Abstract
BACKGROUND: Hamstring strain injuries (HSIs) have a high rate of recurrence, highlighting the need for effective tertiary prevention strategies. Flywheel resistance training appears effective in targeting muscular risk factors for HSI. HYPOTHESIS: Flywheel leg curls will result in greater improvements in eccentric knee flexor strength and biceps femoris long head (BF(LH)) fascicle length compared with conventional leg curls. STUDY DESIGN: Randomized controlled trial. LEVEL OF EVIDENCE: Level 2. METHODS: Twenty-six athletes with a history of HSI within the past 18 months participated in an 8-week preventive training program. Athletes were assigned randomly to perform leg curls using either conventional (CON) or flywheel (FLY) equipment. Primary outcomes included eccentric knee flexor strength and BF(LH) fascicle length. Secondary outcomes included isometric strength, maximal hip flexion active knee extension (MHFAKE), passive straight leg raise (PSLR), BF(LH) muscle thickness, and pennation angle. Reinjury occurrence was monitored over a 6-month period. RESULTS: The FLY group showed significantly greater improvements in eccentric strength (19 ± 19% vs 6 ± 9%; P = 0.04) and BF(LH) fascicle length (9 ± 8% vs 2 ± 3%; P = 0.01) compared with the CON group. The FLY group also exhibited superior gains in isometric strength and flexibility (MHFAKE), whereas the CON group showed a larger increase in BF(LH) pennation angle. During follow-up, the CON group sustained 3 reinjuries, whereas the FLY group reported only 1 (reinjury risk ratio 3.0, 95% CI, 0.31-28.9). CONCLUSION: Athletes with a history of HSI who participated in a preventive training program including flywheel leg curls showed greater improvements in knee flexor strength, fascicle length, and flexibility, as well as a lower reinjury occurrence compared with those trained with conventional leg curls. CLINICAL RELEVANCE: Flywheel resistance training offers enhanced muscular adaptations that may reduce the risk of reinjury in athletes with a history of HSI.