The acute effects of an unstable shoe on energy expenditure

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Recently, the concept of constructing a rocker-bottom unstable shoe has become increasingly popular in the shoe industry. Proposed benefits based on this type of unstable shoe include increased lower extremity muscle activation and energy expenditure. Therefore, unstable shoes could be used to improve physical fitness, induce weight loss, and improve balance. Although several recent studies have examined the chronic physiological responses of wearing these shoes over long periods of time, few have investigated the changes occurring in the initial acclimation phase within the first hour of use. Purpose: The purpose of this study was to quantify energy expenditure of wearing an unstable shoe (US), as compared to control shoe (CS) or a participant's own athletic shoe matched to the mass of an US, during an initial acclimation period of 40 minutes. Methods: Thirty healthy volunteer participants (17 females, 13 males, age 21.77 ± 3.16 years, mass 67.27 ± 10.29 kg, stature 167.61 ± 7.85 cm), who had not previously worn any type of US, were recruited. Energy expenditure was measured via oxygen consumption (VO2) method of indirect calorimetry during steady-state. Resting energy expenditure (REE) was determined in static sitting. Following REE, participants were instructed to walk at a self-selected speed on a treadmill (3.30 ± 0.66 km·h−1). Steady-state energy expenditure for CS at time point 0 minute (CS 0’) was collected. Following CS 0’, US data was collected at time point 0’ (US 0’) which represented the first 5 minutes of the acclimation period. Steady-state energy expenditure was measured again during the last 5 minutes of the 40 minute acclimation period of wearing the US (US 40’). Subsequently, CS data at time point 40 minute (CS 40’) was measured. Results: A two-way analysis of variance (ANOVA) for repeated measures revealed no difference in energy expenditure from time point 0 minute to time point 40 minute within shoe conditions, and no time x shoe type interaction effects. However, there was a main effect of shoe type (F1,29 = 13.02, p = 0.001), with post-hoc tests showing US having increased energy expenditure at time 0 minute, but not at 40 minute. Conclusion: Findings suggest that within the first five minutes of wearing the US, energy expenditure is increased when compared to CS. However, by the end of the 40 minute acclimation period, no significant difference between shoes was found.