Effect of continuous stimulation on force development in mouse soleus. Muscles from 12.5-wk-old WT and mutant mice were mounted in force transducers for isometric contractions and stimulated for the indicated time using 0.2-ms pulses at 12 V and 120 Hz. Each point represents the mean of observations on four muscles, with error bars denoting SEM. (A) Force in milliNewtons; (B) force in percentage of the initial value. The difference between mutants and WT was significant at the times indicated by the asterisks and p-values.