Extent of motor unit activation during effort

Bélanger, Alain; McComas, Alan J.

doi:10.1152/jappl.1981.51.5.1131

Cited by 505 publications

(416 citation statements)

References 6 publications

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“…In addition, no significant gender difference was found in motor unit activation for either the elbow flexors or the knee 108 extensors (Figure 23). This finding is in agreement with that of a previous investigation (Belanger & McComas 1981) and indicates that males are no better able to maximally activate their available motor units than females.…”

Section: Motor Unit Characteristicssupporting

confidence: 93%

“…It is unlikely that the variability observed in the strength to GSA ratio results from differences in either fiber type distribution (Schantz et al 1983;Sale et al 1987) or motor unit activation (Belanger & McComas 1981;Young et al 1985). Anatomical differences which affect the mechanical advantage acting across a joint could account for some of the observed variability in the strength to CSA ratio (McCullagh et al 1984) as might the greater proportion of connective tissue (non-contractile) found in female muscle (Sale et al 1987).…”

Section: Introductionmentioning

confidence: 99%

“…A true maximal voluntary contraction requires that all motor units be recruited. There does not appear, however, to be any evidence to suggest that males are better able to maximally activate their motor units than females (Belanger & McComas 1981;Young et al 1985). The possibility remains, however, that a gender difference in motor unit number and/or motor unit size may affect recruitment and synchronization patterns which could influence the expression of maximal voluntary strength.…”

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confidence: 99%

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Gender differences in strength and muscle fiber characteristics

Miller

MacDougall

Tarnopolsky

et al. 1993

Europ. J. Appl. Physiol.

881

591

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A gender difference in absolute muscle strength is well documented.The e'xtent to which quantitative (fiber area and number) and qualitative (specific tension) differences in muscle contribute to this is not well understood. The purpose of this study was to examine a variety of muscle characteristics in the biceps brachii and vastus lateralis in a sample of males (n-8) and females (n=8) The difference in type II fiber area in the biceps brachii was not statistically significant despite the fact that these fibers were almost twice as large in the males as in 2 the females (8207 vs. 4306 urn). No significant gender difference was found in biceps fiber number (180,620 vs.l56,872) or muscle area to fiber area ratio in the vastus lateralis (451,468 vs. 465,007).No significant gender differences were found in any of the motor unit characteristics.The results indicate that the primary determinant of the greater muscle strength of males is their larger mean fiber areas which results in greater muscle cross-sectional areas.iv ACKNOWLEDGEMENTS

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Section: Motor Unit Characteristicssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Gender differences in strength and muscle fiber characteristics

Miller

MacDougall

Tarnopolsky

et al. 1993

Europ. J. Appl. Physiol.

881

591

View full text Add to dashboard Cite

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“…Each contraction was identified, and the peak torque (the highest instantaneous torque), mean torque (the arithmetic mean torque produced during the 3-s contraction), as well as the torque impulse (the integral of torque and time during the 3-s contraction; N·m·s) were calculated. The resting potentiated doublet torque was calculated as the highest torque measured following the resting stimuli delivered 1 s following a MVC, while voluntary activation was calculated using twitch interpolation (8,9):…”

Section: Discussionmentioning

confidence: 99%

Distinct profiles of neuromuscular fatigue during muscle contractions below and above the critical torque in humans

