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Abstract

This investigation sought to determine the effect of resistance training to failure on functional, structural and neural elbow flexor muscle adaptation. Twenty-eight males completed a 4-week familiarization period and were then counterbalanced on the basis of responsiveness across; non-failure rapid shortening (RS; rapid concentric, 2 s eccentric), non-failure stretch-shortening (SSC; rapid concentric, rapid eccentric), and failure control (C, 2 s concentric, 2 s eccentric), for a 12-week unilateral elbow flexor resistance training regimen, 3 × week using 85% of one repetition maximum (1RM). 1RM, maximal voluntary contraction (MVC), muscle cross-sectional area (CSA), and muscle activation (EMGRMS ) of the agonist, antagonist, and stabilizer muscles were assessed before and after the 12-week training period. The average number of repetitions per set was significantly lower in RS 4.2 [confidence interval (CI): 4.2, 4.3] and SSC 4.2 (CI: 4.2, 4.3) compared with C 6.1 (CI: 5.8, 6.4). A significant increase in 1RM (30.5%), MVC (13.3%), CSA (11.4%), and agonist EMGRMS (22.1%) was observed; however, no between-group differences were detected. In contrast, antagonist EMGRMS increased significantly in SSC (40.5%) and C (23.3%), but decreased in RS (13.5%). Similar adaptations across the three resistance training regimen suggest repetition failure is not critical to elicit significant neural and structural changes to skeletal muscle. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
1
IS REPETITION FAILURE CRITICAL FOR THE DEVELOPMENT OF MUSCLE
HYPERTROPHY AND STRENGTH?
John A Sampson
1
and Herbert Groeller
1
1
Centre for Human and Applied Physiology, School of Medicine, Faculty of Science,
Medicine and Health, University of Wollongong, NSW 2522, Australia
Running head: Failure is not necessary for strength gain
Corresponding author:
John A. Sampson, Ph.D.
Centre for Human and Applied Physiology
School of Medicine, University of Wollongong
Northfields Avenue, Wollongong, NSW, 2522, Australia
Telephone: 61-2-4221-5597
Facsimile: 61-2-4221-5945
Electronic mail: jsampson@uow.edu.au
2
ABSTRACT
This investigation sought to determine the effect of resistance training to failure on
functional, structural and neural elbow flexor muscle adaptation. Twenty-eight males
completed a 4-week familiarisation period and were then counterbalanced on the basis of
responsiveness across; non-failure rapid shortening (RS; rapid concentric, 2 s eccentric), non-
failure stretch-shortening (SSC; rapid concentric, rapid eccentric) and failure control (C, 2 s
concentric, 2 s eccentric), for a 12-week unilateral elbow-flexor resistance training regimen, 3
× week using 85% of one repetition maximum (1RM). 1RM, maximal voluntary contraction
(MVC), muscle cross-sectional area (CSA) and muscle activation (EMG
RMS
) of the agonist,
antagonist and stabiliser muscles were assessed before and after the 12-week training period.
The average number of repetitions per set was significantly lower in RS 4.2 (CI:4.2,4.3) and
SSC 4.2 (CI:4.2,4.3) compared to C 6.1 (CI:5.8,6.4). A significant increase in 1RM (30.5%),
MVC (13.3%), CSA (11.4%) and agonist EMG
RMS
(22.1%) was observed, however no
between group differences were detected. In contrast, antagonist EMG
RMS
increased
significantly in SSC (40.5%) and C (23.3%), but decreased in RS (13.5%). Similar
adaptations across the three resistance training regimen suggest repetition failure is not
critical to elicit significant neural and structural changes to skeletal muscle.
Keywords: resistance training, fatigue, electromyography, velocity, one repetition maximum,
neural.
3
INTRODUCTION 1
First proposed as a means of accelerating the rehabilitation of injured World War II soldiers 2
(Delorme, 1945), the use of repetition failure is now an established cornerstone of modern 3
resistance training regimen (Anderson and Kearney, 1982; Campos et al., 2002; Hakkinen et 4
al., 1985). Resistance exercise performed to failure elevates muscle protein synthesis 5
independent of volume (sets × reps) or %1RM load (Burd et al., 2010b; Mitchell et al., 2012). 6
For example, low load blood flow restricted exercise has been shown to elicit significant 7
increases in muscle hypertrophy and strength (Fujita et al., 2007; Takada et al., 2012). 8
Furthermore, investigations that controlled relative %1RM training load and volume reported 9
that repetition failure led to significantly greater gains in muscular strength (Drinkwater et al., 10
2005; Rooney et al., 1994). Thus, collectively the evidence appears to suggest that repetition 11
failure is an essential characteristic of resistance training regimen (Phillips, 2009). 12
13
However, accumulation of intramuscular metabolites or elevated endogenous circulating 14
hormones, physiological responses associated with resistance exercise to failure, are not 15
necessarily required to elicit significant changes in skeletal muscle structure or function 16
(West et al., 2009; Wilkinson et al., 2006), suggesting that there are multiple signalling 17
pathways that may promote muscular hypertrophy and strength in the absence of repetition 18
failure (Goldberg, 1967; Spangenburg et al., 2008). For example, when experimental groups 19
were matched for total work, both Folland et al. (2002) and Izquierdo et al. (2006) observed 20
isometric force production, single repetition maximum strength, local muscle endurance and 21
explosive power gains were similar regardless of the level of local muscle fatigue induced by 22
the resistance training regimen (Folland et al., 2002; Izquierdo et al., 2006). Furthermore, 23
greater gains in muscular strength have been reported with increased resistance exercise 24
volume but in the absence of repetition failure (Kramer et al., 1997; Sanborn et al., 2000). 25
4
Collectively these findings suggest repetition failure may not be important to elicit changes in 26
skeletal muscle function. However, to our knowledge, no current investigation has reported 27
upon the effect of repetition failure on skeletal muscle cross-sectional area. 28
29
Mechanical force is a factor that regulates protein function (Seifert and Gräter, 2013), has 30
direct effects upon the nucleus of the cell (Fedorchak et al., 2014) and skeletal muscle is 31
sensitive to changes in mechanical tensile loading (Martineau and Gardiner, 2001). At an 32
integrated level, rapid muscle activations have been shown to increase exposure of skeletal 33
muscle to peak mechanical force (Newton et al., 1997; Sampson et al., 2014) and 34
simultaneously elevate motor unit recruitment via decreased recruitment thresholds and 35
increased rate of motor unit discharge (Desmedt and Godaux, 1977). Munn et al. 2005, 36
clearly showed that rapid muscle activations performed to failure led to similar gains in 37
elbow flexor strength than was observed with a two-fold increase in resistance training 38
volume at slower movement speeds (Munn et al., 2005). These findings suggest that rapid 39
muscle activation may increase adaptive sensitivity to resistance training independent of 40
training volume and repetition failure. 41
42
This investigation therefore determined if repetition failure was a critical characteristic for 43
skeletal muscle adaptation to resistance training. A novel loading strategy was used, where 44
the experimental groups performed only four of the six elbow flexor repetitions required for 45
repetition failure and thus also, these groups had a reduced resistance training volume. 46
Furthermore, to minimise heterogeneity in responsiveness to resistance training, all subjects 47
completed a 4-week familiarisation period prior to commencing the investigation. 48
49
50
5
METHODS 51
Subjects 52
Twenty-eight males, who had not participated in resistance exercise for a minimum of six 53
months, volunteered to participate in this investigation. All subjects completed a physical 54
activity readiness questionnaire and provided written informed consent. All procedures were 55
approved by the University of Wollongong Human Ethics Research Committee. 56
57
Experimental familiarisation and randomisation 58
All subjects completed a 4-week familiarisation phase, that consisted of controlled (2-second 59
concentric, 2-second eccentric) resisted unilateral elbow flexor exercise to repetition failure 60
(Sampson et al., 2013). Resistance loading commenced at 50% of single repetition maximum 61
(1RM) and increased by 10% each Week, thus in the fourth and final Week of familiarisation 62
a load of 80% of 1RM was used. The relative gain (%) in 1RM during the familiarisation 63
period was calculated for each subject and using a triplet method subjects were 64
