Muscle fascicle strains in human gastrocnemius during backward downhill walking

Hoffman, B. W. and Cresswell, A. G. and Carroll, T. J. and Lichtwark, G. A. (2014) Muscle fascicle strains in human gastrocnemius during backward downhill walking. Journal of Applied Physiology, 116 (11). pp. 1455-1462. ISSN 8750-7587

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Extensive muscle damage can be induced in isolated muscle preparations by performing a small number of stretches during muscle activation. While typically these fiber strains are large and occur over long lengths, the extent of exercise-induced muscle damage (EIMD) observed in humans is normally less even when multiple high-force lengthening actions are performed. This apparent discrepancy may be due to differences in muscle fiber and tendon dynamics in vivo; however, muscle and tendon strains have not been quantified during muscle-damaging exercise in humans. Ultrasound and an infrared motion analysis system were used to measure medial gastrocnemius fascicle length and lower limb kinematics while humans walked backward, downhill for 1 h (inducing muscle damage), and while they walked briefly forward on the flat (inducing no damage). Supramaximal tibial nerve stimulation, ultrasound, and an isokinetic dynamometer were used to quantify the fascicle length-torque relationship pre- and 2 h postexercise. Torque decreased ~23%, and optimal fascicle length shifted rightward ~10%, indicating that EIMD occurred during the damage protocol even though medial gastrocnemius fascicle stretch amplitude was relatively small (~18% of optimal fascicle length) and occurred predominantly within the ascending limb and plateau region of the length-torque curve. Furthermore, tendon contribution to overall muscle-tendon unit stretch was ~91%. The data suggest the compliant tendon plays a role in attenuating muscle fascicle strain during backward walking in humans, thus minimizing the extent of EIMD. As such, in situ or in vitro mechanisms of muscle damage may not be applicable to EIMD of the human gastrocnemius muscle.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to published version in accordance with copyright policy of publisher.
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Health, Nursing and Midwifery
Date Deposited: 13 Feb 2018 00:31
Last Modified: 28 Aug 2018 01:02
Uncontrolled Keywords: Length-tension relationship; lengthening exercise; muscle fiber dynamics; strain-induced muscle damage; ultrasonography
Fields of Research : 11 Medical and Health Sciences > 1106 Human Movement and Sports Science > 110602 Exercise Physiology
11 Medical and Health Sciences > 1106 Human Movement and Sports Science > 110601 Biomechanics
Identification Number or DOI: 10.1152/japplphysiol.01431.2012

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