People with knee OA experience pain and the sensation of buckling in their knees that leads to diminished function. Maximum quadriceps force production relates to high function in this group, however, maximum force is rarely used during daily activities. Rate of muscle force development (RFD) is important in maintaining balance and declines with age and disuse, but it is unclear what relationship RFD has with function in people with knee OA. PURPOSE: To examine the relationship between quadriceps RFD and knee function in 3 groups: people with knee OA whose knees were stable (OAS) unstable (OAU) and controls (C). METHODS: Knee joint stiffness and maximum volitional isometric force was measured in 28 people with knee OA (15 OAS and 13 OAU) and 21 C. Functional measures included the KOOS and stair climbing test. The peak instantaneous RFD (RFDi) and average RFD (RFDa) over the interval from 0-200 msec were compared between groups using a one-way ANOVA and post-hoc tests. Pearson's correlation coefficients were used to examine relationships. RESULTS: Significant differences between groups were found in the RFDa (F=5.563, p=.007) and in both relaxed short range and total stiffness (F=4.205, p=.022 and 4.916, p=.012). Post hoc tests revealed that the OAU subjects had higher RFDa and had a higher short range stiffness than controls (p=.006 and p=.021). OAU also had a greater relaxed total stiffness than the OA stable group (p=.010). RFDa correlated negatively with the stair climbing time (r= -0.544, p=.036) in the OAS group. The peak RFDi correlated positively with the KOOS -ADL scores in the OAU group only (r=0.570, p=.042). In the OAU group the peak RFDi and RFDa significantly correlated with the KOOS symptom scores (r=-0.622, p=.023, r=0.606, p=.028) respectively. CONCLUSION: The relationship between RFD and knee function and symptoms in people with knee OA who experience buckling suggests an attempt to stabilize the knee joint. Higher knee joint stiffness in the OAU subjects may allow for these increases in RFD. Accurately assessing and understanding the role of RFD in knee OA may indicate that rehabilitation should involve activities relating to speed in addition to the force of quadriceps contraction. Funded By: NIH P20 RR16458, NIH S10RR022396, ACR REF Health Professional Graduate Student Research Preceptorship
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