Purpose: This study aimed to establish the true influence of spinal cord injury (SCI) level on core temperature and sweating during exercise in the heat independently of biophysical factors.
Methods: A total of 31 trained males (8 with tetraplegia [TP; C5-C8], 7 with high paraplegia [HP; T1-T5], 8 with low paraplegia [LP; T6-L1], and 8 able bodied [AB]) performed 3 × 10 min of arm ergometry with 3-min rest at a metabolic heat production of (a) 4.0 W·kg (AB vs TP) or (b) 6.0 W·kg (AB vs HP vs LP), in 35°C, 50% relative humidity. Esophageal (Tes) and local skin temperatures and local sweat rate (LSR) on the forehead and upper back were measured throughout.
Results: Change in Tes was greatest in TP (1.86°C ± 0.32°C vs 0.29°C ± 0.07°C, P < 0.001) and greater in HP compared with LP and AB, reaching 1.20°C ± 0.50°C, 0.66°C ± 0.23°C, and 0.53°C ± 0.12°C, respectively (P < 0.001). Approximately half of the variability in end-trial ΔTes was described by SCI level in paraplegics (adjusted R = 0.490, P = 0.005). Esophageal temperature onset thresholds of sweating at the forehead and upper back were similar among HP, LP, and AB, whereas no sweating was observed in TP. Thermosensitivity (ΔTes vs ΔLSR) was also similar, except for LP demonstrating lower thermosensitivity than AB at the upper back (0.78 ± 0.26 vs 1.59 ± 0.89 mg·cm·min, P = 0.039). Change in skin temperature was greatest in denervated regions, most notably at the calf in all SCI groups (TP, 2.07°C ± 0.93°C; HP, 2.73°C ± 0.68°C; LP, 2.92°C ± 1.48°C).
Conclusion: This study is the first to show the relationship between ΔTes and SCI level in athletes with paraplegia after removing variability arising from differences in metabolic heat production and mass. Individual variability in ΔTes is further reduced among athletes with TP because of minimal evaporative heat loss secondary to an absence of sweating.