scholarly journals Prolonged depression of knee extensor torque complexity following eccentric exercise

2018 ◽  
Author(s):  
Jamie Pethick ◽  
Katherine Whiteaway ◽  
Samantha Lee Winter ◽  
Mark Burnley
Keyword(s):  
Eccentric Exercise ◽  
Isometric Exercise ◽  
Femoral Nerve ◽  
Knee Extensor ◽  
Approximate Entropy ◽  
Surface Emg ◽  
Voluntary Contraction ◽  
Fluctuation Analysis ◽  
Muscle Torque ◽  
Fatiguing Exercise

Neuromuscular fatigue reduces the complexity of muscle torque output. Exercise-induced muscle damage reduces muscle torque output for considerably longer than high-intensity fatiguing contractions. We therefore hypothesized that muscle damaging eccentric exercise would lead to a persistent decrease in torque complexity, whereas fatiguing exercise would not. Ten healthy participants performed five isometric contractions (6 s contraction, 4 s rest) at 50% maximal voluntary contraction (MVC) before, immediately after, 10, 30 and 60 minutes, and 24 hours after eccentric (muscle damaging) and isometric (fatiguing) exercise. Further measures were taken 48 hours and one week after eccentric exercise. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA). Global, central and peripheral perturbations were quantified using MVCs with femoral nerve stimulation. Complexity decreased following both eccentric (ApEn, mean (SD), from 0.39 (0.10) to 0.20 (0.12), P < 0.001) and isometric exercise (from 0.41 (0.13) to 0.09 (0.04); P < 0.001). After eccentric exercise ApEn and DFA α required 24 hours to recover to baseline levels, compared to only 10 minutes following isometric exercise. MVC torque remained reduced (from 233.6 (74.2) N.m to 187.5 (64.7) N.m) and submaximal EMG amplitude increased (from 51.2 (6.9)% to 68.4 (11.3)%) 48 hours after eccentric exercise, with such changes only evident up to 60 minutes following isometric exercise (MVC torque, from 246.1 (77.2) to 217.9 (71.8) N.m; submaximal EMG from 52.9 (6.4)% to 66.2 (9.0)%). The prolonged depression in maximal muscle torque output is therefore accompanied by a reduction in torque complexity, suggesting that eccentric exercise diminishes motor control as well as muscle force-generating capacity.

scholarly journals Fatigue reduces the complexity of knee extensor torque during fatiguing sustained isometric contractions

2018 ◽  
Author(s):  
Jamie Pethick ◽  
Mark Burnley ◽  
Samantha Lee Winter
Keyword(s):  
Temporal Structure ◽  
Femoral Nerve ◽  
Knee Extensor ◽  
Approximate Entropy ◽  
Task Demands ◽  
Peripheral Fatigue ◽  
Knee Extensors ◽  
Fluctuation Analysis ◽  
Isometric Contractions ◽  
Scaling Exponent

The temporal structure, or complexity, of muscle torque output reflects the adaptability of motor control to changes in task demands. This complexity is reduced by neuromuscular fatigue during intermittent isometric contractions. We tested the hypothesis that sustained fatiguing isometric contractions would result in a similar loss of complexity. To that end, nine healthy participants performed, on separate days, sustained isometric contractions of the knee extensors at 20% MVC to task failure and at 100% MVC for 60 seconds. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling were quantified by calculating approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Global, central and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. Fatigue reduced the complexity of both submaximal (ApEn from 1.02 ± 0.06 to 0.41 ± 0.04, P < 0.05) and maximal contractions (ApEn from 0.34 ± 0.05 to 0.26 ± 0.04, P < 0.05; DFA α from 1.41 ± 0.04 to 1.52 ± 0.03, P < 0.05). The losses of complexity were accompanied by significant global, central and peripheral fatigue (all P < 0.05). These results demonstrate that a fatigue-induced loss of torque complexity is evident not only during fatiguing intermittent isometric contractions, but also during sustained fatiguing contractions.

scholarly journals Loss of knee extensor torque complexity during fatiguing isometric muscle contractions occurs exclusively above the critical torque

2016 ◽  
Vol 310 (11) ◽  
pp. R1144-R1153 ◽  
Author(s):  
Jamie Pethick ◽  
Samantha L. Winter ◽  
Mark Burnley
Keyword(s):  
Femoral Nerve ◽  
Knee Extensor ◽  
Approximate Entropy ◽  
Knee Extension ◽  
Muscle Contractions ◽  
Peripheral Fatigue ◽  
Fluctuation Analysis ◽  
Scaling Exponent ◽  
Extensor Torque ◽  
Isometric Muscle

