A study of the contractile force and fatigue resistance of the latissimus dorsi muscle of growing lambs

Abstract

In adult organisms, when stimulation of skeletal muscle is stopped, all changes revert to control after 10–14 days. This is the reason that training of the skeletal muscle before cardiomyoplasty is not done. We hypothesized that the muscle of a growing organism would not revert during a delay. Four lambs received 8 weeks of electrical stimulation of the left latissimus dorsi muscle (LDM) with the right LDM as control. Contractility force and positive and negative dF/dt were measured after 8 weeks conditioning, 2 weeks delay, and control. Conditioned muscle during a 30-minute fatigue test had decreased contractile force on an average of 7 ± 2%; control muscle had decreased contractile force on an average of 39 ± 4%; and after 2 weeks delay, there was a decrease in the contractile force of 12 ± 2%. A stronger fatigue test was performed after 10 minutes of rest. Conditioned muscle lost an average of 15 ± 5% of their contractile force, 16 ± 2% positive dF/dt, and 14 ± 2% negative dF/dt. Control muscle lost 40 ± 3%, 39 ± 4%, and 42 ± 5%, respectively. After 2 weeks delay, previously conditioned muscle showed the following decreases: contractile force 21 ± 3%, positive dF/dt 19 ± 3%, and negative dF/dt 16 ± 3%. Skeletal muscle biopsies were also taken and levels of lactate dehydrogenase (LDH) fractions were measured. LDH fractions one and two (LDH-1 + 2) after 8 weeks conditioning consisted of 6.7 ± 1.9% (p <0.05 vs control) of total LDH, 7.2 ± 1.5% (p <0.05 vs control) after 2 weeks delay, and 2.5 ± 0.9% in control muscle. LDH-5 levels decreased to 77 ± 8%, 68 ± 3%, and 91 ± 5%, respectively. Percent of mitochondrial area on conditioned muscle increased and remained elevated after the delay. There was good correlation between fatigue resistance in conditioned and delay muscles with decreasing total units LDH, decreasing LDH-5, and increasing LDH-1 + 2 levels (compared with control muscle). Contractile force, LDH, and mitochondrial data in the delay muscle more closely resemble conditioned muscle than control. This may be very useful for clinical congenital heart surgery.