A male kayaker covered approximately 1,000 km along a sea coast over a period of ~40 days. Each night, after setting up camp, he noninvasively self-recorded at rest several systemic variables and transmitted them to a remote medical center via a telemedicine platform developed by the research team. This system employed a custom-built wearable device based on electrical impedance to acquire beat-to-beat cardiodynamic variables. Additional measurements included arterial blood pressure, expiratory peak flow, maximal handgrip force, tympanic temperature, and urine specific gravity. Over the course of the expedition, cardiac output linearly increased by 65 ml min-1 per day, primarily due to a rise in stroke volume and a concomitant reduction in total peripheral vascular resistance which, in turn, led to a decrease in mean arterial pressure. The mechanical work of the heart showed no significant variation during navigation. However, towards the end of the journey, the rate–pressure product—an indicator of myocardial oxygen consumption—rose exponentially, indicating a progressive decline in cardiac mechanical efficiency. This trend paralleled a decrease in maximal handgrip strength and an increase in perceived exertion. Overall, the kayaking expedition promoted an improvement in oxygen delivery capacity and blood pressure lowering, although signs of cardiac and muscular fatigue became evident toward the end of the trip.
Tocco et al. (Wed,) studied this question.