Burnley

Vanhatalo

Jones

2012

Journal of Applied Physiology

176

260

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Burnley M, Vanhatalo A, Jones AM. Distinct profiles of neuromuscular fatigue during muscle contractions below and above the critical torque in humans. J Appl Physiol 113: 215-223, 2012. First published May 3, 2012 doi:10.1152/japplphysiol.00022.2012Whether the transition in fatigue processes between "low-intensity" and "high-intensity" contractions occurs gradually, as the torque requirements are increased, or whether this transition occurs more suddenly at some identifiable "threshold", is not known. We hypothesized that the critical torque (CT; the asymptote of the torqueduration relationship) would demarcate distinct profiles of central and peripheral fatigue during intermittent isometric quadriceps contractions (3-s contraction, 2-s rest). Nine healthy men performed seven experimental trials to task failure or for up to 60 min, with maximal voluntary contractions (MVCs) performed at the end of each minute. The first five trials were performed to determine CT [ϳ35-55% MVC, denoted severe 1 (S1) to severe 5 (S5) in ascending order], while the remaining two trials were performed 10 and 20% below the CT (denoted CT-10% and CT-20%). Dynamometer torque and the electromyogram of the right vastus lateralis were sampled continuously. Peripheral and central fatigue was determined from the fall in potentiated doublet torque and voluntary activation, respectively. Above CT, contractions progressed to task failure in ϳ3-18 min, at which point the MVC did not differ from the target torque (S1 target, 88.7 Ϯ 4.3 N·m vs. MVC, 89.3 Ϯ 8.8 N·m, P ϭ 0.94). The potentiated doublet fell significantly in all trials, and voluntary activation was reduced in trials S1-S3, but not trials S4 and S5. Below CT, contractions could be sustained for 60 min on 17 of 18 occasions. Both central and peripheral fatigue developed, but there was a substantial reserve in MVC torque at the end of the task. The rate of global and peripheral fatigue development was four to five times greater during S1 than during CT-10% (change in MVC/change in time S1 vs. CT-10%: Ϫ7.2 Ϯ 1.4 vs. Ϫ1.5 Ϯ 0.4 N·m·min Ϫ1 ). These results demonstrate that CT represents a critical threshold for neuromuscular fatigue development. central and peripheral fatigue; maximal voluntary contraction; muscle stimulation; exercise

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“…As previously stated, both techniques depend on the effort of the subjects being truly maximal. Belanger and McComas [2] suggested that producing maximal isometric force is not a common activity and therefore not a part of the normal motor program. It is imperative therefore that for all strength testing (e.g.…”

Section: Relationship Between Voluntary Activation and Quadriceps Indexmentioning

confidence: 99%

A prospective analysis of incidence and severity of quadriceps inhibition in a consecutive sample of 100 patients with complete acute anterior cruciate ligament rupture

Chmielewski

Stackhouse

Axe

et al. 2004

Journal Orthopaedic Research

128

106

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Background Weakness of the quadriceps femoris muscle after anterior cruciate ligament injury and reconstruction has been attributed to incomplete voluntary activation of the muscle. The literature is conflicting on the incidence of incomplete voluntary quadriceps activation after anterior cruciate ligament injury because of differences in testing methods and population biases. The purpose of this study was to systematically examine the incidence and severity of quadriceps voluntary activation failure in both lower extremities after acute anterior cruciate ligament injury. We hypothesized that the incidence of quadriceps inhibition would be higher in the anterior cruciate ligament injured limbs than the uninvolved limbs, that the incidence of inhibition in the anterior cruciate ligament deficient limbs would be larger than in our historical sample of healthy young individuals tested in the same manner and that there would be no difference in inhibition by gender.Study design: Prospective, descriptive. Methods: One hundred consecutive patients with acute anterior cruciate ligament rupture (39 women and 61 men) were tested when range of motion was restored and effusion resolved, an average of 6 weeks after injury. A burst superimposition technique was used to assess quadriceps muscle activation and strength in all patients. Dependent t-tests were used to compare side-to-side differences in quadriceps strength. Independent t-tests were used to compare incidence of activation failure by gender and make comparisons to historical data on young, active individuals.Results: The average iqvolved side quadriceps activation was 0.92, and ranged from 0.60 to 1.00. The incidence of incomplete activation in the involved side quadriceps was 33 per cent and uninvolved side quadriceps was 31 per cent after acute anterior cruciate ligament rupture. The incidence of incomplete activation bilaterally was 21 per cent. There was no difference in incidence of quadriceps inhibition by gender.Conclusion: The incidence of voluntary quadriceps inhibition on the involved side was three times that of uninjured, active young subjects, but the magnitude was not large. The incidence of quadriceps inhibition on the uninjured side was similar to the injured side.Clinical relevance: Both the incidence and magnitude of quadriceps inhibition after ACL rupture are lower than have previously been reported. The conventional wisdom, therefore, that quadriceps inhibition is a significant problem in this population is challenged by the results of this study. Differences between this study and others include sufficient practice to ensure a maximal effort contraction and rigorous inclusion criteria. The findings have implications for strength testing as well as rehabilitation. The quadriceps index, an assessment of the injured side quadriceps strength deficit may be affected by the presence of voluntary activation failure in the uninvolved side.

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Extent of motor unit activation during effort

Cited by 505 publications

References 6 publications

Gender differences in strength and muscle fiber characteristics

Gender differences in strength and muscle fiber characteristics

Distinct profiles of neuromuscular fatigue during muscle contractions below and above the critical torque in humans

A prospective analysis of incidence and severity of quadriceps inhibition in a consecutive sample of 100 patients with complete acute anterior cruciate ligament rupture

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