counterbalanced across the three experimental training conditions on the basis of 65
responsiveness to the familiarisation period. Thus, higher and lower responders to the 4-week 66
elbow flexor resistance exercise period were evenly distributed between the three conditions 67
prior to the 12-week experimental training regimen. The 1RM strength gain during the 68
familarisation period was similar between RS 19.0% (CI: 13.2,24.8), SSC 17.3% (CI: 69
8.3,26.4) and C 15.6% (CI: 7.7,23.4). This investigation focuses upon reporting physiological 70
changes from participation in the 12-week training regimen, and changes related to the 71
familiarisation period have already been reported (Sampson et al., 2013). 72
73
Experimental protocol and regimen 74
Subjects were assessed for elbow flexion performance in dynamic single repetition maximum 75
6
(1RM), isometric maximal voluntary contractile force (MVC), agonist muscle cross-sectional 76
area (CSA), and agonist and antagonist muscle activation (EMG) at four time points, prior to 77
commencing the 12-week regimen (Week 1) in the 4
th
and 8
th
Week (Week 4 and 8) and at 78
the completion of the training regimen (Week 12). All training sessions comprised of 85% 79
1RM unilateral dominant limb elbow flexion-extension exercise, commencing at 60° and 80
terminating at 160° of flexion in a supine position with the hips and knees flexed at 90° as 81
described and illustrated elsewhere (Sampson et al., 2014; Sampson et al., 2013). Each 82
experimental group was required to complete four sets of resistance exercise with a 3-min 83
rest period between each set three times per week on alternate days. 84
85
The treatment groups were differentiated in two ways i) the speed in which the elbow flexion 86
extension movement was performed, and the number of completed repetitions within each 87
set. The control training regimen (C) performed a two-second flexion and two-second 88
extension movement controlled via a metronome, the rapid shortening (RS) performed 89
maximal acceleration during elbow flexion followed by a two-second extension, and the 90
stretch shortening cycle (SSC) regimen completed maximal acceleration during both elbow 91
flexion and extension movements. Participants in C were required to exercise to repetition 92
failure for each set (six repetitions). In contrast, participants in the RS and SSC completed 93
only four repetitions in each set, thus these regimen did not require repetitions to be 94
completed to failure. To ensure the relative loading was comparable to C, RS and SSC 95
performed a single set of elbow flexion to failure once each Week. The training load was 96
then adjusted for the Week on the basis of this assessment. 97
98
Experimental assessment 99
Elbow flexor single repetition maximum (1RM) 100
7
Dominant limb dynamic elbow flexor 1RM strength was assessed from the experimental 101
training position (60°-160°) before (Week 1), during (Week 4 and 8) and after (Week 12) the 102
12-week intervention. During these assessments the dominant and contralateral glenohumeral 103
joints were secured to prevent unwanted movement. A minimum 2-min rest period was given 104
between successive attempts, and 1RM was recorded as the highest successful repetition 105
completed to the closest 0.25 kg. 1RM was obtained within 6 trials. 106
107
Elbow flexor maximal voluntary contraction torque 108
A 5-s maximal voluntary contraction (MVC) at 90° of elbow flexion was also performed in 109
Weeks 1 and 12. In the experimental position, the forearm was supinated and strapped to a 110
platform and subjects were instructed to produce maximal force as rapidly as possible at the 111
illumination of an LED light. Visual feedback via an oscilloscope, and verbal encouragement 112
to reach maximal force was provided. Peak torque (Nm) over 250 ms was determined from a 113
1000 N load cell (Applied Measurement, X-TRAN, 51W-1kN, Eastwood, NSW, Australia) 114
fixed in series with the experimental equipment, recorded by a DC pressure amplifier 115
(Neurolog, 108A, Digitimer Neurolog, Hertfordshire, UK) collecting data at 200 Hz. After 5-116
minutes of rest, MVC tests were repeated to confirm maximal effort, if the difference was 117
>5%, a third MVC was performed. 118
119
Elbow flexor muscle activation 120
During 1RM and MVC strength assessments, muscle activity was recorded. The surface of 121
the skin was shaved, abraded and cleansed with alcohol at the electrode sensor placement site 122
Surface electrodes (Ag/AgCL contact diameter 15 mm) were adhered central to the muscle 123
belly of the biceps brachii and triceps brachii midway between the acromion process and 124
elbow crease. Movement of the proximal radioulnar joint was controlled by maintaining the 125
8
forearm in supination. Surface electrodes were also applied to monitor shoulder stabilisation 126
during 1RM assessments at the anterior deltoid 40 mm below the clavicle, and upper 127
trapezius, along the ridge of the shoulder, halfway between the cervical spine and the 128
acromion. A reference electrode was adhered to the most prominent portion of the right 129
clavicle with the intra-electrode distance set at 20mm. Electrode positions were marked with 130
henna dye and maintained throughout the 12-week training period to ensure reliable 131
placement of electrodes during each subsequent trial. Electromyographic signals were pre-132
amplified with a low frequency cut-off (3 Hz), amplified 1000 times, and high- and low band 133
pass filtered (10-500 Hz, Neurolog 844, 820, 144, 135, Digitimer Neurolog, Hertfordshire, 134
U.K.). This system provides a 100 input impedance and common mode rejection ratio 135
>120dB. Data were collected at 2000 Hz per channel, processed via an analogue-to-digital 136
converter (Power 1401, Cambridge Electronic Design, Cambridge, U.K.) and assessed via a 137
series of 250 ms windows with a 50% overlap using Spike 2 software (Ver 5.13, Cambridge 138
Electronic Design, Cambridge, U.K.). Elbow flexion and extension was identified from a 139
shaft encoder with a resolution of 0.07 mm (E6C2-CWZ6C-1000, Omron, Minato-ku, 140
Tokyo, Japan), acting as the first pulley wheel within the experimental equipment to provide 141
distance, time and direction data during muscular contractions. Shaft encoder data were 142
processed through the Power 1401 analogue-digital converter and synchronised with EMG 143
through the Spike 2 software program. In this investigation, average electromyographic root 144
mean square amplitude (EMG
RMS
, mV) was calculated over concentric and eccentric phases 145
of the contraction during 1RM assessments. Peak EMG
RMS
(mV) during the MVC was 146
recorded over 250 ms central to peak isometric torque (Nm) developed by each subject. 147
EMG
RMS
values recorded in Week 12 were normalised to the respective 1RM or MVC value 148
recorded in Week 1(Newton et al., 1996; Newton et al., 1997; Sampson et al., 2014). 149
150
9
Elbow flexor muscle cross-sectional area 151
Elbow flexor cross-sectional area was recorded by an experienced radiologist at Week 1 and 152
Week 12. Scans were performed a minimum of 24 hours after the final training session of 153
each respective week. A total of 44 muscle slices were recorded (thickness 6.35 mm, 1 mm 154
inter-slice gap) via magnetic resonance imaging (MRI), Turbo Spin Echo, T2 images, (1.5 T 155
Philips Intera, Philips Healthcare, Da Best, Netherlands). Participants were supine for these 156
scans with the superior margin of the coil positioned level with the acromioclavicular joint. 157
Imaging commenced at the superior portion of the humeral head, extending distally along the 158
length of the muscle. The biceps brachii and brachialis (Figure 1) were traced individually 159
using commercially available software (3d-Doctor, Able Software Corporation, Lexington, 160
MA, U.S.A.) with care taken to trace round any visible intramuscular fat and connective 161
tissue. Cross-sectional area was calculated as the mean across three images central to the 162
muscle belly (slices 21-23). 163
164
INSERT FIGURE 1 ABOUT HERE 165
166
Elbow flexion kinematics 167
Kinematic data in each of the three exercise conditions was captured during one training 168
session in Week 11. Limb movement velocity (m∙s
1
, d / t
-1
) was calculated from time and 169
displacement data provided by the shaft encoder by setting cursors to count the number of 170
pulses delivered from the start of movement, to the end of the last completed repetition prior 171
to task failure. A calibration reference was gained by moving the arm of each subject 172
passively through a 100° range of motion prior to exercise. Significant kinematic differences 173
