Comparison of six methods for force normalization in muscles from malnourished rats.

We have investigated six methods for normalizing isometric force in skeletal muscles from malnourished rats. Adult male Wistar rats were anesthetized, and the maximum isometric force production of soleus and extensor digitorum longus (EDL) muscles was measured after a 2-d fast or 1 wk of hypocaloric feeding. The force was expressed per unit muscle wet weight, dry weight, cross-sectional area, total creatine, total protein, and myofibrillar protein. We found that the absolute force of the muscles (N) and the force expressed in relation to total creatine were similar in muscles from fasted, hypocaloric, and control rats. Regardless of the method of normalization, forces produced by soleus muscles from fasted rats were the same as control values. Force expressed in relation to wet weight, dry weight, cross-sectional area, and total protein was greater in muscles from malnourished animals except for the soleus muscles from fasted rats. Force per mg myofibrillar protein was greater in the EDL muscles from fasted and hypocaloric rats than in controls, but the values for the soleus muscles were similar in the three groups. The data indicate that different methods of force normalization can lead to different conclusions concerning the ability of muscles to generate force after nutritional intervention.