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

Key points

1. 01Median return to sport was 23 days (early group) versus 33 days (delayed group), but this difference was not statistically significant (adjusted HR 0.95, 95% CI 0.56 to 1.60, p=0.84).
2. 02Reinjury rates were similar at all follow-up points: 8.3-8.8% within 2 months, 3.2-6.2% at 2-6 months, and 3.4-5.9% at 6-12 months for both groups.
3. 03The early lengthening group had significantly greater eccentric strength at return to sport (198 Nm vs 182 Nm at 60 degrees/s, p=0.029), though this isolated finding should be interpreted with caution.
4. 04The trial was underpowered due to a higher-than-expected loss to follow-up (19% vs anticipated 10%), meaning a clinically relevant benefit of up to 14 days cannot be ruled out.
5. 05Both protocols were safe; pain exacerbation rates during rehabilitation were not significantly different between groups.

How it was conducted

Design

Single-centre parallel-group randomised controlled superiority trial (Aspetar Hospital, Doha, Qatar)

Participants

90 male athletes aged 18-36 (median 26 years) with MRI-confirmed grade I-II acute hamstring injury; predominantly professional football players

Groups

Early lengthening (n=44): Askling lengthening exercises introduced on day 1 of rehabilitation. Delayed lengthening (n=44): same exercises introduced only after athlete could run at >70% self-rated maximal speed

Primary outcome

Days from injury to full unrestricted training and/or match play

Secondary outcome

Reinjury rate within 2, 6, and 12 months after return to sport

Follow-up

12 months post return to sport; recruitment March 2014 to December 2018

What they found

• Median return to sport: 23 days (IQR 16-35) early lengthening vs 33 days (IQR 23-40) delayed lengthening; median difference 8 days (95% CI 0 to 14), Cohen's d=0.39.
• Adjusted Cox regression HR for early vs delayed lengthening: 0.95 (95% CI 0.56 to 1.60, p=0.84) - no significant difference.
• Unadjusted Cox regression HR: 1.15 (95% CI 0.72 to 1.84, p=0.57).
• Sensitivity analysis adjusted HR: 0.82 (95% CI 0.49 to 1.37, p=0.44).
• Reinjury within 2 months: 3/36 (8.3%) early vs 3/34 (8.8%) delayed; OR=0.94 (95% CI 0.18 to 5.0, p=0.94).
• Reinjury 2-6 months: 1/31 (3.2%) early vs 2/32 (6.2%) delayed; OR=2.00 (95% CI 0.17 to 23.3, p=0.58).
• Reinjury 6-12 months: 2/34 (5.9%) early vs 1/29 (3.4%) delayed; OR=0.57 (95% CI 0.05 to 6.6, p=0.66).
• Eccentric isokinetic strength at 60 degrees/s at return to sport: 198 Nm (IQR 175-241) early vs 182 Nm (IQR 149-201) delayed (p=0.029).
• Median days from injury to first lengthening exercise: 5 days (IQR 3-6) early group vs 16 days (IQR 11-23) delayed group.

Limitations

• Loss to follow-up was 19%, higher than the anticipated 10%, leaving the study potentially underpowered to detect the observed 8-day median difference.
• Only male athletes from a single sports medicine centre in Qatar were studied, limiting generalisability to female athletes and other settings.
• Treating physiotherapists could not be blinded to group allocation, introducing possible bias in rehabilitation progression decisions.
• Reinjuries were not systematically confirmed by MRI, so the exact location and severity of reinjuries was not always known.

Why it matters

For patients

An athlete recovering from a hamstring strain can expect a similar recovery timeline regardless of whether their physiotherapist starts eccentric loading exercises immediately or waits until they can run comfortably - both approaches are safe.

For clinicians

Clinicians have flexibility in when to introduce Askling-style lengthening exercises during hamstring rehabilitation; early introduction does not accelerate return to sport but also carries no additional risk of reinjury.

For readers

This well-designed RCT closes a specific gap in hamstring rehabilitation evidence, confirming that the timing of eccentric lengthening exercise introduction is less important than including such exercises at some point in the programme.