Moist heat (warm bath or moist-heat pack) is often used by physios prior to stretching to increase muscle temperature and improve musculotendinous tissue flexibility (muscle flexibility). A recent study completed in America ('Effects of moist heat on hamstring flexibility and muscle temperature', Journal of Strength and Conditioning Research, Vol 17 (2) 285-290) looked at the direct effects of moist heat on hamstring muscle flexibility and muscle temperature.
Twenty-seven male subjects completed the study. Baseline hamstring flexibility was assessed using an active knee-extension test, and hamstring temperature was measured using a thermister that was inserted into the muscle. Once the baseline temperature had been recorded, two moist-heat packs were placed on either side of the thermister until the temperature had increased by 0.4Â°C. Once this temperature had been reached, hamstring flexibility was reassessed at 0, 4, 8 and 16 minutes. The research team found that application of moist-heat packs alone failed to significantly affect muscle flexibility.
The team suggested that moist-heat packs should be applied for at least 20-25 minutes in order to gain an appropriate increase in muscle temperature and that stretching must be included if flexibility is to be significantly increased. The team noted that application of moist heat allowed muscle temperature to remain elevated for a longer period, giving athletes an extended time period for use of other techniques to improve flexibility.