Effects of acute resistance training modality on corticospinal excitability, intra-cortical and neuromuscular responses

Abstract

Objective:
Although neural adaptations from strength training are known to occur, the acute responses associated with heavy-strength (HST) and hypertrophy training (HYT) remain unclear. Therefore, we aimed to compare the acute behaviour of corticospinal responses following a single session of HST vs HYT over a 72-h period.

Methods:
Fourteen participants completed a random counterbalanced, crossover study that consisted of a single HST session [5 sets × 3 repetition maximum (RM)], a HYT session (3 sets × 12 RM) of the leg extensors and a control session (CON). Single- and paired-pulse transcranial magnetic stimulation (TMS) was used to measure changes in motor-evoked potential (MEP) amplitude, corticospinal silent period (CSP), intra-cortical facilitation (ICF), short-interval intra-cortical inhibition (SICI) and long-interval intra-cortical inhibition (LICI). Additionally, maximal muscle compound wave (M MAX) of the rectus femoris (RF) and maximal voluntary isometric contraction (MVIC) of the leg extensors were taken. All measures were taken at baseline, immediately post and 2, 6, 24, 48 and 72 h post-training.

Results:
A significant condition x time interaction was observed for MVIC (P = 0.001), M MAX (P = 0.003), MEP amplitude (P < 0.001) and CSP (P = 0.002). No differences were observed between HST and HYT for all neurophysiological measures. No changes in SICI, ICF and LICI were observed compared to baseline.

Conclusion:
Our results suggest that: (1) the acute behaviour of neurophysiological measures is similar between HST and HYT; and (2) the increase in corticospinal excitability may be a compensatory response to attenuate peripheral fatigue.

Full text

Vol.:(0123456789)
1 3
Eur J Appl Physiol
DOI 10.1007/s00421-017-3709-7
ORIGINAL ARTICLE
Effects ofacute resistance training modality oncorticospinal
excitability, intra‑cortical andneuromuscular responses
ChristopherLatella1· Wei‑PengTeo1,4· DaleHarris1· BrendanMajor2·
DanVanderWesthuizen3· AshleeM.Hendy1,4
Received: 18 January 2017 / Accepted: 13 August 2017
© Springer-Verlag GmbH Germany 2017
extensors were taken. All measures were taken at baseline,
immediately post and 2, 6, 24, 48 and 72h post-training.
Results A significant condition x time interaction was
observed for MVIC (P=0.001), MMAX (P=0.003), MEP
amplitude (P<0.001) and CSP (P=0.002). No differences
were observed between HST and HYT for all neurophysi-
ological measures. No changes in SICI, ICF and LICI were
observed compared to baseline.
Conclusion Our results suggest that: (1) the acute behav-
iour of neurophysiological measures is similar between HST
and HYT; and (2) the increase in corticospinal excitability
may be a compensatory response to attenuate peripheral
fatigue.
Keywords Transcranial magnetic stimulation· Heavy-
strength· Hypertrophy· Neurophysiological· Fatigue·
Recovery
Abbreviations
CSP Corticospinal silent period
HST Heavy-strength training
HYT Hypertrophy training
TMS Transcranial magnetic stimulation
ICF Intra-cortical facilitation
LICI Long interval cortical inhibition
MEP Motor evoked potential
MVIC Maximal voluntary isometric contraction
MMAX Maximal compound wave
RF Rectus femoris
RM Repetition maximum
RT Resistance training
sEMG Surface electromyography
SICI Short interval cortical inhibition
Abstract
Objective Although neural adaptations from strength
training are known to occur, the acute responses associated
with heavy-strength (HST) and hypertrophy training (HYT)
remain unclear. Therefore, we aimed to compare the acute
behaviour of corticospinal responses following a single ses-
sion of HST vs HYT over a 72-h period.
Methods Fourteen participants completed a random coun-
terbalanced, crossover study that consisted of a single HST
session [5 sets×3 repetition maximum (RM)], a HYT
session (3 sets×12 RM) of the leg extensors and a con-
trol session (CON). Single- and paired-pulse transcranial
magnetic stimulation (TMS) was used to measure changes
in motor-evoked potential (MEP) amplitude, corticospinal
silent period (CSP), intra-cortical facilitation (ICF), short-
interval intra-cortical inhibition (SICI) and long-interval
intra-cortical inhibition (LICI). Additionally, maximal mus-
cle compound wave (MMAX) of the rectus femoris (RF) and
maximal voluntary isometric contraction (MVIC) of the leg
Communicated by William J. Kraemer.
* Christopher Latella
clatella@deakin.edu.au
1 School ofExercise andNutrition Sciences, Deakin
University, 221 Burwood Highway, Burwood, VIC3125,
Australia
2 Cognitive Neuroscience Unit (CNU), School ofPsychology,
Deakin University, Burwood, Australia
3 Clinical Exercise Science andRehabilitation, Institute
ofSport, Exercise andActive Living (ISEAL), Victoria
University, Footscray, Australia
4 Institute forPhysical Activity andNutrition (IPAN), School
ofExercise andNutrition Sciences, Deakin University,
Geelong, Australia

