Effects on torque angle curve of differences between the recorded tibia-calcaneal angle and the true anatomical angle

The present study gives the results of a comparison of the recorded and true tibia-calcaneal angles in 17 normal subjects and in 14 patients with abnormally hypoextensible non contracting triceps. 1. For a minimal passive torque, the difference between true and recorded angles varied considerably from one individual to another. The means and ranges for the two groups were respectively: −8‡ (+7‡, −21‡) and −7‡ (+5‡, −20‡). 2. When the passive torque increased as a result of slow passive lengthening of the muscle, the true curve was steeper than the recorded one, owing to differences between the two angle measurements. For each of the two groups the differences in means and ranges were respectively: 6‡ (0‡, +13.5‡) and 8‡ (3‡, 12‡). 3. Subjects made isometric voluntary contractions of the triceps surae at fixed angles which corresponded to step by step muscle lengthening. The resulting true curve was much steeper than the recorded curve. The differences in means and ranges were: 7‡ (1.5‡, +15‡) in children of the two groups and respectively 3‡ (0‡, +9‡) and 12‡ (10‡, 14‡) in adults of the two groups. The present results show that this methodology was the only reliable way of correctly obtaining passive and active torque-angle curves, measuring differences between subjects, appreciating the effects of treatments and these by ascertaining whether or not trophic muscle regulation was defective.