Injury Guide · Physio-Led
Hamstring Strains in Runners — Why They Keep Coming Back, and How to Fix Them for Good
Most runners treat hamstring injuries wrong. Here’s the evidence-based approach that actually works.
Hamstring strains are the most common muscle injury in runners and sprinters. More frustrating than the injury itself is the recurrence rate — research consistently shows that once you’ve had a hamstring strain, you’re two to six times more likely to get another one. Most of that recurrence isn’t bad luck. It’s the result of going back too soon, rehabbing the wrong way, or not understanding what the hamstring actually needs to stay healthy under running loads.
This post covers the full picture: why hamstrings get injured during running, what the best evidence tells us about rehab, and a practical ten-exercise phased framework to get you back running — and keep you there.
Why Hamstrings Get Injured During Running
The hamstring’s most vulnerable moment isn’t when you push off the ground — it’s during the late swing phase of the gait cycle, just before your foot contacts the ground. At this point your hip is flexed and your knee is rapidly extending, placing the hamstring under significant eccentric load while it’s near its maximum length. It’s a combination of high force and high stretch that most muscles never have to deal with.
“The hamstring is asked to decelerate the swinging leg eccentrically at near-maximum muscle length — precisely the condition it’s least prepared for after conventional rest-based rehab.”
— Clinical context from sports physiotherapy literature
The biceps femoris long head (BF long head) is by far the most commonly injured part. EMG studies show it reaches its peak activation during late swing, and it’s the structural architecture of this muscle — particularly its fascicle length — that determines how well it tolerates repeated high-speed eccentric loading. Short fascicles mean less capacity to absorb energy, and a higher risk of injury at speed.
This is why simply resting until the pain goes and then jogging a few easy miles is such a poor rehab strategy. The hamstring heals, but it heals without the eccentric strength, fascicle length adaptations, or neuromuscular timing it needs to survive the specific demands of running at pace.
What the Research Tells Us
Freeman et al. (2019) found that just 4 weeks of Nordic hamstring training produced a 9.8% eccentric strength gain — significantly outperforming sprint training alone, which produced 6.2%. The implication: you cannot rely on running itself to rebuild the specific eccentric capacity the hamstring needs.
Mendiguchia et al. (2020) compared sprint training with isolated eccentric training and found that sprint training produced significant changes in BF long head architecture — meaning sprinting isn’t just a performance test, it’s a training stimulus in its own right. But this only holds if you’re ready for it. Sprinting before adequate eccentric foundation work is when re-injury happens.
Askling et al. (2013) is the landmark study in this area. Athletes following the L-Protocol — a progressive eccentric programme focused on loading the hamstring at long muscle-tendon lengths — returned to sport in a mean of 28 days. The conventional rehab group took 52 days. That’s an 85% faster return to sport, with no increased re-injury rate. EMG analysis of the L-Protocol’s Glider exercise showed it elicits up to 60% MVC at hip and knee angles that closely mirror the late swing phase — exactly where injuries occur and exactly where the hamstring needs to be trained.
The thread running through all of this research is the same: eccentric loading at long muscle-tendon lengths is the key stimulus. It builds fascicle length, increases eccentric strength, and trains the hamstring in the position it will actually be challenged in when you’re running hard.
The 10-Exercise Phased Framework
What follows is a phased programme that progresses from early-stage pain management through to full return-to-performance sprint work. It draws directly on the L-Protocol, Nordic hamstring research, and sprint-based conditioning work. The phases are sequential — do not skip ahead, even if you feel good.
The goal in the first week is not rest — it is pain-free movement. Early loading prevents excessive scar tissue formation, maintains tissue extensibility, and begins the neural re-education process. Keep pain at or below 3/10 throughout.
Lie supine with your heel resting on a chair or bench at approximately 30° of knee flexion. Gently press your heel into the surface as if trying to drag it towards you — without movement. Hold the contraction. This recruits the hamstring through isometric tension, which has an analgesic effect on irritable tissue and begins to re-establish motor control without loading the muscle-tendon junction under stretch.3 × 30–45 sec hold · Pain ≤ 3/10 · Twice daily
Lie supine with one leg straight and the injured leg bent to 90°. Slowly straighten the injured leg while keeping the thigh vertical — extending the knee against gravity. The hamstring works eccentrically under load as it lengthens to control the extension. This is the first L-Protocol exercise because it loads the hamstring at a relatively short length, making it well tolerated in early stages. Move slowly and with complete control; never force range.
Once you can complete Phase 1 pain-free, you begin building the eccentric foundation that will protect you on return to running. The key shift here is moving to longer muscle-tendon lengths — this is where the adaptation that prevents re-injury actually happens.
Stand on the injured leg. Slowly hinge at the hip and glide forward, lowering your trunk while the standing leg remains mostly straight and the opposite leg trails behind — mimicking the late swing posture of running. The hamstring of the standing leg works eccentrically at increasing length as you lower. EMG data shows the Glider produces up to 60% MVC at hip and knee angles that closely replicate late swing phase — the exact position of injury. Control is everything; this is not a ballistic movement.
Stand on the injured leg, hold a light weight in the opposite hand. Hinge slowly at the hip, lowering the weight towards the floor while the standing leg stays soft at the knee and the rear leg extends behind you. The hamstring lengthens under load through a significant range. Unlike the Glider this adds external load, increasing the training stimulus while still controlling the range. Crucial: your back stays neutral throughout — do not round to reach further down.