Eur J Appl Physiol
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Introduction
Different modes of resistance training (RT) are applied
in athletics, conditioning rehabilitation and general RT
practice to promote targeted gains in neuromuscular per-
formance (Ratamess etal. 2009). Hypertrophy training
(HYT), characterised by higher volume and low-to-mod-
erate intensity loads (67–75% of 1 RM, 6–15 repetitions)
is commonly employed during the early phase of a training
program to increase muscle mass (Bompa and Haff 2009;
Haff and Triplett 2016). On the other hand, heavy-strength
training (HST) is characterised by low repetition and high
intensity loads (≥80% of 1 RM, 1–6 repetitions) intended
to increase maximal strength (Ratamess etal. 2009). HST
is often introduced after the hypertrophy phase or where
specific strength adaptations are required (Bompa and Haff
2009).
While the neuromuscular adaptations from repeated HST
are well-established (Latella etal. 2012; Hendy and Kidgell
2013; Kidgell and Pearce 2010; Carroll etal. 2011; Selva-
nayagam etal. 2011; Folland and Williams 2007), the acute
intra-cortical and corticospinal responses have seldom been
directly compared with other RT modes such as HYT. Fur-
thermore, previous investigations into HYT have primarily
focused on physiological changes (Schoenfield 2014; Phil-
lips etal. 2002; Kim etal. 2005; Walker etal. 2011), whilst
the neural basis of HYT has not been well-established. We
have previously reported that the MEP amplitude and MMAX
is impaired following and acute session of HST in the elbow
flexors (Latella etal. 2016). No intra-cortical changes were
observed following the protocol indicating that the responses
were modulated downstream of the primary motor cortex.
Contrarily, Roustsalianen etal. (2014) also showed that
an initial increase in MEP amplitude and CSP duration
occurred following an acute session of HYT. Increases in
corticospinal excitability and decreases in SICI have also
been shown with various contraction types (ballistic and
slow ramp isometric, dynamic metronome paced) of the
elbow flexors (Nuzzo etal. 2016a; Leung etal. 2015). At the
peripheral level, changes in peripheral nerve excitability are
also known to occur with fatiguing exercises such that both
reductions (Behm and St-Pierre 1997; Sacco etal. 1997;
Nuzzo etal. 2016c) and increases (Behm and St-Pierre 1997;
Nuzzo etal. 2016b) in MMAX have been shown following
resistance exercise. These studies suggest that dynamic RT
duration may have a differential effect on peripheral nerve
excitability (Behm and St-Pierre 1997), while others have
showed no differences between 2 and 12 sets of isometric
training (Nuzzo etal. 2016b). Despite these suggestions,
and to the best of our knowledge, there have been no direct
investigations comparing the acute central and peripheral
neural responses following a single session of applied HST
and HYT.
From a neuromuscular standpoint, acute impairments in
force production have been investigated extensively following
strength, hypertrophy and power training (Walker etal. 2012;
Howatson etal. 2016; Brandon etal. 2015; Nicholson etal.
2014). However, due to differences in exercise selection and
training parameters (i.e., load and volume), the literature has
produced conflicting results. Nicholson etal. (2014) showed
no differences in reduction in peak force of the lower limbs
following HST or HYT squat training when the load was equal
between conditions. However, volume equated loads are not
traditionally used for HST and HYT protocols in applied
settings. The similarities in the reduction of maximal force
production of the lower limbs following HST and HYT pro-
tocols has also demonstrated in later studies (Brandon etal.
2015; Howatson etal. 2016). Conversely, Walker etal. (2012)
showed impairment of the MVIC to be greater following
(5×10RM) compared to (15×1RM) leg presses. However,
some evidence has suggested that shorter rest period durations
can impair in session neuromuscular performance (Scudese
etal. 2015) with less direct evidence on the subsequent effect
of altered exercise volume and intensity. However, it must be
acknowledged that this comparison was using the same vol-
ume and intensity between conditions and may not accurately
reflect the changes associated with typical HST and HYT.
Therefore, based upon previous findings it remains unclear
whether the force generating capacity of a joint is differentially
affected by the combination of intrinsic session variables (i.e.,
volume, intensity and rest period duration) typically seen in
separate RT modalities.
The aim of this study was to directly compare the acute
changes in central and peripheral neural responses, and neu-
romuscular torque between HST and HYT in the leg exten-
sor muscles over a 72-h period post-training. Specifically,
we aim to determine differences in corticospinal excitability,
short-/long-interval intra-cortical inhibition and facilitation,
and maximal M-wave responses following HST and HYT.
Given the variance in load and intensity between both train-
ing modalities, we hypothesised that the change in central
and peripheral neural excitability would be greater with
HST due to the proposed demands placed on the central
and peripheral nervous system. The results from our study
will be important to understand the underlying neurophysi-
ological responses to different applied RT modalities used
by strength and conditioning professionals aimed at targeting
specific performance adaptations in athletes.
Methods
Participants
Fourteen (M = 9, F = 5) healthy individuals
(26.2±3.1years, 81.3±9.6kg, 174.2±10.5cm) with

