contractions of the
knee extensors (each set lasting ~60 s). However, the type
of contractions performed differed between the training
groups. The MST group were instructed to increase force
over a 1-s period, up to 75 % of their MVF, hold for 3 s,
and then relax for 2 s before completing the next contrac-
tion in the set. There was no specific instruction to produce
force rapidly during the MST. In contrast, the EST group
were instructed to contract as “fast and hard” as possi-
ble for ~1 s without producing a prior knee-flexor force,
in an attempt to achieve at least 90 % of their MVF, and
then relax for 5 s before completing the next contraction
in the set. Thus, whilst the duration of loading was greater
for the MST group, the peak loads and loading rates were
greater for the EST group (Fig. 1). For biofeedback in the
MST group, a computer monitor displayed the force–time
curve with a horizontal cursor on 75 % MVF, whilst in the
EST group the monitor displayed the slope of the force–
time curve (established with a 1-ms constant epoch) and
the baseline of the force–time curve that was used to con-
firm that no prior knee-flexor force had occurred. MVF was
initially established in familiarisation and the pre-training
measurement sessions (see below) and re-established at the
start of the first training session each week.
Force and EMG recording
Measurement and training sessions were completed in
an isometric strength testing chair (Bojsen-Moller et al.
2005), with knee and hip angles of 85° and 100°, respec-
tively (180° representing full extension). Participants
were secured firmly in the chair with a waist belt and
shoulder straps. An ankle strap was consistently placed
3 cm proximal to the medial malleolus and was in series
with a calibrated linear response strain gauge (Jones and
Parker 1989) positioned perpendicular to the tibia. This
low noise strain gauge [range of baseline noise <0.2 N
or <0.02 % full scale deflection (Tillin et al. 2010)] con-
sisted of a U-shaped aluminium beam with two high-fre-
quency response silicon strain gauges bonded either side
of the horizontal section. The force signal from the strain
gauge was amplified (×500), sampled at 2,000 Hz using
Table 1 Physical characteristics of the maximal and explosive
strength training groups prior to the training
MVF maximal voluntary force
** Denotes a significant difference between the groups (P < 0.01)
Strength training group
Maximal Explosive
Age (years) 20.9 ± 1.1 20.2 ± 2.4
Height (m) 1.82 ± 0.05 1.82 ± 0.08
Body mass (kg) 81.1 ± 6.8 73.6 ± 7.4**
MVF (N) 585 ± 84 482 ± 58**
MVF/body mass (N.kg1) 7.2 ± 0.8 6.6 ± 0.8
368 Eur J Appl Physiol (2014) 114:365–374
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an external A/D converter (16-bit signal recording resolu-
tion; Micro 1401, CED, Cambridge, UK), interfaced with
a personal computer using Spike 2 software (CED, Cam-
bridge, UK), and digitally notch filtered at 100 and 200 Hz
[q factor of 100; (Tillin et al. 2010)]. Baseline resting force
was subtracted from all active force recordings to provide
gravity correction.
Single differential EMG surface electrodes (Delsys Bag-
noli-4, Boston, USA) were placed: over the belly of the
rectus femoris (RF), vastus lateralis (VL), and vastus medi-
alis (VM); parallel to the presumed orientation of the mus-
cle fibres; and at ~50 % (RF), 55 % (VL), and 90 % (VM)
of the distance between the greater trochanter and lateral
femoral condyle. EMG signals were amplified (×100 dif-
ferential amplifier 20–450 Hz), sampled at 2,000 Hz via the
same A/D convertor and PC software as the force signal,
and band-pass filtered (6–500 Hz) using a fourth-order,
zero-lag Butterworth digital filter.
Pre- and post-training measurement sessions
M‑wave recordings
M-waves were elicited by electrically stimulating the
femoral nerve (DS7AH, Digitimer Ltd., UK) with square
wave pulses (0.1 ms duration). The anode (carbon rubber,
7 × 10 cm; EMS Physio Ltd, Greenham, UK) was taped to
the skin over the greater trochanter. The cathode, a custom-
adapted stimulation probe (1-cm diameter, Electro Medi-
cal Supplies, Wantage, UK) protruding 2 cm perpendicular
from the centre of a plastic base (4 × 5 cm), was taped to
the skin over the femoral nerve in the femoral triangle. The
precise location of the cathode was determined as the posi-
tion that evoked the greatest twitch response for a particular
submaximal electrical current (typically 30–50 mA).
The maximal knee extensor twitch response for a sin-
gle electrical impulse was first established before eliciting
three supramaximal (120 % of the current required to evoke
a maximal twitch) twitch contractions at 12-s intervals.
Peak–peak M-wave (Mmax) responses of the RF, VL, and
VM were averaged across the three supramaximal twitch
contractions.
Explosive voluntary contractions
Following the evoked contractions and a warm-up of sub-
maximal voluntary contractions, participants completed
ten explosive voluntary contractions (each ~20 s apart).
Prior to each contraction, participants were provided with
the same instruction as that given during the training con-
tractions performed by the EST group. Explosive volun-
tary contractions were completed separately from MVCs
(detailed below) because previous work has reported the
performance outcome of voluntary contractions to be spe-
cific to the instruction given to the participants (Sahaly
et al. 2001). During off-line analysis, the three explosive
voluntary contractions with the largest peak rate of force
development (determined from a 1-ms moving epoch)
and no change in baseline force >0.5 N during the 100 ms
prior to contraction onset were used for analysis. Volun-
tary explosive force was measured at 50, 100, and 150 ms
from force onset (F50, F100, F150) and normalised to body
mass to account for the group differences in body mass at
the start of the study. Voluntary explosive force values are
also expressed relative to MVF to assess how explosive and
maximal strengths changed in proportion to each other fol-
lowing the two types of training.
