CUR - The Council on Undergraduate Research

The Effects of Intensive Exercise on the Knee Flexion Angle While Changing Direction and Thus the Correlation with ACL Strain

Brittany Cook, Leon Laskowski, and Dr. Susan Renner, Department of Natural and Health Sciences, University of St. Francis, 500 Wilcox St., Joliet Il, 60435

The anterior cruciate ligament (ACL) is one of the six ligaments found in the knee joint that is crucial to restricting excess movement of the tibia. Along with the ACL, contraction of the hamstring and quadricep muscle groups contribute aid to knee stability. Fatigue in these muscles may be an underlying factor in noncontact ACL injuries. Flexion and extension movements of the knee greatly affect strain in the ACL; a flexed knee results in an unstrained ACL, whereas an extended knee results in a strained ACL. When exercise intensity increases, the knee flexion angle will decrease in both men and women during rapid change of direction movements due to muscle fatigue. Participants were subjected to increasing fatigue levels, then performed change of direction (COD) tests where the knee flexion angles were measured during impact and release. When each individual was their own control, the paired t-test showed a significant difference between the control heart rate and 70% heart rate during release (p-value: 0.0047866). However, the Bonferroni correction showed no significance between control and 40%, 50%, and 60% heart rates during release (p-values: 0.06080317, 0.166188, and 0.11762947). Although there was no significant difference between control and 40%, 50%, and 60%, a significant decrease between control and 70% supports the hypothesis that knee flexion angles decrease with high levels of fatigue. This may be due to the fact that 70% of the max heart rate most closely reflects the intensity of higher competition of sports. Future tests will involve calculating joint reaction forces acting on the knee during rapid cutting movements. 

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