The effect of lower limb muscle fatigue on obstacle negotiation during walking in older adults

Tripping over obstacles is a common cause of falls in older adults, and muscle fatigue, which can alter walking patterns, may add to this risk. To date, no study has examined the effect of lower limb muscle fatigue on obstacle negotiation in older adults. 30 older adults (13 women, aged 78.3 [6.2] years) negotiated a 12 m obstacle course, while completing a visual secondary task, under two randomized conditions: rested or fatigued. For the fatigue condition, participants performed a repeated sit-to-stand movement, as fast as possible, until they could no longer continue. Participants then immediately began walking trials. Kinematic and kinetic data were collected on approach to, during, and after crossing a height-adjustable target obstacle (10% and 20% of leg length). Repeated measures ANOVA showed a statistically significant increase in lead limb vertical loading rate after stepping over the 10% obstacle when fatigued, relative to rested (P=0.046). No other significant between-condition differences (>0.05) were observed for the other kinematic variables when negotiating the 10% obstacle. Furthermore, no significant between-condition differences (P>0.05) were observed for any kinetic or kinematic variables when negotiating the 20% obstacle. This study describes a feasible method for investigating the consequences of lower limb muscle fatigue on obstacle crossing. The current finding of increased vertical loading rate when fatigued supports the need for further investigation into the effect of muscle fatigue on gait under different environmental conditions, fatiguing a range of muscles, analyzing a more comprehensive array of kinetic and kinematic measures, and in healthy and clinical populations.