To assess agonist neural drive, the root mean square
(RMS) of the EMG signal of each muscle was measured
over three time periods (0–50 ms, EMG0–50; 0–100 ms,
Fig. 1 Example force–time
curves recorded during the
first (two) and last isometric
knee extension contractions
of one training set performed
by participants in the maximal
strength training (black line)
and explosive strength training
(grey line) groups. The duration
of loading in each contraction
was greater in the maximal
strength training group (~4 vs.
~1 s), but the explosive strength
training group experienced
greater peak loads (~90 vs.
75 % maximal voluntary force)
and rate of loading (slope of the
force–time curve) 0
10
20
30
40
50
60
70
80
90
100
0510
% Maximal Voluntary Force
Time (s)
55 60
369Eur J Appl Physiol (2014) 114:365–374
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EMG0–100; and 0–150 ms, EMG0–150) from EMG onset
(first agonist muscle to be activated). Agonist (RF, VL, and
VM) RMS EMG values were normalised to Mmax and aver-
aged across the three muscles to give a mean agonist value.
Agonist RMS EMG values recorded during the explo-
sive contractions were also expressed relative to EMG at
MVF (EMGMVF; see below) and averaged across the three
muscles.
All explosive voluntary force and EMG variables were
averaged across the three explosive voluntary contractions
chosen for analysis. Force and EMG onsets were identi-
fied manually by the same trained investigator using a sys-
tematic previously published protocol (Tillin et al. 2010,
2013b). Briefly, force and EMG signals were viewed on a
constant x axis scale of 500 ms, and constant y axes scales
of 1 N (force) and 10 mV (EMG). This provided a good
resolution from which to establish the baseline noise pat-
tern and interpolate onset, defined as the last peak/trough
before the signal deflected away from the baseline. Manual
identification is considered the ‘gold standard’ method for
detecting signal onsets (Allison 2003; Moretti et al. 2003;
Pain and Hibbs 2007; Pulkovski et al. 2008; Tillin et al.
2013b).
Maximal voluntary contractions
Following the explosive contractions, participants com-
pleted at least three knee extensor isometric MVCs (sepa-
rated by 30 s), in which participants were instructed to
push as hard as possible for 3–5 s. Biofeedback and verbal
encouragement were provided during and between each
MVC. Knee extensor MVF was the greatest instantaneous
voluntary force achieved by a participant in any of the knee
extensor MVCs or explosive contractions during that labo-
ratory visit, and was normalised to body mass. RMS EMG
of each agonist muscle at MVF (EMGMVF) was recorded
during a 500-ms epoch (250 ms either side of MVF), nor-
malised to Mmax (Sale 2003) and averaged across the three
quadriceps muscles.
Statistical analysis
The influence of time (pre- vs. post-training) and group
(MST vs. EST) on each dependent variable was assessed
via a two-way repeated measures ANOVA with train-
ing and group as within- and between-participant factors,
respectively. When an interaction or main-training effect
occurred, paired t tests were used to assess the influence
of training within each group. Statistical significance was
set at P < 0.05. Statistical analysis was completed using
SPSS version 19. All data are presented as mean ± stand-
ard deviation; apart from those in the figures where data are
mean ± standard error of the mean for presentation pur-
poses. Percentage change in each dependent variable was
calculated as the mean percentage change of all partici-
pants within a group.
Results
Force variables
There was a main effect of time on MVF (ANOVA,
P < 0.001), due to an increase in MVF (Table 2) after
both MST (+21 ± 12 %) and EST (+11 ± 7 %). The
increase in MVF was greater in the MST group resulting
in a time × group interaction effect (ANOVA, P = 0.02;
Table 2; Fig. 2).
There was a main effect of time on F50 (ANOVA,
P = 0.041), F100 (ANOVA, P = 0.002), and F150 (ANOVA,
P < 0.001). Post hoc analysis revealed no change in F50
or F100 following MST (Table 2), whilst EST increased
Table 2 Maximal voluntary force (MVF) and explosive force (F) production (recorded at 50-ms intervals from force onset) pre- and post-train-
ing in the maximal (MST) and explosive strength training (EST) groups
All variables were normalised to body mass, and explosive force variables are also expressed relative to MVF. Time (pre vs. post) × group
(MST vs. EST) interaction effects are also reported. Data are mean ± SD
Within-group effects of training are denoted by * (P < 0.05), ** (P < 0.01), or *** (P < 0.001)
MST group EST group Interaction effect (P value)
Pre Post Pre Post
MVF (N. kg1) 7.22 ± 0.80 8.70 ± 1.19** 6.58 ± 0.83 7.28 ± 0.71*** 0.020
F50 (N.kg1)1.64 ± 0.71 1.70 ± 0.72 1.23 ± 0.43 1.89 ± 0.65* 0.083
F100(N.kg1)4.21 ± 0.78 4.34 ± 0.72 3.94 ± 0.61 4.53 ± 0.62** 0.030
F150 (N.kg1)5.55 ± 0.76 5.96 ± 0.80 5.05 ± 0.70 5.71 ± 0.63*** 0.235
F50 (%MVF) 23.1 ± 11.2 19.9 ± 9.3 19.0 ± 7.3 25.8 ± 8.1* 0.032
F100 (%MVF) 58.6 ± 10.8 50.4 ± 9.4** 59.9 ± 5.6 62.1 ± 5.2 0.002
F150 (%MVF) 77.2 ± 10.5 69.2 ± 10.7* 76.7 ± 4.5 78.5 ± 4.3 0.005
370 Eur J Appl Physiol (2014) 114:365–374
1 3
both of these variables (F50, +70 ± 77 % and F100,
+16 ± 14 %; Table 2). This resulted in a time × group
interaction effect for F100 (Table 2; Fig. 3a) and a tendency
for a time × group interaction effect for F50 (ANOVA,
P = 0.083; Table 2; Fig. 3a). For F150 there was no
time × group interaction effect (Table 2; Fig. 2a), as there
were similar increases in the MST (+8 ± 10 %; paired t
test, P = 0.059) and EST groups (+14 ± 8 %; Table 2).
