Paralytic and nonparalytic muscle adaptations to exercise training versus high-protein diet in individuals with long-standing spinal cord injury

Abstract

This study compares the effects of an 8-wk isocaloric high-protein (HP) diet versus a combination exercise (Comb-Ex) regimen on paralytic vastus lateralis (VL) and nonparalytic deltoid muscle in individuals with long-standing spinal cord injury (SCI). Fiber-type distribution, cross-sectional area (CSA), levels of translation initiation signaling proteins (Erk-1/2, Akt, p70S6K1, 4EBP1, RPS6, and FAK), and lean thigh mass were analyzed at baseline and after the 8-wk interventions. A total of 11 participants (C5-T12 levels, 21.8 ± 6.3 yr postinjury; 6 Comb-Ex and 5 HP diet) completed the study. Comb-Ex training occurred 3 days/wk and consisted of upper body resistance training (RT) in addition to neuromuscular electrical stimulation (NMES)-induced-RT for paralytic VL muscle. Strength training was combined with high-intensity arm-cranking exercises (1-min intervals at 85-90%, V̇o_2peak) for improving cardiovascular endurance. For the HP diet intervention, protein and fat each comprised 30%, and carbohydrate comprised 40% of total energy. Clinical tests and muscle biopsies were performed 24 h before and after the last exercise or diet session. The Comb-Ex intervention increased Type IIa myofiber distribution and CSA in VL muscle and Type I and IIa myofiber CSA in deltoid muscle. In addition, Comb-Ex increased lean thigh mass, V̇o_2peak, and upper body strength ( P < 0.05). These results suggest that exercise training is required to promote favorable changes in paralytic and nonparalytic muscles in individuals with long-standing SCI, and adequate dietary protein consumption alone may not be sufficient to ameliorate debilitating effects of paralysis. NEW & NOTEWORTHY This study is the first to directly compare the effects of an isocaloric high-protein diet and combination exercise training on clinical and molecular changes in paralytic and nonparalytic muscles of individuals with long-standing spinal cord injury. Our results demonstrated that muscle growth and fiber-type alterations can best be achieved when the paralyzed muscle is sufficiently loaded via neuromuscular electrical stimulation-induced resistance training.

Keywords: diet; exercise; fiber type; skeletal muscle; spinal cord injury.

Fig. 1.

Effects of high-protein (HP) diet and combination exercise (Comb-Ex) training on muscle fiber cross-sectional area (CSA; μm²) in nonparalytic deltoid and paralytic vastus lateralis (VL) muscle in individuals with long-standing spinal cord injury (SCI). Values are expressed as means ± SE *P < 0.05, different from Pre-Comb-Ex. Dot plots show the complete data set.

Fig. 2.

Effects of high-protein (HP) diet and combined exercise (Comb-Ex) training on muscle fiber-type distribution (%) in nonparalytic deltoid and paralytic vastus lateralis (VL) muscle in individuals with long-standing spinal cord injury (SCI). Values are expressed as means ± SE *P < 0.05, different from Pre-Comb-Ex. Dot plots represent the complete data set.

Fig. 3.

Representative immunoblots for 12 studied proteins and loading control (β-actin) in nonparalytic deltoid and paralytic vastus lateralis (VL) in combined exercise (Comb-Ex) vs. high-protein (HP)-diet group. The samples were loaded in the order as shown. 0DD = week 0, deltoid-diet; 0DE = week 0, deltoid-exercise; 0VLD = week 0, VL-diet; 0VLE: week 0, VL-exercise; 8DD = week 8 deltoid-diet; 8DE = week 8 deltoid-exercise; 8VLD = week 8, VL-diet; 8VLE = week 8, VL-exercise. Total and phosphorylated proteins were blotted in two separate membranes.