Comparison of the effects of backpack loading and of walking speed on foot-floor contact patterns.

Load-bearing over variable distances at diverse speeds constitutes a major component of manual materials handling activities that persist as ergonomic concerns even in the most technologically advanced societies. The mechanisms of slipping and tripping relate in part to the way pedal segments approach or leave the walking surface. To demonstrate the kinematic effects of load and speed, as measured underfoot, i.e. at the worker-substrate interface, 45 young adult males traversed a 40 m walkway unburdened, and with 20%, 30%, 40%, 50% and 60% bodyweight backpack loads, under controlled speed conditions. The same subjects also walked unburdened at 0.83 m s-1 to 2.22 m s-1 (i.e. in 1 km h-1 increments between 3 and 8 km h-1). Telemetric footswitch technology was used to obtain temporal patterns of heel, lateral and medial ball and toe of each foot. The findings of this study, in which subjects were shoeless, help to establish 'baseline' descriptions of foot-floor contact patterns, unaffected by interindividual differences due to shoe or boot rigidity. From these, measured or derived data on temporal statistical parameters were obtained which show that all make- and break-contacts of pedal segments occur absolutely and relatively faster as speed increases, whereas forefoot contacts are made faster and broken slower as loads increase. Under loading the earlier phases of stance simulate an increased speed pattern, whereas the later phases of stance simulate a reduced speed pattern.