between the C, RS and SSC groups have been reported previously (Sampson et al., 2014). 174
175
10
Psychophysical response 176
At the end of each set, subjects were asked “how hard were you exercising” to provide a 177
rating of perceived exertion (Borg, 1970) and the total resistance exercise volume (repetitions 178
× load) was quantified over the 12-week training regimen. 179
180
Statistical analysis 181
A two-way repeated measures ANOVA examined treatment effects over time, and where 182
interactions were observed a post hoc Tukey's was applied (Prism Ver. 6.00, GraphPad 183
Software, San Diego California USA). Where significant differences over time were 184
observed and no between groups interactions were detected, data were also pooled and one-185
way ANOVA, or paired t-test analysis was performed. Data are reported as means ± 95% 186
confidence intervals (CI), unless otherwise stated as standard deviation (SD). Significance is 187
set at an alpha level of < 0.05 for all statistical analyses. 188
189
RESULTS 190
Baseline characteristics 191
Twenty eight subjects completed the investigation; C (n=10) RS (n=10) SSC (n=8), and their 192
results are reported herein. Group characteristics at Week 1 are reported in Table 1. No 193
significant difference in the age, stature, mass and elbow flexor cross-sectional area was 194
observed between RS, SSC, and C. Force production characteristics at Week 1 were also 195
similar for elbow flexor 1RM and MVC in RS, SSC, and C respectively. 196
197
INSERT TABLE 1 ABOUT HERE 198
199
Training regimen characteristics and compliance 200
11
Characteristics of the training regimen for each treatment group are highlighted in Table 2. 201
Each exercise regimen required subjects to perform resistance exercise with a relative 85% 202
1RM load. Over the 12-weeks of training no significant difference was observed in the 203
average load lifted between groups. In contrast, and in line with the experimental design, the 204
average number of repetitions completed per set throughout the 12-week regimen was 205
significantly greater (P<0.0001) in C compared to RS and SSC. Thus, the training volume 206
(repetitions x sets) was significantly (P<0.0001) lower in RS and SSC than C. In Week 11, 207
during kinematic assessment, the control group (26.5 s CI:25.5,27.5) spent significantly 208
greater time under elbow flexor tension compared to RS (13.2 s CI:12.5,13.8) and SSC (8.0 s 209
CI:7.3,8.8). The significant difference in time under tension between the groups was 210
explained by the marked increase in movement velocity (Figure 2) in SSC than RS than C. 211
Overall participants reported significantly lower (P=0.0013) ratings of perceived exertion 212
when performing the RS and SSC training regimen compared to C. We observed similar 213
levels of compliance to the training regimen between RS, SSC and C, with 94% of the 214
training sessions attended by participants. 215
216
INSERT TABLE 2 ABOUT HERE 217
INSERT FIGURE 2 ABOUT HERE 218
219
Physiological adaptations to the training regimen 220
Despite the significant difference in the volume of the training stimulus, no significant 221
difference in 1RM, MVC, MRI, or agonist EMG
RMs
was observed between groups (Table 3). 222
A significant (P<0.001) 30.5% increase in pooled 1RM strength was observed over the 12-223
week training period and significant (P<0.001) gains in 1RM strength were expressed 224
throughout the training period with 11.4% (CI:8.7,14.2), 9.4% (CI:7.2,11.6) and 7.3% 225
12
(CI:5.1,9.5) increase detected between Weeks 1-4, 4-8 and 8-12 respectively (Figure 3). 226
Maximal voluntary contractile strength was similar at Week 1 between SSC (93.9 Nm, 227
CI:69.8,118), RS (91.4 Nm, CI:81.6101.2) and C (80.9 Nm CI:61.8,99.9) and increased by 228
Week 12 in SSC (105.1 Nm CI:79.3,130.1), RS (103.6 Nm CI:83.9,123.2) and C (90.3 Nm 229
CI:72.4,108.2) with no between groups interaction detected. Over the duration of the 12-week 230
regimen a significant (P=0.003) 13.3% (CI:5.9,20.7) increase in pooled MVC elbow flexor 231
torque was observed. Similarly, no significant difference was observed in elbow flexor 232
muscle cross-sectional area at Week 1 SSC (14.4 cm
2
CI:12.6,16.7), RS (12.2 cm
2
233
CI:10.8,13.5) and C (13.0 cm
2
CI:10.9,15.0) and increased by Week 12 in SSC (15.8 cm
2
234
CI:13.8,17.8), RS (13.4 cm
2
CI:12.0,14.8) and C (14.6 cm
2
CI:12.9.7,16.5) with no between 235
groups interaction detected. Over the duration of the 12-week regimen a significant (P<0.001) 236
pooled increase of 11.4% (CI:8.7,14.1) was observed in all participants in muscle cross-237
sectional area. 238
239
A significant interaction in antagonist EMG
RMS
activity was observed (P=0.029) with a 240
relative increase observed in SSC and C, and a decrease in RS during the MVC assessment 241
(Table 3). No significant between group interaction was observed in 1RM flexor muscle 242
activation, however, a significant (P=0.005) 22.1% (CI:5.9,38.4) pooled increase in biceps 243
brachii average EMG
RMS
was observed over the 12-week regimen. Antagonist muscle 244
activation also changed significantly (P=0.028) during a single repetition maximum after 12-245
weeks of training. Similarly in MVC, a significant interaction was seen (P=0.016) as triceps 246
brachii average EMG
RMS
amplitude increased following SSC and C, but declined following 247
RS (Table 3). Shoulder stabilisers, anterior deltoid and upper trapezius showed no change in 248
average EMG
RMS
amplitude during 1RM assessments following the 12-week experimental 249
training period, suggesting subjects successfully maintained shoulder joint stabilisation 250
13
throughout assessment and training. 251
252
INSERT FIGURE 3 ABOUT HERE 253
INSERT TABLE 3 ABOUT HERE 254
255
DISCUSSION 256
A 30% decrease in training volume and 90% reduction in the number of sets performed to 257
repetition failure, had no significant effect on gains in 1RM (~30%) and maximal voluntary 258
force production (~15%) after 12-weeks of heavy 85% 1RM unilateral resistance exercise. 259
Indeed the regimen used within this investigation was very effective in developing elbow 260
flexor strength when considered in light of a 17% increase observed in the preceding 4-week 261
familiarisation period (Munn et al., 2005; Rooney et al., 1994). These are interesting findings 262
as they suggest that repetition failure and training volume may be of less importance for the 263
development of muscle hypertrophy and strength when the characteristics of the muscle 264
activation are manipulated. 265
266
Non-ballistic rapid elbow flexor movement is associated with a significant increase in muscle 267
activation and near two-fold increase in peak force (Sampson et al., 2014). It was this 268
modification of transient tensile loading and muscle recruitment that this investigation sought 269
to manipulate. It is well known that eccentric muscle activations are very effective in eliciting 270
muscle hypertrophy (Farthing and Chilibeck, 2003; Higbie et al., 1996) and that these rapid 271
or explosive movements are associated with the facilitation of skeletal muscle work (Komi 272
and Bosco, 1978; Newton et al., 1997), declining motor unit recruitment thresholds (Desmedt 273
and Godaux, 1977) and increased muscle activation (Newton et al., 1997; Sampson et al., 274
2014). 275
14
Our findings with respect to the manipulation of resistance training volume are supported by 276
Munn et al. (2005) who observed no difference in 1RM strength gain in subjects that 277
completed a single set of fast elbow flexor training than those subjects that completed three 278
slower sets. The authors also observed that the training regimen utilising a single set of 279
slower joint speeds resulted in attenuated elbow flexor strength gains in comparison to other 280
regimens (Munn et al., 2005). However, the investigators ensured all regimens were 281
completed to repetition failure. The regimen utilised within the current investigation required 282
two of the experimental groups (RS and SSC) to complete 1 set to repetition failure each 283
Week, in contrast to C who completed 12 sets to repetition failure. 284
285
Significant gains in muscular strength have been reported when resistance exercise is 286
performed to repetition failure (Drinkwater et al., 2005; Rooney et al., 1994). These gains in 287
muscle strength and hypertrophy have been found to be independent of exercise load and 288
volume (Mitchell et al., 2012; Takada et al., 2012). Fatiguing bouts of resistance exercise are 289
associated with increased metabolite accumulation, motor unit recruitment and endogenous 290
hormone secretion, physiological signals that may contribute to muscle hypertrophy and 291
