Published by ProMOTION Physiotherapy Clinical Team · Clinically reviewed · Published: 11 September 2026
A hamstring strain is a tear in the muscle fibres or tendon at the back of the thigh, most often where the muscle meets the tendon near the sit bone. Runners usually feel it as a sudden grabbing or sharp pain during a fast stride or sprint finish, sometimes followed by bruising. Most recreational-runner strains are Grade I or II: fibres torn but the muscle not completely ruptured.
The most common cause is a mismatch between the load a stride demands and the hamstring’s current capacity, particularly during the late swing phase of running when the hamstring is lengthening and decelerating the leg at speed. Fatigue, a recent jump in mileage or pace, and reduced hip control all raise the load on that single moment in the stride.
In the first 48 to 72 hours, protect the area: reduce load, use compression, avoid aggressive stretching into pain. After that, gentle movement starts sooner than most runners expect, because prolonged rest weakens the muscle further. A same-day chartered physiotherapist assessment grades the tear and builds a loading plan around your stage of healing.
The rest of this article covers what is happening in the tissue, a self-check to grade your strain, why resting too long can backfire, how to tell a strain from referred back pain, what the evidence shows, and the red flags that mean urgent care rather than a physio appointment.
Why hamstring strains happen when you run
A hamstring strain happens when the muscle-tendon fibres stretch beyond their current capacity while contracting, usually in late swing phase just before the foot strikes the ground.
At that instant the hamstring is doing two jobs at once: lengthening rapidly as the knee straightens, and generating high force to slow the shin before impact. This eccentric contraction under high velocity puts more strain through the muscle-tendon junction than almost any other point in the stride. The free tendon near the ischial tuberosity (the sit bone) and the junction between the biceps femoris muscle belly and its tendon are the weakest points mechanically, which is why strains cluster there. When fibres tear, the muscle lays down new tissue that is initially disorganised and less extensible than mature muscle, part of why the area feels tight for weeks after pain settles, not because it is still “damaged” as on day one. Rest alone does not resolve this: unloaded muscle regenerates weaker, so a hamstring simply rested and returned straight to sprinting is set up to re-tear. Morning stiffness is common because overnight immobility lets healing tissue shorten and the first steps re-stretch it; this is expected, not a sign of worsening.
Grade your strain and know your next step
Hamstring strains are graded 1 to 3 by how much tissue is torn; this is not a diagnosis, but it flags who needs an urgent assessment.
| What you notice | Likely grade | What it suggests |
|---|---|---|
| Tightness or a pulling sensation, no loss of strength, ran the rest of the session | Grade I (mild) | Reduce load for a few days, gentle range-of-motion work, reassess at 5 to 7 days |
| Sharp pain that stopped the run, some bruising or swelling within 48 hours, weaker when you contract the hamstring | Grade II (moderate) | Book an assessment within the week; loading plan needed, not full rest |
| A “pop” felt at the moment of injury, significant bruising, difficulty walking normally, or a palpable gap in the muscle | Grade III (severe, possible tear or avulsion) | See a physiotherapist or GP promptly; imaging may be needed to check for a tendon avulsion |
If unsure which row fits, book an assessment rather than guess: a chartered physiotherapist grades the strain in one session using strength and flexibility testing, more useful for early rehabilitation than waiting for a scan.
Why two weeks of rest often backfires
Complete rest for a fortnight feels sensible, but it usually delays return: strength and stretch tolerance drop faster than they can be regained.
Runners who stop all loading tend to come back to a hamstring that is stiffer, weaker, and less coordinated than the one injured, then re-injure it within the first two weeks of resumed training. This is one of the gaps in most online hamstring advice, which still frames rest as the default first step. A better approach starts pain-free isometric holds within days, moves to slow eccentric loading such as Nordic curl progressions once pain allows, and only reintroduces sprinting once the hamstring produces near-normal force. A 2022 study found low-volume Nordic exercise raised eccentric strength and cut hamstring injuries in professional footballers. This earlier reload window is the biggest difference between runners who return once and those who re-strain repeatedly.
Hamstring pain or referred back pain? How to tell the difference
Posterior thigh pain that started gradually or comes with lower back stiffness is more likely referred from the lumbar spine or sciatic nerve than a true muscle strain.
A genuine strain has a clear onset during a specific stride, and is reproduced by resisting a hamstring contraction or stretching the muscle directly. Referred pain from the lower back or an irritated sciatic nerve builds over days without one obvious moment of injury, can travel below the knee, and changes with back movements rather than hamstring-specific tests. Runners sometimes treat a “stubborn strain” with rest and stretching for weeks when a lumbar or neural component was driving the pain the whole time. A physiotherapist checks both the hamstring and the lower back and nerve mobility in the same session, to rule this in or out early.
