Abstract
Individuals regulate the transmission of shock to the head during running at different stride frequencies although the consequences of this on head-gaze stability remain unclear. The purpose of this study was to examine if providing individuals with visual feedback of their head-gaze orientation impacts tibial and head accelerations, shock attenuation and head-gaze motion during preferred speed running at different stride frequencies. Fifteen strides from twelve recreational runners running on a treadmill at their preferred speed were collected during five stride frequencies (preferred, ±10% and ±20% of preferred) in two visual task conditions (with and without real-time visual feedback of head-gaze orientation). The main outcome measures were tibial and head peak accelerations assessed in the time and frequency domains, shock attenuation from tibia to head, and the magnitude and velocity of head-gaze motion. Decreasing stride frequency resulted in greater vertical accelerations of the tibia (p<0.01) during early stance and at the head (p<0.01) during early and late stance; however, for the impact portion the increase in head acceleration was only observed for the slowest stride frequency condition. Visual feedback resulted in reduced head acceleration magnitude (p<0.01) and integrated power spectral density in the frequency domain (p<0.01) in late stance, as well as overall of head-gaze motion (p<0.01). When running at preferred speed individuals were able to stabilize head acceleration within a wide range of stride frequencies; only at a stride frequency 20% below preferred did head acceleration increase. Furthermore, impact accelerations of the head and tibia appear to be solely a function of stride frequency as no differences were observed between feedback conditions. Increased visual task demands through head gaze feedback resulted in reductions in head accelerations in the active portion of stance and increased head-gaze stability.
Highlights
Human locomotion has been described as self-optimizing in order to produce stable coordinated patterns that are energy efficient [1, 2]
The aim of this study was to examine the effect of providing visual feedback of head-gaze orientation on the magnitude, integrated power of tibial and head accelerations, the attenuation of shock from the tibia to the head, and head-gaze dynamics
We had similar findings to Hamill et al [10], in that the changes in the amount of high-frequency impact shock attenuated through the kinematic chain yielded near constant head accelerations
Summary
Human locomotion has been described as self-optimizing in order to produce stable coordinated patterns that are energy efficient [1, 2]. The optimization of these patterns affords the selection of safe and efficient paths of navigation [3,4,5,6]. The stabilization of head accelerations across a range of speed and stride characteristics emerges through modification of the movement kinetics, kinematics and muscular activation patterns, and will afford a stable visual field and the identification of salient visual information and safe navigation through their environment [12]
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