The complexity of knee extensor torque time series decreases during fatiguing isometric muscle contractions. We hypothesized that because of peripheral fatigue, this loss of torque complexity would occur exclusively during contractions above the critical torque (CT). Nine healthy participants performed isometric knee extension exercise (6 s of contraction, 4 s of rest) on six occasions for 30 min or to task failure, whichever occurred sooner. Four trials were performed above CT (trials S1–S4, S1 being the lowest intensity), and two were performed below CT (at 50% and 90% of CT). Global, central, and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. The complexity of torque output was determined using approximate entropy (ApEn) and the detrended fluctuation analysis-α scaling exponent (DFA-α). The MVC torque was reduced in trials below CT [by 19 ± 4% (means ± SE) in 90%CT], but complexity did not decrease [ApEn for 90%CT: from 0.82 ± 0.03 to 0.75 ± 0.06, 95% paired-samples confidence intervals (CIs), 95% CI = −0.23, 0.10; DFA-α from 1.36 ± 0.01 to 1.32 ± 0.03, 95% CI −0.12, 0.04]. Above CT, substantial reductions in MVC torque occurred (of 49 ± 8% in S1), and torque complexity was reduced (ApEn for S1: from 0.67 ± 0.06 to 0.14 ± 0.01, 95% CI = −0.72, −0.33; DFA-α from 1.38 ± 0.03 to 1.58 ± 0.01, 95% CI 0.12, 0.29). Thus, in these experiments, the fatigue-induced loss of torque complexity occurred exclusively during contractions performed above the CT.

scholarly journals Effects of ipsilateral and contralateral fatigue and muscle occlusion on the complexity of knee extensor torque output in humans

2018 ◽  
Author(s):  
Jamie Pethick ◽  
Samantha Lee Winter ◽  
Mark Burnley
Keyword(s):  
Dominant Role ◽  
Recovery Period ◽  
Knee Extensor ◽  
Approximate Entropy ◽  
Voluntary Contraction ◽  
Peripheral Fatigue ◽  
Knee Extensors ◽  
Fluctuation Analysis ◽  
The Right ◽  
Cuff Occlusion

To determine whether the fatigue-induced loss of torque complexity could be accounted for by central or peripheral factors, nine healthy participants performed four experimental trials involving intermittent isometric contractions of the knee extensors at 50% of the maximal voluntary contraction (MVC) torque. These trials involved: 1) two bouts of contractions to failure using the right leg separated by 3 min recovery (ISP); 2) the same protocol but with cuff occlusion during the 3-min recovery (ISP-OCC); 3) contractions of the left leg to failure, followed 1 min later by contractions of the right leg to failure (CONT); and 4) the same protocol but with cuff occlusion applied to the left leg throughout both the recovery period and right leg contractions (CONT-OCC). Supramaximal electrical stimulation during MVCs was used to determine the degree of central and peripheral fatigue, whilst complexity was determined using Approximate Entropy (ApEn) and Detrended Fluctuation Analysis alpha-exponent (DFA alpha). Neuromuscular fatigue was consistently associated with a loss of torque complexity in all conditions (e.g., ISP bout 1 ApEn from [mean +/- SD]: 0.46 +/- 0.14 to 0.12 +/- 0.06 [P < 0.001]). In ISP-OCC, occlusion abolished the recovery from fatigue and torque complexity remained at the values observed at task failure in the preceding bout (IPS-OCC bout 2, first minute: 0.14 +/- 0.03, P < 0.001). Prior contralateral contractions had no effect on torque complexity. These results demonstrate that peripheral fatigue plays a dominant role in the loss of torque complexity.

scholarly journals Ischaemic pre-conditioning attenuates fatigue-induced loss of knee extensor torque complexity during submaximal intermittent isometric contractions

2019 ◽  
Author(s):  
Jamie Pethick ◽  
Charlotte Casselton ◽  
Samantha Lee Winter ◽  
Mark Burnley
Keyword(s):  
Near Infrared ◽  
Temporal Structure ◽  
Knee Extensor ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
Fluctuation Analysis ◽  
Scaling Exponent ◽  
Potent Effect ◽  
Task Failure ◽  
Muscle Torque