There were time × group interaction effects for F50,
F100, and F150 relative to MVF (Table 2; Fig. 3c). This
was due to relative explosive force changing in opposite
directions for the two groups (Fig. 3c). Specifically, EST
induced an increase in F50 relative to MVF (+53 ± 64 %;
Table 2), but no change in F100 or F150 (Table 2) relative
to MVF. In contrast, after MST there was no change in
F50, but a decrease in F100 (14 ± 10 %; Table 2) and F150
(10 ± 11 %; Table 2) relative to MVF.
EMG variables
There was a main effect of time on EMGMVF normalised
to Mmax (ANOVA, P < 0.001), and whilst there was no
time × group interaction effect (Table 3; Fig. 2), post hoc
analysis revealed an increase in EMGMVF normalised to
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
3.2
3.6
4.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
in EMG MVF (% Mmax )
in MVF (N.kg
-1
)
MVF EMG
MVF
P = 0.02
Fig. 2 Pre- to post-training changes in maximal voluntary force
(MVF) and mean quadriceps EMG at MVF (EMGMVF) during iso-
metric knee extensions in the maximal (filled bars) and explosive
(open bars) strength training groups. MVF and EMGMVF were nor-
malised to body mass and maximal M-wave (Mmax), respectively,
prior to calculating changes. The P value denotes a time × group
interaction effect (P < 0.05) determined via a two-way ANOVA (time,
pre vs. post; by group, maximal vs. explosive). Data are mean ± SEM
Fig. 3 Pre- to post-training
changes in force production and
mean quadriceps EMG during
explosive isometric knee exten-
sions in the maximal (filled
bars) and explosive (open bars)
strength training groups. Force
is expressed relative to body
mass (a) and maximal voluntary
force (MVF; c), whilst EMG is
expressed relative to maximal
M-wave (Mmax; b) and EMG
at MVF (EMGMVF; d) prior
to calculating changes. The
P-value denotes a time × group
interaction effect (P < 0.05),
or tendency for a time × group
interaction effect (0.1 > P>0.05)
determined via a two-way
ANOVA (time, pre vs. post; by
group, maximal vs. explosive).
Data are mean ± SEM
-25
-20
-15
-10
-5
0
5
10
15
20
25
MVF
)
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
max
)
-12
-9
-6
-3
0
3
6
9
12
in EMG (% EMG
in EMG (% M
in Force (% MVF)
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
in Force (N.kg
-1
)
0-50 0-100 0-150
Force Variables EMG Variables
AB
CD
Time point from force onset (ms) Time window from EMG onset (ms)
P = 0.030
P = 0.032
50 100 150
P = 0.083
P = 0.002
P = 0.005
P = 0.007
P = 0.034 P = 0.087
P = 0.052
371Eur J Appl Physiol (2014) 114:365–374
1 3
Mmax after MST (+34 ± 38 %; Table 3), but no change fol-
lowing EST (Table 3).
There was a main effect of time on EMG0–50, EMG0–100,
and EMG0–150 (ANOVAs, 0.013 P0.039). Post hoc
analysis revealed an increase in EMG0–50 (+65 ± 73 %)
and EMG0–100 (+18 ± 28 %) normalised to Mmax (Table 3),
and a tendency for an increase in EMG0–150 (+26 ± 50 %;
paired t tests, P = 0.073; Table 3), following EST. In con-
trast, the MST group displayed no change in EMG0–50
or EMG0–100 normalised to Mmax (Table 3), but a simi-
lar increase to EST in EMG0–150 (+26 ± 31 %: paired t
test, P = 0.073; Table 3). There was a near-significant
time × group interaction effect on EMG0–50 normalised to
Mmax (ANOVA, P = 0.052; Table 3; Fig. 3b).
There was a time × group interaction effect on EMG0–50
and EMG0–100 relative to EMGMVF (Table 3; Fig. 3d), and a
tendency for a time × group interaction effect on EMG0–150
relative to EMGMVF (ANOVA, P = 0.087; Table 3;
Fig. 3d), due to these variables changing in opposite direc-
tions for the two groups. Specifically, MST induced a
decrease in EMG0–50 (10 ± 47 %; Table 3) and EMG0–
150 relative to EMGMVF (5 ± 11 %; Table 3), and a ten-
dency for the same effect on EMG0–100 relative to EMGMVF
(10 ± 18 %; paired t test, P = 0.065; Table 3). In con-
trast, there was a tendency for an increase in EMG0–50 rela-
tive to EMGMVF (+43 ± 64 %; Table 3) and no change in
EMG0–100 or EMG0–150 (Table 3) following EST.
Discussion
This investigation directly compared the functional and
neural adaptations to maximal vs. explosive strength train-
ing and found distinct changes during the explosive and
maximum phases of contraction that were specific to the
training stimulus. MST produced greater improvements in
maximal strength, and EST was more effective at improv-
ing early phase explosive strength. In addition, relative
explosive strength (to MVF) showed more pronounced
contrasts, with more positive changes after EST than MST.
These effects appeared to be underpinned by training-spe-
cific changes in neuromuscular activation during the explo-
sive and maximum phases of contraction. MST produced
twofold greater changes in EMGMVF than EST, although
this difference was not significant, and EST produced
greater changes in early phase neuromuscular activation
during explosive contractions.
Maximal strength (MVF) increased in both groups,
clearly showing that both training methods provided suf-
ficient stimuli for functional changes at the peak of the
force–time curve. Other investigations have also reported
improved maximal strength following maximal strength
training, explosive strength training, or a combination of
both (Andersen et al. 2010; Barry et al. 2005; de Ruiter et al.
2012; Del Balso and Cafarelli 2007; Jones and Rutherford
1987; Kubo et al. 2001; Rich and Cafarelli 2000; Suetta et al.
