Abstract: Objective This study applied surface electromyography (sEMG) to analyze muscle activation intensity in patients with knee osteoarthritis (KOA) during physical activity and investigated the impact of exercise-related fear on lower limb muscle function in these patients. Methods A total of 30 KOA patients were selected and categorized into a high-fear group (n = 16) and a low-fear group (n = 14) based on the TSK-17 scale (Tampa Scale for Kinesiophobia) scores, with 14 healthy individuals serving as the control group. A wireless sEMG system recorded muscle activity in the bilateral rectus femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus, tibialis anterior, and the medial and lateral heads of the gastrocnemius. Test activities included walking at normal speed, stair ascent, and stair descent. Muscle activation was normalized to maximal voluntary contraction (MVC) by calculating the root mean square (RMS) of the EMG signals to compare muscle activation under different conditions. Correlation analyses were conducted to evaluate the relationship between muscle activation and TSK-17 scores. Results A total of 30 KOA patients were selected and categorized into a high-fear group (n = 16) and a low-fear group (n = 14) based on the TSK-17 scale (Tampa Scale for Kinesiophobia) scores, with 14 healthy individuals serving as the control group. A wireless sEMG system recorded muscle activity in the bilateral rectus femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus, tibialis anterior, and the medial and lateral heads of the gastrocnemius. Test activities included walking at normal speed, stair ascent, and stair descent. Muscle activation was normalized to maximal voluntary contraction (MVC) by calculating the root mean square (RMS) of the EMG signals to compare muscle activation under different conditions. Correlation analyses were conducted to evaluate the relationship between muscle activation and TSK-17 scores. Results: In normal walking, the high-fear group's healthy side showed significantly greater activation in the rectus femoris (35.32±20.82 vs. 27.32±12.20, P=0.02), vastus medialis (43.57±23.30 vs. 30.33±13.54, P<0.01), and vastus lateralis (52.89±34.44 vs. 38.25±22.51, P<0.01) compared to the affected side. Similarly, muscle activation was elevated during stair ascent in the high-fear group, with significant differences in the rectus femoris (32.03±14.26 vs. 22.91±11.42, P<0.01), vastus medialis (43.93±18.35 vs. 29.14±16.57, P<0.01), and vastus lateralis (55.45±27.88 vs. 36.00±25.47, P<0.01). Furthermore, in the high-fear group, the affected side exhibited significantly increased activation in the rectus femoris during normal walking compared to the low-fear group and controls. Correlation analysis revealed a significant positive association between TSK-17 scores and rectus femoris activation on the healthy side during stair descent (r=0.952, P<0.01).Conclusions Exercise-related fear has a significant impact on muscle activation patterns in KOA patients, particularly during stair descent, which places greater functional demand on the lower limbs. These findings underscore the importance of addressing psychological factors in KOA rehabilitation to improve both motor function and quality of life comprehensively.