Kneel with feet anchored (under a sofa, or with a partner holding your ankles). From upright, slowly lower your body forward towards the floor under complete hamstring control. Use your hands to catch yourself at the bottom, then push back to the start. Begin with hands closer to your knees — this reduces the lever arm and makes the load manageable in early Phase 2. The Nordic is one of the highest-evidence exercises in hamstring rehab and prevention. Research by Freeman et al. showed greater eccentric strength gains from four weeks of Nordics than from sprint training alone.
By now you should be running pain-free at easy pace. Phase 3 builds on the eccentric foundation with higher-load exercises that develop the fascicle length and tendon stiffness adaptations needed to tolerate fast running. This is where many runners get complacent — because they feel fine — but the structural adaptations that prevent re-injury take weeks to develop even after pain resolves.
The most demanding of the three L-Protocol exercises. Stand on the injured leg. With both arms extended forward, hinge deeply at the hip while simultaneously extending the non-stance leg behind you — creating a full body-length eccentric load on the hamstring at maximum muscle-tendon length. This is a single-leg Romanian deadlift taken to its full range, and it closely replicates the late swing demands of sprinting. Only progress to this exercise when the Glider and RDL are consistently pain-free at full range.
Progress to the full Nordic from the assisted version — allowing your body to lower all the way to the floor under hamstring control, using your hands only for the final catch. The progressive overload here comes from controlling a greater portion of the movement under bodyweight. Research consistently shows this exercise produces structural adaptations in biceps femoris fascicle length — making the muscle physically better able to absorb eccentric loads at speed.
Stand tall, drive one knee up to hip height, then reach that leg forward into a long stride while keeping a slight lean and a flat back. The hamstring of the reaching leg works eccentrically to control the reach and the landing. Walk through 10 reps, alternating legs. This exercise bridges the gap between isolated eccentric work and the dynamic demands of running — introducing the hamstring to a moving, multi-joint eccentric challenge with a stride-like pattern. It is particularly valuable because it trains the deceleration component of the swing phase in a controlled, low-velocity environment before reintroducing running speed.
Mendiguchia et al. (2020) demonstrated that sprinting itself produces changes in BF long head architecture. This means sprint-based work isn’t just a test of readiness — it’s a training tool. But it must be introduced progressively and only once Phase 3 exercises are fully consolidated. Begin with acceleration-focused drills before any maximal sprinting.
A-skips develop the hip flexion pattern and ground contact mechanics that underpin efficient sprinting. Drive the knee up rhythmically while landing on the ball of the foot with a slight forward lean. High knee drills progress this further. Both exercises recruit the hamstring in a fast, cyclical pattern that begins to replicate running demands without the full eccentric load of top-speed sprinting. These should feel smooth and controlled — never forced or compensated. If you feel a pull or tightness, drop back to Phase 3.
Begin at 60% of your maximum effort for 40m accelerations, progressing over two to three weeks to 80–90% and then full sprint efforts. This graduated exposure allows the BF long head to adapt progressively to increasing eccentric demands at speed — the same mechanism Mendiguchia’s group showed produces architectural change. Only progress speed when the previous intensity was completed pain-free across multiple sessions. Do not rush this phase. The hamstring is structurally sound when you are pain-free at 90%+ effort on repeated sprint efforts. Anything less and it is not ready, regardless of how good it feels at easy pace.
Programme Summary
| Phase | Timeframe | Key Goal | Exercises |
|---|---|---|---|
| Phase 1 | Days 1–7 | Pain-free movement, early load | Isometric Hold, Extender |
| Phase 2 | Days 7–21 | Eccentric foundation at length | Glider, SL RDL, Nordic (assisted) |
| Phase 3 | Weeks 3–5 | Load, architecture, dynamic control | Diver, Nordic (full), Walkouts |
| Phase 4 | Weeks 5–8 | Return to sprint performance | A-skips, Sprint build-ups |
The Honest Summary
Hamstring strains keep coming back because most runners return to running before the hamstring has the eccentric capacity to handle it. The research is clear on what works: progressive eccentric loading at long muscle-tendon lengths, starting early and progressing through to sprint-specific work before returning to race pace.
The L-Protocol’s 28-day return-to-sport figure sounds almost too good — but it’s grounded in sound biomechanics. By replicating the late-swing loading position through the Extender, Glider, and Diver, it prepares the hamstring for exactly what running will ask of it. Nordic training builds the underlying eccentric strength. Sprint drills and build-ups develop the architecture. Do all three, in order, without skipping phases, and the recurrence risk drops dramatically.
If you’re currently managing a hamstring injury, use the Capacity Checker in the PhysioRun app to objectively assess your readiness for each phase — it takes the guesswork out of the return-to-run decision.
Use the PhysioRun App
The Capacity Checker and Body Hub have guided rehab videos and objective return-to-run tests — free to use, built by a physio.
References
- Askling CM, Tengvar M, Thorstensson A. Acute hamstring injuries in Swedish elite football: a prospective randomised controlled clinical trial comparing two rehabilitation protocols. Br J Sports Med. 2013;47(15):953–9.
- Freeman BW, Young WB, Talpey SW, et al. The effects of sprint training and the Nordic hamstring exercise on eccentric hamstring strength and sprint performance in adolescent athletes. J Sports Med Phys Fitness. 2019;59(7):1119–1125.
- Mendiguchia J, Conceição F, Edouard P, et al. Sprint versus isolated eccentric training: comparative effects on hamstring architecture and performance in soccer players. PLoS One. 2020;15(2):e0228283.
- Askling CM, Malliaropoulos N, Karlsson J. High-speed running type or stretching-type of hamstring injuries makes a difference to treatment and prognosis. Br J Sports Med. 2012;46(2):86–7.
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