Neuromuscular fatigue reduces the temporal structure, or complexity, of muscle torque output. Ischaemic pre-conditioning (IPC) has been demonstrated to have a potent effect on motor output. We therefore tested the hypothesis that IPC would attenuate the fatigue-induced loss of muscle torque complexity. Ten healthy participants performed intermittent isometric knee extension contractions (6 s contraction, 4 s rest) to task failure at 40% maximal voluntary contraction (MVC). Contractions were preceded by either IPC (three bouts of 5 minutes proximal thigh occlusion at 225 mmHg, interspersed with 5 minutes rest) or SHAM (as IPC, but occlusion at only 20 mmHg) treatments. Torque and EMG signals were sampled continuously. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Muscle metabolic rate (mV̇O2) was determined using near-infrared spectroscopy. IPC increased time to task failure by 43 ± 13% (mean ± SEM, P = 0.047). Complexity decreased in both trials (decreased ApEn, increased DFA α; both P < 0.001), though the rate of decrease was significantly slower following IPC (ApEn, –0.2 ± 0.1 vs. –0.4 ± 0.1, P = 0.013; DFA α, 0.2 ± 0.1 vs. 0.3 ± 0.1, P = 0.037). Similarly, the rates of increase in EMG (P = 0.022) and mV̇O2 (P = 0.043) were significantly slower following IPC. These results indicate that IPC slowed the fatigue-induced loss of muscle torque complexity consequent to mechanisms related to motor unit activation.

Initial phase of maximal voluntary and electrically stimulated knee extension torque development at different knee angles

2004 ◽  
Vol 97 (5) ◽  
pp. 1693-1701 ◽  
Author(s):  
C. J. de Ruiter ◽  
R. D. Kooistra ◽  
M. I. Paalman ◽  
A. de Haan
Keyword(s):  
Muscle Activation ◽  
Knee Extensor ◽  
Surface Emg ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Knee Angle ◽  
Time Integral ◽  
Voluntary Contractions ◽  
Torque Development

We investigated the capacity for torque development and muscle activation at the onset of fast voluntary isometric knee extensions at 30, 60, and 90° knee angle. Experiments were performed in subjects ( n = 7) who had high levels (>90%) of activation at the plateau of maximal voluntary contractions. During maximal electrical nerve stimulation (8 pulses at 300 Hz), the maximal rate of torque development (MRTD) and torque time integral over the first 40 ms (TTI40) changed in proportion with torque at the different knee angles (highest values at 60°). At each knee angle, voluntary MRTD and stimulated MRTD were similar ( P < 0.05), but time to voluntary MRTD was significantly longer. Voluntary TTI40 was independent ( P > 0.05) of knee angle and on average (all subjects and angles) only 40% of stimulated TTI40. However, among subjects, the averaged (across knee angles) values ranged from 10.3 ± 3.1 to 83.3 ± 3.2% and were positively related ( r2 = 0.75, P < 0.05) to the knee-extensor surface EMG at the start of torque development. It was concluded that, although all subjects had high levels of voluntary activation at the plateau of maximal voluntary contraction, among subjects and independent of knee angle, the capacity for fast muscle activation varied substantially. Moreover, in all subjects, torque developed considerably faster during maximal electrical stimulation than during maximal voluntary effort. At different knee angles, stimulated MRTD and TTI40 changed in proportion with stimulated torque, but voluntary MRTD and TTI40 changed less than maximal voluntary torque.

Changes of muscular sound during sustained isometric contraction up to exhaustion

1989 ◽  
Vol 66 (4) ◽  
pp. 1593-1598 ◽  
Author(s):  
C. Orizio ◽  
R. Perini ◽  
A. Veicsteinas
Keyword(s):  
Isometric Contraction ◽  
Exercise Intensity ◽  
Maximum Voluntary Contraction ◽  
Isometric Exercise ◽  
Surface Emg ◽  
Voluntary Contraction ◽  
Biceps Muscle ◽  
Output Force ◽  
Contact Transducer ◽  
Four Levels

The sound (SMG) generated by the biceps muscle during isometric exercise at 20, 40, 60, and 80% of maximum voluntary contraction (MVC) up to exhaustion has been recorded by a contact transducer and integrated (iSMG), together with the surface electromyogram (EMG) in eight young untrained men. At the onset of exercise, iSMG and integrated surface EMG (iEMG) amplitude increased linearly with exercise. iSMG remained constant for 253 +/- 73 (SD), 45 +/- 16, 21 +/- 5, and 0 s at the four levels of contraction. Then iSMG increased linearly at 20% MVC, fluctuated at 40% MVC, and decreased exponentially at 60 and 80% MVC. iSMG exhaustion-to-onset ratio was 5.0 at 20%, 1.0 at 40%, and 0.2 at 60 and 80% MVC. On the contrary, independently of exercise intensity, iEMG increased with time, being 1.4 higher at exhaustion than at the onset. The nonunivocal iSMG changes with time and effort of exercise suggest that the sound may be a useful tool to acquire different information to EMG and output force during muscle contraction up to fatigue.

