Abstract
Muscular fatigue and interlimb strength asymmetry are factors known to influence hamstring injury risk; however, limb-specific exacerbation of knee flexor (hamstrings) torque production after fatiguing exercise has previously been ignored. To investigate changes in muscular force production before and after sport-specific (repeated-sprint) and non-specific (knee extension-flexion) fatiguing exercise, and explore the sensitivity and specificity of isokinetic endurance (ie, muscle-specific) and single-leg vertical jump (ie, whole limb) tests to identify previous hamstring injury. Twenty Western Australia State League footballers with previous unilateral hamstring injury and 20 players without participated. Peak concentric knee extensor and flexor (180°∙s-1 ) torques were assessed throughout an isokinetic endurance test, which was then repeated alongside a single-leg vertical jump test before and after maximal repeated-sprint exercise. Greater reductions in isokinetic knee flexor torque (-16%) and the concentric hamstring:quadriceps peak torque ratio (-15%) were observed after repeated-sprint running only in the injured (kicking) leg and only in the previously injured subjects. Changes in (1) peak knee flexor torque after repeated-sprint exercise, and (2) the decline in knee flexor torque during the isokinetic endurance test measured after repeated-sprint exercise, correctly identified the injured legs (N=20) within the cohort (N=80) with 100% specificity and sensitivity. Decreases in peak knee flexor torque and the knee flexor torque during an isokinetic endurance test after repeated-sprint exercise identified previous hamstring injury with 100% accuracy. Changes in knee flexor torque, but not SLVJ, should be tested to determine its prospective ability to predict hamstring injury in competitive football players.
Highlights
Hamstring injuries comprise 12%-1 6% of all injuries in football
No significant differences were found in knee flexor torque changes between kicking (−6%; Effect sizes (ES) = 0.41) and non- kicking (−3%; ES = 0.20) legs in uninjured group (UG) (P = .182); differences were observed between the changes in flexor torques between kicking (−16%; ES = 0.89) and non-k icking (−4%; ES = 0.33) legs in IG (P = .006)
The purpose of this study was to (a) quantify differences in interlimb force production in the kicking and non-kicking legs in previously injured and uninjured footballers, and (b) compare responses between kicking and non-kicking legs in fatigue-related decreases in voluntary knee extensor and flexor torque (H:Q ratio) as well as both force production and jump height measured during a single-leg vertical jump (SLVJ)
Summary
Hamstring injuries comprise 12%-1 6% of all injuries in football. While muscular fatigue and interlimb strength imbalances are believed by practitioners to influence hamstring injury risk,[10,11,12,13] it is rarely documented whether the weaker leg might fatigue faster during intense running activities and whether this may increase injury risk. While most footballers exhibit limb dominance during kicking (ie, they have a preferred and non- preferred kicking leg), it is not known whether this preference is a predisposing factor for hamstring injuries[14] because little research has attempted to discriminate between kicking and non-k icking legs while investigating hamstring injury.[5,9,15,16].
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