Mechanical properties of rabbit latissimus dorsi muscle after stretch and/or electrical stimulation

The work loop technique was used to measure the mechanical performance in situ of the latissimus dorsi (LD) muscles of rabbits maintained under fentanyl anesthesia. After 3 wk of incrementally applied stretch the LD muscles were 36% heavier, but absolute power output (195 mW/muscle) was not significantly changed relative to that of external control muscle (206 mW). In contrast, continuous 10-Hz electrical stimulation reduced power output per kilogram of muscle >75% after 3 or 6 wk and muscle mass by 32% after 6 wk. When combined, stretch and 10-Hz electrical stimulation preserved or increased the mass of the treated muscles but failed to prevent an 80% loss in maximum muscle power. However, this combined treatment increased fatigue resistance to a greater degree than electrical stimulation alone. These stretched/stimulated muscles, therefore, are more suitable for cardiomyoplasty. Nonetheless, further work will be necessary to find an ideal training program for this surgical procedure.