Energy-saving mechanisms are used in human walking. In obese adults the energy cost of walking (Cw) is higher compared with normal-body mass adults. However, the biomechanical factors involved in this extra cost should result in a higher Cw. The aim of this study was to compare energy-saving walking mechanisms [i.e., mechanical energy saved via pendulum (Recovery) and maximum possible elastic energy usage (MPEEu)] and their influence on Cw in obese vs. lean individuals. The net Cw (NetCw), external work (Wext), Recovery, MPEEu, and gait weight transfer duration (gWT) were computed for 13 lean [L; body mass index (BMI) 21.9 ± 1.5 kg/m2] and 13 obese (O; BMI 33.8 ± 2.5 kg/m2) individuals during treadmill walking at five speeds (0.56, 0.83, 1.11, 1.39, 1.67 m/s). No significant difference was found between groups in relative (per kg of body mass) NetCw ( P = 0.13). Relative positive Wext was significantly lower at the three fastest speeds ( P ≤ 0.003) whereas Recovery was higher at the two fastest speeds ( P ≤ 0.01) in O than in L individuals. MPEEu tended to be lower in O than in L ( P = 0.06), with significantly lower values in O compared with L at 1.39 and 1.67 m/s ( P ≤ 0.017). gWT was significantly shorter in O than in L individuals at 1.67 m/s ( P = 0.001). The present results reveal that obese adults rely more on the pendular mechanism than on the storage and release of elastic energy for decreasing the amount of positive Wext and thus limiting the increase in the relative NetCw. NEW & NOTEWORTHY We observed that obese individuals had a lower maximum possible elastic energy usage per kilogram of body mass than their lean counterparts and they may rely more on the pendular mechanism of walking than on the storage and release of elastic energy for decreasing the external mechanical work and thus limiting the increase in the relative net energy cost of walking.

It has been suggested that internal mechanical work (i.e., the work required to move the limbs with respect to the center of mass, Wint) may be responsible for the higher net cost of walking in obese adults, but this variable has not yet been studied in individuals with obesity. The main finding of the present study is that individuals with class III obesity exhibit a similar amount of mass-normalized Wint to that of adults with a normal body weight, suggesting that body mass-relative Wint is not affected by obesity and is not responsible for the higher energy cost and the lower efficiency of walking in this population.

A walking training program under hypoxia at slower PWS than in normoxia elicited similar responses in metabolic risk factors, energetics, and mechanics of walking in individuals with obesity. Both programs increased PWS, decreased RPE, and induced gait-pattern adaptations, which protected against orthopedic injury in these individuals.

He received a BSc, MSc and PhD in Human Movement Sciences. He is interested in the energetics and biomechanics of locomotion in healthy and pathological conditions. His current research focuses on the effect of obesity and ageing on walking economy and mechanics.

<b><i>Background:</i></b> The preferred walking speed (PWS), also known as the “spontaneous” or “self-selected” walking speed, is the speed normally used during daily living activities and may represent an appropriate exercise intensity for weight reduction programs aiming to enhance a more negative energy balance. <b><i>Objectives:</i></b> The aim of this study was to examine, simultaneously, the energetics, mechanics, and perceived exertion determinants of PWS in individuals with obesity. <b><i>Methods:</i></b> Twenty-three adults with obesity (age 32.7 ± 6.8 years, body mass index 33.6 ± 2.6 kg/m²) were recruited. The participants performed 10 min of treadmill familiarization, and PWS was determined. Each subject performed six 5-min walking trials (PWS 0.56, 0.83, 1.11, 1.39, and 1.67 m/s). Gas exchanges were collected and analyzed to obtain the gross energy cost of walking (G_Cw), rated perceived exertion (RPE) was measured using a 6–20 Borg scale, and the external mechanical work (W_ext) and the fraction of mechanical energy recovered by the pendular mechanism (Recovery) were computed using an instrumented treadmill. Second-order least-squares regression was used to calculate the optimal walking speed (OWS) of each variable. <b><i>Results:</i></b> No significant difference was found between PWS (1.28 ± 0.13 m/s) and OWS for G_Cw (1.28 ± 0.10 m/s), RPE cost of walking (1.38 ± 0.14 m/s), and Recovery (1.48 ± 0.27 m/s; <i>p</i> &#x3e; 0.06 for all), but the PWS was significantly faster than the OWS for W_ext (0.98 ± 0.56 m/s; <i>p</i> &#x3c; 0.02). Multiple regression (<i>r</i> = 0.72; <i>p</i> = 0.003) showed that ∼52% of the variance in PWS was explained by Recovery, W_ext, and height. <b><i>Conclusion:</i></b> The main finding of this study was that obese adults may select their PWS in function of several competing demands, since this speed simultaneously minimizes pendular energy transduction, energy cost, and perceived exertion during walking. Moreover, recovery of mechanical work, external work, and height seem to be the major determinants of PWS in these individuals.