EFFECT OF HYPOHYDRATION ON MOTOR UNIT RECRUITMENT AND ENDURANCE DURING ADDUCTOR POLLICIS EXERCISE

Abstract

Hypohydration reduces muscular endurance but it remains unclear whether the premature fatigue is due to peripheral mechanisms or altered central motor drive. PURPOSE: To assess the impact of hypohydration on endurance, rate of muscle fatigue, and central motor drive during exhaustive adductor pollicis exercise. METHODS: Fourteen subjects (12 men, 2 women) performed intermittent isometric exercise to exhaustion when hypo-hydrated (HY) by 4% of normal body mass and when euhydrated (EU). Hypohydation was produced by not drinking during an exercise-heat stress protocol completed 3 h before testing. For EU, the same exercise-heat stress protocol was performed but fluids were consumed to maintain body water. The endurance test consisted of 5 sec contractions at 50% MVC followed by 5 sec rest until exhausted. Maximal strength of the thumb was measured before and every minute of exercise. EMG was measured throughout exercise. RESULTS: Hypohydration did not reduce endurance (HY = 754 ± 255; EU = 714 ± 318 sec), muscle strength, or increase the rate of fatigue. The adductor pollicis EMG root mean square increased during exercise (P < 0.05) but was not different between HY and EU. CONCLUSION: The effects of hypohydration on endurance may be dependent on the exercise protocol as there were no deterimental effects of hypohydration on adductor pollicis performance.