Synergist muscle ablation and recovery from nerve-repair grafting: contractile and metabolic function

Abstract

After nerve-repair grafting of medial gastrocnemius muscle, there is incomplete recovery of specific force and sustainable power, perhaps due to overcompensation by synergistic muscles. We hypothesized that increased workload due to synergist ablation would enhance graft recovery. Contractile and metabolic properties of control and nerve-repair grafted muscles, with and without synergist ablation, were determined after 120 days recovery. Specific force (N/cm(2)) and normalized power (W/kg) were less in the experimental groups compared with controls. Sustained power (W/kg) in the synergist-ablated nerve-repair grafted muscle was higher than nerve-repair grafted muscle, returning to control values. GLUT-4 protein was higher and glycogen content was diminished in both synergist-ablated groups. In summary, synergist ablation did not enhance the recovery of specific force or normalized power, but sustained power did recover, suggesting that metabolic and not mechanical parameters were responsible for this recovery. The enhanced endurance after synergist ablation was accompanied by increased GLUT-4 protein, suggesting a role for increased uptake of circulating glucose during contraction.

Fig. 1

Sustained power developed at increasing duty cycles in control (A) and grafted (B) medial gastrocnemius muscles in 6-mo-old male Fischer 344 rats. A stimulation frequency (100 Hz) and train duration (67 ms) that produced ~75% of maximum power in both the control and grafted muscles was used for all tests of sustained power. Values are means ± SE; n, no. of rats. A: at each duty cycle, normalized sustained power of the synergist-ablated control muscle was slightly, but significantly, less compared with values for sham control muscles (P = 0.0133; repeated-measures ANOVA). B: normalized sustained power of the synergist-ablated nerve-repair grafted muscle was significantly greater compared with values for nerve-repair grafted muscle (P = 0.0038; repeated-measures ANOVA). There was no significant difference in the ability to sustain power in the synergist-ablated nerve-repair grafted muscle compared with the sham control muscle.