Electromyographic activity in expert downhill skiers using functional knee braces after anterior cruciate ligament...

We studied six expert downhill skiers who had sustained anterior cruciate ligament injuries and had different degrees of knee instability. The aim was to measure possible changes in electromyographic activity recorded from lower extremity muscles during downhill skiing in a slalom course without and with a custom-made brace applied to the injured knee. Surface electrodes were used with an eight-channel telemetric electromyographic system to collect recordings from the vastus medialis, biceps femoris, semimembranosus, semitendinosus, and gastrocnemius medialis muscles from both legs. Without the brace, the electromyographic activity level of all muscles increased during knee flexion. The biceps femoris muscle was the most activated and reached 50% to 75% of the maximal peak amplitude. With the brace, the electromyographic activity increased in midphase during the upward push for the weight transfer and the peak activity occurred closer to knee flexion in midphase. Also, the uninjured knee was influenced by the brace on the injured leg, a decrease in electromyographic activity was seen in midphase. Spearman's rank correlation revealed a significant correlation between an increase in biceps femoris activity of the injured leg and increasing knee instability. We suggest that the brace caused an increased afferent input from proprioceptors, resulting in an adaptation of motor control patterns secondarily modifying electromyographic activity and timing.