enhanced force production capacity (Burd et al., 2012; Burd et al., 2010a). The hypertrophic 292
response of skeletal muscle may be dependent on muscle fatigue with greater gains observed 293
when higher volumes are applied (Mitchell et al., 2012). However, in this investigation 294
despite the relative absence of fatiguing bouts of resistance exercise to failure and significant 295
reduction in the total exercise volume, our investigation detected no significant difference in 296
agonist muscle cross-sectional area between the experimental groups after 12-weeks of 297
resistance training. 298
299
Furthermore, an 11% change in muscle cross-sectional area observed within our investigation 300
15
was consistent with the increase in muscle hypertrophy reported by other investigations using 301
a similar training duration and loading strategy (Holm et al., 2008; Mitchell et al., 2012). 302
Thus, the loading strategies adopted within this investigation did not compromise muscle 303
hypertrophy. Given the unique experimental design adopted within this investigation our 304
findings suggest performing additional repetitions to failure maybe superfluous when the 305
%1RM resistance training load is high. Whilst other researchers have assessed the effect of 306
repetition failure upon dynamic and static force production capacity (Folland et al., 2002; 307
Izquierdo et al., 2006; Rooney et al., 1994) this is the first investigation to our knowledge to 308
also consider the effect of repetition failure upon muscle cross-sectional area. Significantly, 309
these previous investigations had utilised a model that ensured total training volume was 310
identical between the experimental groups (Folland et al., 2002; Izquierdo et al., 2006; 311
Rooney et al., 1994). In contrast, the absence of repetition failure in RS and SSC within this 312
investigation was deliberately used to reduce the training volume by over 30%, a decline that 313
did not compromise structural or functional changes in the elbow flexor skeletal muscles. 314
Thus, whilst our experimental design cannot confirm if the rapid muscle activations 315
associated with RS and SSC regimen lead to an enhanced sensitivity to the training stimulus, 316
they are encouraging and suggest further investigation is warranted. 317
318
Significant gains in strength within the first 4-weeks of resistance training are apportioned to 319
neurally mediated adaptation (Moritani and DeVries, 1979). In this investigation, a 22% 320
increase in biceps brachii muscle activity was observed during dynamic 1RM assessment in 321
all three groups. Thus, although all subjects had participated in a 4-week familiarisation 322
period where significant neural adaptation was observed (Sampson et al., 2013), significant 323
improvements in agonist muscle activation continued to occur during the subsequent 12-week 324
regimen. These adaptations explain much of the 30% improvement observed in 1RM elbow 325
16
flexor strength within our 12-week training regimen. However, no change in agonist muscle 326
activation was observed during maximal isometric elbow flexor force production, suggesting 327
changes observed in muscle activation were specific to those utilised within the training 328
regimen (Higbie et al., 1996). However, we did observe a significant increase in antagonist 329
muscle activation in SSC and C during dynamic assessment of strength. An absolute or 330
relative decline in antagonist muscle activation is typically observed during 1RM and MVC 331
assessments (Andersen et al., 2005; Tillin et al., 2011) following resistance training. The 332
increase in antagonist activity may be due to increased co-contraction permitting improved 333
joint stability for the development of force (Bennett, 1993; Hagood et al., 1990). However, 334
we observed no change in anterior deltoid or upper trapezius muscle activation, suggesting 335
changes in co-contraction where isolated only to the elbow joint and not more broadly to 336
stabilisation of the shoulder complex. 337
338
One of the challenges of inter-subject experimental designs is accounting for the large 339
heterogeneity in responsiveness to resistance training within the sample population (Hubal et 340
al., 2005). Some authors have suggested given the magnitude of this biological variance intra-341
subject designs should be utilised as an experimental design alternative (Folland et al., 2002). 342
We adopted a different approach. This investigation acknowledged a priori the heterogenic 343
nature of adaptive responsiveness to resistance training by incorporating a 4-week 344
familiarisation period prior to the 12-week regimen. Uniquely this investigation also 345
counterbalanced subjects to C, RS and SSC on the basis of 1RM strength gain 346
(responsiveness) obtained during the familiarisation period. While a significant difference 347
was observed in 1RM strength gain in higher and lower responders during the familiarisation 348
period, no significant difference was observed during the subsequent 12-week training 349
regimen, demonstrating the effectiveness of allocating subjects to experimental groups on the 350
17
basis of responsiveness to a familiarisation period (Sampson et al., 2013). 351
352
In conclusion, strength gains following a 12-week resistance training regimen are not 353
dependent on repetitions performed to failure, nor in such conditions, is it necessary to 354
equalise the training volume. Similar skeletal muscle adaptations can be gained with rapid 355
muscle activation in the absence of repetition failure and a concurrent reduction in the total 356
exercise volume. 357
358
Perspectives 359
Repetition failure is considered an essential characteristic of resistance training for over 70 360
years (Delorme, 1945), with more recent evidence supporting this view (Drinkwater et al., 361
2005; Rooney et al., 1994). However, others have observed equivalent strength gain when 362
exercise volume were matched in repetition failure and non-failure resistance training 363
regimen (Folland et al., 2002; Izquierdo et al., 2006). This investigation has shown that a 364
reduced volume, non-failure resistance training regimen can elicit equivalent gains in 365
strength, muscle activation and muscle cross-sectional area than increased training volume 366
regimen to failure. Rapid muscle activation may be the distinguishing feature that lead to 367
similar adaptive changes in muscle structure and function despite marked differences in 368
resistance training volume (Munn et al., 2005). However, the current research design cannot 369
confirm this outcome particularly for compound multi-joint movements. Thus, further 370
investigations appear warranted to determine the influence of rapid muscle activation, 371
repetition failure and resistance training volume. 372
373
374
375
18
ACKNOWLEDGEMENTS 376
This project was funded in part by a grant from the New South Wales Fire Brigades 377
(Australia) with magnetic resonance imaging support from Whistler Radiology (Nowra, 378
Australia). 379
380
381
382
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548
549
22
Figure captions 550
551
Figure 1: Representation of an MRI trace from one subject highlighting the combined biceps 552
and brachialis area assessed for measures of muscle cross-sectional area in this investigation. 553
554
Figure 2: Movement profiles depicting the average movement velocity (m∙s-
1
) calculated and 555
displayed as mean for every 5% of movement relative to displacement during lengthening 556
and shortening muscle contractions within rapid shortening (RS; dotted line, squares), 557
stretch-shortening cycle (SSC; dashed line, triangles), and control (C; solid line, circles) 558
groups. Data was collected during the first and last repetitions of the first set of exercise 559
performed in the final week of training. 560
561
Figure 3: Dominant limb one repetition maximum strength gain (kg) recorded in control (C), 562
stretch shortening cycle (SSC), and rapid shortening (RS) resistance exercise groups. 563
Strength assessments performed at baseline (Week 0), during (Week 4 and 8) and following 564
the 12 week training intervention (Week 12). Data represent means and 95% confidence 565
intervals. *= significant within groups difference from baseline, **=significant within groups 566
difference from week 4, ***=significant within groups difference from week 8. Significance 567
is set at P<0.05. 568
569
Table 1: Characteristics of participants in the Rapid Shortening (RS), Stretch Shortening
Cycle (SSC) and Control (c) groups prior to the 12 week training period. Data are displayed
as within group averages and standard deviation (SD).
