Abstract
BACKGROUND: Knee stiffness is a common complaint experienced during prolonged periods of sedentary behaviour, including following prolonged sitting, in both healthy and people with musculoskeletal conditions. Reduction of self-reported knee stiffness is important to patient-centred outcomes. Our aim was to obtain pilot data to determine the timeframe for knee stiffness onset in healthy populations. METHODS: Forty-two participants (20-76 years) with no diagnosed chronic musculoskeletal condition were recruited. After pilot testing, perceived knee joint stiffness and pain (Visual Analogue Scale) were measured while sitting (at 15, 30, 60, and 90 min) with the knee joint held at 90°. Correlations between knee stiffness after 90 min of sitting and baseline demographic data, and knee range of motion were analysed. RESULTS: Greater levels of self-reported stiffness were observed (mean ± SD) after sitting still for 30 (1.8 ± 1.6; p < 0.001), 60 (3.4 ± 2.4; p < 0.001) and 90 min (4.1 ± 2.6; p < 0.001) compared to baseline (n = 31). Increase of self-reported pain occurred by 60 and 90 min of sitting (p < 0.001). Minimal clinical important difference (MCID) (±2 cm) in stiffness occurred by 60 min of sitting (+2.6 cm) with pain not reaching MCID by 90 min. Self-reported stiffness at 90 min of sitting was negatively correlated with participant age (r = -0.433, p = 0.004). CONCLUSIONS: Healthy adults begin to experience knee stiffness when sitting still after 30 min, though this was only clinically relevant by 60 min. Moving the joint, even whilst still sitting, helped to alleviate joint stiffness and pain, which may assist in providing advice to all adults on sedentary behaviours.