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 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 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.

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 Complexity of Knee Neuromuscular Control in Uninjured Physically Active Adults: Right/Left and Dominant/Nondominant Asymmetry Analyses

2021 ◽  
Author(s):  
Nicholas Clark ◽  
Jamie Pethick
Keyword(s):  
Motor Neurons ◽  
Neuromuscular Control ◽  
Approximate Entropy ◽  
Knee Extension ◽  
Fluctuation Analysis ◽  
Temporal Behavior ◽  
Individual Level ◽  
Significant Difference ◽  
Clinically Significant ◽  
The Right

Context: Motor pathways include upper motor-neurons from the cerebrum and brainstem and lower motor-neurons from the spinal cord. Together, these physiological components are effectors of knee neuromuscular control. Because multiple components are involved, each with an output that is asynchronous to the others, ‘whole-system’ output is characterized by irregular temporal behavior and signal fluctuations. The irregular temporal behavior of physiological signals is analyzed using ‘complexity’. Complexity-based measures reflect the ability to adapt motor output rapidly and accurately in response to external perturbations and provide physiological information missed by magnitude-based (variability) measures.Objective: To characterize side-to-side symmetry of knee neuromuscular control (sub-maximal isometric knee extension constant-force task) using variability (coefficient of variation [CV%]) and complexity (approximate entropy [ApEn], detrended fluctuation analysis [DFA α]) measures.Design: Cross-sectional.Setting: Laboratory.Patients or Other Participants: Sixteen (male/female n=11/5; age 24.0±5.3yr; height 1.74±0.08m; body-mass 68.3±11.1kg).Main Outcome Measure(s): Right/left and dominant/nondominant group-level (t-test) and individual-level (absolute-asymmetry [%]) comparisons. A limb-symmetry-index was calculated for each variable and clinically-significant absolute-asymmetry defined (>15%). Clinically-significant absolute-asymmetry prevalence (%) was computed for each variable.Results: The only significant side-to-side difference was for right/left DFA α (P=.000). Maximum absolute-asymmetries were (right/left, dominant/nondominant): CV 18.2%, 18.0%; ApEn 34.5%, 32.3%; DFA α 4.9%, 5.0%. Clinically-significant absolute-asymmetry prevalence was (right/left, dominant/nondominant): CV 43.8%, 43.8%; ApEn 62.5%, 50.0%; DFA α 0.0%, 0.0%.Conclusions: Different side-to-side comparison methods yield different findings. Large proportions of participants demonstrated wide ranges of side-to-side absolute-asymmetries. The finding of a significant difference for the right/left DFA α comparison but not for the right/left ApEn comparison suggests that different complexity variables assess different aspects of complexity. Consideration for how side-to-side comparisons are performed (right/left, dominant/nondominant) is required. Approximate entropy and DFA α assess different aspects of complexity and both should be used alongside other traditional magnitude-based measures when studying knee neuromuscular control.

scholarly journals Brain Activation During Maximum Concentric and Eccentric Knee Extension Muscle Contractions

2020 ◽  
pp. 1-6
Author(s):  
Ali Sharifnezhad ◽  
Moein Koohestani ◽  
Ali Sharifnezhad ◽  
Ali Abbasi ◽  
Amir-Homayoun Javadi ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Task Complexity ◽  
Control Strategies ◽  
Knee Extensor ◽  
Eccentric Contraction ◽  
Cortical Activity ◽  
Knee Extension ◽  
Muscle Contractions ◽  
System Control ◽  
Alpha Power