2004). However, to the best of our knowledge this is the first
study to directly compare the different training stimuli and
observe greater improvements in MVF following maximal
strength training than explosive strength training. Given that
greater training loads are considered to be more conducive
to improvements in maximal strength (Crewther et al. 2005),
it is interesting that the EST group, which aimed to achieve
at least 90 % MVF in the training contractions, experienced
smaller maximal strength gains than the MST group, which
experienced smaller training loads (75 % MVF). However,
time under tension is also considered an important training
stimulus for maximal strength gains (Crewther et al. 2005)
and was considerably longer for MST (MST, ~4 s vs. EST,
~1 s per contraction), so may therefore be a more important
determinant of maximal strength gains than the amplitude of
the training load.
Table 3 EMG recorded at maximal voluntary force (EMGMVF) and over different time periods from EMG onset (0–50, 0–100, and 0–150 ms)
during explosive contractions performed pre- and post-training in the maximal (MST) and explosive strength training (EST) groups
All variables were normalised to maximal M-wave (Mmax), and EMG variables during the explosive contractions are also expressed relative to
EMGMVF. Time (pre vs. post) × group (MST vs. EST) interaction effects are also reported. Data are mean ± SD
Within-group effects of training are denoted by * (P < 0.05)
MST group EST group Interaction effect (P value)
Pre Post Pre Post
EMGMVF (%Mmax)9.6 ± 1.9 12.3 ± 2.3* 9.6 ± 2.3 10.9 ± 2.1 0.278
EMG0–50 (%Mmax)6.8 ± 2.5 6.9 ± 2.2 5.0 ± 2.0 7.1 ± 2.0* 0.052
EMG0–100 (%Mmax)8.9 ± 2.8 9.6 ± 2.7 8.0 ± 1.9 10.0 ± 2.3* 0.228
EMG0–150 (%Mmax)9.5 ± 3.0 10.7 ± 2.6 8.9 ± 2.2 10.7 ± 2.3 0.565
EMG0–50 (%EMGMVF) 74.7 ± 23.7 58.2 ± 17.7* 54.3 ± 20.6 68.7 ± 19.4 0.007
EMG0–100 (%EMGMVF) 96.7 ± 22.7 82.1 ± 22.5 87.2 ± 19.6 94.8 ± 17.0 0.034
EMG0–150 (%EMGMVF) 102.8 ± 20.6 90.8 ± 19.8* 95.8 ± 20.6 101.0 ± 15.2 0.087
372 Eur J Appl Physiol (2014) 114:365–374
1 3
In contrast to the functional changes at the peak of
the force–time curve, EST produced greater increases in
explosive force production during the initial 100 ms of
contraction than MST. Thus, explosive strength training
provided an effective stimulus for improving early phase
(first 0–100 ms) explosive force production, whilst maxi-
mal strength training did not. Previous investigations have
consistently reported improvements in explosive force
when training this component of strength via short (1-s),
rapid contractions (Barry et al. 2005; de Ruiter et al. 2012;
Gruber et al. 2007; Van Cutsem et al. 1998). In compari-
son, training involving more prolonged contractions (>2 s)
and thus more closely associated with the maximal strength
training protocol in the current study have reported incon-
sistent effects on explosive strength (Andersen et al. 2010;
Del Balso and Cafarelli 2007; Kubo et al. 2001; Rich and
Cafarelli 2000; Suetta et al. 2004). These studies employed
a variety of different training protocols (e.g. intensity, vol-
ume, and duration) and may have used different instruc-
tions during the training contractions (e.g. “push fast and
hard” vs. “push hard”), which would be expected to alter
the training stimulus and result in differential changes in
explosive strength. In the current study the EST group were
instructed to push as “fast and hard” as possible, whilst the
MST group received no instruction to produce force rapidly
during the training contractions. Therefore, our results pro-
vide direct evidence that training contractions must be per-
formed ‘explosively’ with an emphasis on high rate of force
development to elicit short-term improvements in explosive
strength.
The increase in EMGMVF was only significant following
MST, which induced a twofold greater change than after
EST. On the other hand, there was no time × group inter-
action effect which would suggest the groups had similar
changes in EMGMVF. The high between-day variability in
EMG even after normalisation to Mmax (Buckthorpe et al.
2012), may have reduced the chances of observing a sig-
nificant group × time interaction effect and/or a significant
change in EMGMVF after EST, and so these results should
be interpreted with caution. Nevertheless, it seems likely
that there were improvements in neuromuscular activation
at MVF in both groups which contributed to their increases
in MVF, but that these neural adaptations were only large
enough to render a significant change in EMGMVF in the
MST group. Thus, it appears the MST provides a greater
stimulus for changes in neural drive during the maximum
(plateau) phase of contraction, which would explain the
greater increases in MVF after MST compared to EST.
During the early phase of explosive contraction (0–50 ms),
neuromuscular activation increased more after EST than
MST, and thus appears to explain the greater improvements
in explosive force after EST. Therefore, in overview this
study indicates that the training-specific functional changes
in the response to explosive and maximal strength train-
ing are underpinned by changes in neuromuscular activa-
tion specific to the training performed. Whilst past research
has linked short-term (within 4 weeks) improvements in
maximal and explosive strength to increased neuromuscu-
lar activation during the maximum (Del Balso and Cafarelli
2007; Tillin et al. 2011) and explosive (Barry et al. 2005;
de Ruiter et al. 2012; Tillin et al. 2012b) phases of contrac-
tion, respectively, to the best of our knowledge, this is the
first study to directly show that distinct training stimuli are
required to elicit these adaptations.
The distinct functional and neural adaptations to train-
ing for maximal vs. explosive strength are emphasised
when considering changes during the rising force–time
curve relative to those at the peak of the force–time curve
(Fig. 3c, d). Specifically, the EST group showed increases
in relative explosive force and EMG, due to improve-
ments in neuromuscular activation during the explosive
phase of contraction that did not transfer to the maxi-
mum phase of contraction. In contrast, the MST group
showed a decrease in relative explosive force and EMG,
due to improvements in neuromuscular activation during
the maximum phase of contraction that did not transfer to
the explosive phase of contraction. These disproportion-
ate changes during the explosive and maximum phases
of contraction for both types of training provide evidence
that the capacity to voluntarily activate the muscles and
produce force during the rising force–time curve can be
trained independently of the capacity to voluntarily acti-
vate the muscles and produce force at the peak of the
force–time curve, and vice versa. This is a particularly
interesting finding considering there is good evidence to
suggest that a similar mechanism, specifically increased
motor unit firing frequency, is likely to be the dominant
adaptive response underpinning improvements in neural
drive during both the explosive (Van Cutsem et al. 1998)
and maximum (Kamen and Knight 2004, 2008) phases of
contraction (Duchateau et al. 2006).
