OBJECTIVE: To examine motor unit changes during the development of fatigue in healthy subjects. DESIGN: Automated decomposition-enhanced spike-triggered averaging was used to characterize motor unit size and firing rate in the dominant vastus medialis during maintained contractions at 10% and 30% of maxima voluntary contraction (MVC). SETTING: Academic outpatient neuromuscular clinic. PARTICIPANTS: Healthy laboratory personnel. MAIN OUTCOME MEASURES: Surface electromyogram, surface-detected motor unit action potential amplitude (S-MUAP), mean firing rate, force (MVC), motor unit index. RESULTS: Surface electromyogram values and S-MUAP amplitudes increased during both 10% and 30% MVC fatiguing contractions, while mean firing rates decreased. A motor unit index, indicating the degree of motor unit pool activation, increased similarly to S-MUAP size, implying that new and larger units were recruited to maintain the contraction. Repeated contractions led to earlier motor unit changes and fatigue. CONCLUSION: During submaximal fatiguing contractions, additional motor units are activated to maintain strength. These changes begin early, within the first minute, particularly after a previous fatiguing effort.
OBJECTIVE: To examine motor unit changes during the development of fatigue in healthy subjects. DESIGN: Automated decomposition-enhanced spike-triggered averaging was used to characterize motor unit size and firing rate in the dominant vastus medialis during maintained contractions at 10% and 30% of maxima voluntary contraction (MVC). SETTING: Academic outpatient neuromuscular clinic. PARTICIPANTS: Healthy laboratory personnel. MAIN OUTCOME MEASURES: Surface electromyogram, surface-detected motor unit action potential amplitude (S-MUAP), mean firing rate, force (MVC), motor unit index. RESULTS: Surface electromyogram values and S-MUAP amplitudes increased during both 10% and 30% MVC fatiguing contractions, while mean firing rates decreased. A motor unit index, indicating the degree of motor unit pool activation, increased similarly to S-MUAP size, implying that new and larger units were recruited to maintain the contraction. Repeated contractions led to earlier motor unit changes and fatigue. CONCLUSION: During submaximal fatiguing contractions, additional motor units are activated to maintain strength. These changes begin early, within the first minute, particularly after a previous fatiguing effort.
Authors: S M Ling; R A Conwit; L Talbot; M Shermack; J E Wood; E M Dredge; M J Weeks; D R Abernethy; E J Metter Journal: Osteoarthritis Cartilage Date: 2007-05-31 Impact factor: 6.576
Authors: Nathaniel D M Jenkins; Terry J Housh; Haley C Bergstrom; Kristen C Cochrane; Ethan C Hill; Cory M Smith; Glen O Johnson; Richard J Schmidt; Joel T Cramer Journal: Eur J Appl Physiol Date: 2015-07-10 Impact factor: 3.078