Group
Age (years)
Stature (cm)
Mass (kg)
CSA (cm
2
)
1RM (kg)
MVC (Nm)
RS
23.7
SD 6.2
179.1
SD 7.5
85
SD 13.7
13.3
SD 2.0
22.3
SD 3.6
91.4
SD 13.7
SSC
24.3
SD 7.0
179.0
SD 8.8
77.9
SD 12.1
11.9
SD 2.3
19.2
SD 1.8
93.9
SD 28.8
C
23.4
SD 6.6
180.3
SD 5.8
76.9
SD 0.2
12.0
SD 1.8
19.9
SD 3.7
80.1
SD 26.6
Table 2: Characteristics of the 12 week training regimen in the rapid shortening (RS), stretch
shortening cycle (SSC) and control (C) groups.
Variable
RS
Group
SSC
C
Training load (kg)
22.6 (20.2,25.0)
19.3 (17.4,21.3)
21.0 (18.8,23.3)
Repetitions (reps·set
-1
)
4.2 (4.2,4.3)*
4.2 (4.2,4.3)*
6.1 (5.8,6.4)
Training volume (reps × sets)
17.0 (16.8,17.2)*
17.0 (16.9,17.1)*
24.4 (23.4,25.4)
RPE
16.0 (15.3,16.7)*
15.5 (14.9,16.2)*
17.0 (16.6,17.4)
Attendance (%)
99.3 (98.1,100)
98.8 (97.0,100)
99.1 (98.1,100)
Data are reported as means and 95% confidence intervals.*Significantly different to Control
(C).
Table 3: Change in one repetition maximum (1RM), maximal voluntary contraction
(MVC), muscle cross sectional area (CSA), raw (mV) and normalised (%) agonist and
antagonist EMG
RMS
activity in the rapid shortening (RS), Stretch shortening cycle
(SSC) and Control (C) groups over the 12-week experimental training period.
Variable
Group
RS
SSC
C
1RM (%)
28.6 (23.6,33.5)
32.8 (29.2,36.4)
30.6 (22.1,39.1)
MVC (%)
12.7 (-2.6,28.0)
12.8 (2.7,22.9)
14.3 (-2.0,30.6)
CSA (%)
10.9 (7.4,14.4)
7.1 (0.8,13.5)
11.6 (5.7,17.4)
1RM EMG
RMS
(mV)
Biceps pre training
Biceps post training
Triceps pre training
Triceps post training
1RM EMG
RMS
(%)
Biceps
0.63 (0.49,0.76)
0.69 (0.49,0.89)
0.07 (0.06,0.09)
0.06 (0.05.0.08)
7.7 (-4.0,19.3)‡
0.62 (0.36,0.88)
0.81 (0.64,0.99)
0.09 (0.06,0.12)
0.12 (0.08,0.17)
47.0 (-4.5,98.5)‡
0.60 (0.51,0.68)
0.69 (0.53,0.84)
0.08 (0.06,0.09)
0.09 (0.08,0.09)
16.7 (-8.5,41.9)‡
Triceps
-13.45 (-29.3,2.4)
40.5 (-7.6,88.7)*
23.3 (2.0,44.6)‡*
MVC EMG
RMS
(mV)
Biceps pre training
Biceps post training
Triceps pre training
Triceps post training
MVC EMG
RMS
(%)
Biceps
Triceps
0.89 (0.60,1.18)
0.92 (0.68, 1.12)
0.09 (0.07,0.11)
0.07 (0.05,0.08)
10.1 (-11.1,31.2)
-20.4 (-41.1,0.35)
1.19 (0.69,1.70)
1.33 (0.73,1.93)
0.11 (0.08,0.14)
0.12 (0.07, 0.18)
22.5 (-43.4,88.6)
12.4 (-11.4,36.2)*
0.82 (.062, 1.03)
0.87 (0.59, 1.12)
0.10 (0.08,0.12)
0.10 (0.09,0.12)
5.5 (-18.6,29.7)
8.0 (-9.2,25.2)*
Data are reported as means and 95% confidence intervals, ‡significant change over
time; *significantly different to RS
... (1) Theme A: Studies comparing a group(s) performing RT to momentary muscular failure to a non-failure group(s) (Amdi et al., 2021;Fonseca et al., 2020;Gantois et al., 2021;Kassiano et al., 2021;Lacerda et al., 2020;Lasevicius et al., 2019;Mangine et al., 2022;S Martorelli et al., 2017;Nobrega et al., 2018;Santanielo et al., 2020;Santos et al., 2019). (2) Theme B: Studies comparing a group(s) performing RT to set failure (defined as anything other than the definition of momentary muscular failure) to a non-failure group(s) (Bergamasco et al., 2020;Costa et al., 2021;Garcia-Ramos et al., 2020;Gonzalez-Badillo et al., 2016;Gonzalez-Hernandez et al., 2021;Gorostiaga et al., 2012Gorostiaga et al., , 2014Karsten et al., 2021;Linnamo et al., 2005;AS Martorelli et al., 2021;Moran-Navarro et al., 2017;Pareja-Blanco, Rodriguez-Rosell, et al., 2020; Pareja-Blanco, Rodriguez-Rosell, Sanchez-Medina, Ribas-Serna, et al., 2017; Raastad et al., 2000;Sampson & Groeller, 2016;Sanchez-Medina & Gonzalez-Badillo, 2011;Shibata et al., 2019;Terada et al., 2021;Vasquez et al., 2013). (3) Theme C: Studies theoretically comparing different proximities-to-failure (i.e., applying different velocityloss thresholds that modulate set termination and albeit indirectly, influence proximity-to-failure), with no inclusion of a group performing RT to momentary muscular failure per se (Andersen et al., 2021;Pareja-Blanco, Rodriguez-Rosell, Sanchez-Medina, Sanchis-Moysi, et al., 2017;Pareja-Blanco, Villalba-Fernandez, et al., 2019;Rodriguez-Rosell et al., 2018;Weakley et al., 2019). ...
... Four studies (Bergamasco et al., 2020;Karsten et al., 2021;Sampson & Groeller, 2016;Terada et al., 2021) that investigated the effects of RT performed to set failure versus non-failure on muscle hypertrophy applied various definitions of set failure (not including momentary muscular failure) had relatively consistent findings (Theme B), with three (Karsten et al., 2021;Sampson & Groeller, 2016;Terada et al., 2021) out of the four studies finding no statistically significant difference in muscle hypertrophy between conditions and one study (Bergamasco et al., 2020) in older adults finding no statistically significant pre-to post-intervention changes in muscle size for either condition. Importantly, one of the studies included in Theme B did not explicitly state the definition of set failure used (Sampson & Groeller, 2016) and considering a traditional prescription (sets × repetitions × relative load) was applied to both set failure (4 sets × 6 repetitions) and non-failure (4 sets × 4 repetitions) conditions, it is unclear whether momentary muscular failure was reached, highlighting the importance for future research to state definitions of key terms and clearly explain how set termination was controlled. ...
... Four studies (Bergamasco et al., 2020;Karsten et al., 2021;Sampson & Groeller, 2016;Terada et al., 2021) that investigated the effects of RT performed to set failure versus non-failure on muscle hypertrophy applied various definitions of set failure (not including momentary muscular failure) had relatively consistent findings (Theme B), with three (Karsten et al., 2021;Sampson & Groeller, 2016;Terada et al., 2021) out of the four studies finding no statistically significant difference in muscle hypertrophy between conditions and one study (Bergamasco et al., 2020) in older adults finding no statistically significant pre-to post-intervention changes in muscle size for either condition. Importantly, one of the studies included in Theme B did not explicitly state the definition of set failure used (Sampson & Groeller, 2016) and considering a traditional prescription (sets × repetitions × relative load) was applied to both set failure (4 sets × 6 repetitions) and non-failure (4 sets × 4 repetitions) conditions, it is unclear whether momentary muscular failure was reached, highlighting the importance for future research to state definitions of key terms and clearly explain how set termination was controlled. ...
