ISOKINETIC STRENGTH, MACRO EMG AND MUSCLE BIOPSY OF PARETIC FOOT DORSIFLEXORS IN CHRONIC NEUROGENIC PARESIS

Ten ambulatory patients with chronic dorsiflexor paresis due to prior poliomyelitis or lumbar root (LV) lesion and without recent decline of the foot dorsiflexor strength were examined with isokinetic strength measurement, macro EMG and muscle biopsy. Isokinetic strength measurem ent showed peak torques at 30 degrees/s angular velocity ranging 6-44 Nm and at 240 degrees/s 1-10 Nm. Mean of individual median macro EMG m otor unit potential amplitudes was 2020 mu V (SD 1040) which was 5-10 times higher than expected values in healthy subjects. Muscle biopsies showed a mean type 1 fibre proportion of 91% (SD 14) and a mean type 1 fibre area of 8561 mu m(2) (SD 2773) which was about 2 times larger than those observed in healthy subjects. Peak torque and both motor un it potential amplitude and area were inversely correlated at 30 (p < 0 .01 and p < 0.025), 60 (p < 0.025 and p < 0.025) and 120 (p < 0.05 and p < 0.05) degrees/s angular velocity, as were peak torque and type 1 muscle fibre proportion at 30 (p < 0.05) and 60 (p < 0.05) degrees/s a ngular velocity. Peak torque or macro EMG parameters were not correlat ed to muscle fibre area. The data suggest that the remaining muscle st rength was directly correlated to the degree of collateral sprouting a nd that about half of it could be attributed to compensatory muscle fi bre hypertrophy.