Seat-Height Effects During Seated Shoe Donning in Older Adults: A Multi-Stage Ergonomic Evaluation Integrating Muscle Activity, Postural Exposure, and Subjective Comfort

Inappropriate seat height may affect muscle activity, observational musculoskeletal postural exposure, and subjective comfort during seated shoe donning in older adults. This study characterized seat-height effects across four task stages and explored the combined pattern of these outcomes. Thirty-five community-dwelling older adults with basic self-care ability recruited from a residential community affiliated with Southwest Forestry University (12 men and 23 women; age: 74.60±7.87 years) completed seated shoe donning at 60%, 80%, 100%, and 120% of individual popliteal height. sEMG quantified muscle activity using natural-log-transformed task RMS as the primary analytical measure, with ΔRMS% retained as a secondary quiet-standing-normalized measure; REBA assessed observational postural exposure; subjective comfort was assessed using a study-specific seven-category numerical rating scale; and CRITIC provided an exploratory multi-indicator summary. Primary sEMG inference based on natural-log-transformed task RMS showed seat-height main effects for the BB and the FCU and seat-height × stage interactions for the BB, the FCU, the ES, the RF, and the MG; the LM interaction was not significant. Across the log-RMS mixed-effects, ΔRMS%-based mixed-effects, and log-RMS Gaussian GEE analyses, the BB seat-height main effect and the RF seat-height × stage interaction were the most consistently supported seat-height-related findings, while other muscle-specific effects varied across models. REBA showed a consistent seat-height × stage interaction across analyses, but the overall seat-height main effect was non-significant in the ordinal GEE and significant in the Gaussian GEE sensitivity analysis. Subjective comfort showed consistent seat-height and seat-height × stage effects across the primary and sensitivity analyses. An exploratory CRITIC integration using a within-muscle-standardized log-RMS sEMG summary placed H2 (80% of popliteal height) first among the four tested conditions; the leading position of H2 was retained across alternative sEMG scaling approaches and when the sEMG component was excluded or its orientation reversed, although H2 and H4 nearly tied under the reversed orientation. Overall, seat-height effects varied across task stages and outcome domains. H2 emerged as the highest-scoring tested condition under the present protocol, providing a task-specific basis for future validation.