Article
While proximity-to-failure is considered an important resistance training (RT) prescription variable, its influence on physiological adaptations and short-term responses to RT is uncertain. Given the ambiguity in the literature, a scoping review was undertaken to summarise evidence for the influence of proximity-to-failure on muscle hypertrophy, neuromuscular fatigue, muscle damage and perceived discomfort. Literature searching was performed according to PRISMA-ScR guidelines and identified three themes of studies comparing either: i) RT performed to momentary muscular failure versus non-failure, ii) RT performed to set failure (defined as anything other than momentary muscular failure) versus non-failure, and iii) RT performed to different velocity loss thresholds. The findings highlight that no consensus definition for "failure" exists in the literature, and the proximity-to-failure achieved in "non-failure" conditions is often ambiguous and variable across studies. This poses challenges when deriving practical recommendations for manipulating proximity-to-failure in RT to achieve desired outcomes. Based on the limited available evidence, RT to set failure is likely not superior to non-failure RT for inducing muscle hypertrophy, but may exacerbate neuromuscular fatigue, muscle damage, and post-set perceived discomfort versus non-failure RT. Together, these factors may impair post-exercise recovery and subsequent performance, and may also negatively influence long-term adherence to RT. KEY POINTS (1) This scoping review identified three broad themes of studies investigating proximity-to-failure in RT, based on the specific definition of set failure used (and therefore the research question being examined), to improve the validity of study comparisons and interpretations. (2) There is no consensus definition for set failure in RT, and the proximity-to-failure achieved during non-failure RT is often unclear and varies both within and between studies, which together poses challenges when interpreting study findings and deriving practical recommendations regarding the influence of RT proximity-to-failure on muscle hypertrophy and other short-term responses. (3) Based on the limited available evidence, performing RT to set failure is likely not superior to non-failure RT to maximise muscle hypertrophy, but the optimal proximity to failure in RT for muscle hypertrophy is unclear and may be moderated by other RT variables (e.g., load, volume-load). Also, RT performed to set failure likely induces greater neuromuscular fatigue, muscle damage, and perceived discomfort than non-failure RT, which may negatively influence RT performance, post-RT recovery, and long-term adherence.
... In this case, athletes perform the same number of sets and repetitions per set (e.g., 3 × 8RM) in all sessions of the training cycle [117,[121][122][123]. However, although it appears that RT using repetitions to failure does not produce the greatest performance gains [23,24,32,48,124,125], this type of training is very likely to result in strength gains [126,127]. Therefore, if we aim to maintain the same number of maximum repetitions in each set (e.g., 8RM, 6RM or 4RM) for a given exercise during the training period, it would be necessary to modify (increase) the absolute load used in training. ...
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For more than a century, many concepts and several theories and principles pertaining to the goals, organization, methodology and evaluation of the effects of resistance training (RT) have been developed and discussed between coaches and scientists. This cumulative body of knowledge and practices has contributed substantially to the evolution of RT methodology. However, a detailed and rigorous examination of the existing literature reveals many inconsistencies that, unless resolved, could seriously hinder further progress in our field. The purpose of this review is to constructively expose, analyze and discuss a set of anomalies present in the current RT methodology, including: (a) the often inappropriate and misleading terminology used, (b) the need to clarify the aims of RT, (c) the very concept of maximal strength, (d) the control and monitoring of the resistance exercise dose, (e) the existing programming models and (f) the evaluation of training effects. A thorough and unbiased examination of these deficiencies could well lead to the adoption of a revised paradigm for RT. This new paradigm must guarantee a precise knowledge of the loads being applied, the effort they involve and their effects. To the best of our knowledge, currently this can only be achieved by monitoring repetition velocity during training. The main contribution of a velocity-based RT approach is that it provides the necessary information to know the actual training loads that induce a specific effect in each athlete. The correct adoption of this revised paradigm will provide coaches and strength and conditioning professionals with accurate and objective information concerning the applied load (relative load, level of effort and training effect). This knowledge is essential to make rational and informed decisions and to improve the training methodology itself.
... In studies of low-intensity resistance training, it is assumed that exercises must be performed to total exhaustion to achieve the training effect 10) ; however, the present result supported those from other studies which argued that as long as there is adequate mechanical activation of the fast-twitch fibers, total exhaustion is not always necessary 59,60) . The results of this study (Fig. 4) indicated that the slow movement is quite effective in low-intensity training. ...
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This study conducted a secondary survey based on the hypothesis that the “total mechanical activation of fast-twitch fibers in the muscles determines the effects of muscle hypertrophy”, with resistance training of the knee extensor muscles as the target because of its importance in preventing sarcopenia. Using a mathematical model that estimates the mechanical activation of each muscle fiber (fast-twitch and slow-twitch fiber) during exercise, which was developed in a previous study, we estimated the total mechanical activation of fast-twitch fibers in 30 training programs described in 23 selected previous studies on leg extension exercise programs and their muscle hypertrophy effect. With the estimated value and other factors of the training effect described in previous studies (training volume, etc.) as explanatory variables and muscle hypertrophy effect as an objective variable, we performed multiple regression analysis. The results revealed that the training effect was related to total mechanical activation of the fast-twitch fibers (standardized partial regression coefficient: 0.66), training load (standardized partial regression coefficient, 0.29) and number of sets (standardized partial regression coefficient: −0.37). The total mechanical activation of fast-twitch fibers was the strongest determinant of the muscle hypertrophy effect. In addition, we predicted the relationship between the level of the training effect of leg extension exercise and program variables. This study is the first to demonstrate “the relationship between total mechanical activation of fast-twitch fibers and muscle hypertrophy effect” in the field of muscle physiology, and the first to elucidate the association between the program variables and the training effect.
... Training to failure and the maximum number of repetitions (MNR) strategy, according to [9,10], are not optimal for maximizing performance. Additionally, it is difficult to determine the exact number of repetitions left in reserve. ...
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The aim of this paper is to analyze the physiognomy of unique sets in the maximum number of repetitions (MNR) strategy and different correlations between the maximal forces, duration and volume for a relevant exercise in the case of a small muscle group. The research methodology proposes testing, in two phases, a total of 30 male students, for bicep curl exercises carried out on a bicep Scott machine. The obtained results showed that there were significant differences between the maximum forces (Fmax) developed during the initial and final repetitions of the exercise sets or for different machine loads. There was a large correlation between the load and Fmax and an inverse correlation between the load and MNR or between the MNR and Fmax. The deterioration of the execution mode, represented by the profile of the final repetition of high-duration sets, was also tested and analyzed. We concluded that the study of the physiognomy of cycles and comparisons at the level of relevant repetitions have revealed new perspectives for the design of periodization strategies, for the possibility of manipulating adapted muscular response or compensatory acceleration training for small muscle groups or the MNR strategy.
... In addition, muscle activation, International Journal of Exercise Science http://www.intjexersci.com 915 assessed by superficial electromyography, does not seem to differentiate between failure vs nonfailure conditions (87,88), with full motor unit activation being reached within 3-5 repetitions next to failure (105). ...
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International Journal of Exercise Science 15(4): 910-933, 2022. The regular practice of resistance training (RT) has been shown to induce relevant increases in both muscle strength and size. In order to maximize these adaptations, the proper manipulation of RT variables is warranted. In this sense, the aim of the present study was to review the available literature that has examined the application of the acute training variables and their influence on strength and morphological adaptations of healthy young adults. The information presented in this study may represent a relevant approach to proper training design. Therefore, strength and conditioning coaches may acquire a fundamental understanding of RT-variables and the relevance of their practical application within exercise prescription.
... In addition, muscle activation, International Journal of Exercise Science http://www.intjexersci.com 6 assessed by superficial electromyography, does not seem to differentiate between failure vs nonfailure conditions (87,88), with full motor unit activation being reached within 3-5 repetitions next to failure (105). ...
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International Journal of Exercise Science 15(4): X-Y, 2022. The regular practice of resistance training (RT) has been shown to induce relevant increases in both muscle strength and size. In order to maximize these adaptations, the proper manipulation of RT variables is warranted. In this sense, the aim of the present study was to review the available literature that has examined the application of the acute training variables and their influence on strength and morphological adaptations of healthy young adults. The information presented in this study may represent a relevant approach to proper training design. Therefore, strength and conditioning coaches may acquire a fundamental understanding of RT-variables and the relevance of their practical application within exercise prescription.
