Weight losses in the dog's gastroenemius and anterior tibial muscles were measured after periods of denervation under a variety of conditions of fixation or lack of fixation of the limb involved.

The smallest loss in the gastroenemius and the greatest loss in the tibialis anterior occurred in the group with limbs left unfixed. As the animal used the denervated limb for some weight-bearing when standing, the gastroenemius was stretched and the tibialis anterior was shortened.

In the unfixed limbs and in limbs fixed with gastroenemius muscles lengthened and anterior tibial muscles shortened, weight losses were much less in the gastroenemius muscles than in the tibialis anterior (P < 0.01).

Losses in gastroenemius and anterior tibial muscles were not significantly different in limbs fixed in the neutral position and fixed with the gastroenemius muscle shortened and the anterior tibial muscle lengthened.

The passively lengthened position provides an important degree of protection against weight loss as compared with the shortened position in the denervated gastroenemius muscle, but comparable protection was not found in the tibialis anterior. Measurements of blood flow through these muscles in the lengthened and shortened positions have not shown significant differences related to these procedures. Reasons for the differences demonstrated remain unknown.