Independent Influence of Spinal Cord Injury Level on Thermoregulation during Exercise.

PURPOSE: 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: 31 trained males (8 tetraplegic (TP; C5-C8), 7 high paraplegic (HP; T1-T5), 8 low paraplegic (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 (RH). 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±0.32°C vs. 0.29±0.07°C, p<0.001), and greater in HP compared to LP and AB, reaching 1.20±0.50°C, 0.66±0.23°C and 0.53±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, while 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 mg·cm·min 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±0.93°C, HP: 2.73±0.68°C, LP: 2.92±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 tetraplegia due to minimal evaporative heat loss secondary to an absence of sweating.