The aim of this study was to assess the impact of heat applied for 8 hours immediately after or 24 hours after exercise on delayed-onset muscle soreness (DOMS) in large skeletal muscle groups measured by subjective and objective means. Three groups of 20 subjects (20-40y.o) performed squats for three sets of 5 minutes to initiate DOMS. There was 3 minutes rest between sets. One group had heat applied immediately after exercise, and a second group had heat applied 24 hours after exercise. A third group was the control group where no heat was applied. Visual analog pain scales, muscle strength of quads, range of motion of quads, stiffness of quads (Continuous Passive Motion machine), algometer to measure quadriceps soreness, and blood myoglobin were all used as outcome measures. The most significant outcome was a reduction in soreness in the group that had low-temperature heat wraps applied immediately after exercise (P < 0.01). There was benefit to applying heat 24 hours after exercise, but to a smaller extent. This was corroborated by myoglobin, algometer, and stiffness data.
Low-level continuous heat wraps left for 8 hours just after heavy exercise reduced DOMS in the population tested as assessed by subjective and objective measures. Although cold is commonly used after heavy exercise to reduce soreness, heat applied just after exercise seems very effective in reducing soreness. Unlike cold, it increases flexibility of tissue and tissue blood flow. For joint, it is still probably better to use cold to reduce swelling.