Purpose: In spite of mounting evidence indicating that concentric and eccentric knee extensor muscle contractions might have special nervous system control strategies, the differentiation of brain frequencies between concentric and eccentric movements and how the motor cortex programs this contraction has been less studied. In this study, the brain and muscle activation differences during maximum concentric and eccentric contractions were compared. Methods: Nine healthy volunteers performed 20 maximum eccentric and 20 maximum concentric knee extensor contractions. Electroencephalography (EEG) signals from sensorimotor-related cortical areas were recorded simultaneous with the electromyography (EMG) of the knee extensor muscles. In the spectral analysis the performance related power values were calculated for Theta (4-7 Hz) and Alpha (7-12 Hz). Results: The time-domain results revealed, longer time and greater cortical activity is required for the preparation of an eccentric contraction. For the eccentric task, the cortical activity was greater, but the EMG was lower in comparison to the concentric task values. Statistical analysis showed significant higher and lower Theta and Alpha power in both types of contractions compared to the resting state, respectively. Conclusion: These findings suggest that increased Theta power is associated with task complexity and focused attention and decreased Alpha power values with increased information processing in the somatosensory cortex.

SCALING IN COGNITION

Fractals ◽  
2001 ◽  
Vol 09 (04) ◽  
pp. 379-391 ◽  
Author(s):  
VASILE V. MORARIU ◽  
AUREL COZA ◽  
MINERVA ALOUETTE CHIS ◽  
ADRIANA ISVORAN ◽  
LAURA-CORNELIA MORARIU
Keyword(s):  
Human Subjects ◽  
Approximate Entropy ◽  
Characteristic Number ◽  
Fluctuation Analysis ◽  
Scaling Exponent ◽  
Random Series ◽  
Dimension Analysis ◽  
Range Correlation ◽  
Short Memory ◽  
Detrended Fluctuation

Conscious activity is generally consistent with a deterministic mode of action, however some activities demand randomness. The goal of this study was to find whether mind can produce randomness. We asked various human subjects, aged between 21 and 57, to produce sequences of random integers. The non-repetition of the terms in the series was the "algorithm" generally used by all the subjects. The series were analyzed by using spectral analysis (SA), detrended fluctuation analysis (DFA), information (I2) and approximate entropy (AE) and correlation dimension analysis (CDA). SA of the series revealed 1/fβ(-0.4<β<1) types of spectra. The α scaling exponent resulting from DFA ranged between 0.2 and 1.1. The maximum of the distribution of α was centered at about 0.62. This is equivalent to a quarter power law in spectral terms. A significant percentage of subjects were able to produce random series. I2 of mental series revealed short-range correlation for pairs of successive numbers in the series. The correlation decreased gradually and it disappeared at a delay step of about 7 which is the characteristic number of short memory. AE had a minimum value at α=1 and a maximum value at α=0.5 for mental and random series, respectively. CDA showed no presence of attractors in the series, therefore none of the randomness produced by the subjects was of deterministic origin. A comparison of the scaling exponents revealed that the mental series have a certain long-range characteristic which is common to the human language as evident in the literature writings.

scholarly journals Neuromuscular Fatigue at Task Failure and During Immediate Recovery after Isometric Knee Extension Trials

Sports ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 156
Author(s):  
Christian Froyd ◽  
Fernando Beltrami ◽  
Timothy Noakes
Keyword(s):  
Femoral Nerve ◽  
Force Production ◽  
Knee Extension ◽  
Voluntary Contraction ◽  
Peak Force ◽  
Fatigue Threshold ◽  
Peripheral Fatigue ◽  
Neuromuscular Activation ◽  
Task Failure ◽  
Immediate Recovery

We asked whether the level of peripheral fatigue would differ when three consecutive exercise trials were completed to task failure, and whether there would be delayed recovery in maximal voluntary contraction (MVC) force, neuromuscular activation and peripheral fatigue following task failure. Ten trained sport students performed three consecutive knee extension isometric trials (T1, T2, T3) to task failure without breaks between trials. T1 and T2 consisted of repeated 5-s contractions followed by 5-s rests. In T1, contractions were performed at a target force at 60% pre-exercise MVC. In T2, all contractions were MVCs, and task failure occurred at 50% MVC. T3 was a sustained MVC performed until force fell below 15% MVC. Evoked force responses to supramaximal electrical femoral nerve stimulation were recorded to assess peripheral fatigue. Electromyography signals were normalized to an M-wave amplitude to assess neuromuscular activation. Lower levels of evoked peak forces were observed at T3 compared with T2 and T1. Within 5 s of task failure in T3, MVC force and neuromuscular activation recovered substantially without any recovery in evoked peak force. Neuromuscular activation 5–10 s after T3 was unchanged from pre-exercise values, however, evoked peak forces were substantially reduced. These results challenge the existence of a critical peripheral fatigue threshold that reduces neuromuscular activation. Since neuromuscular activation changed independently of any change in evoked peak force, immediate recovery in force production after exercise is due to increased central recruitment and not to peripheral mechanisms.

