title: A new method for measuring passive length-tension properties of human gastrocnemius muscle in vivo.
abstract: The study of muscle growth and muscle length adaptations requires measurement of passive length-tension properties of individual muscles, but until now such measurements have only been made in animal muscles. We describe a new method for measuring passive length-tension properties of human gastrocnemius muscles in vivo. Passive ankle torque and ankle angle data were obtained as the ankle was rotated through its full range with the knee in a range of positions. To extract gastrocnemius passive length-tension curves from passive torque-angle data it was assumed that passive ankle torque was the sum of torque due to structures which crossed only the ankle joint (this torque was a 6-parameter function of ankle joint angle) and a torque due to the gastrocnemius muscle (a 3-parameter function of knee and ankle angle). Parameter values were estimated with non-linear regression and used to reconstruct passive length-tension curves of the gastrocnemius. The reliability of the method was examined in 11 subjects by comparing three sets of measurements: two on the same day and the other at least a week later. Length-tension curves were reproducible: the average root mean square error was 5.1+/-1.1 N for pairs of measurements taken within a day and 7.3+/-1.2 N for pairs of measurements taken at least a week apart (about 3% and 6% of maximal passive tension, respectively). Length-tension curves were sensitive to mis-specification of moment arms, but changes in length-tension curves were not. The new method enables reliable measurement of passive length-tension properties of human gastrocnemius in vivo, and is likely to be useful for investigation of changes in length-tension curves over time.
authors.affiliation: School of Physiotherapy, University of Sydney, P.O. Box 170, Lidcombe, NSW 1825, Australia.
authors.forename: P D
authors.initials: PD
authors.lastname: Hoang
authors.forename: R B
authors.initials: RB
authors.lastname: Gorman
authors.forename: G
authors.initials: G
authors.lastname: Todd
authors.forename: S C
authors.initials: SC
authors.lastname: Gandevia
authors.forename: R D
authors.initials: RD
authors.lastname: Herbert
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods*; D003198:Computer Simulation; D004548:Elasticity; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology*; D010808:Physical Examination / Q000295:instrumentation / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology; D013314:Stress, Mechanical; D019415:Torque