Joint angle and movement velocity effects on muscle activity of elderly with knee osteoarthritis - Categorized and probabilistic analysis

The aim of the study was to determine the effects of joint angle position and angular velocity on concentric and eccentric knee muscles activity of elderly with osteoarthritis (OA) in a deterministic and probabilistic approach compared to matched controls. Concentric and eccentric muscle activation of vastus medialis (VM) and semitendinous (ST) muscles were recorded of eleven elderly women with knee OA (median (Md (25-75%)) age of 62 years (60-72) and Md of body mass index (BMI) of 26 kg/m2 (24.5-27.2)) and ten controls (Md 65 years (62-69) and Md of BMI 24.5 kg/m2 (23.6-28.9), during twenty-five knee extension-flexion movements. Activation type, angular velocities (90° s−1 and 240° s−1) and joint angle intervals were categorized into groups. The cumulative frequency distributions of the normalized sEMG envelope were computed and the probability to be out of specific norm-reference limits (controls) was calculated. No statistical differences between groups were found. Higher probabilities were found for VM and ST (concentric) and ST (eccentric) activation to be out of norm (55%, 53% and 84%, respectively) at 240 s−1 in different joint angles. During dynamic contractions, concentric and eccentric activity of medial knee muscles of elderly with OA were affected in a different way by joint angles and angular velocity compared to matched controls. The probabilistic analysis provided an additional understanding of the muscle activation between elderly with knee OA and healthy older people.