Change of Muscular Activity and Dynamic Stability of the Knee Joint Due to Excessive and Repetitive Jumping or Cutting by Female Athletes

[Purpose] Previous studies have reported that physical activity is increasingly being encouraged as an essential part of a healthy lifestyle; thus, sports and preventable injury are becoming an important public health issue. Using an isokinetic test, we evaluated muscular activities and dynamic stability of the knee joint of skilled female athletes. [Methods] The subjects were 42 females aged 24.5 +/- 0.9 years old, weighing 61.5 +/- 1.1 kg; they were 169.6 +/- 1.3 cm in height and had a body mass index (BMI) of 18.2 +/- 0.5. We used a Biodex 3 System Pro (R) as the isokinetic dynamometer. [Results] The extensor in the dominant leg of the jumping group showed significantly higher strength than its counterpart in the cutting group. However, knee flexors showed no significant difference between groups. Furthermore, the H:Q ratios of the jumping group (ND: 45.4 +/- 2.3%, D: 45.0 +/- 1.2%) and the cutting group (ND: 48.1 +/- 1.9%, D: 51.5 +/- 1.6%) were lower than 60%. In addition, the ratio of dominance in the jumping group was significantly lower than in the cutting group. [Conclusion] These results suggest that skilled female athletes who perform excessive and repetitive jumping actions need to be more aware of their risk of developing anterior cruciate ligament (ACL) injury, and they need a more specific therapeutic program for this injury.