Can stabilization analysis following a single leg drop jump be compared between young and middle-aged adults

We aimed to verify whether the computational approaches previously proposed to analyze stability after a single-leg drop-jump (SLDJ) could be applied to a population of middle-aged adults. Fifteen middle-aged (56.4 ± 4.6 years) and 15 young adults (26.7 ± 3.9 years) performed five SLDJs. Stabilization measurements included (1) time to stabilization (TTS) based on vertical ground reaction force (GRF) (TTSv) and a fixed stabilization threshold; (2) TTS based on medio-lateral GRF (TTSml) using five different methods to preprocess the signal and stabilization threshold; (3) early medio-lateral stabilization- the averaged absolute values of the GRF in 0.2–1.4 s post-landing; (4) late medio-lateral stabilization - the averaged absolute values of the GRF at 1 s–5 s after landing. TTSv showed longer TTS values in middle-aged participants. In addition, middle-aged adults showed greater sway in late stabilization. However, TTSml values varied considerably between calculation methods, and early stabilization showed no significant differences between groups except in the first 0.2 s after landing. The results of the current study suggest that TTS calculations are sensitive to signal and threshold selection, and to the processing method. Calculations based on a fixed threshold are more appropriate for studying dynamic postural stability in middle age. With appropriate method selection, a decreased stabilizing performance can be demonstrated in middle-aged adults compared to young adults.