Abstract: BACKGROUND: During stair walking, different muscles work in concert and compensate for each other, and it is unclear whether weakened muscle strength actually affects stair fall risk in older adults. Real-time electromyographic signals from older adults during stair walking are used to reflect high fall risk in older adults during stair walking, which may further improve the accuracy of prediction methods.
OBJECTIVE: To investigate the effects of aging on lower limb muscle activation in older adults during stair walking and to analyze the relationship between their muscle activation characteristics and stair fall risk.
METHODS: Subjects were divided by age into an older group (n=19) and a younger group (n=18) group and were asked to walk on a 10-step staircase at a natural speed, incorporating surface electromyography acquisition technology, to capture surface electromyography signals during stair walking and calculate the root mean square (RMS) to analyze differences in muscle activation levels. Logistic regression analysis was utilized to establish a predictive model for stair fall risk in older adults by incorporating the lateral femoral and gastrocnemius muscle RMS. The discrimination of the model was evaluated by the receiver operating characteristic curve and area under the curve, and the fit of the model was evaluated using the Hosmer-Lemeshow test
RESULTS AND CONCLUSION: Activation of the rectus femoris (Z=-3.464, P=0.001; t=3.379, P=0.002) and lateral gastrocnemius muscle (Z=-2.978, P=0.003; Z=-3.555, P < 0.001) was higher in older adults than in younger adults when walking up and down stairs. Activation of the anterior tibialis (Z=-2.350, P=0.019) and medial (Z=2.321, P=0.020) and lateral (t=3.158, P=0.004) gastrocnemius muscles was higher in older adults when ascending stairs than descending stairs. Older adults at risk for falls had less activation of the lateral femoral muscle (Z=-2.613, P=0.009), medial gastrocnemius muscle (Z=-2.286, P=0.022) when walking upstairs, and lateral femoral muscle (Z=-2.368, P=0.018) when walking downstairs than did older adults not at risk for falls. The predictive ability, goodness of fit, and discrimination of the stair fall prediction model for older adults based on surface electromyography were good (P-value of 0.010 for the Omnibus test of the model coefficients, P-value of 0.214 for the Hosmer-Lemeshow test, and the area of the curve of the upper staircase lateral femoral muscle=0.856, P=0.009). (5) The model was modeled with a cut-off value of 38.64 for the upper staircase lateral femoral muscle RMS value and there was a 0.952-fold increase in the risk of staircase falls for each unit decrease in the upper staircase lateral femoral muscle RMS in older adults.

Key words: surface electromyography, stair walking, older adults, muscle activation characteristics, fall prediction