Voluntary low-force contraction elicits prolonged low-frequency fatigue and changes in surface electromyography and mechanomyography.
Controversies exist regarding objective documentation of fatigue development with low-force contractions. We hypothesized that non-exhaustive, low-force muscle contraction may induce prolonged low-frequency fatigue (LFF) that in the subsequent recovery period is detectable by electromyography (EMG) and in particular mechanomyography (MMG) during low-force rather than high-force test contractions. Seven subjects performed static wrist extension at 10% maximal voluntary contraction (MVC) for 10 min (10%MVC10 min). Wrist force response to electrical stimulation of extensor carpi radialis muscle (ECR) quantified LFF. EMG and MMG were recorded from ECR during static test contractions at 5% and 80% MVC. Electrical stimulation, MVC, and test contractions were performed before 10%MVC10 min and at 10, 30, 90 and 150 min recovery. In spite of no changes in MVC, LFF persisted up to 150 min recovery but did not develop in a control experiment omitting 10%MVC10 min. In 5% MVC tests significant increase was found in time domain of EMG from 0.067+/-0.028 mV before 10%MVC10 min to 0.107+/-0.049 and 0.087+/-0.05 mV at 10 and 30 min recovery, respectively, and of the MMG from 0.054+/-0.039 ms(-2) to 0.133+/-0.104 and 0.127+/-0.099 ms(-2), respectively. No consistent changes were found in 80% MVC tests. In conclusion, non-exhaustive low-force muscle contraction resulted in prolonged LFF that in part was identified by the EMG and MMG signals.
Blangsted
Anne Katrine
AK
Department of Physiology, National Institute of Occupational Health, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark. akb@ami.dk
Sjøgaard
Gisela
G
Madeleine
Pascal
P
Olsen
Henrik Baare
HB
Søgaard
Karen
K
D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D009213:Myography / Q000379:methods*; D005082:Physical Exertion / Q000502:physiology; D013314:Stress, Mechanical; D013997:Time Factors; D014953:Wrist / Q000502:physiology