• Michelle A Cleary, Lori A Sweeney, Zebulon V Kendrick, and Michael R Sitler.
• Department of Health, Physical Education, and Recreation, Florida International University, Miami, FL 33199, USA. clearym@fiu.edu
• J Athl Train. 2005 Oct 1; 40 (4): 288-97.

ContextExercise in the heat produces cellular conditions that may leave skeletal muscle susceptible to exercise-induced microdamage. Delayed-onset muscle soreness (DOMS) is a clinical model of contraction-induced skeletal muscle injury.ObjectiveTo determine whether thermoregulation during exercise heat stress adversely affects muscle injury and the accompanying DOMS.DesignRandomized group test-retest design.SettingLaboratory.Patients Or Other ParticipantsTen healthy male volunteers were randomly assigned to either the euhydration/hyperthermic or dehydration/hyperthermic group.Intervention(S)Participants were randomly assigned to treadmill walking in a hot, humid environmental chamber (40 degrees C and 75% relative humidity) with either oral rehydration (euhydration/hyperthermic) or fluid restriction (dehydration/hyperthermic). Immediately after heat exposure and while hyperthermic, participants performed an eccentrically biased downhill run to induce DOMS.Main Outcome Measure(S)We measured DOMS characteristics pre-exercise and at 0.5, 24, 48, 72, and 96 hours postexercise.ResultsTreadmill exercise and exposure to the hot ambient environment elicited a 0.9% body mass loss for the euhydrated/ hyperthermic (mean rectal temperature after 60 minutes of heat-stress trial = 38.2 +/- 0.4 degrees C) and 3.3% body mass loss for the dehydrated/hyperthermic participants (mean rectal temperature after 60 minutes of heat-stress trial = 38.1 +/- 0.4 degrees C). Quadriceps perceived pain was significantly higher (F(5,40) = 18.717, P ConclusionsSkeletal muscle microdamage, indirectly evidenced by DOMS, was exacerbated in hyperthermic participants dehydrated by exercise in a hot ambient environment. Individuals performing novel exercise, particularly with a significant eccentric component, should use caution when training in a hot, humid environment and implement frequent rest and rehydration breaks.

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