Effects of Upper-Extremity Heat Stress Combined with Resistance Training on Skill and Basal Fitness, Isokinetic Muscle Strength, and Anabolic Hormones in Wheelchair Rugby Athletes with Spinal Cord Injury

Background: This study aimed to investigate the effects of upper-extremity heat stress combined with resistance training and resistance training alone on body composition, skill and basal fitness, isokinetic muscle strength, and anabolic hormone levels in wheelchair rugby athletes with spinal cord injury.Methods: Fourteen male national wheelchair rugby athletes with cervical-level spinal cord injury were randomly assigned to the heat stress combined with resistance training (n=7) or resistance training group (n=7). Both groups completed a 10-week upper-extremity resistance training program. Additionally, heat stress was applied to the upper-extremity of the heat stress combined with resistance training group using steam-generating thermal sheets three times per week. Measurements conducted pre- and post-intervention included body composition, skill and basal fitness (one-hand throw, chest throw, 28 m shuttle sprint, and 20 m sprint), isokinetic strength (using the Cybex system at 60°/sec and 180°/sec), and anabolic hormones (growth hormone and insulin-like growth factor). Non-parametric tests (Wilcoxon signed-rank and Mann-Whitney U test) were used for statistical analysis (α=0.05).Results: The heat stress combined with resistance training group showed significant increases in skeletal muscle mass and upper-extremity isokinetic elbow joint strength, particularly in flexion (%BW) and extension (%BW) at 60°/sec. Growth hormone levels increased significantly only in this group, while insulin-like growth factor levels showed marginal improvement. Both groups improved in 28 m shuttle sprint and one-hand throw; however, the heat stress combined group showed a greater effect size in the 20 m sprint. No significant changes were observed in body mass index or body fat percentage.Conclusions: The combination of heat stress and resistance training may provide additional benefits in enhancing upper-extremity muscle strength and stimulating anabolic hormone responses in wheelchair rugby athletes with spinal cord injury. These findings suggest a promising and practical strategy for optimizing training adaptations in this athletic population.