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.

In contrast to what happens with healthy subjects, where the SSWS has the lowest CT, CHF patients choose an SSWS with higher CT, but with lower ventilatory cost. These findings are compatible with the concept that interventions that enhance ventilatory efficiency may increase SSWS in CHF.

Subjects with COPD choose their walking speed so as to keep the dyspnea sensation tolerable and to keep gait variability and cost of transport at an acceptable level. These outcomes suggest that interventions acting on dyspnea and gait pattern may increase patients' self-selected walking speed and improve their quality of life.

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