Magnitude and variability of gait characteristics when walking on an irregular surface at different speeds.

Different modes of perturbations have been used to understand how individuals negotiate irregular surfaces, with a general notion that increased locomotion variability induces a positive training stimulus. Individuals tend to walk slower when initially exposed to such locomotion tasks, potentially influencing the magnitude and variability of biomechanical parameters. This study investigated theeffects of gait speed on lower extremity biomechanics when walking on an irregular (IS) and regular surface (RS). Twenty physically active males walked on a RS and IS at three different speeds (4 km/h, 5 km/h, 6 km/h). Lower extremity kinematics (300 Hz) and surface electromyography (3000 Hz) were recorded during the first 90 s of gait. Two-factor repeated measures ANOVA was used to determine surface and speed effects (p < 0.05). Gait speed influences walking biomechanics (kinematic and muscle activity parameters) the same irrespective of surface condition. As walking speed increased, sagittal shoe-surface angle, maximum ankle inversion, ankle abduction, knee and hip flexion increased during stance phase when walking on the IS and RS (p < 0.05). Increasing walking speed caused increased muscle activity of the tibialis anterior, peroneus longus, gastrocnemius medialis, vastus medialis and biceps femoris (p < 0.05) on the IS and RS during the gait cycle. Increased gait, kinematic and muscle activity variability was reported at lower walking speed on both the IS and RS. Further, irrespective of gait speed, walking on an IS triggers postural adjustments, higher muscle activity and increased gait variability compared to RS walking. Our findings suggest the benefits of training on the irregular surface may be further enhanced at slower gait speeds.