Torque-velocity relation and muscle fibre characteristics of foot dorsiflexors after long-term overuse of residual muscle fibres due to prior polio or L5 root lesion
Tollbäck A, Knutsson E, Borg J, Borg K, Jakobsson F
Department of Neurology, Söder Hospital, Stockholm, Sweden
Isokinetic foot dorsiflexion strength and muscle biopsy data from eight patients with overuse of tibialis anterior muscle (TA) fibres due to weakness after prior polio or L5 root lesion were compared to data from age and sex matched, healthy subjects. Concentric peak torque at an angular velocity of 30 degrees/s was 6-24 Nm in the patients and 15-34 Nm in the controls (p < 0.01). Muscle biopsies from TA showed a significantly higher proportion of type 1 fibres in the patients as compared to the controls (p < 0.005). The type 1 fibres in the patients had a significantly larger cross-sectional area than in the controls (p < 0.005). The type 1 fibre proportion and relative area were inversely correlated to the relative concentric torque produced at 180 degrees/s (p < 0.05) and 240 degrees/s (p < 0.05) compared to that produced at 30 degrees/s in the controls but not in the patients. However, the relative concentric torque produced at 180 degrees/s and 240 degrees/s compared to that produced at 30 degrees/s was not significantly different in the patients and the controls. This indicates that the contractile properties of the overused muscle fibres do not change in parallel with the histochemical fibre type.
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