Dehydration and Symptoms of Delayed-onset Muscle Soreness in Hyperthermic Males

Context: Exercise 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.

Objective: To determine whether thermoregulation during exercise heat stress adversely affects muscle injury and the accompanying DOMS.

Design: Randomized group test-retest design.

Setting: Laboratory.

Patients Or Other Participants: Ten 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.

Results: Treadmill 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 <or= .001) than baseline at 24 and 48 hours postexercise, following the classic pattern of DOMS. Overall lower extremity perceived pain was significantly higher for the dehydration/hyperthermia group than the euhydration/hyperthermia group (F(1,8) = 6.713, P = .032). Punctate tenderness of the vastus lateralis for the dehydration/hyperthermic group was 6.9% higher (F(5,40) = 4.462, P = .003) than for the euhydration/ hyperthermic group. No clinically important findings were revealed for passive range of motion for knee flexion. For both groups, quadriceps isometric strength (F(5,40) = 12.924, P <or= .001) was 17.5% and 20.0% lower at 0.5 hours postexercise than at 72 and 96 hours postexercise, respectively. Further, quadriceps isometric strength remained 10.5% reduced at 24 hours postexercise compared with 96 hours postexercise.

Conclusions: Skeletal 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.