Early versus delayed lengthening exercises for acute hamstring injury in male athletes: a randomised controlled clinical trial.

When someone tears a hamstring, one of the big questions in rehab is when to start eccentric strengthening exercises, the kind that lengthen the muscle under load. Starting early might build strength and resilience sooner, but there has also been concern that loading an injured muscle too soon could slow healing or increase reinjury risk. This trial compared starting these lengthening exercises on day one of rehabilitation against waiting until an athlete could run at 70% of top speed, in male athletes with an MRI-confirmed acute hamstring injury, all following the same broader rehabilitation programme. Athletes in the early group returned to sport at a median of 23 days versus 33 days in the delayed group, but this difference was not statistically significant once the data were properly analysed, and reinjury rates over the following year were also similar between groups.

In other words, starting lengthening exercises earlier did not clearly speed recovery or change reinjury risk in this trial. The study was relatively small, with 90 participants, which limits how confident we can be in ruling out a real difference either way.

If you have ever had a hamstring strain, you know the frustrating uncertainty around when it is safe to push the muscle harder during recovery. This trial looked at whether starting eccentric exercises, which stretch and strengthen the muscle at the same time, right from day one of rehab helps athletes get back to sport faster than waiting until they can run at a good portion of top speed first. Both groups followed the same overall rehab plan, with only the timing of these particular exercises differing.

Athletes who started early returned to sport somewhat sooner on average, but when researchers accounted for statistical uncertainty, this difference was not considered reliable. Reinjury rates over the next year were also similar between the two approaches.

This suggests that, based on this trial, moving lengthening exercises earlier in rehab did not show a clear benefit for getting back to sport faster or avoiding reinjury. The trial included 90 male athletes, which is a modest number for detecting smaller differences, so this does not rule out the possibility that timing matters in ways this study was not equipped to detect.

This is a summary of research, not medical advice. Talk to your own healthcare provider about anything affecting your care.

This randomised controlled superiority trial compared early (day 1) versus delayed (once running at 70% maximal speed) introduction of eccentric hamstring strengthening within an otherwise standardised rehabilitation programme, in 90 male athletes with MRI-confirmed acute hamstring injury. The primary outcome was time to return to sport, with reinjury within 12 months as a secondary outcome. Median return to sport was 23 days (early) versus 33 days (delayed), but the adjusted hazard ratio was 0.95 (95% CI 0.56 to 1.60, p=0.84), indicating no statistically significant difference despite the numerically shorter median in the early group.

Reinjury odds ratios across three follow-up windows (0 to 2, 2 to 6, and 6 to 12 months) also showed no statistically significant between-group differences, though confidence intervals were wide (for example, 0.18 to 5.0 and 0.17 to 23.3), reflecting low event counts and limited power to detect differences in reinjury risk specifically. With 90 participants, this trial cannot confidently exclude a clinically relevant effect in either direction, and the wide confidence intervals around reinjury estimates are a particular limitation. Secondary functional outcomes at return to sport, including the Askling H-test and strength testing, were reported but not detailed in the abstract's headline results.

Overall, these findings do not support that accelerating eccentric loading changes recovery time or reinjury risk in this population, though the evidence base remains limited in size.