Natalia Andrea Gomeñuka

Adaptations to changing speed, load, and gradient in human walking: cost of transport, optimal speed, and pendulum.

It has been observed that the optimal speed (OPT) of human walking is independent of load on level surfaces because of the unaltered trajectory of the center of mass and consequent conservation of the pendular mechanism. However, the role of the inverted pendulum mechanism that combines speed, load, and gradient during walking remains unknown. In the present study, 10 subjects walked on a treadmill, with and without loading (25% of the body mass), at different speeds and slopes (0%, +7%, and +15%). The three‐dimensional motion and VO2 were simultaneously registered. The mechanical external and internal work and the cost of transport (C) changed with the speed and gradient, but the load only affected C. OPT decreased with increasing gradient, and the pendular mechanics (R) was modified mainly as a result of changes in speed and gradient. OPT and R were independent of the load in these gradients. Remarkably, R increased with increasing speed and decreased (to 30%) with an increasing gradient; moreover, R was independent of load. Therefore, the energy‐saving strategy by the pendular mechanism persists, although at a diminished level, in loaded walking on gradients and partially explains the OPT in this condition.

The pendular mechanism does not determine the optimal speed of loaded walking on gradients

The pendular mechanism does not act as a primary mechanism in uphill walking due to the monotonic behavior of the mechanical energies of the center of mass. Nevertheless, recent evidence shows that there is an important minimization of energy expenditure by the pendular mechanism during walking on uphill gradients. In this study, we analyzed the optimum speed (OPT) of loaded human walking and the pendulum-like determining variables (Recovery R, Instantaneous pendular re-conversion Rint, and Congruity percentage %Cong). Ten young men walked on a treadmill at five different speeds and at three different treadmill incline gradients (0, +7 and +15%), with and without a load carried in their backpacks. We used indirect calorimetry and 3D motion analysis, and all of the data were analyzed by computational algorithms. Rint increased at higher speeds and decreased with increasing gradient. R and %Cong decreased with increasing gradient and increased with speed, independent of load. Thus, energy conversion by the pendular mechanism during walking on a 15% gradient is supported, and although this mechanism can explain the maintenance of OPT at low walking speeds, the pendular mechanism does not fully explain the energy minimization at higher speeds.

Mechanical Work and Long-Distance Performance Prediction: the Influence of Allometric Scaling

Abstract The purpose of this study was to examine the effect of allometric scaling on the relationship between mechanical work and long-distance running performance in recreational runners. Fourteen recreational long-distance runners (male, mean ± SD - age: 29 ± 7 years; body mass: 70.0 ± 10.2 kg; body height: 1.71 ± 0.07 m; maximal oxygen uptake: VO2max 52.0 ± 4.9 ml.kg-1.min-1) performed two tests: a continuous incremental test to volitional exhaustion in order to determine VO2max, and a 6-minute running submaximal test at 3.1 m.s-1, during which segments in the sagittal plane were recorded using a digital camera and the internal (Wint), external (Wext) and total (Wtot) mechanic work, in J.kg-1.m-1, was subsequently calculated. The results indicated a significant correlation between mechanical work and performance, however, the strongest correlations were observed when allometric exponents were used (respectively for Wint, Wext and Wtot; non allometric vs. allometric scaling defined by literature (0.75) or determined mathematically (0.49): r = 0.38 vs. r = 0.44 and r = 0.50; r = 0.80 vs. r = 0.83 and r = 0.82; r = 0.70 vs. r = 0.77 and r = 0.78). These results indicate that mechanical work could be used as a predictor of recreational long-distance performance and an allometric model may improve this prediction. Abstract The purpose of this study was to examine the effect of allometric scaling on the relationship between mechanical work and long-distance running performance in recreational runners. Fourteen recreational long-distance runners (male, mean ± SD - age: 29 ± 7 years; body mass: 70.0 ± 10.2 kg; body height: 1.71 ± 0.07 m; maximal oxygen uptake: VO2max 52.0 ± 4.9 ml·kg-1·min-1) performed two tests: a continuous incremental test to volitional exhaustion in order to determine VO2max, and a 6-minute running submaximal test at 3.1 m·s-1, during which segments in the sagittal plane were recorded using a digital camera and the internal (Wint), external (Wext) and total (Wtot) mechanic work, in J.kg-1·m-1, was subsequently calculated. The results indicated a significant correlation between mechanical work and performance, however, the strongest correlations were observed when allometric exponents were used (respectively for Wint, Wext and Wtot; non allometric vs. allometric scaling defined by literature (0.75) or determined mathematically (0.49): r = 0.38 vs. r = 0.44 and r = 0.50; r = 0.80 vs. r = 0.83 and r = 0.82; r = 0.70 vs. r = 0.77 and r = 0.78). These results indicate that mechanical work could be used as a predictor of recreational long-distance performance and an allometric model may improve this prediction.

Inclined Weight-Loaded Walking at Different Speeds: Pelvis-Shoulder Coordination, Trunk Movements and Cost of Transport

ABSTRACT Although studied at level surface, the trunk kinematics and pelvis-shoulder coordination of incline walking are unknown. The aim of this study was to evaluate the speed effects on pelvis-shoulder coordination and trunk movement and the cost of transport (C) during unloaded and loaded (25% of body mass) 15% incline walking. We collected 3-dimensional kinematic and oxygen consumption data from 10 physically active young men. The movements were analyzed in the sagittal plane (inclination and range of trunk motion) and the transverse plane (range of shoulder and pelvic girdle motion and phase difference). The rotational amplitude of the shoulder girdle decreased with load at all speeds, and it was lower at the highest speeds. The rotational amplitude of the pelvic girdle did not change with the different speeds. The phase difference was greater at optimal speed (3 km.hr−1, at the lowest C) in the loaded and the unloaded conditions. The trunk inclination was greater with load and increased with speed, whereas the range of trunk motion was lower in the loaded condition and decreased with increasing speed. In conclusion, the load decreased the range of girdles and trunk motion, and the pelvis-shoulder coordination seemed to be critical for the incline walking performance.

VELOCIDADE AUTOSSELECIONADA E IDEAL DA CAMINHADA DE AMPUTADOS TRANSFEMORAIS: SOLO E ESTEIRA

Introducao: A velocidade de progressao e, em geral, determinada em pesquisas na area da locomocao. Objetivo: Comparar as medidas de velocidade autosselecionada no solo, na esteira rolante e a velocidade ideal estimada pelo numero de Froude em sujeitos amputados transfemorais. Metodo: Primeiramente foi determinada a velocidade no solo; em seguida, realizou-se o teste na esteira, e a velocidade ideal foi estimada a partir dos dados antropometricos. Todos os sujeitos utilizavam joelho hidraulico e pe em fibra de carbono. Para comparacao entre as velocidades foi realizada ANOVA de duas vias. Resultados: A velocidade autosselecionada na esteira foi menor (22%) do que no solo. Tanto a velocidade autosselecionada na esteira como a do solo foram 44% e 22% menores do que a velocidade ideal estimada, respectivamente. Conclusao: As velocidades analisadas no presente estudo foram diferentes, provavelmente, devido a variacao dos parâmetros cinematicos.