Abstract: BACKGROUND: There are mechanical changes in the lower limb muscles in patients with knee osteoarthritis. These changes can be objectively reflected through surface electromyography. Currently, there is limited research on abnormal electrophysiological signals of lower limb muscles, especially of calf muscles, during walking in patients with unilateral knee osteoarthritis.
OBJECTIVE: To investigate the motor activation status and activation mode of the medial thigh muscle, lateral thigh muscle, tibialis anterior muscle, and gastrocnemius muscle during daily walking in patients with unilateral knee osteoarthritis using surface electromyography. 
METHODS: Fifty subjects with unilateral knee osteoarthritis who met the inclusion criteria underwent surface electromyography walking tests. The target muscles were the medial thigh muscle, lateral thigh muscle, anterior tibialis muscle, and gastrocnemius muscle. The walking time was 60 seconds. Surface electromyography signals were collected from both healthy and affected sides. The main observation indicators were root mean square value, integrated electromyography value, median frequency, and muscle contraction ratio. Whether there is an abnormal activation status and its characteristics of lower limb muscles in unilateral knee osteoarthritis patients were investigated by surface electromyography. The abnormal movement activation of lower limb muscles in unilateral knee osteoarthritis patients during normal activities was investigated. 
RESULTS AND CONCLUSION: (1) During the walking process,  integrated electromyography and root mean square values of the affected medial femoral muscle and lateral femoral muscle were significantly lower than those of the healthy side (P < 0.001). The median frequency value of the affected medial femoral muscle and lateral femoral muscle was significantly lower than that of the healthy side (P < 0.001), and the median frequency shift to the low frequency was more significant. The fatigue risk was more significant than that of the healthy side. (2) The integrated electromyography and root mean square values of the affected tibial anterior muscle during walking were significantly higher than those of the healthy side (P < 0.001). The median frequency value of the affected tibial anterior muscle was significantly lower than that of the healthy side (P < 0.001), and the median frequency shift to the lower frequency was more significant compared with the healthy side. The risk of fatigue was significantly higher than that of the healthy side. (3) The integrated electromyography and root mean square values of the gastrocnemius muscle on the affected side during walking were significantly higher than those of the healthy side (P < 0.001). The median frequency value of the gastrocnemius muscle on the affected side did not show a significant excessive deviation compared with the healthy side (P > 0.05), and the fatigue degree of both the healthy and affected sides was relatively consistent. (4) The ratio of muscle activation on the affected side was significantly lower than that on the healthy side (P < 0.001), and the activation of the medial femoral and lateral femoral muscles on the affected side was significantly unbalanced compared with the healthy side. To conclude, when unilateral knee osteoarthritis patients undergo daily walking, the medial femoral and lateral femoral muscles have significant inadequate activation and reduced activation efficiency. The degree of fatigue is high, and there is a significant fatigue risk. This is significantly unbalanced for muscle activation, which is not conducive to the stability of the movement and joint balance of the knee joint. The affected tibial anterior muscle and gastrocnemius muscle have significant compensatory activation and abnormal co-activation levels, which are important factors that aggravate joint stiffness. Among them, the compensation of the anterior tibial muscle is the most obvious, and there is fatigue muscle atrophy.

Key words: knee osteoarthritis, surface electromyography, muscle activation ratio, medial femoral muscle, lateral femoral muscle,  tibial anterior muscle, gastrocnemius muscle, muscle fatigue