Influence of stair descent strategies and step height on centre of mass and gait kinetics in the elderly

Age-associated alterations in balance mechanisms and deteriorations in muscle strength may necessitate alternate stair descent strategies to ensure safe negotiation. The aim of the study was to compare the influence of increased step height and stair negotiation strategies; step-over-step (SoS) and step-by-step (SbS) on gait patterns in the elderly. Eleven elderly participants descended a four step custom built instrumented staircase at a self-selected speed. Participants descended using a SoS or SbS strategy on two step configurations: a rise height of 170mm (STD) and a rise height of 255mm (INC). A 3D motion analysis system synchronised with force platforms embedded into the staircase, was used to capture whole body centre of mass (CoM) velocity, acceleration and kinetic data of the leading limb.Compared to STDSoS, STDSbS resulted in reduced CoM vertical (-0.48m/s vs -0.09m/s) and A/P velocity (0.50m/s vs 0.21m/s) during late stance and swing transition with similar reductions in vertical and A/P velocity in INCSoS vs INCSbS (-0.67m/s vs -0.11m/s and 0.49m/s vs 0.23m/s). INCSoS resulted in increased plantarflexor (1.10Nm/kg vs 1.45Nm/kg) and hip extensor moment (-0.08Nm/kg vs 0.43Nm/kg) compared to STDSoS with no differences seen in SbS strategy. An alternate stair descent strategy offers greater CoM control in the potentially dangerous transition between stance and swing. Concurrently, the tandem double stance period negates the need for increased muscle moments in late stance required to eccentrically control the falling body mass in the traditional SoS strategy. SbS could offer increased CoM control and stability during stair descent

Control of the Centre of Mass during different stair descent strategies in the elderly

The elderly are at an increased risk of falls and trips during stair descent due to the increased musculoskeletal demand imposed by this task (Reeves et al. 2008). Reduced functional capacity, muscle recruitment, coordination or strength may limit the ability to adjust the limb to safely control the body in instances of unexpected instability (Buckley et al. 2013). The aim of this study was to determine how the elderly controlled their centre of mass (CoM) during different stair descent strategies. Eleven elderly participants descended a four step custom built instrumented staircase at a self-selected speed. Two step configurations were tested: 1) a standard rise height of 170mm using a step over step strategy (STD SoS) and 2) a rise height of 255mm using step over step, (INC SoS), step by step (INC SbS) and side step (INC SS) strategies. The going stayed constant at 280mm. Centre of pressure (CoP) and whole body model accelerations and A/P displacement were captured at 1080Hz and 120Hz respectively. Data were analysed using a repeated measures GLM. Significance was accepted at p<0.05.Significantly reduced CoP-CoM A/P separation during the landing phase was evident in STD SoS compared to INC SoS and INC SbS (6.1vs10.6 and 10.7cm, p<0.05). INC SS resulted in significantly greater separation during mid-stance compared to STD SoS, INC SbS, INC SS (10.4vs-4.3,-2.2,-2.5cm, p<0.01). During toe off, INC SbS resulted in a larger A/P acceleration compared to STD SoS and INC SoS (0.8vs-0.7 and -1.0m/s/s, p<0.01) with a reduced CoP-CoM separation compared to INC SoS and INC SS (2.5vs10.0 and 6.2cm, p<0.02).The capability of the elderly to control their CoM during stair descent can fluctuate. During the landing phase a greater posterior ‘lean’ towards the staircase occurs with increased step rise, which could reduce the eccentric muscle action necessary to control lowering of the CoM. This lean was maintained by the SS strategy during mid-stance suggesting that this approach provides a mechanism for a safer single limb support. However, this strategy resulted in a simultaneous rapid CoM acceleration (1m/s/s) and large CoP-CoM separation (10cm) prior to toe off, indicating an unstable and potentially dangerous transition into swing. Whilst the INC SbS strategy also resulted in a large peak acceleration, a smaller CoP-CoM separation (1.2cm) occurred at a slower rate (0.07m/s/s) during this transition. This INC SbS strategy could offer increased CoM control, stability and support during stair descent