Previous investigations have reported evidence of mor-
phological adaptations (e.g. increased muscle size, shifts
in fibre type, and increased electrically evoked force
response) within just 4 weeks of strength training (Jurimae
et al. 1996; Seynnes et al. 2007; Staron et al. 1994; Tillin
et al. 2012b), so we cannot rule out the possibility that mor-
phological adaptations contributed to the training × group
interaction effects observed in the current study. How-
ever, given there was a close association between neural
and functional adaptations, we believe the contribution of
any morphological adaptations to the observed interaction
effects were minimal.
In conclusion, short-term training for maximal or explo-
sive strength elicited distinct functional and neural adapta-
tions which were specific to the training stimulus. There
373Eur J Appl Physiol (2014) 114:365–374
1 3
were greater improvements in maximal strength in the
MST group, which appeared due to their twofold greater
improvements in neuromuscular activation at MVF, whilst
early phase explosive strength increased in the EST group
only, due to greater improvements in early phase neuro-
muscular activation following EST. These results demon-
strate the independent adaptability of maximal and explo-
sive strength in response to training.
Acknowledgments The authors would like to extend their sincere
gratitude to: Mark Anthony Curbishley, Josh Bakker-Dyos, Christo-
pher Davison, and Matt Cross for their help during the training and
data collection.
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... De plus, ces consignes ont l'avantage de réduire le volume d'exercice ce qui permet de réduire l'inconfort et la fatigue engendrée par rapport à un renforcement musculaire traditionnel . La comparaison directe entre un renforcement musculaire hypertrophique par rapport à un renforcement musculaire explosif montre que les bénéfices sont spécifiques au type d'entrainement, si bien que les adaptations neuromusculaires engendrés lors d'exercices hypertrophiques ne se transfèrent pas (ou très peu) aux capacités explosives (Tillin et Folland, 2014). Dans l'objectif d'améliorer la fatigabilité neuromusculaire spécifiquement liée aux capacités explosives, les recommandations en activités physiques adaptées doivent se baser sur les guidelines largement utilisées de l'American College of Sport Medicine détaillant les principes d'exercice sous les termes de Fréquence (e.g., tous les combiens de jours), Intensité (e.g., à quelle difficulté), Temps (e.g., quelle durée d'activité), Type (e.g., quelle modalité), Volume (e.g., quelle quantité) et Progression (e.g., quelle augmentation de la difficulté), résumés avec l'acronyme FITT-VP (ACSM, 2018). ...
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Les patients souffrant d’insuffisance rénale chronique avancée (IRCa) ont une diminution de la masse et de la force musculaire, souvent cumulée à une profonde fatigue. Il a été récemment reconnu que la quantification du lien entre fatigue et fatigabilité neuromusculaire permet d’améliorer la compréhension du symptôme de fatigue chez ces patients, tout en permettant de renforcer l’arsenal thérapeutique non-médicamenteux par le biais d'interventions en activité physique adaptée. Des résultats divisés concernant la fatigabilité neuromusculaire ressortent de la littérature. Les patients avec une IRCa ont des limitations à l’effort liées à une perturbation de l’homéostasie musculaire, mais aucune autre cause n’a été reportée et le lien avec le symptôme de fatigue n’a jamais été étudié. Dans ce contexte, ce travail de doctorat a cherché à quantifier la fatigabilité neuromusculaire, tout en mesurant sa contribution au symptôme de fatigue, chez des patients avec une IRCa par rapport un des individus contrôles de même âge, sexe et prévalence de diabète. Les résultats montrent que les patients avec une IRCa ont une fatigabilité neuromusculaire plus importante que les contrôles, spécifiquement lorsqu’elle est évaluée à travers le taux de monté en force, mais pas avec la force maximale. De plus, les patients avec une IRCa souffrent d’une fatigue plus importante qui est associée à une perturbation du recrutement musculaire et à la fatigabilité neuromusculaire. Ces résultats suggèrent que les patients avec une IRCa développent potentiellement des phénomènes centraux à l’effort. De plus, la fatigabilité neuromusculaire évaluée avec la force maximale contribue à la description de la fatigue, indiquant qu’une activité physique adaptée pourrait permettre d’améliorer le symptôme de fatigue et la qualité de vie.
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... However, how strong is strong enough, or what the maximal strength threshold is across competitive levels, remains elusive. Because different types of strength are underpinned by distinct neuromuscular qualities specific to the sport stimulus (74), it is important to consider how other types of strength, such as explosive strength and strength endurance, contribute to judo performance. ...
... While explosive IST would generate more positive effects on explosive strength, sustained submaximal contraction would do so on MVIC. 22,29 Along with the described factors, the effect of the interaction of the IST with the technical and tactical usual academy training (15 h·wk −1 ) might also exert an effect on most of the adaptation differences. ...
