Relationship Between Incidence of Knee Pain and Ground Reaction Force During Stepping Motion in Older Adults

<b>Background:</b> This 2-year longitudinal study was undertaken to investigate the relationship between incidence of knee pain and ground reaction force (GRF) in stepping motion in older adults. <b>Methods:</b> In all, 29 older participants, aged 50 and over (11 males and 18 females; 63.0 ± 6.2 years), presented without knee pain at baseline. The participants performed a 10 s stepping motion at optimal speed on a force plate, and 14 mechanical and temporal parameters of vertical GRF were obtained. Knee pain was evaluated based on subjective complaint during daily activities. The participants were classified into a no pain (NP) group or a knee pain (KP) group. <b>Results:</b> Of the 29 participants (11 males, 18 females), 9 (all female) developed knee pain, representing 31.0% of the total participants and comprising the KP group at the follow-up. We compared the amount of change in the evaluated parameters between the two groups and found moderate effect sizes for the mechanical parameters, ΔMshaped (<i>p</i> = 0.07, d = 0.77) and ΔF2 (<i>p</i> = 0.08, d = 0.72), as well as a flatter change in the bimodal waveform of the GRF in the KP group. <b>Conclusions:</b> It was thus suggested that a flattening of the vertical GRF waveform during stepping motion may indicate early biomechanical changes associated with incident knee pain and that waveform changes in GRF may be useful for early detection of functional decline.