Contribution of mono- and biarticular muscles to extending knee joint moments in runners and cyclists.
Motor actions are governed by coordinated activation of mono- and biarticular muscles. This study considered differences in mono- and biarticular knee extensors between runners and cyclists in the context of adaptations to task-specific movement requirements. Two hypotheses were tested: 1) the length-at-use hypothesis, which is that muscle adapts to have it operate around optimal length; and 2) the contraction-mode hypothesis, which is that eccentrically active muscles prefer to operate on the ascending limb of the length-force curve. Ten runners and ten cyclists performed maximal, isometric knee extensions on a dynamometer at five knee and four hip joint angles. This approach allowed the separation of the contribution of mono- and biarticular extensors. Three major differences occurred: 1) compared with runners, monoarticular extensors of cyclists reach optimal length at larger muscle length; 2) in runners, optimal length of the biarticular extensor is shifted to larger lengths; and 3) the moment generated by monoarticular extensor was larger in cyclists. Mono- and biarticular extensors respond to different adaptation triggers in runners and cyclists. Monoarticular muscles seem to adapt to the length-at-use, whereas biarticular muscles were found to be sensitive to the contraction-mode hypothesis.
Savelberg
H H C M
HH
Department of Human Movement Science, Nutrition and Toxicology Research Institute Maastricht, Faculty of Health Sciences, Universiteit Maastricht, NL-6200 MD Maastricht, The Netherlands. hans.savelberg@bw.unimaas.nl
Meijer
K
K
D000222:Adaptation, Physiological; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D005260:Female; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology*; D012420:Running / Q000502:physiology*