No abstract

Background-The objective of this study was to investigate changes in active and passive biomechanical properties of the calf muscle-tendon unit induced by controlled ankle stretching in stroke survivors.

Biomechanical properties of calf muscles and Achilles tendon may be altered considerably in children with cerebral palsy (CP), contributing to childhood disability. It is unclear how muscle fascicles and tendon respond to rehabilitation and contribute to improvement of ankle-joint properties. Biomechanical properties of the calf muscle fascicles of both gastrocnemius medialis (GM) and soleus (SOL), including the fascicle length and pennation angle in seven children with CP, were evaluated using ultrasonography combined with biomechanical measurements before and after a 6-wk treatment of passive-stretching and active-movement training. The passive force contributions from the GM and SOL muscles were separated using flexed and extended knee positions, and fascicular stiffness was calculated based on the fascicular force-length relation. Biomechanical properties of the Achilles tendon, including resting length, cross-sectional area, and stiffness, were also evaluated. The 6-wk training induced elongation of muscle fascicles (SOL: 8%, P = 0.018; GM: 3%, P = 0.018), reduced pennation angle (SOL: 10%, P = 0.028; GM: 5%, P = 0.028), reduced fascicular stiffness (SOL: 17%, P = 0.128; GM: 21%, P = 0.018), decreased tendon length (6%, P = 0.018), increased Achilles tendon stiffness (32%, P = 0.018), and increased Young's modulus (20%, P = 0.018). In vivo characterizations of calf muscles and Achilles tendon mechanical properties help us better understand treatment-induced changes of calf muscle-tendon and facilitate development of more effective treatments.

Gao F, Zhang L-Q. Altered contractile properties of the gastrocnemius muscle post stroke. J Appl Physiol 105: 1802-1808, 2008. First published October 23, 2008 doi:10.1152/japplphysiol.90930.2008.-Spasticity, contracture and muscle weakness often occur together poststroke and cause considerable motor impairments to stroke survivors. The underlying changes in contractile properties of muscle fascicles are still not clear. The purpose of this study was to investigate the contractile property changes of the medial gastrocnemius muscle fascicles poststroke. Ten stroke survivors and ten healthy subjects participated in the study. The medial gastrocnemius fascicular length was measured at various combinations of ankle and knee positions using ultrasonography, with the muscle activated selectively using electrical stimulation. The stimulation intensity was kept constant across different ankle and knee positions to establish the active force-length relationship of the muscle fascicles. It was found that stroke survivors showed a shift of the force-length curve with a significantly shorter optimal fascicle length (33.2 Ϯ 3.2 mm) compared with that of healthy controls (47.4 Ϯ 2.7 mm) with P Ͻ 0.001. Furthermore, the width span of the fascicular force-length curve of stroke survivors was significantly narrower with steeper slopes than that of controls (P Յ 0.001), suggesting reduced number of sarcomeres along the fascicles and/or reduced sarcomere length poststroke. Regression analysis showed that the medial gastrocnemius fascicular length of stroke survivors varied significantly less with ankle and knee flexions (P Յ 0.001) than that of controls, suggesting shorter and stiffer muscle fascicles poststroke, which might be attributed to muscle architectural adaptation. This study showed that there are considerable changes in the contractile properties of muscle fascicles poststroke, which may contribute directly to the joint-level changes of decreased range of motion, increased stiffness, muscle weakness, and impaired motor functions in stroke survivors. stroke; ultrasound; muscle fascicle; force length; spasticity; gastrocnemius STROKE SURVIVORS OFTEN DEVELOP spasticity, contractures, and muscle weakness, which severely affect their daily activities (33). Clinically, the ankle is often affected post stroke, with ϳ60% of stroke survivors discharged from in-patient rehabilitation requiring an ankle orthosis and ϳ34% of stroke survivors developing ankle contracture (38,39,47). The impaired ankle dorsiflexion poststroke makes it hard for the foot to clear the ground in the early swing phase during locomotion, and the associated lack of ankle plantar flexion results in reduced forward propulsion (47, 52). Although poststroke biomechanical changes at ankle have been investigated in a number of studies, there is a lack of evaluation on the changes of contractile properties of muscle fascicles.Ultrasonography has been used in recent studies to investigate muscle/tendon functions in vivo and noninvasively (10,11,16,18,21,24,26,29,3...

The changes in Achilles tendon properties could be a result of adaptation to calf muscle fascicle shortening and stiffening, which may affect performance of the muscles. A better understanding of the interactions between calf muscle fascicles and Achilles tendon in children with CP may help treat the pathologic changes more effectively.