Eur J Appl Physiol
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no reported incidence of neuromuscular injury to the lower
limb completed a randomised, counterbalanced crossover
study comparing HST and HYT, and a control (CON) condi-
tions. All participants were recreationally resistance-trained
(6–12months experience) and reported training at least
twice a week. Written informed consent was obtained for
each participant prior to the start of the study. To determine
limb dominance, the Waterloo Footedness Questionnaire
(Elias etal. 1998) was administered and only participants
that were right foot dominant were included in this study.
Prior to TMS, all participants were screened using a TMS
safety questionnaire to exclude potential participants with
contraindications to TMS (Rossi etal. 2009). Female par-
ticipants were screened to ensure they were not undertaking
any part of the protocol during menstruation. All procedures
used in this study were approved by the Deakin University
Human Research Ethics Committee (Project ID: 2013-198)
and conducted to the standards set by the Declaration of
Helsinki.
Transcranial magnetic stimulation andsurface
electromyography recording
Single- and paired-pulse TMS was used to measure changes
in corticospinal excitability and cortical inhibition and facil-
itation. All TMS measurements were taken with the par-
ticipant seated upright with their right knee flexed at a 45°
angle (full knee extension equates to 0 degrees), hip flexed
at 90° and was conducted on the same chair as used for
MVIC measurements. Surface electromyography (sEMG)
was recorded from the RF muscle in the dominant leg using
Ag–AgCL electrodes. Two electrodes were placed 20mm
apart on the midpoint of the belly of RF, with the ground
electrode placed over the patella according to SENIAM
guidelines (Hermens etal. 2000). The skin was prepared by
removing any hair and cleaned with 70% isopropyl alcohol
swabs prior to the placement of the electrodes. Surface elec-
tromyography signals were amplified (1000×) with bandpass
filtering between 20Hz and 1kHz and digitised at 10kHz
for 500ms, recorded and analysed using PowerLab 4/35
(ADinstruments, Australia).
To ensure consistent delivery of TMS stimuli within and
between testing sessions, all participants wore a custom-
made snug-fitted cap (EasyCap, Germany) positioned in
relation to nasion–inion and inter-aural lines. The cap was
marked with points at 1cm intervals in a longitude–latitude
matrix to allow repeated stimuli to be performed at the same
point over the primary motor cortex (M1) each time. Single
and paired-pulse TMS were applied over the cortical motor
representation of the RF on the M1, using a double cone
110-mm coil attached to a BiStim 2002 magnetic stimula-
tor (Magstim Co., Dyfed, UK). The double cone coil was
placed over the vertex of the scalp and the ‘optimal site’
that elicited the largest and most consistent motor-evoked
potentials (MEP) from the RF, determined through initial
exploration in areas surrounding the vertex for each indi-
vidual. Once the optimal site was located, the resting motor
threshold (RMT), used for calculating paired-pulse stimula-
tion of the RF muscle was determined by the lowest TMS
intensity at which an MEP could be obtained with at least 5
of the 10 stimuli with peak-to-peak amplitude of 50–100µV
at rest (Rothwell etal. 1999; Westin etal. 2014). Determina-
tion of the active motor threshold (AMT), used for single-
pulse stimulation, required the participant to hold a steady
contraction at 10% MVIC and defined as the lowest TMS
intensity at which a MEP could be obtained with at least 5
of the 10 stimuli with peak-to-peak amplitude being greater
than 200µV (Rothwell etal. 1999). Ten single-pulse TMS
were applied at 20% above AMT and were administered
with a randomly chosen 5–8s intervals between stimuli.
To account for any differences in peripheral nerve excit-
ability, all measures of single-pulse MEP amplitude were
normalised to MMAX (MEP amplitude/MMAX=Normalised
MEP). The CSP duration was calculated as the time from
the onset of the MEP to the return of the sEMG signal in
(ms). Paired-pulse TMS was conducted with the muscle at
rest as used in other exercise fatigue studies (Verin etal.
2004; Benwell etal. 2006) using RMT for the calculation of
stimulation intensities.
Paired-pulse was used to measure changes in intra-cor-
tical measures of SICI, LICI and ICF. Paired-pulse TMS
consisted of a conditioning (CS) and test stimulus (TS) sep-
arated by a specified interstimulus intervals (ISI) and the
configuration for SICI, LICI and ICF were as follows; SICI
(CS=90% RMT, TS=120% RMT, ISI=3ms) (Kujirai
etal. 1993), LICI (CS=120% RMT, TS=120% RMT,
ISI=100ms) (Du etal. 2014; McNeil etal. 2011) and ICF
(CS=90% RMT, TS=120% RMT, ISI=12ms) (Kob-
ayashi & Pascual-Leone 2003; Kujirai etal. 1993). Both
SICI and ICF were expressed as a percentage of the uncon-
ditioned single-pulse MEP amplitude, while LICI was cal-
culated and expressed as a percentage of the test to condi-
tioning MEP amplitude for each individual paired stimuli.
Maximal M‑wave measurements
Maximal M-wave (MMAX) responses, measured as the peak-
to-peak amplitude of the wave-form were obtained from
sEMG recording of the right RF muscle by direct supramaxi-
mal electrical stimulation (pulse duration 100ms) of the
femoral nerve under resting conditions using a high-volt-
age constant current electrical stimulator (Nihon Khoden,
Japan). Nerve stimulation was delivered using bipolar
electrodes positioned over the right femoral nerve in the
femoral triangle approximately 3–5cm below the inguinal
ligament (Doguet and Jubeau 2014) along the right inguinal

