title: Frequent alternate muscle activity of plantar flexor synergists and muscle endurance during low-level static contractions as a function of ankle position.
abstract: We have investigated the appropriate joint angle for detecting frequent alternating activity in synergistic muscles and the relationship between muscle activation patterns and endurance during static low-level contractions. Eleven healthy men performed prolonged static plantar flexion of the ankle at 10% of the maximal voluntary contraction, with the ankle flexed at 100°, 110°, or 120°, while seated with the right leg in full extension. The onset of muscle activation and/or inactivation was detected using quantitative analysis, and alternate activity among muscles was detected using a threshold criterion of ×e or ×1/e multiplied by the levels of mean electromyograms (EMG) calculated at 1-min intervals. Surface EMG revealed frequent alternations of activity among the lateral and medial gastrocnemius and soleus muscles at an ankle flexion of 110°. The first alternation occurred after approximately 15 min of exercise. The number of alternations per hour was four- to sevenfold higher at 110° than at 100° or 120°. Endurance was longest and shortest at 110° and 120°, respectively. These findings suggest that synergistic motor pools activated at a specific joint angle (110°) affect muscle endurance during static low-level fatiguing tasks.
authors.affiliation: Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, 1398 Shimami, Kita-ku, Niigata City, Niigata 950-3198, Japan. hiroyuki-tamaki@nuhw.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tamaki
authors.forename: Hikari
authors.initials: H
authors.lastname: Kirimoto
authors.forename: Kengo
authors.initials: K
authors.lastname: Yotani
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Takekura
mesh_terms: D000328:Adult; D000842:Ankle / Q000502:physiology*; D004576:Electromyography; D015444:Exercise / Q000502:physiology; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D055815:Young Adult