What the evidence actually says
The research has shifted markedly over the past decade, and does not fully support the “rest and stretch” advice still common online.
A 2016 review in Current Sports Medicine Reports (Chu and Rho) found recovery timelines vary enormously by strain type, from eight to twenty-five days for professional athletes with lower-grade strains up to fifty weeks in overstretch-type injuries, and that imaging identifies the injury well but does not reliably predict recovery time, meaning clinical assessment still guides the return-to-run decision more than a scan. The same review found recurrence is common, roughly one in three strains recurring, often within two weeks of returning to sport, which supports a graded, supervised return. Where evidence is mixed is on stretching: some studies support early gentle range-of-motion work, others find no added benefit over strengthening alone.
When to worry: red flags that need same-day care
Most hamstring strains are safe to manage with physiotherapy, but some need same-day medical attention instead of a booked physio appointment.
Seek same-day GP, NHS 24 on 111, or A&E assessment if you experience a loud pop with immediate inability to bear weight, a visible or palpable gap in the muscle with significant swelling (possible complete rupture or tendon avulsion, more common in sprinters), numbness, tingling or weakness spreading down the leg alongside back pain (possible nerve involvement), calf or thigh swelling with warmth unrelated to a specific running moment (possible deep vein thrombosis), or fever and increasing redness around the injury (possible infection). NHS Inform Scotland’s guidance on thigh injuries sets out this same threshold for when self-management is appropriate and when urgent care is needed; if in doubt, treat it as urgent.
Getting back to running from our Davidsons Mains clinic
A hamstring assessment at our Davidsons Mains clinic runs to a full hour for the first visit, enough time to grade the strain, test hip and trunk control, and build a week-by-week plan rather than a generic handout.
Because most runners we see train along the Silverknowes and Cramond coastal path, Trinity, or the hillier routes around Corstorphine, we look at how your terrain and pace sessions load the hamstring, not just the injury alone. Where stride seems to be contributing, gait analysis shows exactly what is happening at the point of injury on video. A typical phased return: weeks 0 to 2, pain-free isometric work plus walking; weeks 2 to 6, progressive eccentric loading and hip strengthening, with easy running once strength testing clears you; weeks 6 to 12, pace work and sprint drills once the hamstring matches the uninjured side. Runners building back towards races often combine this with our Pilates classes for hip and core control.
Common questions
How long does a hamstring strain take to heal?
It depends heavily on grade and location: mild Grade I strains often settle within one to three weeks with the right loading, while Grade II strains can take four to eight weeks, and severe tears longer still. Location matters too, tendon-based strains near the sit bone tend to take longer than strains within the muscle belly itself.
Can I keep running with a mild hamstring strain?
Usually not at full pace. Light, pain-free walking or very gentle jogging may be appropriate for a true Grade I strain once assessed, but running through sharp pain risks converting a mild strain into a more significant tear. An assessment tells you which category you fall into.
Should I stretch a strained hamstring?
Gentle, pain-free range-of-motion work is usually fine once the acute stage has settled, but aggressive stretching into pain in the first days after injury can aggravate healing tissue. Evidence on stretching specifically is mixed, so this is best guided individually rather than from a generic routine.
What is the single-leg bridge test and how do I use it?
Lying on your back, bend one knee and place that foot flat on the floor, then lift your hips while keeping the other leg straight, holding for a few seconds. Pain, a noticeable strength difference, or shaking compared with the uninjured side suggests the hamstring is not yet ready for running loads; a smooth, symmetrical hold is a reasonable sign to progress toward light jogging under guidance.
Why do I keep re-straining the same hamstring?
Repeated strains usually mean the muscle returned to running before it regained full strength, often because rest alone replaced progressive loading, or because hip weakness or a back or nerve component was never addressed. An assessment looks beyond the hamstring itself for what is actually driving the pattern.
Do I need a scan for a hamstring strain?
Not usually. Clinical assessment, including strength and flexibility testing, grades most strains accurately without imaging. A scan is more useful when a complete tear or tendon avulsion is suspected, or when recovery is not progressing as expected.
About the author
This article was written and clinically reviewed by the ProMOTION Physiotherapy Clinical Team, Chartered Physiotherapists (CSP) and HCPC registered, with backgrounds spanning NHS musculoskeletal services, elite sport, and private practice. Read more about the team on our practitioner page.
Book your hamstring assessment
If you have strained your hamstring or keep re-injuring the same one, book online for an assessment at our Davidsons Mains clinic, or call 0131 538 5467. We see runners from across Edinburgh, including Cramond, Silverknowes, Trinity, Corstorphine and Barnton. If you are building back towards regular running, download our free running injury guide for a structured return-to-run framework.
