Excess post-exercise oxygen consumption is not associated with mechanomyographic amplitude after incremental cycle ergometry in the quadriceps femoris muscles

Introduction: The purpose of this study was to understand the relationship between the mechanical activities of the three superficial quadriceps muscles and excess post‐exercise oxygen consumption (EPOC) after incremental cycle ergometer exercise. Methods: Twelve healthy male volunteers had mechanomyographic (MMG) and electromyographic (EMG) activity of the superficial quadriceps muscles recorded 30 minutes before incremental cycle ergometry and 60 minutes after the exercise work bout. Results: The results indicate significant time‐constant values for EPOC and MMG amplitude for the three superficial quadriceps muscles during the 60‐minute post‐exercise recovery period. For EMG amplitude no decay patterns were found for the three muscles. In addition, there were no mean differences between the MMG values for the three muscles that were significantly different from EPOC. Conclusions: These results suggest that EPOC after exercise could not be exclusively attributed to elevated activity of the working muscles. Muscle Nerve 44: 432–438, 2011     

Electromyographic responses of the superficial quadriceps femoris muscles during incremental treadmill running

Introduction: We examined the individual patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during incremental treadmill running. Methods: Nine physically active men performed incremental treadmill running at a constant grade of 1%. The EMG signal was recorded from the 3 superficial quadriceps femoris muscles during the work bout. Results: The results of the polynomial regression indicated that the linear model best fit the data for the composite data for all 3 muscles and the majority (7 of 9) of subjects. There were no consistent patterns of responses for the EMG MPF responses. Also, there were no significant (P > 0.05) muscle × running velocity interactions for EMG amplitude and MPF. Conclusions: These results indicate consistent patterns of responses for EMG amplitude during incremental treadmill running, regardless of which muscle was studied. Muscle Nerve 48 : 938–944, 2013     

Comparison of electromyographic responses for the superficial quadriceps muscles: Cycle versus knee‐extensor ergometry

The purpose of this study was to compare the electromyographic (EMG) amplitude and mean power frequency (MPF) versus power output relationships for the three superficial quadriceps muscles during incremental cycle (CE) and knee‐extensor (KE) ergometry in the same subjects. Eight men performed incremental CE and KE tests to exhaustion. Surface EMG signals were recorded simultaneously from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). Polynomial regression analyses on a subject‐by‐subject basis indicated that the relationship between EMG amplitude versus power output was best‐fit with either a linear, quadratic, or cubic model for CE, whereas the relationship was best‐fit with a linear model for all subjects for the KE test. No consistent relationship was found for EMG MPF within subjects and between muscle groups for CE or KE. Compared with CE, however, the EMG amplitude during KE exercise was, on average, approximately 87% and 30% higher for the RF and VM muscles, respectively. These results suggest that KE exercise may be a better mode of examining EMG amplitude in the quadriceps muscle during incremental exercise than traditional CE. Muscle Nerve, 2009     

Reliability of the log‐transformed EMG amplitude‐power output relationship for incremental knee‐extensor ergometry

Introduction: The purpose of this investigation was to determine the reproducibility of the log‐transformed model for electromyography (EMG) amplitude during incremental single‐leg knee‐extensor exercise. Methods: Eight healthy college‐aged men performed 3 incremental tests on separate occasions on a knee‐extensor ergometer. EMG amplitude was analyzed for each participant on each occasion for the rectus femoris and vastus medialis muscles at 4 different exercise power outputs (30%, 50%, 70%, and 90%) corresponding to each participant's maximal power output. Intraclass correlation coefficients (ICC) were determined for the slope and y‐intercept terms derived from the log‐transformed EMG amplitude‐power output relationship for each muscle. Results: The ICC values for the rectus femoris (slope = 0.779; y‐intercept = 0.787) and vastus medialis (slope = 0.756; y‐intercept = 0.763) muscles were high. Conclusions: The log‐transformed EMG amplitude‐power output relationship is a reliable index for measuring motor unit activation. Muscle Nerve 52:428–434, 2015     

A wavelet‐based analysis of surface mechanomyographic signals from the quadriceps femoris

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to examine the MMG responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Fifteen healthy men [age (mean ± SD): 26.4 ± 6.1 years] volunteered to perform isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). During each muscle action, surface MMG signals were detected from the VL, RF, and VM and processed with the MMG wavelet analysis. The results show that, for the VL and VM muscles, there was compression of the total MMG intensity spectra toward low frequencies for most force levels above 20% MVC. For the RF, however, the peak of the total MMG intensity spectrum occurred at approximately 30–40 HZ for all force levels. Because the VL, RF, and VM are all innervated by the femoral nerve, the discrepancies among the three muscles for total MMG intensity in each wavelet band may have been due to differences in architecture, muscle stiffness, and/or intramuscular pressure. Muscle Nerve 39: 355–363, 2009     

Linearity and reliability of the mechanomyographic amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles

