title: The frequency of alternate muscle activity is associated with the attenuation in muscle fatigue.
abstract: Alternate muscle activity between synergist muscles has been demonstrated during low-level sustained contractions [< or =5% of maximal voluntary contraction (MVC) force]. To determine the functional significance of the alternate muscle activity, the association between the frequency of alternate muscle activity during a low-level sustained knee extension and the reduction in knee extension MVC force was studied. Forty-one healthy subjects performed a sustained knee extension at 2.5% MVC force for 1 h. Before and after the sustained knee extension, MVC force was measured. The surface electromyogram was recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles. The frequency of alternate muscle activity for RF-VL, RF-VM, and VL-VM pairs was determined during the sustained contraction. The frequency of alternate muscle activity ranged from 4 to 11 times/h for RF-VL (7.0 +/- 2.0 times/h) and RF-VM (7.0 +/- 1.9 times/h) pairs, but it was only 0 to 2 times/h for the VL-VM pair (0.5 +/- 0.7 times/h). MVC force after the sustained contraction decreased by 14% (P < 0.01) from 573.6 +/- 145.2 N to 483.3 +/- 130.5 N. The amount of reduction in MVC force was negatively correlated with the frequency of alternate muscle activity for the RF-VL and RF-VM pairs (P < 0.001 and r = 0.65 for both) but not for the VL-VM pair. The results demonstrate that subjects with more frequent alternate muscle activity experience less muscle fatigue. We conclude that the alternate muscle activity between synergist muscles attenuates muscle fatigue.
authors.affiliation: Dept. of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Meguro, Tokyo 153-8902, Japan. kouzaki@idaten.c.u-tokyo.ac.jp
authors.forename: Motoki
authors.initials: M
authors.lastname: Kouzaki
authors.forename: Minoru
authors.initials: M
authors.lastname: Shinohara
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009991:Oscillometry / Q000379:methods; D010507:Periodicity; D005082:Physical Exertion / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D013223:Statistics as Topic; D013314:Stress, Mechanical