[Relation between muscle energetics and the strength, shortening and work of the muscle]

The rat isolated m. soleus perfused with bicarbonate buffer at 37 degrees C performed rhythmic work either with different loads and constant shortening or vice versa. The interrelationship between the work and the energy expenditure was the same in both cases. The energetic equivalence of strength and shortening at small loads in the skeletal muscle seems obvious as well as the absence of energy expenditure for shortening in the complete energetic cycle of muscle contraction, irrespective of the work. The energetic role of strength and shortening in the heart muscle is discussed.