Purpose: Evaluate the effects of 6 weeks of specific-joint isometric strength training on serve velocity (SV), serve accuracy (SA), and force-time curve variables. Methods: Sixteen young competition tennis players were divided into an intervention (n = 10) or control group (n = 6). SV, SA, maximal voluntary isometric contraction, peak rate of force development, rate of force development, and impulse (IMP) at different time frames while performing a shoulder internal rotation (SHIR) or flexion were tested at weeks 0, 3, and 6. Results: The intervention group showed significant increases in SV from pretest to posttest (7.0%, effect size [ES] = 0.87) and no variations in SA. Moreover, the intervention group showed significant increases from pretest to posttest in shoulder-flexion rate of force development at 150 (30.4%, ES = 2.44), 200 (36.5%, ES = 1.26), and 250 ms (43.7%, ES = 1.67) and in SHIR IMP at 150 (35.7%, ES = 1.18), 200 (33.4%, ES = 1.19), and 250 ms (35.6%, ES = 1.08). Furthermore, significant increases were found in shoulder-flexion rate of force development from intertest to posttest at 150 ms (24.5%, ES = 1.07) and in SHIR IMP at 150 (13.5%, ES = 0.90), 200 (19.1%, ES = 0.98), and 250 ms (27.2%, ES = 1.16). SHIR IMP changes from pretest to intertest were found at 150 ms (25.6%, ES = 1.04). The control group did not show changes in any of the tested variables. Conclusions: Six weeks of upper-limb specific-joint isometric strength training alongside habitual technical-tactical workouts results in significant increases in SV without SA detriment in young tennis players.
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ABSTRACT Introduction: Comparison of the neuromuscular performance of different athlete types may give insight into the in-vivo variability of these measures and their underpinning mechanisms. The study aims to compare the neuromuscular function of the plantar flexors of sprinters and physically active individuals to assess any differences in explosive force performance. Methods: Neuromuscular performance of a group of sprinters (highly trained/national level, n = 12; elite/international level, n = 2) and physically active individuals (n = 14) were assessed during involuntary, explosive, and maximum voluntary isometric plantar flexions, across different muscle-tendon unit (MTU) lengths (10° plantarflexion (PF), 0° (anatomical zero/neutral, AZ), and 10° dorsiflexion (DF)). Plantarflexion rate of torque development (RTD) was measured in three 50-ms time windows from their onset. The synchronous activation of the plantar flexor agonist muscles was calculated as the time difference between 1) the first and last muscle onset and 2) the onsets of the two gastrocnemii muscles. Muscle size and MTU stiffness were assessed using sonograms of the medial gastrocnemius and myotendinous junction. Results: Sprinters exhibited greater involuntary RTD across time points (0-50, 50-100 ms) and MTU lengths. Additionally, sprinters demonstrated greater early phase voluntary RTD (0-50, 50-100 ms) across MTU lengths. Sprinters also demonstrated greater late-phase RTD (100-150 ms), and relative maximal voluntary torque at the DF angle only. The sprinters demonstrated a more synchronous activation of the gastrocnemii muscles. There were no observable differences in muscle size and MTU stiffness between groups. Conclusions: These findings suggest sprint-specific training could be a contributing factor toward improved explosive performance of the plantar flexors, particularly in the early phase of muscular contraction, evidenced by the greater explosive torque producing capabilities of sprinters.
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Purpose: To evaluate the contribution of splenius capitis, sternocleidomastoid, and upper fibers of trapezius activation to the gains in rate of force development (RFD) of the head and neck during maximum voluntary ballistic contractions. Methods: RFD gain was facilitated by a single-session intervention for maximum voluntary ballistic contractions in the anterior direction, oriented at 45° to the midsagittal plane, which require active restraint of axial rotation. Muscle activation for the agonist (sternocleidomastoid) and 2 antagonists (splenius capitis and upper fibers of trapezius) was evaluated. The study sample included 12 physically active men (mean age, 22.6 y). RFD (N·m·s-1; 0-100 ms) and integrated muscle activity (50 ms before and 100 ms after force onset) were measured at 10 minutes, 20 minutes, and 2 days postintervention, relative to baseline. Muscle activation predictive of RFD gains was evaluated by linear regression analysis. RFD reproducibility was evaluated using the coefficient of variation of the typical error. Results: The intervention yielded a 1.95- to 2.39-fold RFD gain (P ≤ .05), with greater RFD gain for participants with a lower peak moment of force (<10.9 N·m) than those with a higher peak moment (≥10.9 N·m) at baseline (P ≤ .002). For the low group, 65% to 74% of the RFD gain was predicted by ipsilateral sternocleidomastoid activation, with ipsilateral splenius capitis activation predicting 77% to 92% of RFD gain for the high group. Absolute peak and impulse of static force were greater for the high than for the low group (P ≤ .04). RFD reproducibility was high (coefficient of variation of the typical error ≤ 14.4%). Conclusions: The agonist- and antagonist-focused synergies might reflect different functional priorities, higher RFD gain compared with higher head-neck force.
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Tennis serve is considered the most complex, powerful and determinant stroke in high level tennis competition. Specifically, serve velocity (SV) alongside serve accuracy (SA) plays a preponderant role in elite competitions. Considering that serve performance is influenced by different kind of parameters, the presented doctoral thesis was planned in order to provide a multifactorial approach of the topic of the study. The influence of disparate nature of variables on SV and SA in real match (study I), laboratory (study II)and training (study III and IV) conditions were analyzed. To begin, we determined the influence of anthropometric, ball impact and landing location parameters in elite tennis competition (study I). Then, we analysed the associations between SV and various single-joint upper limb isometric force-time curve parameters (Isometric force [IF], rate of force development [RFD] and impulse [IMP]) in competition tennis players (study II). Finally, we observed if joint-specific post-activation potentiation enhancement (PAPE) and isometric strength training (IST) training methods improves SV in young tennis players (study III and IV). We conclude that anthropometric, ball impact and bounce landing location parameters influence SV during a professional competition. We demonstrate that force-time parameters (IF, RFD and IMP) at different time frames in upper limb joints involved in the serve kinetic chain moderate to very largely influence SV in competitive players. Concretely, the capability to develop force in short periods of time (< 250 ms) in the shoulder joint was shown to be relevant to develop high SV. Lastly, we proved that performing two short upper-limb tennis-specific joint isometric exercises elicits PAPE increasing SV without SA impairment. In addition, combining 6-week of IST with the habitual tennis workouts results in significant increases in SV without SA detriment in young competitive players.