Assessment of low-frequency fatigue with two methods of electrical stimulation

2004 ◽  
Vol 97 (5) ◽  
pp. 1923-1929 ◽  
Author(s):  
V. Martin ◽  
G. Y. Millet ◽  
A. Martin ◽  
G. Deley ◽  
G. Lattier
Keyword(s):  
Motor Nerve ◽  
Femoral Nerve ◽  
Low Frequency ◽  
Knee Extensor ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Significant Time ◽  
Activation Level ◽  
Voluntary Activation Level ◽  
Low Frequency Fatigue

The aim of this study was to compare the use of transcutaneous vs. motor nerve stimulation in the evaluation of low-frequency fatigue. Nine female and eleven male subjects, all physically active, performed a 30-min downhill run on a motorized treadmill. Knee extensor muscle contractile characteristics were measured before, immediately after (Post), and 30 min after the fatiguing exercise (Post30) by using single twitches and 0.5-s tetani at 20 Hz (P20) and 80 Hz (P80). The P20-to-P80 ratio was calculated. Electrical stimulations were randomly applied either maximally to the femoral nerve or via large surface electrodes (ES) at an intensity sufficient to evoke 50% of maximal voluntary contraction (MVC) during a 80-Hz tetanus. Voluntary activation level was also determined during isometric MVC by the twitch-interpolation technique. Knee extensor MVC and voluntary activation level decreased at all points in time postexercise ( P < 0.001). P20 and P80 displayed significant time × gender × stimulation method interactions ( P < 0.05 and P < 0.001, respectively). Both stimulation methods detected significant torque reductions at Post and Post30. Overall, ES tended to detect a greater impairment at Post in male and a lesser one in female subjects at both Post and Post30. Interestingly, the P20-P80 ratio relative decrease did not differ between the two methods of stimulation. The low-to-high frequency ratio only demonstrated a significant time effect ( P < 0.001). It can be concluded that low-frequency fatigue due to eccentric exercise appears to be accurately assessable by ES.

Mechanisms contributing to knee extensor strength loss after prolonged running exercise

2003 ◽  
Vol 94 (1) ◽  
pp. 193-198 ◽  
Author(s):  
G. Y. Millet ◽  
V. Martin ◽  
G. Lattier ◽  
Y. Ballay
Keyword(s):  
Mechanical Response ◽  
Vastus Lateralis ◽  
Femoral Nerve ◽  
Knee Extensor ◽  
Central Fatigue ◽  
Strength Loss ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Running Exercise ◽  
Highly Correlated

The aim of this study was to identify the mechanisms that contribute to the decline in knee extensor (KE) muscles strength after a prolonged running exercise. During the 2 days preceding a 30-km running race [duration 188.7 ± 27.0 (SD) min] and immediately after the race, maximal percutaneous electrical stimulations (single twitch, 0.5-s tetanus at 20 and 80 Hz) were applied to the femoral nerve of 12 trained runners. Superimposed twitches were also delivered during isometric maximal voluntary contraction (MVC) to determine the level of voluntary activation (%VA). The vastus lateralis electromyogram was recorded. KE MVC decreased from pre- to postexercise (from 188.1 ± 25.2 to 142.7 ± 29.7 N · m; P < 0.001) as did %VA (from 98.8 ± 1.8 to 91.3 ± 10.7%; P < 0.05). The changes from pre- to postexercise in these two variables were highly correlated ( R = 0.88; P < 0.001). The modifications in the mechanical response after the 80-Hz stimulation and M-wave peak-to-peak amplitude were also significant ( P < 0.001 and P < 0.05, respectively). It can be concluded that 1) central fatigue, neuromuscular propagation, and muscular factors are involved in the 23.5 ± 14.9% reduction in MVC after a prolonged running bout at racing pace and 2) runners with the greatest KE strength loss experience large activation deficit.

scholarly journals Improving the measurement of TMS-assessed voluntary activation in the knee extensors

2018 ◽  
Author(s):  
Jeanne Dekerle ◽  
Aaron Greenhouse-Tucknott ◽  
James Graeme Wrightson ◽  
lisa Schäfer ◽  
Paul Ansdell
Keyword(s):  
Isometric Exercise ◽  
Femoral Nerve ◽  
Internal Validity ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Alternative Methods ◽  
Knee Extensors ◽  
Post Exercise ◽  
Assessment Protocol ◽  
Neuromuscular Assessment

