Systematic evaluation of the physiological load of mountain climbing from the relation between inclination of walking path, walking speed, and backpack weight ; simulation using walking on a treadmill

Abstract

We simulated mountain climbing using walking on a treadmill in order to systematically evaluate the physical load during mountain climbing. The conditions of three types of load- (1) inclination of the walking path (walking uphill and downhill), (2) walking speed, and (3) backpack weight-were varied within the range assumed for normal mountain climbing (40 sets of conditions in total). When the three types of load were expressed as vertical work rate, energy expenditure (V4 O2) during walking uphill and downhill was distributed along roughly the same curve. The following characteristics of walking uphill and downhill were observed. A. Walking uphill For all three types of load, increase in load gave a linear increase in V4 O2 and heart rate (HR). A lactate threshold (LT) appeared at an intensity of 62%V4 O 2max, when HR was 78% HRmax. Rating of perceived exertion (RPE) was evaluated for the "Breathlessness" and "Leg Fatigue", and both of these increased roughly in proportion to %V4 O2max. B. Walking downhill When walking downhill, V4 O2 was 35?50% the intensity of V4 O2 when walking uphill on the same slope and at the same speed. Energy expenditure did not exceed 60%V4 O2max in any of the load conditions, and no LT was seen. RPE values were higher for walking downhill than walking uphill, even when %V4 O2max values were the same. RPE values for the "Leg Fatigue" tended to be higher than for the "Breathlessness" at the same speed in downhill walking. Using these data, we created a table giving the intensity of exercise of mountain climbing expressed as V4 O2 per unit body mass and metabolic equivalents (Mets) with vertical migration velocity and total weight (Body weight + Backpack weight) as variables. This table gives mountain climbers a systematic understanding of the physical load under various mountain climbing conditions. It is likely to be of use as a reference for mountain climbers of different levels of physical fitness when practicing mountain climbing appropriate to their individual level. The present results suggest that in downhill walking, it is insufficient to express the physical load in energy expenditure (V4 O2 and Mets) alone, and the load on the leg muscles must also be judged using the RPE in the "Leg Fatigue".