Rehabilitative Exercise Training Increases Skeletal Muscle Contractile and Metabolic Function in Severely Burned Children

Abstract

Wasting and deconditioning of skeletal muscle contributes to the prolonged morbidity observed in burn victims. PURPOSE: To study the impact of rehabilitative exercise training (RET) on skeletal muscle contractile and metabolic function in children recovering from major burns. METHODS: Twenty-one children (7-18 years) with burns covering ≥30% of their total body surface area were studied at approximately three and six months post-injury. Body composition, muscle strength (peak torque) and endurance (total work), insulin sensitivity (euglycemic-hyperinsulinemic clamp), and mitochondrial function (muscle biopsies) measurements were performed at each study. In the twelve intervening weeks, n=8 patients received standard rehabilitative care including occupational and physical therapy (standard of care, SoC), while n=13 patients performed a 12-week supervised outpatient RET program in addition to receiving standard care. RET consisted of progressive resistive and aerobic exercise performed at least 5-times weekly. RESULTS: Total and fat-free body mass significantly increased in the RET group only (P<0.05). Peak torque significantly increased with RET (+51%, P<0.001) but not in SoC (+35%, P=0.08). Total work significantly increased with RET (+66%, P<0.001) but not in SoC (+44%, P=0.23). Insulin stimulated glucose disposal tended to decrease in the SoC group (1.87±0.31 vs. 1.35±0.24 mg/min/kg; P=0.07) but significantly increased in the RET group (1.12±0.11 vs. 1.59±0.10 mg/min/kg; P=0.004). ADP-dependent mitochondrial respiration increased with RET (25.0±4.3 vs. 52.8±4.1 pmol/s/mg; P<0.001) but not SoC (37.6±4.7 vs. 41.7±6.4 pmol/s/mg). The mitochondrial respiratory control ratio for ADP increased with RET (1.54±0.12 vs. 2.27±0.12 pmol/s/mg; P=0.01) but not SoC (1.72±0.12 vs. 1.45±0.07). CONCLUSIONS: In agreement with previous studies, RET increases muscle strength and endurance in burn survivors. Here, we show that this is accompanied by increased peripheral insulin stimulated glucose disposal and skeletal muscle mitochondrial respiratory capacity and coupling control. These data demonstrate that in addition to contractile function, RET improves skeletal muscle metabolic function in burn survivors.