... immediately after exercise. Training until fatigue in contrast has presented muscle hypertrophy and increased muscle strength even at low-intensity exercise (Sampson & Groeller, 2016). In terms of training efficiency, training with BFR reduces exercise repetition until fatigue to approximately 50% (T. ...
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Purpose: We assessed the effects of low-intensity exercise with blood flow restriction (BFR) during rest intervals on recovery of muscle function and pain during exercise and rest intervals. Methods: Participants were 10 males, and study arms of the participants were randomly assigned into three conditions; low-intensity exercise with BFR during rest intervals (rBFR), low-intensity exercise with BFR during exercise (eBFR) and low-intensity exercise only (EO). The exercise task was elbow flexion until repetition failure at 30% of 1 RM, and cuff pressure was 120 mmHg. The maximum voluntary isometric contraction (MVIC) and the muscle endurance (ME) were measured pre, post, 1 h, 24 h and 48 h after the exercise. Pain during exercise and rest intervals were evaluated using Numerical Rating Scale. Results: MVIC and ME significantly decreased after exercise in all conditions. Pain during exercise was lower in rBFR (4.2 ± 2.9) (p = 0.007) and EO (4.4 ± 2.7) (p = 0.014) conditions compared to eBFR condition (6.7 ± 1.7), but the pain during rest intervals was more intense in rBFR condition (5.2 ± 1.6) compared to eBFR (1.5 ± 1.4) and EO (1.7 ± 1.2) conditions (all: p < 0.001). Conclusion: We discovered that recovery of muscle function was the same as BFR during rest intervals and BFR during exercise. Also, our results suggested that BFR itself may cause the perception of pain. Future studies are thus required to investigate the optimal dosage focusing on the pressure volume and intensity used in BFR during intervals. This article is protected by copyright. All rights reserved.
... Nevertheless, our findings of similar increases in vastus lateralis CSA agree with a recent meta-analysis suggesting that training (close) to failure did not provide additional benefit (Grgic et al. 2021), and another study where rapid concentric action did not dilute hypertrophy gains versus a controlled lifting tempo (Sampson and Groeller 2016). However, training with too few repetitions per set (e.g., 10% velocity loss) would seem to compromise muscle hypertrophy gains (Pareja-Blanco et al. 2020a), at least in men. ...
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Purpose Men and women typically display different neuromuscular characteristics, force–velocity relationships, and differing strength deficit (upper vs. lower body). Thus, it is not clear how previous recommendations for training with velocity-loss resistance training based on data in men will apply to women. This study examined the inter-sex differences in neuromuscular adaptations using 20% and 40% velocity-loss protocols in back squat and bench press exercises. Methods The present study employed an 8-week intervention (2 × week) comparing 20% vs. 40% velocity-loss resistance training in the back squat and bench press exercises in young men and women (~ 26 years). Maximum strength (1-RM) and submaximal-load mean propulsive velocity (MPV) for low- and high-velocity lifts in squat and bench press, countermovement jump and vastus lateralis cross-sectional area were measured at pre-, mid-, and post-training. Surface EMG of quadriceps measured muscle activity during performance tests. Results All groups increased 1-RM strength in squat and bench press exercises, as well as MPV using submaximal loads and countermovement jump height ( P < 0.05). No statistically significant between-group differences were observed, but higher magnitudes following 40% velocity loss in 1-RM ( g = 0.60) and in low- ( g = 1.42) and high-velocity ( g = 0.98) lifts occurred in women. Training-induced improvements were accompanied by increases in surface EMG amplitude and vastus lateralis cross-sectional area. Conclusion Similar increases in strength and power performance were observed in men and women over 8 weeks of velocity-based resistance training. However, some results suggest that strength and power gains favor using 40% rather than 20% velocity loss in women.
... However, other studies [33,34] reported that subjects trained to volitional failure, described as a subject failing on a repetition or terminating a set when they believed another repetition was not possible. Moreover, various longitudinal studies comparing failure vs non-failure have simply stated that subjects performed sets to failure without providing a working definition [11,35]. These discrepancies make it difficult to compare findings between studies and to provide generalizable recommendations. ...
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Resistance training variables such as volume, load, and frequency are well defined. However, the variable proximity to failure does not have a consistent quantification method, despite being defined as the number of repetitions in reserve (RIR) upon completion of a resistance training set. Further, there is between-study variability in the definition of failure itself. Studies have defined failure as momentary (inability to complete the concentric phase despite maximal effort), volitional (self-termination), or have provided no working definition. Methods to quantify proximity to failure include percentage-based prescription, repetition maximum zone training, velocity loss, and self-reported RIR; each with positives and negatives. Specifically, applying percentage-based prescriptions across a group may lead to a wide range of per-set RIR owing to interindividual differences in repetitions performed at specific percentages of 1 repetition maximum. Velocity loss is an objective method; however, the relationship between velocity loss and RIR varies set-to-set, across loading ranges, and between exercises. Self-reported RIR is inherently individualized; however, its subjectivity can lead to inaccuracy. Further, many studies, regardless of quantification method, do not report RIR. Consequently, it is difficult to make specific recommendations for per-set proximity to failure to maximize hypertrophy and strength. Therefore, this review aims to discuss the strengths and weaknesses of the current proximity to failure quantification methods. Further, we propose future directions for researchers and practitioners to quantify proximity to failure, including implementation of absolute velocity stops using individual average concentric velocity/RIR relationships. Finally, we provide guidance for reporting self-reported RIR regardless of the quantification method.
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• In the case of both low- and high-intensity resistance training (RT), fitness professionals should teach their clients to lift near failure without achieving complete momentary muscular failure (MMF), as indicated by a ratings of perceived exertion value of 8 to 9 or repetitions in reserve value of 1 to 2. • MMF and volitional interruption (VI) elicit comparable improvements in strength and hypertrophy at high intensities (75% to 85% 1RM), so both may be integrated into a single training session (i.e., 4 sets of bench press, first three performed to VI, final set to MMF). • Program failure training to align with your client's goals — performing RT sets to failure — may be more effective for hypertrophy, whereas nonfailure sets may be more beneficial for power.
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We have reported that the acute postexercise increases in muscle protein synthesis rates, with differing nutritional support, are predictive of longer-term training-induced muscle hypertrophy. Here, we aimed to test whether the same was true with acute exercise-mediated changes in muscle protein synthesis. Eighteen men (21 ± 1 yr, 22.6 ± 2.1 kg/m(2); means ± SE) had their legs randomly assigned to two of three training conditions that differed in contraction intensity [% of maximal strength (1 repetition maximum)] or contraction volume (1 or 3 sets of repetitions): 30%-3, 80%-1, and 80%-3. Subjects trained each leg with their assigned regime for a period of 10 wk, 3 times/wk. We made pre- and posttraining measures of strength, muscle volume by magnetic resonance (MR) scans, as well as pre- and posttraining biopsies of the vastus lateralis, and a single postexercise (1 h) biopsy following the first bout of exercise, to measure signaling proteins. Training-induced increases in MR-measured muscle volume were significant (P < 0.01), with no difference between groups: 30%-3 = 6.8 ± 1.8%, 80%-1 = 3.2 ± 0.8%, and 80%-3= 7.2 ± 1.9%, P = 0.18. Isotonic maximal strength gains were not different between 80%-1 and 80%-3, but were greater than 30%-3 (P = 0.04), whereas training-induced isometric strength gains were significant but not different between conditions (P = 0.92). Biopsies taken 1 h following the initial resistance exercise bout showed increased phosphorylation (P < 0.05) of p70S6K only in the 80%-1 and 80%-3 conditions. There was no correlation between phosphorylation of any signaling protein and hypertrophy. In accordance with our previous acute measurements of muscle protein synthetic rates a lower load lifted to failure resulted in similar hypertrophy as a heavy load lifted to failure.