Eur J Appl Physiol
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fold. The nerve stimulation current intensity was progres-
sively increased until there was no further increase in sEMG
amplitude. To ensure maximal responses were obtained, the
maximal current intensity was further increased by 20% and
the highest MMAX obtained from 5 stimuli was recorded.
Maximal voluntary isometric contraction oftheleg
extensor muscles
Maximal torque of the RF muscle was measured using a 5s
MVIC (2s ramp up followed by 3s maximal effort). Three
MVIC trials, separated by a 60s rest period, were conducted
with the participants seated upright on a Cybex dynamom-
eter (Cybex, USA) and strapped across the chest and hips to
prevent extraneous movements of the upper body. The ankle
of the right foot was strapped to the immovable leg extension
arm of the dynamometer, approximately 7.5cm proximal to
the medial malleolus (Krishnan etal. 2011). The hip was
positioned at 90° of flexion with a 45° flexion angle of the
right knee (Krishnan etal. 2011). Verbal encouragement and
real-time visual force feedback were provided for each effort.
All torque signals were sampled at 1000Hz, with additional
filtering not required. The maximal recorded peak torque
(Nm) of the three trials was reported as MVIC.
Experimental protocol
Figure1 shows the setup and timeline for each testing ses-
sion. The study consisted of a familiarisation session prior
to testing, to reduce the potential of any learning effects
on the outcome measures of the study (described in the
subsequent sections), followed by three testing conditions
(HST vs HYT vs CON) performed in a counterbalanced
randomised order. During the familiarisation session, the
outcome measures included maximal voluntary isometric
contraction on dynamometer (Cybex Humac Norm, USA),
single- and paired-pulse TMS using a (Bistim 2002, mag-
netic stimulator (Magstim Co., Wales, UK) and peripheral
nerve stimulation using a constant direct current electric
stimulator (Nihon Koden, Japan) were recorded. Each par-
ticipant’s 1 RM single leg extension strength was also meas-
ured on a leg extension machine (Nautilus Pin Loaded Leg
Extension, Canada) and recorded to determine the training
load intensity for the subsequent HST and HYT sessions. A
1-week inter-protocol period was implemented between each
of the four visits (familiarisation, HST, HYT and CON).
Participants were instructed to refrain from any strenuous
lower body exercise 72h prior to and during all conditions,
asked to refrain from stretching, active recovery and asked
to maintain usual dietary and sleeping habits throughout the
testing period. During the 1-week intermissions, participants
were allowed to continue usual training as long as this did
not interfere with the 72-h period prior to the subsequent
testing protocol. All testing sessions and associated outcome
measures for each session were tested on the same time-of-
day in a shielded laboratory to account for any circadian
fluctuations in neuromuscular performance (Teo etal. 2011)
and effects on arousal from external distractions.
The training load intensity for HST and HYT of the leg
extensor muscles was set at the participant’s calculated 3 RM
(94% of 1RM), and 12 RM (67% of 1 RM), respectively,
that was derived from the 1 RM obtained in the familiarisa-
tion session using the formula developed by Brzycki (1993).
The HST protocol consisted of 5 working sets consisting
of 3 RM with 180s recovery in between (total volume 15
repetitions). The HYT protocol consisted of 3 working sets
consisting of 12 RM with 60s recovery in between (total
volume 36 repetitions). The differences in training volume
between HST and HYT were acknowledged as an impor-
tant factor in maintaining the integrity of real-world RT pro-
grams which have a disparate training volumes and intensi-
ties. The training load was increased if the researcher (a
Fig. 1 Schematic overview of
chapter four protocols. Depicts
HST, HYT and CON protocols
and neurophysiological testing
measures at proposed stages of
the super-compensation cycle
over a 72h period

Eur J Appl Physiol
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certified strength and conditioning practitioner) deemed that
extra repetitions could be performed, and likewise, lowered
if there was failure to complete the repetitions with proper
form. The contraction tempo for the leg extension exercise
was set at 3s eccentric phase, 0s pause, 3s concentric phase
(Ackerley etal. 2011; Latella etal. 2012; Hendy and Kidgell
2013). Prior to the resistance exercise, all participants per-
formed a 5min warm up on a cycle ergometer at 60% esti-
mated maximum predicted heart rate, and 2 warm up sets
of leg extensions at 12 and 10 repetitions at an increasing
weight. During the control session, all participants per-
formed the warm ups on the cycle ergometer sat quietly for
15min (average training time of HST and HYT conditions)
between pre and post neurophysiological measures. All out-
come measures were assessed at baseline (prior to the warm
up of each testing session), immediately after and at 2, 6, 24
and 48 and 72h post-training. These specified time points
corresponded to the fatigue (post-training—2h), recovery
(6, 24 and 48h) and adaptation (72h) phases as reported
by the super-compensation theory (Bompa and Haff 2009).
Statistical analysis
All data were analysed using IBM SPSS Statistics v.22
(IBM, USA). Data were screened for outliers followed by a
Shapiro–Wilk test and found to be normally distributed prior
to further analysis. A 3×7 repeated measures analysis of
variance (ANOVA) with factors CONDITION (HST, HYT
and CON) and TIME (Pre, post, 2, 6, 24, 48 and 72h) were
used to compare changes in MVIC, MMAX, MEP amplitude,
CSP, SICI, LICI and ICF between conditions and across
time. Where statistical significance was detected between
conditions, post-hoc paired t tests with a Bonferroni correc-
tion were conducted to test for differences between individ-
ual groups (Field 2013). For all tests, the Greenhouse–Geis-
ser correction was applied if the assumption of sphericity
was violated. Alpha level was set at P<0.05, and all results
are displayed as mean±SE. Within participant reliability
data was calculated for MEP, ICF and SICI using intra-
class correlation coefficients (ICCs) and Pearson’s product-
moment coefficient (r) at baseline for each condition across
time for the CON condition. ICC’s were classified as poor
(<0.40), fair (0.40–0.59), good (0.60–0.74) and excellent
(≥0.75) as used in previous TMS research (Temesi etal.
2017). In addition, the within participant coefficient of vari-
ation (CV) was expressed as a percentage derived from the
formula (poolSD/poolMean)×100 where the SD and mean is
a pooled value of the sample with ≤10% indicating low vari-
ability. Absolute reliability was calculated to establish the
variability of repeated measurements (Atkinson and Nevill
1998) using the standard error of the mean (SEM)=SD
√(1−ICC) and the minimal detectable change at the 95%
confidence interval (MDC95)=SEM×√(2)×1.96 was
also calculated as similarly displayed in other physical
research studies (Overend etal. 2010). All reliability data
has been reported in (Tables1 and 2).
Results
Neuromuscular, corticospinal andintra‑cortical data
The raw data for (Torque, MMAX, MEP/MMAX and CSP) is
displayed in Table1 and for each (ICF, SICI and LICI) dis-
played in Table2 for each condition across time points.
Maximal voluntary isometric contraction
Figure2 shows the percentage change in torque for MVIC
following HST, HYT and CON conditions from base-
line to 72h post-training. Repeated measures ANOVA
showed a significant CONDITION x TIME interaction
(F12,132=3.188, P<0.001). Post-hoc analyses revealed
MVIC was significantly reduced immediately post-training
for HST (p=0.004) and HYT (p<0.001), and at 2h for
HST (p=0.024), when compared to CON. No differences
were observed between HST and HYT immediately post-
training (p=0.086), at 2h (p=0.242) and at all other
time points (p>0.05). A significant main effect of TIME
(F6,66=11.534, P<0.001) was also observed. Post-hoc
analyses revealed a significant reduction compared to base-
line at immediately post-training (p=0.001) for HST and
HYT and at 2h (p=0.003) for HST.
Peripheral nerve excitability
Figure3 shows the percentage change in mV for MMAX
following HST, HYT and CON conditions from base-
line to 72h post-training. Repeated measures ANOVA
showed a significant CONDITION x TIME interaction
(F12,132=2.684, P=0.003). Post-hoc analyses revealed
MMAX was significantly reduced immediately post-training
for HST (p=0.001) and HYT (p=0.004), and 2h for HYT
(p=0.010), when compared to CON. No differences were
observed between HST and HYT immediately post-training
(p=0.831) and at all other time points (p>0.05). A signifi-
cant main effect of TIME (F6,66=5.965, P<0.001) was also
observed. Post-hoc analyses revealed a significant reduction
compared to baseline at immediate post-training (p<0.001)
for.HST and HYT and at 2h (p=0.001) for HYT.
Corticospinal excitability
Figure4a shows the percentage change in mV for MEP
following HST, HYT and CON conditions from baseline
to 72h post-training. Repeated measures ANOVA showed

