Exercise effects on the strength of the rat anterior cruciate ligament.

Seventy-five rats were divided into a control and four exercise groups of differing frequency and duration. After 8 weeks of endurance-type exercise on a motorized treadmill, the rats were sacrificed and the anterior cruciate ligaments were tested to failure on an Instron materials testing machine at a strain rate of 95% sec-1. Of the 121 ligaments tested, 119 failed by pure interstitial failure. There was significant increase in both the strength and stiffness of the anterior cruciate ligaments in the exercised rats but those rats exercised more frequently (daily vs. every other day) and for shorter duration (30 min rather than 60 min) had the greatest increase in strength. This study has shown that endurance-type exercise is beneficial to the anterior cruciate ligament as both strength and stiffness are increased and functionally the ligament remains unchanged by exercise.