The purpose of this investigation was to examine the linearity and reliability of the mechanomyographic (MMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Nine healthy men and 11 healthy women performed submaximal to maximal, concentric, isokinetic muscle actions of the leg extensors at 30° s^?1 on two occasions. Surface MMG signals were detected from the VL, RF, and VM of the dominant thigh during both trials. The ranges of the coefficients of determination for the MMG amplitude versus dynamic torque relationships were 0.01–0.94 for the VL, 0.01–0.84 for the RF, and 0.19–0.96 for the VM. The intraclass correlation coefficients for the linear MMG amplitude versus torque slope coefficients were 0.823 (VL), 0.792 (RF), and 0.927 (VM). These results indicate that, when analyzed for individual subjects, the MMG amplitude versus dynamic torque relationships demonstrated inconsistent linearity. When using MMG in the clinical setting, dynamic muscle actions of the superficial quadriceps femoris muscles do not appear to be appropriate for assessing changes in muscle function during strength training. Muscle Nerve, 2009     

Test–retest reliability of the electromyographic fatigue threshold for cycle ergometry

Introduction: The purpose of this study was to determine the intersession reliability of the electromyographic fatigue threshold (EMG_FT) for cycle ergometry. Methods: On separate occasions, 10 healthy, college‐aged men performed an incremental test to voluntary exhaustion on a cycle ergometer. The EMG amplitude vs. time relationships for each power output from the quadriceps femoris muscles were analyzed using linear regression. EMG_FT was defined operationally as the average of the highest power output that resulted in a non‐significant slope coefficient (P > 0.05) and the lowest power output that resulted in a significant (P < 0.05) positive slope coefficient. The EMG_FT values for trials 1 and 2 were used to calculate the intraclass correlation coefficient (ICC). Results: Overall, the reliability of the EMG_FT (ICC_2,1 = 0.85; 95% confidence interval 0.49–0.96) was in the “excellent” category. Conclusions: The EMG_FT for cycle ergometry is a reliable measure for assessing muscular fatigue. Muscle Nerve 53 : 803–807, 2016     

Reliability of a novel approach for quadriceps motor point assessment

Introduction: We studied the ability of clinicians to identify quadriceps motor points using a transcutaneous electrical stimulation unit (TENS). Methods: Twenty‐two certified athletic trainers and 1 expert‐rater identified the 7 motor points of the quadriceps at 2 time‐points separated by 1 week. The difference was calculated between where each participant and the expert‐rater identified each motor point using an x–y coordinate system. Bland–Altman plots were used to compare differences between 2 testing sessions. Results: No differences were observed between participants and the expert‐rater for motor point location. The smallest variability in the limits of agreements were observed in the distal vastus medialis oblique (–1.89 to 1.86 cm) and proximal vastus lateralis (–1.61 to 2.35 cm). Discussion: Our results suggest the utilization of a TENS unit may be 1 way to identify quadriceps motor points to improve electrical stimulation applications. The smallest limits of agreement were over the most common quadriceps electrical stimulation electrode positions. Muscle Nerve 57 : E1–E7, 2018     

Effect of knee position on quadriceps muscle force steadiness and activation strategies

Introduction: In this study we investigated the effect of knee position on quadriceps force steadiness and activation strategies. Methods: Quadriceps force steadiness was evaluated in 22 volunteers at two knee positions by testing their ability to regulate submaximal force. Muscle activation strategies were studied in both time and frequency domains using surface electromyography. Results: Quadriceps force fluctuations and the associated agonist and antagonist activity were significantly higher at 90° than at 30° of flexion (P < 0.05). The quadriceps median frequency recorded at 30° was significantly higher than at 90° of flexion (P < 0.05). Regression analyses revealed that force steadiness was related to quadriceps activation and median frequency (P < 0.001), but not to hamstring coactivation (P > 0.05). Conclusions: The results indicate that knee position significantly affects quadriceps force steadiness and activation strategies. This finding may have important implications for designing a force control testing protocol and interpreting test results. Muscle Nerve, 2011     

Assessment of muscle fatigue during exercise in chronic obstructive pulmonary disease

Contractile fatigue is associated with exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). Contractile fatigue may be assessed by quantifying the decline in strength after a fatiguing protocol but this may pose practical problems. The purpose of this study was to investigate the relationship between the decline in quadriceps strength, quadriceps electrical activity, perception of leg fatigue, and arterial lactate level in patients with COPD during constant work-rate cycling exercise. The decline in quadriceps strength was significantly associated with the decrease in electromyographic median frequency (r = 0.606), leg fatigue perception (r = 0.453), and arterial lactate level (r = 0.384). Using the receiver-operating-characteristic curve, it was found that a 4% decline in electromyographic median frequency had a 94% sensitivity and a 75% specificity to predict contractile fatigue. We conclude that contractile fatigue commonly occurs during cycling exercise in COPD. The electromyographic median frequency appears to be a valuable indirect marker to predict contractile leg fatigue.     

