Effect of Water Depth on Heart Rate and Core Temperature During Underwater Treadmill Walking

Abstract

Exercising using an underwater treadmill (UTM) has become a popular modality; however, few studies have focused on the physiological demands of UTM walking at varying water depths. Thus, the objective of this study was to investigate changes in heart rate (HR) and core temperature (CT) values in college-aged males and females while exercising at different water immersion depths using an UTM. Twenty participants (age = 21.50 ± 2.19 years; height = 169.04 ± 10.85cm; weight = 75.56 ± 22.28kg) walked at water depths of 10cm below the xiphoid process and at the level of the superior iliac crest (I.C.). Each UTM session lasted 15 minutes, consisting of 5-minute bouts at 1, 2, and 3 mph. Polar HR monitors and ingestible thermoregulatory pills were used to measure HR and CT. Results indicated that HR at 1 (p = .305) and 2 mph (p = .864) were not significantly different between water depths. Heart rate was significantly higher at 3 mph (p = .003) at the I.C. water level. No significant differences were found in CT at 1 (p = .919), 2 (p = .392), or 3 mph (p = .310) during either immersion depth. As a result, higher immersion depths resulted in a lower average HR during higher intensity exercise due to the increased buoyancy effects and the reduced gravity environment of the water. Thus, exercising in higher immersion depths allows participants to exercise at a higher intensity with less overall stress placed on the lower extremities.