Effect of muscle fatigue and dehydration on exercise induced muscle cramp (EIMC)

The purposes of this study were to 1) develop "cramp screening tests" to investigate susceptibility to exercise induced muscle cramp (EIMC) and 2) examine the effect of muscle fatigue and dehydration-rehydration on EIMC using the tests. Twenty healthy male subjects were placed into three groups based on their experience of EIMC; high (n=4, frequent cramps in daily life), low-medium (n=12, cramps with special conditions such as strenuous exercise) and no cramps (n=4), and performed two cramp screening tests for the toe flexors and hamstrings. The results indicated that the higher the frequency of muscle cramps in daily life, the higher the cramp induction rates in the tests. To investigate the effect of muscle fatigue on EIMC, 15 out of the 20 subjects performed 100 rhythmic isometric (knee joint angle of 90degrees) or isokinetic contractions (range of motion : 60-120degrees, flexion : 60degrees/s, extension : 300degrees/s) of the knee flexors in separate days. Susceptibility to EIMC decreased in the exercised muscle after the fatiguing exercises, but significantly increased in the toe of the exercised limb. To verify the effect of dehydration on EIMC, nine out of the 20 subjects were dehydrated to reduce 3% of body weight by an intermittent sauna exposure and rehydrated by giving the dehydrated amount of plain water. Dehydration significantly increased the susceptibility to EIMC, and rehydration did not contribute to decrease the susceptibility. These results suggest that the susceptibility to EIMC would be estimated by using the tests, and dehydration is associated with EIMC, but muscle fatigue does not seem to be a direct factor for EIMC.