Measuring the Energy of Ventilation and Circulation during Human Walking using Induced Hypoxia

Abstract

Energy expenditure (EE) during walking includes energy costs to move and support the body and for respiration and circulation. We measured EE during walking under three different oxygen concentrations. Eleven healthy, young, male lowlanders walked on a treadmill at seven gait speeds (0.67–1.83 m s−1) on a level gradient under normobaric normoxia (room air, 21% O2), moderate hypoxia (15% O2), and severe hypoxia (11% O2). By comparing the hypoxia-induced elevation in heart rate (HR [bpm]), ventilation (VE [L min−1]) with the change in energy expenditure (EE [W]) at each speed, we were able to determine circulatory and respiratory costs. In a multivariate model combining HR and VE, respiratory costs were 0.44 ± 0.15 W per each L min−1 increase in VE, and circulatory costs were 0.24 ± 0.05 W per each bpm increase in HR (model adjusted r2 = 0.97, p < 0.001). These VE costs were substantially lower than previous studies that ignored the contribution of HR to cardiopulmonary work. Estimated HR costs were consistent with, although somewhat higher than, measures derived from catheterization studies. Cardiopulmonary costs accounted for 23% of resting EE, but less than 5% of net walking costs (i.e., with resting EE subtracted).

Impact of Resistance Exercise under Hypoxia on Postexercise Hemodynamics in Healthy Young Males

“…Thereafter, a 60-minute sitting recovery was set while breathing room air ( Figure 1 ). Hypoxic gas was supplied via a 200 liter Douglas bag reservoir through a two-way, nonrebreathing valve and face mask using a hypoxic generator system (Hypoxico Everest Summit II: Will Co., Ltd., Tokyo, Japan), as previously reported in our recent study [ 22 ]. The inspired oxygen concentration was verified before and after each experiment (AE-310; Minato Medical Science, Osaka, Japan).…”

Differential kinetics of the cardiac, ventilatory, and gas exchange variables during walking under moderate hypoxia

“…However, the increased energy expenditure at severe hypoxia would be derived from the HR and during walking; in our previous study using a bivariate regression model, the contribution of heart beats accounted for 60%~80% of the approx. 5% increase in energy expenditure during walking [ 24 ]. Our present finding of a deceleration in HR kinetics with an increase in the Mx suggests that hypoxia has a greater influence on the HR than on the during sinusoidal walking.…”

Impact of ambient temperature on energy cost and economical speed during level walking in healthy young males

“…We calculated EE by using and based on previous studies ( Horiuchi et al, 2016 , 2017 ). To date, there is a debate whether the was unchanged in a hot environment ( Hayashi et al, 2006 ; No and Kwak, 2016 ; Nybo and Nielsen, 2001a ; Périard and Racinais, 2015 , 2016 ), and findings are equivocal.…”

“…To calculate EE at rest and at each gait speed, and were determined using the following equation. ( Brouwer, 1957 ; Horiuchi et al, 2016 , 2017 )…”

“…It is known that there is a U-shaped relationship between energy expenditure (EE) per unit of distance, calculated by oxygen consumption and carbon dioxide output during walking, and gait speed ( Horiuchi et al, 2016 , 2017 ). This indicates that there is also a particular gait speed in each individual which can minimize the energy cost of walking; the so-called economical speed (ES) ( Horiuchi et al, 2016 ; Saibene, 1990 ; Wezenberg et al, 2013 ).…”