The up and down bobbing of human walking: a compromise between muscle work and efficiency

Abstract

Human walking has a peculiar straight-legged style. Consequently, the body's centre of mass (CM) moves up and down with each step, which is noticeable in their up and down head bobbing while walking. This vertical CM movement enables humans to save energy via a pendulum-like mechanism but is probably a relatively recent locomotor innovation insofar as earliest bipeds may have walked flexed and flat. We investigated the mechanics, energetics, muscle efficiency and optimization of human walking by decreasing and increasing the vertical CM displacement (flat and bouncy walking) in comparison to normal walking at six speeds (1-6 km h −1 ). In both flat and bouncy walking, the pendular mechanism was reduced and the energy cost was increased. However, this increase was unexpectedly much sharper in flat walking where muscles provided normal mechanical work but with a decrease in muscle efficiency. In bouncy walking, muscles provided extra mechanical work in an efficient way. Our results showed that not only do humans bob up and down in normal walking to save energy via a pendulum-like mechanism but also to make their muscles work efficiently. Actually, walking flat makes the muscles work in unfavourable conditions that waste energy. Furthermore, we are still close to a flat CM displacement relative to our current ability to change this displacement, which suggests that reducing vertical CM displacement is indeed important but only to certain limits. Evolution may ultimately have chosen the best compromise between flat locomotion that requires little work to move and bouncy locomotion that improves muscle efficiency to minimize energy consumption.

Symmetrical kinematics does not imply symmetrical kinetics in people with transtibial amputation using cycling model

“…Some reports suggest asymmetry in ground reaction forces are related to biasing the body's center of mass toward the contralateral limb [14][15]. Indeed, the center of mass position is dictated by limb kinematics [16][17], and this creates one link between limb kinematics and kinetics. However, other factors produce interlimb asymmetries, e.g., interactions between the limb and socket interface [3,5], loss of sensorimotor input [4], altered musculoskeletal geometry [1,5], and loss of propulsion due to the lack of ankle plantarflexors [2,4,13].…”

Locomotor impact of beneficial or nonbeneficial H-reflex conditioning after spinal cord injury

“…These features appear to be preserved by changes in muscular and kinematic details, such as the locomotor contributions of different leg muscles or the withinlimb relationships among ankle, knee, and hip angles over the step-cycle (e.g., Chen et al 2011). [Other key features may include parameters such as muscle efficiency, total energy consumption, or whole limb kinematics (e.g., Chang et al 2009;Latash et al 2007;Massaad et al 2007). ]…”

Planar covariation of limb elevation angles during bipedal locomotion in common quails (Coturnix coturnix)

“…Horizontal velocity reaches minimum at the mid-stance phase and is maximum in the double-support phase, and potential and kinetic energy therefore fluctuate out of phase, resulting in high walking efficiency. This mutual exchange of two types of mechanical energy is called the inverted-pendulum mechanism and is considered the fundamental mechanism of energy conservation in human bipedal locomotion (Cavagna et al, 1977;Ortega and Farley, 2005;Massaad et al, 2007). The characteristic two-peaked profile of the vertical ground reaction force in human locomotion is linked to the vertical oscillation of the CoM and hence to the efficient utilization of pendular mechanics (Cavagna et al, 1977).…”