Abstract
Societal erosion of daily life low-level physical activity has had a great influence on the obesity epidemic. Given that low fat oxidation is also a risk factor for obesity, we investigated, in a repeated measures design, the dynamics of fat oxidation from a resting state to a light-intensity leg cycling exercise (0–50 watts) in inactive, healthy young adults. Using indirect calorimetry, energy expenditure and the respiratory quotient (RQ) were assessed in a sitting posture at rest and during a cycling exercise in 35 subjects (20 women). The rate of perceived exhaustion (RPE) was assessed using the Borg Scale. During graded leg cycling, the mean RPE did not exceed values corresponding to the exercise being perceived as ‘light’. However, analysis of individual data at 50 watts revealed two distinct subgroups among the subjects: those having RPE values corresponding to the exercise being perceived as ‘very light to light’ and showing no increase in RQ relative to resting levels, as opposed to an increase in RQ in those who perceived the exercise as being ‘somewhat hard to hard’ (p < 0.001). Our study in inactive individuals showing that high fat oxidation was maintained during ‘light-perceived’ physical activity reinforced the potential importance of light physical activity in the prevention of obesity.
Highlights
The matching of energy expenditure (EE) to energy intake is a fundamental feature of the long-term regulation of body weight [1,2]
Because of longer periods spent in a sitting position, even the low-level physical activity of everyday life has been on the decline, leading to diminished physical fitness, as sitting is replacing a large proportion of day-to-day life, non-exercise physical activity that people had in former times [7]
Based upon previous studies [27,28] indicating that no-load cycling could lead to an increase in EE above rest by more than 50%, we investigated, in 16 subjects (8 men and 8 women), the impact of this minimal cycling movement on both EE and respiratory quotient (RQ) using two cycling modalities: a bicycle ergometer and a car seat ergometer (Figure 1, panels A and B, respectively)
Summary
The matching of energy expenditure (EE) to energy intake is a fundamental feature of the long-term regulation of body weight [1,2]. The importance of physical activity in this matching has centred upon moderate- to vigorous-intensity exercises, and a lack of such structured physical activities has been commonly implicated in the development of obesity and other health risks [3] While such structured exercises are beneficial in the prevention and management of cardiometabolic diseases, individuals most often do not closely adhere to training programs, outside medically-supervised settings, mainly due to their monotony and difficulty and/or to the subjects’ motivation and way of life. There is considerable interest in analysing the potential role of low-intensity physical activities of everyday life in health strategies and in human susceptibility or resistance to weight gain [8,9,10,11] In this context, there is growing interest in increasing EE by maintaining standing posture rather than sitting comfortably, but the impact of longer-duration standing postures on clinical outcomes in body fatness management are controversial [12,13,14]. The use of structured and unstructured low-intensity physical activities to increase EE is receiving more attention as a way to help weight regulation and to counteract the burden of sedentariness in healthy inactive subjects or those with chronic diseases [9,15]
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