Neuromuscular fatigue of the knee extensors during repeated maximal intensity intermittent‐sprints on a cycle ergometer

Introduction: We studied the time course of neuromuscular fatigue during maximal intensity intermittent‐sprint cycling. Methods: Eight participants completed 10, 10‐s sprints interspersed with 180 s of recovery. The power outputs were recorded for each sprint. Knee extensor maximum voluntary contraction (MVC) force, voluntary activation, and evoked contractile properties were recorded presprint, postsprint 5, and postsprint 10. Results: Total work over the 10 sprints decreased significantly (P < 0.05) and could be described by 2 linear relationships from sprints 1–5 compared with sprints 6–10. Participants had significantly (P < 0.05) lower MVC and twitch forces postsprint 5 compared with presprint. MVC, voluntary activation, and twitch force were decreased (P < 0.05) postsprint 10 compared with postsprint 5. Conclusions: The maximal intermittent sprints induced neuromuscular fatigue. Neuromuscular fatigue in the first 5 sprints was mainly peripheral, whereas in the last 5 sprints it was both peripheral and central. Muscle Nerve 51: 569–579, 2015     

A narrative review of exercise‐associated muscle cramps: Factors that contribute to neuromuscular fatigue and management implications

Although exercise‐associated muscle cramps (EAMC) are highly prevalent among athletic populations, the etiology and most effective management strategies are still unclear. The aims of this narrative review are 3‐fold: (1) briefly summarize the evidence regarding EAMC etiology; (2) describe the risk factors and possible physiological mechanisms associated with neuromuscular fatigue and EAMC; and (3) report the current evidence regarding prevention of, and treatment for, EAMC. Based on the findings of several large prospective and experimental investigations, the available evidence indicates that EAMC is multifactorial in nature and stems from an imbalance between excitatory drive from muscle spindles and inhibitory drive from Golgi tendon organs to the alpha motor neurons rather than dehydration or electrolyte deficits. This imbalance is believed to stem from neuromuscular overload and fatigue. In concert with these findings, the most successful treatment for an acute bout of EAMC is stretching, whereas auspicious methods of prevention include efforts that delay exercise‐induced fatigue. Muscle Nerve 54 : 177–185, 2016     

Multichannel surface EMG: basic aspects and clinical utility

The generation of the surface electromyogram (sEMG) is described with regard to the properties of the single muscle fiber action potential as source, the physical aspects of volume conduction and recording configuration, and the properties and firing pattern of motor units (MUs). The spatial aspect of the motor unit action potential (MUP) is emphasized in relation to the results of high-density, multichannel sEMG measurements. The endplate zone, depth, size, and position of MUs can be estimated. The use of muscle fiber conduction velocity measurements in channelopathies and the changes in pathological fatigue are described. Using the unique patterns of spatial spread of MUPs over the skin (MU fingerprint), MU classification and the determination of firing moments is done noninvasively. Clinical applications of high-density sEMG measurements are reviewed. Emerging possibilities provided by MUP size and fingerprint measurements in neuromuscular disease and motor control are discussed. We conclude that multichannel sEMG adds unique, and sometimes indispensable, spatial information to our knowledge of the motor unit.     

Quantitation of central activation failure during maximal voluntary contractions in humans

Muscle fatigue or neuromuscular disease may result in central activation failure during maximal voluntary contractions (MVCs). Superimposition of an electrically stimulated contraction during an MVC has been used to detect central activation failure. To determine the most sensitive means of quantitating central activation failure using this technique, we compared the increment in isometric force from single-, double-, and high-frequency trains (50 Hz, 500 or 1000 ms) of stimuli of the peroneal nerve imposed during three separate MVCs of the dorsiflexor muscles. Completeness of activation was quantitated with the central activation ratio (CAR) = MVC/(MVC + stimulated force). Comparisons were made of the CARs of three groups of subjects during the three stimulation conditions: 7 healthy subjects, 13 patients with amyotrophic lateral sclerosis, and 5 healthy subjects after fatiguing exercise. For all three groups, the CAR was significantly lower during the train of stimuli condition (means = 0.76–0.89) compared with either the single or double stimuli conditions (means = 0.96–1.00). The results suggest that a superimposed high-frequency train of stimuli is a more sensitive indicator of central activation failure during isometric MVCs compared with either the superimposed single or double stimuli methods. © 1996 John Wiley & Sons, Inc.     

Comparing the force ripple during asynchronous and conventional stimulation

Introduction: Asynchronous stimulation has been shown to reduce fatigue during electrical stimulation; however, it may also exhibit a force ripple. We quantified the ripple during asynchronous and conventional single‐channel transcutaneous stimulation across a range of stimulation frequencies. Methods: The ripple was measured during 5 asynchronous stimulation protocols, 2 conventional stimulation protocols, and 3 volitional contractions in 12 healthy individuals. Results: Conventional 40 Hz and asynchronous 16 Hz stimulation were found to induce contractions that were as smooth as volitional contractions. Asynchronous 8, 10, and 12 Hz stimulation induced contractions with significant ripple. Conclusions: Lower stimulation frequencies can reduce fatigue; however, they may also lead to increased ripple. Future efforts should study the relationship between force ripple and the smoothness of the evoked movements in addition to the relationship between stimulation frequency and NMES‐induced fatigue to elucidate an optimal stimulation frequency for asynchronous stimulation. Muscle Nerve 50: 549–555, 2014