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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
1 3
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.kg−1) 7.2 ± 0.8 6.6 ± 0.8
368 Eur J Appl Physiol (2014) 114:365–374
1 3
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
1 3
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. kg−1) 7.22 ± 0.80 8.70 ± 1.19** 6.58 ± 0.83 7.28 ± 0.71*** 0.020
F50 (N.kg−1)1.64 ± 0.71 1.70 ± 0.72 1.23 ± 0.43 1.89 ± 0.65* 0.083
F100(N.kg−1)4.21 ± 0.78 4.34 ± 0.72 3.94 ± 0.61 4.53 ± 0.62** 0.030
F150 (N.kg−1)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 ≤ P≤0.039). 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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