scholarly journals Fatigue-Mediated Loss of Complexity is Contraction-Type Dependent in Vastus Lateralis Electromyographic Signals

Sports ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 78 ◽  
Author(s):  
Luis Hernandez ◽  
Clayton Camic
Keyword(s):  
Vastus Lateralis ◽  
Knee Extensor ◽  
Sample Entropy ◽  
Fluctuation Analysis ◽  
Scaling Exponent ◽  
Semg Signal ◽  
Contraction Type ◽  
Detrended Fluctuation ◽  
Electromyographic Signals ◽  
Semg Signals

The purpose of this study was to investigate the effect of fatigue status and contraction type on complexity of the surface electromyographic (sEMG) signal. Twelve females (mean age ± SD = 21.1 ± 1.4 years) performed three fatigue-inducing protocols that involved maximal concentric, eccentric, or isometric knee-extensor contractions over three non-consecutive sessions. Pre- and post-fatigue assessments were also completed each session and consisted of three maximal efforts for each type of contraction. Complexity of sEMG signals from the vastus lateralis was assessed using Sample Entropy (SampEn) and Detrended Fluctuation Analysis (DFA) as expressed using the scaling exponent α. The results showed that fatigue decreased (p < 0.05) sEMG complexity as indicated by decreased SampEn (non-fatigued: 1.57 ± 0.22 > fatigued: 1.46 ± 0.25) and increased DFA α (non-fatigued: 1.27 ± 0.26 < fatigued: 1.32 ± 0.23). In addition, sEMG complexity was different among contraction types as indicated by SampEn (concentric: 1.58 ± 0.22 > eccentric: 1.47 ± 0.27 and isometric: 1.50 ± 0.21) and DFA α (concentric: 1.27 ± 0.18 < isometric: 1.32 ± 0.18). Thus, these findings suggested sEMG complexity is affected by fatigue status and contraction type, with the degree of fatigue-mediated loss of complexity dependent on the type of contraction used to elicit fatigue.

scholarly journals Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle

2021 ◽  
Author(s):  
Jamie Pethick ◽  
Samantha L. Winter ◽  
Mark Burnley
Keyword(s):  
Metabolic Rate ◽  
Near Infrared ◽  
Joint Angle ◽  
Knee Extensor ◽  
Inverse Correlation ◽  
Task Demands ◽  
Fluctuation Analysis ◽  
Joint Angles ◽  
Task Failure ◽  
Extensor Torque

Abstract Purpose Joint angle is a significant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate ($${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 ) would be conserved at reduced joint angles (i.e. shorter muscle lengths). Methods Eleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30º, 60º and 90º of flexion (0º = extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 was determined using near-infrared spectroscopy. Results Time to task failure/end increased as joint angle decreased (P < 0.001). Over time, complexity decreased at 90º and 60º (decreased ApEn, increased DFA α, both P < 0.001), but not 30º. $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 increased at all joint angles (P < 0.001), though the magnitude of this increase was lower at 30º compared to 60º and 90º (both P < 0.01). There were significant correlations between torque complexity and $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 at 90º (ApEn, r =  − 0.60, P = 0.049) and 60º (ApEn, r =  − 0.64, P = 0.035; DFA α, ρ = 0.68, P = 0.015). Conclusion The lack of correlation between $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and complexity at 30º was likely due to low relative task demands, given the similar kinetics of $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and torque complexity. An inverse correlation between $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths.

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