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Table 1 Raw data for MVIC, MM4X, MEP/MMaxand CSP presented as Mean±SD
*Indicates a significant difference from baseline for each condition. ICC and Pearson’s r show the reliability of each measure between conditions at baseline (pre column) and of the CON condi-
tion over the 72h period (far right). SEM, SDC95 and CV% show the absolute variability of repeated measurements
Pre Post 2h 6 24 48 72 ICC SEM, SDC95 CV%
MVIC(Nm)
CON 223±24.2 224±13.2 217±22.8 218±29.5 220±19.4 220±16.3 226±21.7 0.91, r=0.001 5.31, 14.73 7.94
HST 225±63.7 204±60.4* 198±62.0* 217±53.3 223±67.2 232±62.6 222±60.5
HYT 242±79.7 193±70.7* 220±67.5 222±67.8 231±71.6 214±93.9 236±70.2
ICC 0.65, r=0.011
SEM, SDC95 30.8, 85.37
CV% 15.72
MMAX(mV)
CON 4.8±1.8 4.7±1.7 4.8±1.7 4.8±1.9 4.9±2.0 4.7±1.9 4.6±1.5 0.99, r=0.001 0.13, 0.35 5.46
HST 4.3±1.8 3.2±1.8* 3.8±1.5 4.2±1.9 4.8±1.8 4.4±0.9 4.3±1.5
HYT 4.6±2.4 3.2±2.0* 3.9±1.7* 4.1±1.7 4.6±1.5 4.0±1.7 4.1±2.0
ICC 0.91, r=0.001
SEM, SDC95 0.58, 1.61
CV% 9.56
MEP/MMAX
CON 0.19±0.17 0.18±0.14 0.19±0.14 0.14±0.06 0.19±0.16 0.21±0.19 0.25±0.19 0.64, r=0.001 0.023, 0.065 37.72
HST 0.21±0.12 0.32±0.14 0.27±0.17 0.22±0.12 0.22±0.12 0.27±0.16 0.25±0.17
HYT 0.26±0.17 0.59±0.27* 0.42±0.30* 0.31±0.28 0.31±0.26 0.31±0.29 0.26±0.21
ICC 0.63, r=0.001
SEM, SDC95 0.07, 0.20
CV% 12.46
CSP (ms)
CON 121.5±19.2 122.5±19.5 121.0±18.5 125.0±21.4 126.4±20.7 124.1±20.8 124.4±20.7 0.98, r=0.001 2.53, 7.02 4.61
HST 138.6±18.2 112.1±15.6* 129.8±19.3* 128.9±18.8 131.6±24.6 135.2±19.4 132.3±19.8
HYT 126.0±17.8 105.3±13.4* 110.7±15.2* 116.3±15.7* 121.1±17.4* 121.3±16.9 122.8±19.8
ICC 0.81, r=0.001
SEM, SDC95 8.23, 22.89
CV% 8.00