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Patellofemoral pain (PFP) is a chronic condition that presents with patellar pain during various daily and recreational activities. Individuals with PFP have a wide range of impairments that result in long-term disability and reduced quality of life. Current interventions target hip muscle weakness with strength-based exercises, but recurrence rates are as high as 90%. A single feasibility study demonstrated success with power-based exercises; however, there is limited evidence evaluating pain or self-reported function in larger cohorts, and no study has assessed recurrence rates. This protocol details a study evaluating a strength-based rehabilitation programme compared with a strength-based programme incorporating power-based exercises in individuals with PFP. This single-blinded randomised controlled trial will evaluate 88 participants with PFP, aged 18–40 years old. Participants will be recruited from three universities, the surrounding community and sports medicine clinics. Participants will receive three telemedicine rehabilitation sessions a week for 6 weeks. The rehabilitation programme will consist of either strength-based exercises or a combination of power and strength-based exercises. Pain, subjective function and recurrence rates will be assessed at baseline, immediately after the intervention and at four follow-up time points: 6-month, 12-month, 18-month and 24-month postintervention. We will also assess neuromuscular function of the hips and global rating of change at each postintervention time point. Trial registration number NCT05403944 .
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Aim: Bioactive collagen peptides (CP) have been suggested to augment the functional, structural (size and architecture) and contractile adaptations of skeletal muscle to resistance training (RT), but with limited evidence. This study aimed to determine if CP vs placebo (PLA) supplementation enhanced the functional and underpinning structural, and contractile adaptations after 15 weeks of lower body RT. Methods: Young healthy males were randomized to consume either 15 g of CP (n=19) or PLA (n=20) once every day during a standardized program of progressive knee extensor, knee flexor and hip extensor RT 3 times/wk. Measurements pre and post RT included: knee extensor and flexor isometric strength; quadriceps, hamstrings and gluteus maximus volume with MRI; evoked twitch contractions, 1RM lifting strength and architecture (with ultrasound) of the quadriceps. Results: Percentage changes in maximum strength (isometric or 1RM) did not differ between groups (0.684≤P≤0.929). Increases in muscle volume were greater (quadriceps 15.2 vs. 10.3%; vastus medialis (VM) 15.6 vs. 9.7%; total muscle volume 15.7 vs. 11.4%; [all] P≤0.032) or tended to be greater (hamstring 16.4 vs. 12.5%; gluteus maximus 16.6 vs. 12.9%; 0.089≤P≤0.091) for CP vs. PLA. There were also greater increases in twitch peak torque (22.3 vs. 12.3%; P=0.038) and angle of pennation of the VM (16.8 vs. 5.8%, P=0.046), but not other muscles, for CP vs. PLA. Conclusions: CP supplementation produced a cluster of consistent effects indicating greater skeletal muscle remodelling with RT compared to PLA. Notably, CP supplementation amplified the quadriceps and total muscle volume increases induced by RT.
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Abstract This study investigated the association between explosive force production during isometric squats and athletic performance (sprint time and countermovement jump height). Sprint time (5 and 20 m) and jump height were recorded in 18 male elite-standard varsity rugby union players. Participants also completed a series of maximal- and explosive-isometric squats to measure maximal force and explosive force at 50-ms intervals up to 250 ms from force onset. Sprint performance was related to early phase (≤100 ms) explosive force normalised to maximal force (5 m, r = -0.63, P = 0.005; and 20 m, r = -0.54, P = 0.020), but jump height was related to later phase (>100 ms) absolute explosive force (0.51 < r < 0.61; 0.006 < P < 0.035). When participants were separated for 5-m sprint time (< or ≥ 1s), the faster group had greater normalised explosive force in the first 150 ms of explosive-isometric squats (33-67%; 0.001 < P < 0.017). The results suggest that explosive force production during isometric squats was associated with athletic performance. Specifically, sprint performance was most strongly related to the proportion of maximal force achieved in the initial phase of explosive-isometric squats, whilst jump height was most strongly related to absolute force in the later phase of the explosive-isometric squats.
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The influence of contraction type on the human ability to use the torque capacity of skeletal muscle during explosive efforts has not been documented. Fourteen male participants completed explosive voluntary contractions of the knee extensors in four separate conditions: concentric (CON) and eccentric (ECC); and isometric at two knee angles (101°, ISO101 and 155°, ISO155). In each condition, torque was measured at 25 ms intervals up to 150 ms from torque onset, and then normalized to the maximum voluntary torque (MVT) specific to that joint angle and angular velocity. Explosive voluntary torque after 50 ms in each condition was also expressed as a percentage of torque generated after 50 ms during a supramaximal 300 Hz electrically evoked octet in the same condition. Explosive voluntary torque normalized to MVT was more than 60 per cent larger in CON than any other condition after the initial 25 ms. The percentage of evoked torque expressed after 50 ms of the explosive voluntary contractions was also greatest in CON (ANOVA; p < 0.001), suggesting higher concentric volitional activation. This was confirmed by greater agonist electromyography normalized to M(max) (recorded during the explosive voluntary contractions) in CON. These results provide novel evidence that the ability to use the muscle's torque capacity explosively is influenced by contraction type, with concentric contractions being more conducive to explosive performance due to a more effective neural strategy.
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1. Increases in strength and size of the quadriceps muscle have been compared during 12 weeks of either isometric or dynamic strength training. 2. Isometric training of one leg resulted in a significant increase in force (35 +/- 19%, mean +/- S.D., n = 6) with no change in the contralateral untrained control leg. 3. Quadriceps cross-sectional area was measured from mid-thigh X-ray computerized tomography (c.t.) scans before and after training. The increase in area (5 +/- 4.6%, mean +/- S.D., n = 6) was smaller than, and not correlated with, the increase in strength. 4. The possibility that the stimulus for gain in strength is the high force developed in the muscle was examined by comparing two training regimes, one where the muscle shortened (concentric) and the other where the muscle was stretched (eccentric) during the training exercise. Forces generated during eccentric training were 45% higher than during concentric training. 5. Similar changes in strength and muscle cross-sectional area were found after the two forms of exercise. Eccentric exercise increased isometric force by 11 +/- 3.6% (mean +/- S.D., n = 6), and concentric training by 15 +/- 8.0% (mean +/- S.D., n = 6). In both cases there was an approximate 5% increase in cross-sectional area. 6. It is concluded that as a result of strength training the main change in the first 12 weeks is an increase in the force generated per unit cross-sectional area of muscle. The stimulus for this is unknown but comparison of the effects of eccentric and concentric training suggest it is unlikely to be solely mechanical stress or metabolic fluxes in the muscle.
