Stair ascent and descent at different inclinations

Abstract

The aim of this study was to investigate the biomechanics and motor co-ordination in humans during stair climbing at different inclinations. Ten normal subjects ascended and descended a five-step staircase at three different inclinations (24°, 30°, 42°). Three steps were instrumented with force sensors and provided 6 dof ground reactions. Kinematics was analysed by a camera-based optoelectronic system. An inverse dynamics approach was applied to compute joint moments and powers. The different kinematic and kinetic patterns of stair ascent and descent were analysed and compared to level walking patterns. Temporal gait cycle parameters and ground reactions were not significantly affected by staircase inclination. Joint angles and moments showed a relatively low but significant dependency on the inclination. A large influence was observed in joint powers. This can be related to the varying amount of potential energy that has to be produced (during ascent) or absorbed (during descent) by the muscles. The kinematics and kinetics of staircase walking differ considerably from level walking. Interestingly, no definite signs could be found indicating that there is an adaptation or shift in the motor patterns when moving from level to stair walking. This can be clearly seen in the foot placement: compared to level walking, the forefoot strikes the ground first—independent from climbing direction and inclination. This and further findings suggest that there is a certain inclination angle or angular range where subjects do switch between a level walking and a stair walking gait pattern.

Introduction

Stairs are frequently encountered obstacles in daily living. Although healthy persons climb stairs quite easily, this movement task is quite demanding when motor functions are reduced, for example in elderly or obese subjects, women during pregnancy, subjects affected by muscle or joint diseases as well as subjects with joint or limb replacements. The analysis of biomechanical and motor control aspects involved in stair ascent and descent can add to our understanding of the diverse and complicated processes involved in human locomotion and also be useful in the design of private and public environments where stairs are employed. Another application is in the field of gait rehabilitation. For instance, a comprehensive movement analysis of stair climbing can support the evaluation of joint replacement or prostheses development.

Several studies were performed to investigate normal human stair ascent and descent [1], [2], [3]. Recently, some researchers focused on the analysis of joint moments [4], joint powers [5], plantar pressure characteristics [6] and reproducibility [7] that occur during staircase walking. Some studies also exist that investigate stair climbing of patients with knee [8] and hip [9] implants, amputees with artificial limbs [10], [11] or athletes with anterior cruciate ligament deficiencies [12].

However, no comprehensive analysis is available in the literature that discusses biomechanics of stair ascent and descent at different inclinations, although staircase slope proves to be an important characteristic affecting temporal and kinematic gait parameters [13] and hip/knee extensor activity [14] at varying step heights. Since previous studies [13], [14] are restricted to rather specific issues, our study is a broader attempt to face the question of how staircase inclination affects the kinematic and kinetic patterns of stair climbing and to ascertain if ascent and descent patterns are to be considered as particular evolution of the level walking pattern. This knowledge can, for example, serve as a reference for the imitation of natural motor control strategies in intelligent prostheses applied to walking on different terrain.