title: Fatigue-induced changes in synergistic muscle force do not match tendon elongation.
abstract: This study aimed to investigate whether fatigue-induced changes in synergistic muscle forces match their tendon elongation. The medial gastrocnemius muscle (MG) was fatigued by repeated electrical stimulation (1 min x 5 times: interval 30 s, intensity: 20-30% of maximal voluntary plantar flexion torque) applied at the muscle belly under a partial occlusion of blood vessels. Before and after the MG fatigue task, ramp isometric contractions were performed voluntarily, during which tendon elongations were determined by ultrasonography, along with recordings of the surface EMG activities of MG, the soleus (SOL) and the lateral gastrocnemius (LG) muscles. The tendon elongation of MG and SOL in post-fatigue ramp was similar, although evoked MG forces dropped nearly to zero. In addition, for a given torque output, the tendon elongation of SOL significantly decreased while that of LG did not, although the activation levels of both muscles had increased. Results suggest that the fatigue-induced changes in force of the triceps surae muscles do not match their tendon elongation. These results imply that the tendons of the triceps surae muscles are mechanically coupled even after selective fatigue of a single muscle.
authors.affiliation: Graduate School of Sport Sciences, Waseda University, Japan.
authors.forename: Naotoshi
authors.initials: N
authors.lastname: Mitsukawa
authors.forename: Norihide
authors.initials: N
authors.lastname: Sugisaki
authors.forename: Naokazu
authors.initials: N
authors.lastname: Miyamoto
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Yanai
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kanehisa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukunaga
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
mesh_terms: D000328:Adult; D003198:Computer Simulation; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D013710:Tendons / Q000502:physiology*