The increased number of people taking part in deep water running (DWR) is attributable to the weight-independent characteristic of this form of exercise. Deep water runners should, however, be aware of the respiratory and cardiovascular repercussions that result from exercising in water. It has been well documented that water immersion (WI) alone results in decrements in respiratory and cardiovascular parameters in young individuals immersed in water to the neck. These decrements become more pronounced with exercise, such that maximal oxygen consumption and heart rate (HR) are lower during DWR compared with running on land. Age also seems to influence these parameters; Derion et al. found little to no change in cardiac output, stroke volume and HR during WI in older individuals compared with the decrease experienced in younger individuals. In contrast, gender appears to have no effect on WI or DWR response.Although differences in acute metabolic responses have been observed in numerous studies, training studies examining the effectiveness of using a DWR training programme found that DWR produced equivocal training responses when compared with fit and highly trained individuals running on land. Less convincing evidence has been provided for untrained individuals seeking benefits from a DWR training programme, as some studies showed significant improvements while others did not. There is a current lack of knowledge regarding the use of this form of exercise by frail elderly individuals and/or those with osteoporosis.