Effect Of Age And Physical Activity On Dynamic Knee Joint Stiffness

Physical activity is a suggested intervention to mitigate risk of knee osteoarthritis (KOA) and ACSM recommends 30 minutes per day of moderate intensity exercise, such as walking. However, there is evidence that older adults experience knee extensor fatigue with a 30-minute treadmill walk (30MTW) as compared to young. Muscle fatigue (acute loss of muscle power) may contribute to altered knee joint mechanics that increase KOA risk. Dynamic knee joint stiffness (Δknee joint moment/Δjoint angle during stance phase of gait) may provide a composite assessment of how muscle fatigue impacts KOA risk. An increase in the external knee flexion moment with a reduced knee flexion excursion due to altered muscle activity in response to muscle fatigue would impact both the magnitude and pattern of joint loading, thus increasing KOA risk. PURPOSE: To 1) assess the impact of habitual physical activity and age on dynamic joint stiffness and 2) determine whether a 30MTW leads to increased dynamic knee joint stiffness. METHODS: 27 individuals participated in this study: highly active and low active older adults (ages 70 – 80 years), and young low active adults (30 – 40 years). PA was measured using accelerometry over a 1-week period. Older were classified as highly active if they had >50 minutes a day of moderate to vigorous PA (MVPA) and 7000 steps a week. Young adults were low active. Maximum isometric voluntary contractions (MVIC) were quantified using dynamometry. One-way ANOVAs were used to assess group differences at baseline and the change post 30MTW between groups (α = .05). RESULTS: At baseline older low active had significantly greater knee stiffness than young low active but not older active (p = .03). There were no significant differences in change with 30MTW between groups (p > .05). CONCLUSION: Physical activity may mitigate age-related changes in knee joint stiffness. While both older groups experienced significant muscle fatigue post 30MTW, knee joint stiffness was not impacted. This research was supported by the National Institute of Aging of the National Institutes of Health under Award Number R01AG068102-03.