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Table 2 Raw data for intra-cortical outcome measures of ICF, SICI (not normalised to the unconditioned MEP) and LICl (ratio of test to conditioning stimulus) presented as Mean±SO
*Indicates a significant difference from baseline for each condition. ICC and Pearson’s r show the reliability of each measure between conditions at baseline (pre column) and of the CON condi-
tion over the 72h period (far right). SEM, SDC95 and CV% show the absolute variability of repeated measurements
Pre Post 2h 6 24 48 72 ICC SEM, SDC95 CV%
ICF (mVl)
CON 0.13±0.13 0.14±0.11 0.15±0.10 0.20±0.15 0.14±0.09 0.14±0.09 0.14±0.05 0.81, r=0.001 0.045, 0.02 34.63
HST 0.17±0.11 0.34±0.28 0.22±0.13 0.20±0.11 0.18±0.11 0.25±0.25 0.18±0.16
HYT 0.19±0.10 0.46±0.15* 0.31±0.07 0.27±0.05 0.25±0.03 0.24±0.03 0.19±0.02
ICC 0.75, r=0.001
SEM, SDC95 0.039, 0.11
CV% 15.30
SICI (mV)
CON 0.07±0.06 0.07±0.08 0.09±0.08 0.09±0.06 0.08±0.08 0.08±0.11 0.08±0.10 0.62, r=0.001 0.010, 0.027 60.55
HST 0.09±0.06 0.24±0.15* 0.14±0.08 0.14±0.09 0.13±0.09 0.15±0.13 0.13±0.11
HYT 0.09±0.02 0.38±0.12* 0.22±0.04* 0.21±0.04 0.19±0.03 0.17±0.04 0.12±0.02
ICC 0.62, r=0.001
SEM, SDC95 0.037, 0.10
CV% 12.89
LICl (test/Cond pulse ratio)
CON 90.5±31.4 95.0±27.2 88.7±28.4 90.5±32.2 92.3±31.9 86.7±33.1 90.2±30.7 0.39, r=0.192 23.98, 66.46 39.55
HST 84.9±35.3 89.1±27.6 82.7±57.4 87.6±50.9 70.7±51.2 61.8±29.6 58.0±35.7
HYT 77.8±30.2 94.1±17.3 92.8±30.3 90.2±18.4 83.9±38.7 84.4±25.7 90.2±33.0
ICC 0.28, r=0.139
SEM, SDC95 29.23, 81.26
CV/% 38.84

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1 3
a CONDITION×TIME interaction (F12,132= 3.213,
P<0.001) was observed. Post-hoc analyses revealed MEP
was significantly increased immediately post-training for
HST (p=0.044), and HYT (p=0.005) when compared to
control. No differences were observed immediately post-
training between HST and HYT (p=0.468) and at all
other time points (p<0.05). A significant main effect
of TIME (F6,66=9.890, P<0.001) was also observed.
Post-hoc analyses revealed a significant increase compared
to baseline immediately post-training (p=0.001) and at
2h (p=0.006) for HYT. Figure4b shows the percentage
change from baseline in CSP for HST, HYT and CON con-
ditions from baseline to 72h post-training. Repeated meas-
ures ANOVA showed a significant CONDITION×TIME
interaction (F12,132=2.755, P=0.002). Post-hoc analyses
revealed CSP was significantly shorter immediately post-
training for HST (p<0.001) and HYT (p<0.001), 2h
for HST (p=0.023) and HYT (p=0.041), 6h for HYT
(p=0.013) and at 24h for HYT (p=0.017) when com-
pared to CON. No differences were observed between HST
Fig. 2 MVIC as a percentage
of baseline values for HST,
HYT and CON. Asterisk indi-
cates a significant interaction
between HST or HYT and CON
while hash tag indicates a sig-
nificant decrease from baseline.
No differences were observed
between HST and HYT imme-
diately post-training (p=0.086)
or at 2h (p=0.242)
Fig. 3 MMAX as a percentage of
baseline values for HST, HYT
and CON. Asterisk indicates a
significant interaction between
HST or HYT and CON while
hash tag indicates a significant
decrease from baseline. No dif-
ferences were observed between
HST and HYT immediately
post-training (p=0.831)

Eur J Appl Physiol
1 3
and HYT immediately post-training (p=0.598) and at all
other time points (p>0.05). A significant main effect of
TIME (F6,66=11.958, P<0.001) was also observed. Post-
hoc analyses revealed a significant increase compared to
baseline immediately post-training (p=0.001) and at 2h
(p=0.006) for HST and HYT and at 6h (p=0.003) and
24h (p=0.004) for HYT only.
Figure5 shows raw sEMG taken from the RF muscle
displaying MEP and CSP in response to single-pulse TMS
stimulation of the motor cortex for (a) HST, (b) HYT, and
(c) CON from a single participant at pre, post-training
and 2h. A decrease in CSP, denoted by the arrows can be
observed post training for HST and HYT and an increase
Fig. 4 a MEP as a percentage
of baseline values for HST,
HYT and CON. Asterisk indi-
cates a significant interaction
between HST and CON while
hash tag indicates a significant
increase from baseline. No dif-
ferences were observed imme-
diately post training between
HST and HYT (p=0.468). b
CSP as a percentage of baseline
values for HST, HYT and CON.
Asterisk indicates a significant
interaction between HST and
CON while hash tag indicates
a significant decrease from
baseline. No differences were
observed immediately post
training between HST and HYT
(p=0.598) and across all time
points (p>0.05)

