Prior heat exposure diminishes upper-body endurance work capacity and maximal arm and leg strength in young men

Workers often experience heat exposure before manual labour. This study investigated whether prior heat exposure diminished upper-body endurance work capacity and maximal isokinetic arm and leg strength in young men. Ten male participants completed two trials in a climatic chamber maintained at 25°C with 50% relative humidity. The two trials required them to complete a 30-min pre-exercise water-immersion at either 40°C (HOT) to provoke an approximately 1°C rise in rectal temperature (T_re) or 36°C (CON) to maintain a normal T_re. Pre- and post-immersion and following arm-cranking, isokinetic maximal voluntary contraction (MVC) torque was assessed for the elbow flexors and knee extensors. During arm-cranking, time to exhaustion was measured using arm crank ergometry at 60% peak oxygen uptake. Electromyography was recorded from the elbow flexors and knee extensors to calculate the integrated electromyography. T_re at post-immersion was higher in HOT (Mean ± SD, 38.1 ± 0.3°C) than CON (37.1 ± 0.3°C; P < 0.01). Time to exhaustion was less in HOT (41 ± 13 min) than CON (52 ± 12 min; P < 0.01). Isokinetic MVC torque in the elbow flexors and knee extensors was lower in HOT than CON (both P < 0.05). The integrated electromyography of the elbow flexors and knee extensors were lower in HOT than CON (both P < 0.05). This study indicates that a 1°C rise in T_re by prior heat exposure reduces time to exhaustion during arm-cranking and isokinetic MVC torque of the elbow flexors and knee extensors. Workers should be careful about reductions in upper-body endurance work capacity and maximal arm and leg strength when exposed to heat before manual labour.