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The aim of this study was to investigate the kinematics, kinetics, and neural activation of the traditional bench press movement performed explosively and the explosive bench throw in which the barbell was projected from the hands. Seventeen male subjects completed three trials with a bar weight of 45% of the subject's previously determined lRM. Performance was significantly higher during the throw movement compared to the press for average velocity, peak velocity, average force, average power, and peak power. Average muscle activity during the concentric phase for pectoralis major, anterior deltoid, triceps brachii, and biceps brachii was higher for the throw condition. It was concluded that performing traditional press movements rapidly with light loads does not create ideal loading conditions for the neuromuscular system with regard to explosive strength production, especially in the final stages of the movement, because ballistic weight loading conditions where the resistance was accelerated throughout the movement resulted in a greater velocity of movement, force output, and EMG activity.
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The aim of this study was to investigate the kinematics, kinetics, and neural activation of the traditional bench press movement performed explosively and the explosive bench throw in which the barbell was projected from the hands. Seventeen male subjects completed three trials with a bar weight of 45% of the subject's previously determined 1RM. Performance was significantly higher during the throw movement compared to tile press for average velocity, peak velocity, average force, average power, and peak power. Average muscle activity during the concentric phase for pectoralis major, anterior deltoid, triceps brachii, and biceps brachii was higher for the throw condition. It was concluded that performing traditional press movements rapidly with light lends does not create ideal loading conditions for the neuromuscular system with regard to explosive strength production, especially in the final stages of the movement, because ballistic weight loading conditions where the resistance was accelerated throughout the movement resulted in a greater velocity of movement, force output, and EMG activity.
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Cells respond to mechanical forces by activating specific genes and signaling pathways that allow the cells to adapt to their physical environment. Examples include muscle growth in response to exercise, bone remodeling based on their mechanical load, or endothelial cells aligning under fluid shear stress. While the involved downstream signaling pathways and mechanoresponsive genes are generally well characterized, many of the molecular mechanisms of the initiating 'mechanosensing' remain still elusive. In this review, we discuss recent findings and accumulating evidence suggesting that the cell nucleus plays a crucial role in cellular mechanotransduction, including processing incoming mechanoresponsive signals and even directly responding to mechanical forces. Consequently, mutations in the involved proteins or changes in nuclear envelope composition can directly impact mechanotransduction signaling and contribute to the development and progression of a variety of human diseases, including muscular dystrophy, cancer, and the focus of this review, dilated cardiomyopathy. Improved insights into the molecular mechanisms underlying nuclear mechanotransduction, brought in part by the emergence of new technologies to study intracellular mechanics at high spatial and temporal resolution, will not only result in a better understanding of cellular mechanosensing in normal cells but may also lead to the development of novel therapies in the many diseases linked to defects in nuclear envelope proteins.
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Regulation of proteins is ubiquitous and vital for any organism. Protein activity can be altered chemically, by covalent modifications or non-covalent binding of co-factors. Mechanical forces are emerging as an additional way of regulating proteins, by inducing a conformational change or by partial unfolding. We review some advances in experimental and theoretical techniques to study protein allostery driven by mechanical forces, as opposed to the more conventional ligand driven allostery. In this respect, we discuss recent single molecule pullingexperiments as they have substantially augmented our view on the protein allostery by mechanical signals in recent years. Finally, we present a computational analysis technique, Force Distribution Analysis, that we developed to reveal allosteric pathways in proteins. Any kind of external perturbation, being it ligand binding or mechanical stretching, can be viewed as an external force acting on the macromolecule, rendering force-based experimental or computational techniques a very general approach to the mechanics involved in protein allostery. This unifying view might aid to decipher how complex allosteric protein machineries are regulated on the single molecular level.
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Objectives: Mechanical and neuromuscular benefits arise during ballistic stretch-shortening cycle muscle activation, yet resistance training regimens are typically non-ballistic, and in contrast to ballistic movement, require a concentric deceleration phase. Design: Twelve healthy males performed a unilateral, six repetition maximum non-ballistic elbow flexion-extension task during; (i) rapid shortening (RS), (ii) stretch-shortening cycle (SSC) and (iii) a 2-s eccentric and 2-s concentric control (C). Methods: A load cell and shaft encoder recorded respectively force and velocity. Surface electromyographic root mean square amplitude (EMGRMS) was recorded in the biceps and triceps brachii, and is reported as the relative (%) difference, normalised to control (C). Results: The average lengthening and shortening velocity of SSC (0.57 ± 0.03 ms(-1); 0.43 ± 0.02 ms(-1)) was significantly greater than RS (0.22 ± 0.01 ms(-1); 0.35 ± 0.01 ms(-1)), and C (0.17 ± 0.00 ms(-1), 0.20 ± 0.00 ms(-1)). Peak eccentric force was increased (P<0.0001) and in the first 5% of concentric movement during SSC, in the first and last repetitions respectively (194.7 ± 8.4N, 164.1 ± 7.5 N) when compared to RS (163.3 ± 8.9 N, 152.4 ± 7.5 N) and C (155.9 ± 8.5 N, 152.2 ± 8.7 N). Eccentric EMGRMS in the biceps brachii was significantly increased during the first three and final repetitions of SSC (31.9 ± 10.9%, 46.7 ± 12.4, 69.3 ± 13.6%, 92.0 ± 16.4%), and the third and last repetitions of RS (35.9 ± 7.4%, 50.3 ± 10.9%), compared to C (0.00%, 15.8 ± 4.0%, 23.7 ± 4.1%, 39.2 ± 8.6%). Conclusions: In the current study, eccentric limb velocity potentiated eccentric and concentric force, concentric velocity, and eccentric EMG amplitude during non-ballistic exercise.
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This study examined the effects of a single set of weight training exercise to failure and 2 multiple-set protocols (not to failure) on the 1-RM parallel squat. Forty-three men were randomly assigned to 1 of 3 weight training protocols emphasizing leg and hip strength: SS = single set to failure of 8-12 reps; MS = 3 x 10 reps; MSV = multiple-set program using a varied set and rep scheme. Relative intensity (% initial 1-RM), intensity (average mass lifted), and volume load (repetitions x mass) differed between groups over 14 weeks. Body mass, body composition, and the 1-RM parallel squat were assessed at baseline and at Weeks 5 and 14. Results showed no significant changes in body mass or body composition. The 1-RM squat increased significantly in all groups. Differences in 1-RM between groups indicate that MS and MSV increased approximately 50% more than SS over the 14 weeks. Results suggest that multiple sets not performed to failure produce superior gains in the 1-RM squat. (C) 1997 National Strength and Conditioning Association
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The purpose of this investigation was to compare the effects of weight training using a single set to failure vs. multiple sets not to failure in young women. The subjects were 17 previously untrained, healthy college-age women (age 18-20 years; 66.8 +/- 12.3 kg). After initial testing, the subjects were randomly assigned to 1 of 2 groups: the single-set group (SS, n = 9) and a multiple-set-variation group (MSV, n = 8). Testing was conducted at the beginning and end of the study. There were no initial differences between the groups. Tests included the 1 repetition maximum parallel squat (1RMS) and countermovement vertical jump (CMVJ). Body mass was measured on a medical scale. Subjects trained 3 days per week for 8 weeks; all training sessions were monitored by investigators. After warm-up, the SS performed 1 set of 8-12 repetitions to muscular failure. If 12 or more repetitions could be performed, an additional 2.5-5.0 kg were added for the next training session. The MSV group performed 3 sets at a target weight (not-to-failure) and used loading variations producing heavy and light training days. All subjects in the MSV were instructed (and encouraged) to move the weight as explosively as possible. The variation in squat training intensity across 1 week allowed the MSV subjects to produce marked differences in velocity of movement in the squat. Data were analyzed using a repeated measures ANOVA. The alpha level was 0.05. Results showed that the 1RMS and CMVJ increased significantly over time (p <0.05). The 1RMS improved 34.7% in the MSV and 24.2% in the SS. The CMVJ showed a significant interaction (p = 0.047). The CMVJ improved 11.2% in the MSV and 0.3% in the SS. Body mass did not change significantly over time or between groups. These results generally show a superior adaptation for the MSV group. (C) 2000 National Strength and Conditioning Association