Eur J Appl Physiol
1 3
in MEP amplitude at post-training and 2h for HST and
HYT, respectively.
Intra‑cortical facilitation andinhibition
Figure6 shows the percentage change in mV for (a) ICF
(b) SICI and (c) LICI following HST, HYT and CON
conditions from baseline to 72h. There were no sig-
nificant CONDITION×TIME interactions observed for
ICF (F11,132=0.907, P=0.478), SICI (F11,132=0.849,
P=0.066) or LICI (F11,143=1.225, P=0.288).
Discussion
The primary aim of this study was to investigate the acute
behaviour of neurophysiological and neuromuscular
responses between a single session of HST and HYT of the
leg extensors. Our results showed that the neurophysiologi-
cal changes in maximal isometric torque, peripheral nerve
and corticospinal excitability and intra-cortical facilita-
tory and inhibitory responses were similar for both train-
ing paradigms. Specifically, the post-exercise decrease in
MVIC torque, MMAX and CSP, coupled with an increase in
MEP were similar between HST and HYT. No changes were
observed from baseline in SICI, ICF and LICI for either con-
dition. Collectively, the results suggested that post-exercise
neurophysiological responses to HST and HYT were not
altered by training modality.
Changes inperipheral measures ofMVIC andMMAX
The results showed that HST and HYT resulted in an imme-
diate reduction in maximal torque production and peripheral
nerve excitability that lasted up to 2h post-training. How-
ever, the reductions were no different between training
modes. It is likely that training to repetition maximum
close to the point of momentary voluntary muscular failure
may be an important factor in this finding. The variation
in MVIC of the leg extensors observed in this study (ICC
0.65 between conditions and 0.91 across time) has also been
demonstrated in other studies (ICC of 0.64–0.91) (Christ
etal. 1994). Given the time of testing was kept consistent
across conditions, the variability is more likely to be attrib-
uted to motor unit activity. Factors such as organization of
the motor unit pool, recruitment and rate-coding and activa-
tion patterns are all thought to contribute to the variability
of force during isometric contractions (Taylor etal. 2003).
Comparatively the reliability of MMAX displayed in this
study between conditions and across days was high (ICC
0.91–0.99) as similarly reported recent studies of the RF
muscle (ICC 0.88–0.90) (Balshaw etal. 2017). Impairment
of MMAX is thought to occur from processes at the neuro-
muscular junction via changes in membrane potentials and
reduced efficacy of sodium/potassium pump (Nielsen and
Clausen 2000; Kirkendall 1990; Mileva etal. 2012; Tucker
etal. 2005; Deschenes etal. 1994; Behm & St-Pierre 1997).
Nuzzo etal. (2016a) also showed a suppression in MMAX
amplitude from the biceps brachii muscle following 12 sets
of 8 maximal ballistic isometric elbow flexion contractions
separated by 4s rest. Interestingly, the authors reported a
similar MMAX response between 2 and 12 sets of isometric
training (Nuzzo etal. 2016b) suggesting that discrepancies
in exercise volume to not have a differential effect on periph-
eral nerve excitability. However, these findings have not
always been shown with Behm and St-Pierre (1997) report-
ing different effects on MMAX depending on the duration of
resistance exercise. The impairment of MMAX may at least
Fig. 5 Raw sEMG traces show-
ing the MEP and CSP of the RF
muscle for a HST, b HYT, and
c CON from a single participant
at pre, post-training and 2h

Eur J Appl Physiol
1 3
in part explain the reductions observed in maximal torque
production. Similar reductions in neuromuscular torque and
force production between training conditions have also been
reported in other studies. Nicholson etal. (2014) showed no
change for peak force between HST and HYT squat proto-
cols using equated loads between conditions. Howatson etal.
(2016) also reported significant reductions in MVIC of the
knee extensors following strength (4×5 RM) and power
(5×5 repetitions at 30% of the strength condition) train-
ing, and also with heavy (85% of 1 RM), moderate (75% of
heavy condition) and light (50% of heavy condition) back
squat exercise to repetition maximum (Brandon etal. 2015).
Conversely, a reduction in MVIC was shown to be greater
with HYT loading strategies compared to HST in the leg
extensors (Walker etal. 2012). However, the large discrep-
ancy in volume between protocols HST (15×1 RM) or
HYT (5×10 RM) may reflect the disparity in this findings
by Walker etal. (2012) compared to Nicholson etal. (2014)
and the current findings of this study.
Changes incorticospinal excitability andvoluntary
activation followingHST andHYT
An immediate increase in MEP amplitude and decrease in
the CSP duration was observed following training, which
was not different between HST and HYT. The low vari-
ability of the CSP baseline between conditions (CV 8.0%)
and across time for CSP (4.61%) provides feasibility for
changes in inhibition to be evaluated. Although MEP was
more reliable at baseline (CV 12.46%), it was more less sta-
ble between days (CV 37.72%) with a higher variability also
demonstrated in other studies (CV 25.0%) (Orth & Rothwell
2004). Kiers etal. (1993) highlight that the variability of the
MEP can be caused by fluctuations in corticospinal and seg-
mental motor neuron excitability. Although this may poten-
tially affect the ability to detect differences in corticospinal
excitability following HST and HYT, the findings of the
current study were in line with recent research showing a
greater MEP amplitude and cervicomedullary MEP follow-
ing slow ramp or ballistic isometric exercise of the elbow
flexors (Nuzzo etal. 2016a). An increase in MEP ampli-
tude was similarly reported by Ruotsalainen etal. (2014)
following HYT protocol of the elbow flexors. Interestingly,
these findings have not always been reported following
acute resistance or fatiguing exercise. Several authors have
reported a decrease in MEP amplitude immediately follow-
ing fatiguing quadriceps exercise (Gruet etal. 2014) and
HST in the elbow flexors (Latella etal. 2016). The discrep-
ancies observed between the current study and Latella etal.
(2016) may be representative of the differences in facilita-
tory and inhibitory control that existed in the musculature of
the upper and lower limbs. The upper limbs are more com-
monly used in the control of fine motor tasks compared to
the lower limbs. Therefore, the responses of the corticospi-
nal tract may in part be reflective of the functional differ-
ences in the musculature. Similarly, CSP duration has been
shown to increase within an exercise session (Ruotsalainen
etal. 2014) and during fatigue (Gruet etal. 2014; Gandevia
etal. 1994; Sacco etal. 1997) fatiguing RT of the upper
Fig. 6 A comparison of post-training TMS measures for ICF, LICI
and SICI in HST, HYT and CON. No significant group x time inter-
actions were observed for ICF (a), SICI (b) and LICI (c) between
conditions

