Atypical hamstrings electromyographic activity as a compensatory mechanismin anterior cruciate ligament deficiency

Anterior cruciate ligament (ACL) deficiency may cause functional instabilit y of the knee (noncopers), while other patients compensate and perform at t he same level as before injury (copers). This pilot study investigated whet her there is a compensatory electromyographic (EMG) activity of the hamstri ngs in copers, noncopers and control patients. Ten patients with an ACL def iciency were equally divided into two groups of copers and noncopers. All p atients underwent gait analysis with EMG of six muscles around the knee. Te n healthy young men formed the control group. In contrast to noncopers, cop ers showed an atypical semitendinosus activity during stance phase; the cor responding trend was found in biceps femoris activity. There was no differe nce between copers and controls in knee extension during stance phase. The noncopers had less knee extension. Atypical hamstring muscle activity may t hus be a compensatory mechanism by which copers enable themselves to perfor m on a normal level.