Assessment of the efficiency of intermittent and continuous walking strategies in hypoxia

In normoxia, work efficiency (total oxygen cost of work) is lower in intermittent than continuous exercise, however, this has yet to be confirmed in hypoxia.We measured the efficiency of two matched-work, hypoxic uphill walks: (1) continuous, slow-steady walk, and (2) intermittent, high-speed walk and rest.Fourteen volunteers naive to high-altitude (8 females, 6 males; age = 21 2 years; height = 170 11 cm; body mass = 66.7 12.5 kg; peak walking speed [PWS] = 7.3 0.6 kmh -1 ) completed two experimental sessions, in a normobarbic chamber at an equivalent altitude of 3,500 m (FiO2 0.135; FiCO2 0.04).The continuous strategy required participants to complete a 30-min walk at 50% of their pre-determined PWS (i.e., transition point between walking and running) with distance recorded.During the intermittent strategy participants completed the 30-min distance at their PWS, interspersed with self-determined rests.Breath-by-breath oxygen consumption, heart rate, and arterial oxygen saturation were measured throughout.The intermittent walk resulted in a 13% shorter 30-min distance completion time (1584 301 s, p = 0.019) compared to the continuous walk, but at a 37% higher total VO2 (continuous VO2 = 73.2 35.2 L vs. intermittent VO2 = 46.1 26.2 L, p = 0.001) and 39% greater energy expenditure (continuous energy expenditure = 1,473 724 kJ vs. Intermittent energy expenditure = 962 548 kJ, p < 0.001).The lower efficiency of the intermittent strategy compared to the continuous, agrees with those data reported for normoxia.It provides useful information for high altitude trekkers and potentially for those looking to identify exercise conditions to maximise weight loss.