Electromyographic Activity in Expert Downhill Skiers Using Functional Knee Braces After Anterior Cruciate Ligament Injuries

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Abstract
We studied six expert downhill skiers who had sus tained anterior cruciate ligament injuries and had dif ferent degrees of knee instability. The aim was to measure possible changes in electromyographic activ ity recorded from lower extremity muscles during downhill skiing in a slalom course without and with a custom-made brace applied to the injured knee. Sur face electrodes were used with an eight-channel tele metric electromyographic system to collect recordings from the vastus medialis, biceps femoris, semimem branosus, semitendinosus, and gastrocnemius media lis muscles from both legs. Without the brace, the electromyographic activity level of all muscles in creased during knee flexion. The biceps femoris mus cle was the most activated and reached 50% to 75% of the maximal peak amplitude. With the brace, the elec tromyographic 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 cor relation 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 propriocep tors, resulting in an adaptation of motor control pat terns secondarily modifying electromyographic activity and timing.