Effect of ambient temperature and hydrated status on heart rate recovery sfter a standardized step test

Introduction

The purpose of the study was to determine whether differences in ambient temperature and water drinking status could cause variation in the result of a government-made standardized step test.

Methods

12 subjects participated this study and always performed the test in the morning under fasted condition. The heart rate response during the 3-min step test and recovery period was recorded under 22 (LT) and 32 (HT) degree C to determine the temperature effect. Under both ambient temperature, all subjects were also tested under hydrated (H) or dehydrated (DH) conditions to determine the water drinking effect. For the dehydration state, water drinking was prohibited for 12 hours. For the hydrated state, 750 ml of water was provided in the morning one-hour before the test.

Results

Blood lactate level was measured for determining the stress level of the test under 4 different testing states. The 12-h dehydration caused approximately 1 kg different in body weight compared to the water-drinking state. Difference in ambient temperature did not alter the resting lactate level in these subjects. Under DH state, resting lactate level was significantly lowered compared to H state. However, under LT state, the increment in lactate level during the test was significantly greater in dehydration state than those in all other states. We found that heart rate response was greater and the time for heart rate recovery was slower under HT state compared to LT state. In addition, dehydration further amplified the difference between the two temperature states.

Discussion/Conclusion

Ambient temperature of the testing environment and dehydration condition of the testing subjects appear to be confounding factors for the result of the 3-min step test as an indicator for cardiopulmonary fitness.