Human spastic Gracilis muscle isometric forces measured intraoperatively as a function of knee angle show no abnormal muscular mechanics

Intraoperative experiments show relevance of inter-antagonistic mechanical interaction for spastic muscle's contribution to joint movement disorder

“…Limb 8 indicates severe movement limitations in the passive state, but shows no abnormality in the active state. Limb 2 may contradict our previous findings (Ates et al, 2013b) which show no abnormal mechanics for the spastic muscle stimulated alone. However, limb 8 agrees with them because that previous study showed no correlation between pre-operational clinical metrics and the key determinants of KA-F GRA characteristics obtained respectively in the passive or active states.…”

“…Substantial inter-subject variability has been shown in measurements of human muscle forces in previous experiments (Ates et al, 2013b;Smeulders et al, 2005;Yucesoy et al, 2010a) and also in this work. Intraoperative testing makes it possible to measure muscle forces directly at the tendon and allows for an awareness of such variability.…”

“…Recently, however, Smith et al (2011) showed that the lengths of sarcomeres in biopsy samples of GRA and semitendinosus muscles of spastic CP patients are longer than those with no muscle spasticity. So far, intraoperative studies argued against this (Ates et al, 2013b;Smeulders et al, 2004): high active forces at high lengths of the spastic muscle indicate no sarcomere overstretching. The expectation for overstretching of most sarcomeres of spastic muscle was generated without accounting for sarcomere length heterogeneity .…”

“…On the other hand, EMFT effects are highly variable across limbs. Although surgical elimination of epimuscular connections may neutralize or limit this, inter-subject variability of human muscle forces (Ates et al, 2013b;Smeulders et al, 2005;Yucesoy et al, 2010a) is important to consider and recurrence of such connections is plausible. Therefore, further research is indicated to better understand the clinical implications of our findings.…”

“…Note that clinical study conditions involve simultaneous activity of several muscles e.g., during walking. Recently, Ates et al (2013b) reported gracilis (GRA) muscle's isometric active forces as a function of knee joint angle (KA) in spastic CP patients undergoing remedial surgery. Operational joint range of force exertion of the spastic muscle stimulated alone was not narrow and the maximal muscle forces were available at intermediate or higher lengths indicating no abnormal muscular mechanics.…”