Quantification of muscle strength in recessive myotonia congenita

In order to quantify muscle strength in recessive myotonia congenita (MC) the peak and average peak torques (PT and APT, respectively) of knee flexion and extension of 19 MC patients were measured at speeds of 60 degrees/s and 200 degrees/s. Muscle endurance was measured at a speed of 200 degrees/s. No differences were found between the patient and control groups for PT and APT values for flexion at the high speed, nor were there any differences between the patients and the controls for PT and APT measured at the low speed for knee flexion and extension or muscle endurance at the high speed. However, PT and APT values of the patients for extension at the high speed, 100 +/- 41 Nm (mean +/- SD) and 95 +/- 39, were significantly lower than those of the controls, 129 +/- 43 and 124 +/- 42, respectively. There was no correlation between muscle strength or endurance and disease severity. The muscle strength of the patient group was diminished (p < 0.0001) during the beginning of the measurement at the high speed. The results suggest that after myotonic inhibition subsides the muscle strength of MC patients ranges within normal limits except in rapid and powerful motor activities.