Low levels of eccentric hamstring strength increased the risk of future HSI. Interaction effects suggest that the additional risk of future HSI associated with advancing age or previous injury was mitigated by higher levels of eccentric hamstring strength.

Although some iterations of the models achieved near perfect prediction, the large ranges in AUC highlight the fragility of the data. The 2013 models performed slightly better than the 2015 models. The predictive performance of between-year HSI models was poor however. In conclusion, risk factor data cannot be used to identify athletes at an increased risk of HSI with any consistency.

The observed increased financial cost of HSIs was ultimately explained by the failure of teams to decrease HSI rates, but coupled with increases in athlete salaries over the past 10 season. The information presented in this report highlights the financial cost of HSIs and other sporting injuries, raising greater awareness and the need for further funding for research into injury prevention strategies to maximise economical return for investment in athletes.

Hamstring strain injuries (HSIs) remain the most prevalent cause of time lost from competition in a range of sports, 14,17,18,53 with associated performance 23 and financial consequences. 28 Deficits in function, such as reduced isometric knee flexor strength, exist acutely following HSI 4,44,58 and may increase reinjury risk if persistent at return-to-play (RTP) clearance. 16 Rehabilitation should aim to restore these deficits as quickly as possible following acute HSI and to return the injured athlete to his or her sport with minimal risk of reinjury. 26 However, even after completion of rehabilitation and RTP clearance, previously injured hamstrings may display eccentric strength 42,49,51,74 and biceps femoris long head (BFLH) fascicle length deficits, 73 which are both modifiable HSI risk factors. 11,52,71,79 Fyfe et al 22 hypothesized that a lack of eccentric loading and longlength exercise during early rehabilitation may contribute to residual deficits and the elevated risk of reinjury seen in previously injured hamstrings. 20,22,50 Eccentric loading and long-length exercises reduce HSI risk, 3,77,80 increase knee flexor strength and BFLH fascicle length in uninjured individuals, 1,10,54,55,72 and accelerate RTP time when emphasized during rehabilitation. 5,6 However, the introduction and progression of eccentric loading and long-length exercises may be delayed by the consistently implemented guideline to only perform and progress exercise in the absence of pain. 30 Delaying the start of exercise rehabilitation by 9U OBJECTIVE: The primary aim was to compare time from acute hamstring strain injury (HSI) to return-to-play (RTP) clearance following a standardized rehabilitation protocol performed within either pain-free or pain-threshold limits. Secondary aims were to compare isometric knee flexor strength, biceps femoris long head (BFLH) fascicle length, fear of movement, and reinjury occurrence at the 6-month follow-up between pain-free and pain-threshold groups.U DESIGN: Randomized controlled trial.U METHODS: Forty-three men with acute HSIs were randomly allocated to a pain-free (n = 22) or painthreshold (n = 21) rehabilitation group. Days from HSI to RTP clearance, isometric knee flexor strength, BFLH fascicle length, fear of movement, and reinjury occurrence at the 6-month follow-up were reported.U RESULTS: Median time from HSI to RTP clearance was 15 days (95% confidence interval [CI]: 13, 17) in the pain-free group and 17 days (95% CI: 11, 24) in the pain-threshold group, which was not significantly different (P = .37). Isometric knee flexor strength recovery at 90° of hip and 90° of knee flexion was greater in the pain-threshold group at RTP clearance by 15% (95% CI: 1%, 28%) and by 15% (95% CI: 1%, 29%) at 2-month follow-up, respectively. Improvement in BFLH fascicle length from baseline was 0.91 cm (95% CI: 0.34, 1.48) greater at 2-month follow-up in the pain-threshold group. Two reinjuries occurred in both the pain-free and pain-threshold groups between RTP clearance and the 6-month follow-up.U CON...

In the Australian Football League (AFL), hamstring strain injuries (HSI) are the most common cause of time lost from training and matches 1 and have a relatively high rate of recurrence compared to other lower limb muscle injuries. 1 These injuries also place a large financial burden on the athlete and their organization with estimates in the AFL placing the average cost of games missed in a season due to an HSI at $242,842 per club. 2 Therefore, more research is required to assist in developing HSI risk mitigation practices within the AFL.