Underwater walking on non-motorized treadmill as a "fitness tool" for both healty and frailty subjects

Underwater walking on non-motorized treadmill is one of the most popular aquatic fitness activity, but little data is available about its metabolic demands. 15 healthy women (age 43±3.7y, height 1.64±0.05m, weight 54±6.6kg, BMI 22.1±2.3kg/m-2, fat mass 25.4±3.4%) performed an incremental underwater walking exercise (100, 110, 120, 130 step per minute) on a non-motorized treadmill (Aqquatix S.r.l., Limena, Italy) at 2 different water heights (iliac crest - xiphoid process). Water heights and exercise intensities were chosen according to the most used among this fitness classes. A dry-land incremental exercise test to exhaustion was also performed on a motorized treadmill. Breath-by-breath oxygen consumption (V'O2) and heart rate (HR) were recorded continuously throughout both the underwater and the dry-land exercises. Compared to dry-land maximal V'O2 and maximal HR, underwater V'O2 and HR ranged from 64% to 85% and from 71% to 90%, respectively. Both relative intensity ranges fall within the 'moderate' or 'vigorous' intensity described in the current guidelines of the American College of Sports Medicine. Same ranges are also advised to the population in order to improve physical fitness status by several internationally recognized organization in the field of exercise sciences. Water is a 'low impact' environment of exercise providing non-weight-bearing conditions that makes exercise suitable for both pathologic and healthy subjects. This indubitable advantage plus the results obtained in this study provide the evidence for prescribing underwater walking exercise on non-motorized treadmills to both healthy and frailty subjects that could benefit exercising at moderate to vigorous intensities.