Heat-induced Body Fluid Loss Causes Muscle Cramp during Maximal Voluntary Contraction for the Knee Flexors

抄録

Exercise associated muscle cramp (EAMC) is common among athletes. However, no study has systematically investigated the effect of the amount of loss of fluid on EAMC. This study was designed to examine the relationship between the amount of decrease in body fluid through sweating and EAMC. A decrease in body fluid by 1%, 2%, and 3% of body mass were induced by sauna exposure on 3 different days, and the occurrence of EAMC was compared between the three conditions and a control (no sauna exposure) condition. Nine young men (age: 22.2 ± 1.4 yrs) who had experienced EAMC during and/or after exercise in the previous year volunteered for the study. A “cramp test”, in which the occurrence of EAMC during maximal voluntary muscle contraction of hamstrings at maximally shortened position for 15 s, was performed before and one hour after the body fluid reduction of 1%, 2%, and 3% of body mass. The cramp test was performed on 2 occasions separated by 3 hours without sauna exposure as the control condition. No EAMC occurred in the control and the 1% condition. Three subjects experienced EAMC in the 2%, and 6 in the 3% condition. These results suggest that body fluid loss of 2% body mass increases the likelihood of EAMC and loss of body fluid is a factor for EAMC.