Does 20-min arm crank ergometer exercise increase plasma interleukin-6 in individuals with cervical spinal cord injury?

Interleukin-6 (IL-6) is produced by contracting skeletal muscles and then released into the circulation and considered to mediate the health benefits of exercise against chronic diseases. Individuals with spinal cord injury (SCI) are reported to be at higher risk of developing metabolic diseases. We investigated the IL-6 responses to 20-min arm crank ergometer exercise at 60% of maximum oxygen consumption in eight trained individuals with cervical SCI (CSCI) between C6 and C7, and eight able-bodied trained healthy subjects. The plasma concentrations of IL-6, adrenaline, prostaglandin E(2) and cortisol were measured before, immediately after the exercise, 1 and 2 h after exercise. At rest, the plasma adrenaline concentration was significantly lower in individuals with CSCI than in able-bodied subjects (P < 0.01). On the other hand, the concentration of IL-6 was significantly higher at rest in individuals with CSCI (2.18 ± 0.44 pg/ml, mean ± SEM) than the control (1.02 ± 0.22 pg/ml, P < 0.05). In able-bodied subjects, the plasma adrenaline concentration increased significantly immediately after the exercise (P < 0.01) and returned to the baseline level at 1 h after exercise, and the plasma IL-6 level increased significantly at 1 h after exercise (1.91 ± 0.28 pg/ml, P < 0.05) and returned to the baseline level at 2 h after exercise. In contrast, adrenaline and IL-6 levels were steady throughout the study in individuals with CSCI. The lack of exercise-related IL-6 response in individuals with CSCI could be due to muscle atrophy and sympathetic nervous system dysfunction.