Twelve subjects completed a progressive treadmill test to maximal aerobic capacity while breathing air or a 79% helium--21% oxygen gas mixture (HeO2). Metabolic and thermoregulatory responses to work while breathing the two mixtures were compared at rest, 30-40%, 60-70%, and 85-90% of maximal performance, and at maximal effort. Ventilation, ventilatory equivalent, and respiratory rates were increased and oxygen uptakes decreased by breathing HeO2 when the level of work exceeded 85-90% of maximum. Heat loss through the respiratory tract was greater breathing HeO2. The reduction in maximal oxygen uptake is probably due to a reduction in the oxygen cost of breathing a less dense gas. It was not related to a lower body temperature and probably not to O2 transport or circulatory limitation. HeO2 breathing had no effect on maximal mechanical work capacity.

No abstract

To evaluate the effect of 26 weeks of moderate- and high-intensity walking training on injury rates in the elderly, 68 healthy volunteers (31 men, 37 women) were assigned to moderate intensity (MOD, n = 26) or high-intensity (HI, n = 24) training, or to a control (CONT, n = 18) group. To achieve prescribed training intensity, many subjects walked uphill on a treadmill. Seven of 50 subjects who trained (14%) suffered a training-related orthopedic injury; one subject was injured during treadmill testing. Four training injuries (lower leg and foot) occurred during weeks 1-13; three training injuries (leg and groin) occurred during weeks 14-26. Six of the injuries were to women. Because only one training injury occurred during uphill treadmill walking, injuries appeared related to fast walking and not exercise intensity. The higher incidence of injury in females is consistent with our earlier work, indicating the importance of further research to determine the underlying cause.