Hamstring and knee injuries are associated with isometric hip and trunk muscle strength in elite Australian Rules and Rugby League players

Objectives: Smaller lumbar multifidus (LM) and larger quadratus lumborum (QL) cross sectional area (CSA) potentially increase lower limb injury risk. Including functional measures (force generating capacity) with structural (muscle CSA) may improve risk models. Relationships between isometric trunk and hip strength and morphology were explored with hamstring and knee ligament injury risk in Australian Football League (AFL) and National Rugby League (NRL) players.

Methods: During the AFL and NRL 2020 preseasons, isometric trunk and hip extensor strength (n = 153, 5 s (maximum strength) and 45 s (strength-endurance), and morphology (n = 238, LM L5 and QL CSA) were assessed. Logistic regression and decision trees explored associations between maximum strength, strength endurance, LM L5 and QL CSA, age, previous injury, and hamstring and knee ligament injuries.

Results: Hamstring (n = 19) and knee ligament (n = 13) injuries occurred. Greater strength endurance (OR = 0.42, 95%CI = 0.23-0.74, p = 0.004) and maximum strength (OR = 0.55, 95%CI = 0.31-0.94, p = 0.039) reduced hamstring injury risk. Knee ligament injury risk increased with larger LM L5 (OR = 1.66, 95%CI = 1.14-2.45, p = 0.008) and LM L5 to QL ratio (OR = 1.57, 95%CI = 1.13-2.23, p = 0.008). Decision tree models suggested low strength endurance (< 99Nm) was characteristic of hamstring strains yet those with high (≥ 1.33) LM L5 to QL ratio were protected. Knee ligament injuries were classified by larger (≥ 8.49 cm2) LM L5 CSA, greater (≥ 1.25) LM L5 to QL ratio, and lower trunk and hip extensor maximum strength (< 9.24 N/kg).

Conclusions: Hamstring injury risk increased in players with lower trunk and hip extensor maximum strength maximum strength and strength-endurance. Knee ligament injury risk greater in players with larger LM L5 CSA and LM L5 to QL ratio and lower maximum trunk and hip extensor strength.