Behavior of human gastrocnemius muscle fascicles during ramped submaximal isometric contractions.
Precise estimates of muscle architecture are necessary to understand and model muscle mechanics. The primary aim of this study was to estimate continuous changes in fascicle length and pennation angle in human gastrocnemius muscles during ramped plantar flexor contractions at two ankle angles. The secondary aim was to determine whether these changes differ between proximal and distal fascicles. Fifteen healthy subjects performed ramped contractions (0-25% MVC) as ultrasound images were recorded from the medial (MG, eight sites) and lateral (LG, six sites) gastrocnemius muscle with the ankle at 90° and 120° (larger angles correspond to shorter muscle lengths). In all subjects, fascicles progressively shortened with increasing torque. MG fascicles shortened 5.8 mm (11.1%) at 90° and 4.5 mm (12.1%) at 120°, whereas LG muscle fascicles shortened 5.1 mm (8.8%) at both ankle angles. MG pennation angle increased 1.4° at 90° and 4.9° at 120°, and LG pennation angle decreased 0.3° at 90° and increased 2.6° at 120°. Muscle architecture changes were similar in proximal and distal fascicles at both ankle angles. This is the first study to describe continuous changes in fascicle length and pennation angle in the human gastrocnemius muscle during ramped isometric contractions. Very similar changes occurred in proximal and distal muscle regions. These findings are relevant to studies modeling active muscle mechanics.
Neuroscience Research Australia, Randwick, New South Wales, Australia School of Medical Sciences, University of New South Wales, Randwick, New South Wales, Australia.
Martin E
ME
Héroux
Neuroscience Research Australia, Randwick, New South Wales, Australia.
Peter W
PW
Stubbs
Neuroscience Research Australia, Randwick, New South Wales, Australia r.herbert@neura.edu.au.
Robert D
RD
Herbert
D000328:Adult; D000843:Ankle Joint / Q000000981:diagnostic imaging / Q000502:physiology; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology; D011897:Random Allocation; D019415:Torque; D014463:Ultrasonography / Q000379:methods
Fascicle length; fascicle pennation angle; isometric contraction; muscle