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High-resistance strength training (HRST) is one of the most widely practiced forms of physical activity, which is used to enhance athletic performance, augment musculo-skeletal health and alter body aesthetics. Chronic exposure to this type of activity produces marked increases in muscular strength, which are attributed to a range of neurological and morphological adaptations. This review assesses the evidence for these adaptations, their interplay and contribution to enhanced strength and the methodologies employed. The primary morphological adaptations involve an increase in the cross-sectional area of the whole muscle and individual muscle fibres, which is due to an increase in myofibrillar size and number. Satellite cells are activated in the very early stages of training; their proliferation and later fusion with existing fibres appears to be intimately involved in the hypertrophy response. Other possible morphological adaptations include hyperplasia, changes in fibre type, muscle architecture, myofilament density and the structure of connective tissue and tendons. Indirect evidence for neurological adaptations, which encompasses learning and coordination, comes from the specificity of the training adaptation, transfer of unilateral training to the contralateral limb and imagined contractions. The apparent rise in whole-muscle specific tension has been primarily used as evidence for neurological adaptations; however, morphological factors (e.g. preferential hypertrophy of type 2 fibres, increased angle of fibre pennation, increase in radiological density) are also likely to contribute to this phenomenon. Changes in inter-muscular coordination appear critical. Adaptations in agonist muscle activation, as assessed by electromyography, tetanic stimulation and the twitch interpolation technique, suggest small, but significant increases. Enhanced firing frequency and spinal reflexes most likely explain this improvement, although there is contrary evidence suggesting no change in cortical or corticospinal excitability. The gains in strength with HRST are undoubtedly due to a wide combination of neurological and morphological factors. Whilst the neurological factors may make their greatest contribution during the early stages of a training programme, hypertrophic processes also commence at the onset of training.
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Introduction: This study determined the between-session reliability of neuromuscular measurements during explosive isometric contractions, with special consideration of electromyography (EMG) normalization. Methods: Following familiarization, 13 men participated in 3 identical measurement sessions involving maximal and explosive voluntary contractions of the knee extensors, while force and surface EMG were recorded. Root mean square EMG amplitude was normalized to different reference measures: (evoked maximal M-wave peak-to-peak amplitude and area, maximum and sub-maximum voluntary contractions). Results: Explosive voluntary force measurements were reliable on a group level, whereas within-subject reliability was low over the initial 50 ms and good from 100 ms onward. Normalization of EMG during explosive voluntary contractions, irrespective of the reference method, did not reduce the within-subject variability, but it did reduce substantially the variability between-subject. Conclusions: The high intra-individual variability of EMG and early phase explosive voluntary force production may limit their use to measuring group as opposed to individual responses to an intervention.
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Tissue Doppler imaging (TDI) is typically used to image and quantify tissue motion. We investigated whether this method would serve as a viable alternative to surface electromyography (EMG) in providing a reliable and valid measure of the onset of muscle activity. Ten healthy subjects performed maximal knee extension exercises at 0°/s (isometric), 60°/s, 120°/s, 180°/s, and 240°/s (5 times each, on each side), using an isokinetic dynamometer. Simultaneous EMG and TDI velocity (superimposed on motion-mode ultrasound cine-loops) recordings were made from vastus lateralis. All tests were repeated 1 week later. There was a good correlation between the onset times determined with TDI velocity and EMG: r = 0.78 (day 1), and r = 0.80 (day 2) (each P < 0.001). The mean difference (and SD) in muscle onset time between the two methods (TDI minus EMG) was −20.3 ± 31.0 ms (day 1) and −17.4 ± 27.2 ms (day 2). TDI represents a reliable and valid measure of detecting onset of muscle activity. The mean difference between EMG and TDI onset times (approximately 20 ms) is likely explained by electromechanical delay. TDI represents a viable method for measuring the onset of muscle activity; it may offer a non-invasive alternative to fine-wire EMG for use with small or deep muscles. Muscle Nerve, 2008
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This study investigated the neural and peripheral adaptations to short-term training for explosive force production. Ten men trained the knee extensors with unilateral explosive isometric contractions (1 s 'fast and hard') for 4 weeks. Before and after training, force was recorded at 50-ms intervals from force onset (F(50), F(100) and F(150)) during both voluntary and involuntary (supramaximal evoked octet; eight pulses at 300 Hz) explosive isometric contractions. Neural drive during the explosive voluntary contractions was measured with the ratio of voluntary/octet force, and average EMG normalized to the peak-to-peak M-wave of the three superficial quadriceps. Maximal voluntary force (MVF) was also measured, and ultrasonic images of the vastus lateralis were recorded during ramped contractions to assess muscle-tendon unit stiffness between 50 and 90% MVF. There was an increase in voluntary F(50) (+54%), F(100) (+15%) and F(150) (+14%) and in octet F(50) (+7%) and F(100) (+10%). Voluntary F(100) and F(150), and octet F(50) and F(100) increased proportionally with MVF (+11%). However, the increase in voluntary F(50) was +37% even after normalization to MVF, and coincided with a 42% increase in both voluntary/octet force and agonist-normalized EMG over the first 50 ms. Muscle-tendon unit stiffness between 50 and 90% MVF also increased. In conclusion, enhanced agonist neural drive and MVF accounted for improved explosive voluntary force production in the early and late phases of the contraction, respectively. The increases in explosive octet force and muscle-tendon unit stiffness provide novel evidence of peripheral adaptations within merely 4 weeks of training for explosive force production.