The present study was designed to test the accuracy, validity, reliability and sensitivity of the main outcomes of alternative methods for the measure of TMS-assessed voluntary activation (VATMS) in the knee extensors. Ten healthy recreationally active males (24 ± 5 years) completed a neuromuscular assessment protocol (NMA) before and immediately after a fatiguing isometric exercise, consisting of two sets of five contractions (50%, 62.5%, 75%, 87.5%, and 100% of Maximal Voluntary Contraction; MVC) with superimposed TMS-evoked twitches (SITs) for calculation of VATMS (1x5C vs. 2x5C). The protocol was performed on two separate occasions for the measurement of between-day reliability. Where deemed appropriate, comparisons were made with a routinely used protocol [i.e. 50%, 75%, and 100% of MVC (1x3C) performed three times (3x3C)] from re-analysed data (Dekerle et al., 2018). Confidence intervals for the measure of a key determinant of VATMS (estimated resting twitch) were similar between 1x5C and 2x5C but improved by six-fold when compared to 1x3C (P&lt;0.05). Potentiated twitch force evoked via percutaneous electrical stimulation of the femoral nerve was unchanged from pre- to post-NMA at baseline for 1x5C (P&gt;0.05) but decreased for 2x5C and 3x3C (P&lt;0.05). Its recovery post-exercise was lesser for 1x5C compared to 2x5C and 3x3C (P&lt;0.05), with no difference between the latter two (P&gt;0.05). Absolute reliability was strong enough for both 1x5C and 2x5C to depict a true detectable change in the sample’s VATMS following the fatiguing exercise (TEM &lt; 3% at rest, &lt;9% post-exercise) but 2x5C was marginally more sensitive to individual’s changes at baseline. In conclusion, both 1x5C and 2x5C provide reliable measures of VATMS. However, the 1x5C protocol may hold stronger internal validity.

scholarly journals Associations of the Stair Climb Power Test With Muscle Strength and Functional Performance in People With Chronic Obstructive Pulmonary Disease: A Cross-Sectional Study

2010 ◽  
Vol 90 (12) ◽  
pp. 1774-1782 ◽  
Author(s):  
Marc Roig ◽  
Janice J. Eng ◽  
Donna L. MacIntyre ◽  
Jeremy D. Road ◽  
W. Darlene Reid
Keyword(s):  
Chronic Obstructive Pulmonary Disease ◽  
Muscle Strength ◽  
Functional Performance ◽  
Knee Extensor ◽  
Chronic Obstructive ◽  
Flexor Muscle ◽  
Cross Sectional ◽  
Obstructive Pulmonary Disease ◽  
Power Test ◽  
Muscle Torque

Background The Stair Climb Power Test (SCPT) is a functional test associated with leg muscle power in older people. Objective The purposes of this study were to compare the results of the SCPT in people with chronic obstructive pulmonary disease (COPD) and people who were healthy and to explore associations of the SCPT with muscle strength (force-generating capacity) and functional performance. Design The study was a cross-sectional investigation. Methods Twenty-one people with COPD and a predicted mean (SD) percentage of forced expiratory volume in 1 second of 47.2 (12.9) and 21 people who were healthy and matched for age, sex, and body mass were tested with the SCPT. Knee extensor and flexor muscle torque was assessed with an isokinetic dynamometer. Functional performance was assessed with the Timed “Up & Go” Test (TUG) and the Six-Minute Walk Test (6MWT). Results People with COPD showed lower values on the SCPT (28%) and all torque measures (∼32%), except for eccentric knee flexor muscle torque. In people with COPD, performance on the TUG and 6MWT was lower by 23% and 28%, respectively. In people with COPD, the SCPT was moderately associated with knee extensor muscle isometric and eccentric torque (r≥.46) and strongly associated (r=.68) with the 6MWT. In people who were healthy, the association of the SCPT with knee extensor muscle torque tended to be stronger (r≥.66); however, no significant relationship between the SCPT and measures of functional performance was found. Limitations The observational design of the study and the use of a relatively small convenience sample limit the generalizability of the findings. Conclusions The SCPT is a simple and safe test associated with measures of functional performance in people with COPD. People with COPD show deficits on the SCPT. However, the SCPT is only moderately associated with muscle torque and thus cannot be used as a simple surrogate for muscle strength in people with COPD.

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