Eur J Appl Physiol
1 3
and lower limbs. Conversely, the current findings suggest
that acute HST and HYT results in a temporary release of
inhibition within the corticospinal tract, and have similarly
been observed with short-term training of the lower limbs
(Christie and Kamen 2014).
Further support for the similarities observed between RT
modalities comes from similar changes in muscular acti-
vation between a 5, 10 or 20 RM elbow flexion protocol
(Behm etal. 2002) suggesting that maximal effort close to
momentary voluntary muscular failure rather than repeti-
tion selection was an important factor in acute neural behav-
iour. Less direct evidence has been provided by Sacco etal.
(2000) showing a similar reduction in the MEP amplitude
between maximal and submaximal sustained contractions of
the biceps brachii. The current findings suggested that the
increase in excitability and decrease in inhibition may be
a compensatory mechanism in an attempt to attenuate the
concurrent peripheral fatigue observed with a reduction in
MMAX and MVIC. Despite the work by Ruotsalainen etal.
(2014), Nuzzo etal. (2016a) and Nuzzo etal. (2016b), this
was the first study to show similarity of corticospinal behav-
iour following HST and HYT protocols reflective of intrinsic
session parameters (intensity, repetition and volume) recom-
mended in current RT guidelines (Ratamess etal. 2009).
Changes inintra‑cortical inhibition andfacilitation
followingHST andHYT
Furthermore, we have presented evidence for similar neu-
romodulation between HST and HYT with intra-cortical
facilitation and inhibition. The findings showed that SICI,
ICF and LICI were not different between training paradigms
or control across time. Although variations in paired-pulse
TMS responses can occur, the consideration of time of day,
footedness and phase of menstrual cycle in this study rules
out several confounding factors. The influence of gender has
also been shown to have little effect on paired-pulse meas-
ures with De Gennaro etal. (2003) showing low reliability
for both females and males. Although the variability in LICI
in this study was large (CV 38.84%), between conditions at
baseline the reliability of SICI and ICF between conditions
was higher (CV 12.89 and 15.30%, respectively) compared
to previous reports (31.0 and 20.0%, respectively) (Orth
etal. 2003) providing support that intra-cortical differences
were unlikely to occur between conditions. This indicated
that changes in the responsiveness of the corticospinal
pathway following one session of acute HST or HYT were
likely to be modulated downstream of the M1 (Nuzzo etal.
2016a). These findings were also in line with Latella etal.
(2016), which showed that HST of the arm was primarily
modulated by changes in corticospinal and peripheral excit-
ability in the absence of any intra-cortical changes following
training. Recently (Hunter etal. 2016) showed a decrease
in ICF and increase in SICI during and 2min following
a sustained submaximal contraction of the biceps brachii,
which suggested that intra-cortical facilitatory and inhibitory
networks become less excitable during fatigue. However,
to date measures of intra-cortical facilitation and inhibition
have seldom been reported with a single session of applied
HST or HYT in the leg extensors. Based upon the findings,
it is suggested that intra-cortical facilitatory and inhibitory
circuits are not affected by intermittent, dynamic contrac-
tions typically used in applied RT and are rather modulated
during the maintenance of force required during sustained
voluntary efforts.
Limitations
In light of the findings, it is acknowledged that several limi-
tations existed in the current experimental design. First,
the acute training session design was in line with current
RT guidelines (Ratamess etal. 2009), however, the inter-
action of several other variables such as exercise selection
(gross vs isolated motor task) and movement velocity could
have influenced the neurophysiological outcomes. Second,
the measures were taken from the RF muscle and may not
provide a global representation of the other leg extensor
muscles involved in the exercise, with intense leg exten-
sion exercise shown to recruit both slow and fast twitch
fibre types and activate all portions of the quadriceps group
(Staron etal. 2000; Krustrup etal. 2004), therefore the neu-
rophysiological behaviour under fatigue may be differently
modulated in fast or slow twitch dominant muscle groups.
Furthermore, population was sampled using convenience-
sampling relying on participants who had easy access to
the university which fitted the selection criteria and was not
designed to detect gender differences that may occur across
the super-compensation cycle. Although the sample size
was similar to other studies investigating strength and neu-
ral responses from RT (Nuzzo etal. 2016a; Howatson etal.
2016) an increased sample size would have provided better
power for the study and considering the higher variability
of single and paired-pulse TMS measurements across time
should be considered in future research studies investigating
neurophysiological outcomes across different days.
Conclusion
The findings of the current study showed that the neuro-
physiological responses were similar between real-world
HST and HYT. Both HST- and HYT-modulated neural
adaptations support the idea that training to repetition
maximum may be an important factor in activating neural
mechanisms in both heavy and moderate load RT. Second,

Eur J Appl Physiol
1 3
the acute increases in corticospinal excitability appear to be
a compensatory mechanism in an attempt to regulate neuro-
muscular performance in the presence of peripheral fatigue.
Strength and conditioning professionals should consider the
potential impact of both HST and HYT on the central and
peripheral nervous system. Acute neural responses should be
acknowledged as an important part of regulating fatigue and
recovery in both high and moderate load resistance training
when designing resistance training programs.
Acknowledgements We would like to thank all participants for
their contribution to this study. CL is supported by an Australian Post-
graduate Award. WPT is supported by an Alfred Deakin Postdoctoral
Fellowship.
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict
of interest.
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