Grant: Travel Awards - Institute Community Support

Females are 4-6 times more likely to injury their knee compared to males. This severely affects their physical activity levels, perceived functional abilities, and quality of life. A common symptom is reduced quadriceps muscle strength, which is also thought to be a main predictor for individuals at risk of experiencing a knee injury. Female knee extensor muscles are less strong than males when normalised to body weight. Also, females activate their muscles differently than males but it remains unclear if this is due to their strength deficit or a more complex muscular or neurological issue. This study evaluated the differences between males and females during an experimental reduction in quadriceps muscle function. A salty saline solution was injected into inner thigh muscle of the dominant leg. This injection causes the perception of pain which decreases voluntary muscle strength. Participants performed a series of squats before and during pain. Squats were divided into two phases: ascent and descent. The activity level of 10 muscles, lower limb joint angles, and forces acting on each joint were compared between condition (before pain vs. during pain) and sex (male vs. female). The pace of the movement did not change between conditions. However, both groups did not squat as low in the pain condition and thus had lower forces acting on the knee compared to before pain. The presence of pain caused a reduction in quadriceps muscle function up to 43% in both groups. No other differences were observed in males. In contrast, females demonstrated an increase of knee forces in the non-dominant leg and decreased hamstring activity during ascent. These differences may be a main contributor to the injury mechanism and may explain the increased injury rates in females. Further research on muscle function and its effect on knee joint stability between sexes are needed.