Influence of Lower Extremity Strength of Healthy Older Adults on the Outcome of an Induced Trip

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Abstract
OBJECTIVES: To determine whether decreased lower extremity strength contributes to trip‐related falls in older adults.DESIGN: A cross‐sectional sample of older adults were safety‐harnessed and tripped while walking using a concealed, mechanical obstacle. Lower extremity strength was compared between trip outcome groups.SETTING: A biomechanics research laboratory.PARTICIPANTS: Seventy‐nine healthy, community‐dwelling adults aged 65 and older (50 women).MEASUREMENTS: Ankle, knee, and hip flexion and extension strength were measured isometrically and isokinetically. Measured strengths were subjected to a factor analysis. Strength factor scores were compared between those who recovered from the trip and those who fell by three previously identified mechanisms: during‐step, after‐step, and elevating‐response falls.RESULTS: Seven common factors, one associated with each direction of exertion at each joint and one with the time rate of moment increase, explained 88% of the variance in measured strength. The during‐step (n = 5) fallers were significantly stronger in the ankle extension (plantarflexion), knee flexion, overall extension, and total strength factors than those who successfully recovered using a similar, lowering strategy (n = 26). The elevating‐response faller (n = 1) was stronger in the plantarflexion and overall extension factors than most of those who recovered using a similar, elevating strategy (n = 11). Two of three after‐step fallers were among the weakest subjects tested.CONCLUSION: Weak older adults and the strongest older adults may be at greater risk of falling from a trip, although by different mechanisms. High strength may increase the likelihood of a during‐step or elevating‐response fall; decreased strength may increase the likelihood of an after‐step fall.