Eccentric Strength and Injury Risk: What the Data Actually Shows
Summary
Eccentric strength deficits are consistently linked to hamstring and other soft tissue injuries in sport. Here's what the evidence shows and how to use it to protect your athletes.
The relationship between eccentric strength and injury risk is one of the more robust findings in sports medicine — and one of the most actionable. Unlike many injury risk factors (age, previous injury, training load) that are either fixed or difficult to modify quickly, eccentric strength deficits can be identified, targeted, and improved.
Why Eccentric Strength Specifically
During high-speed running, the hamstrings undergo an eccentric loading phase in the late swing phase — they are contracting to decelerate the extending knee while the muscle is lengthening. The forces involved are substantial: peak hamstring forces during sprinting have been estimated at over 20 N/kg of body mass (Chumanov et al. 2012). If the eccentric capacity of the hamstrings is insufficient relative to this demand, the risk of strain injury rises.
Bourne et al. (2017) demonstrated in a prospective study that lower eccentric hamstring strength — assessed via the Nordic curl — was significantly associated with hamstring strain injury in professional football players. Athletes in the lowest tertile of eccentric strength were at substantially elevated injury risk compared to those in the upper tertile. This is prospective data, not simply a correlation.
Ekstrand et al. (2011), using data from the UEFA Elite Club Injury Study, showed that hamstring injuries account for 37% of all muscle injuries in professional football and that teams with higher injury burden showed consistently lower eccentric hamstring strength profiles across the squad.
Asymmetry as a Risk Factor
Absolute eccentric strength matters. But interlimb asymmetry may matter more. An athlete whose dominant leg eccentric hamstring strength is 20% greater than the non-dominant side is at elevated risk from the weaker limb — not because that limb is inherently weak, but because the demand is equal on both sides while the capacity is not.
A reasonable working threshold is that asymmetries exceeding 10-15% in eccentric hamstring strength warrant targeted intervention. This is not a hard clinical cut-off — it is a pragmatic threshold for flagging athletes who deserve closer monitoring and specific loading.
Testing Eccentric Strength: The Static vs Dynamic Problem
The gold standard for isolated eccentric strength assessment is isokinetic dynamometry at controlled angular velocities. It is precise, reliable, and well-validated. It is also expensive and not universally available — which is why the Nordic hamstring curl with a NordBoard or similar force-measuring device has become widely used as a field alternative.
The NordBoard approach measures peak force during the eccentric lowering phase of the Nordic curl: the athlete kneels, feet anchored, and falls forward under eccentric hamstring control while a load cell at the ankle records force bilaterally. It is practical and provides genuinely useful bilateral data on eccentric output.
However, there is a meaningful limitation to acknowledge: static or quasi-static eccentric force measurements — including NordBoard-style protocols — do not always correlate well with dynamic movements such as high-speed sprinting. The muscle activation pattern, velocity of lengthening, and joint angle demands during terminal swing in a sprint are fundamentally different from a slow, controlled Nordic eccentric. Strength produced under one set of conditions does not transfer perfectly to the other.
This is not an argument against the Nordic or the NordBoard. It is an argument for not treating them as the sole measure of eccentric capacity, particularly for athletes whose primary injury risk occurs during high-velocity dynamic movements.
Dynamic Bilateral Assessment
A complementary approach — one that addresses the static/dynamic validity gap directly — is measuring force output during actual resisted dynamic movement, with bilateral resolution. Force-measuring sled protocols that capture left and right leg force independently during resisted sprinting generate data in an environment that closely mirrors the injury mechanism itself.
The reason this matters goes beyond movement specificity. Static testing creates conditions that invite compensation. During a NordBoard-anchored Nordic curl, an athlete can unconsciously redistribute load between limbs — subtly shifting body position, adjusting bracing, or favouring the stronger side without either athlete or practitioner being aware of it. The test is controlled enough that these small adjustments are physically tolerated and go undetected. Dynamic movement is not. When an athlete is driving forward against friction resistance at sprint pace, the continuous, momentum-driven nature of the movement limits the scope for compensation significantly. You cannot quietly shift load sideways mid-stride without it showing up immediately in force output and gait.
The practical consequence is that asymmetries measured under dynamic bilateral loading tend to be larger in magnitude than those captured by static eccentric protocols. A test might show 8% left-right asymmetry on a NordBoard; bilateral force profiling during resisted sprinting may reveal 18% on the same athlete. Neither number is wrong — they are measuring genuinely different things. But the dynamic number is closer to what is actually happening during the sprint phase when hamstring eccentric demand is greatest, and it is the number that cannot be masked by compensation. For an athlete returning from hamstring injury, or presenting with a history of it, that bilateral dynamic picture is clinically significant in a way that static assessment alone cannot provide. Used together, the two approaches triangulate a far more complete and honest picture of where the eccentric deficit actually lives.
Training Eccentric Hamstring Strength
Nordic hamstring curls remain the most evidence-backed intervention for developing eccentric hamstring strength at the long muscle lengths relevant to sprinting. Al Attar et al. (2017) showed that Nordic programmes reduced hamstring injury incidence by over 50% in football players. The dose needed for meaningful protection is relatively modest: 2-3 sessions per week, 3-4 sets, during pre-season; 1-2 sessions per week in-season for maintenance.
The athlete does not need to love the Nordic. They need to do it consistently. But the monitoring picture around it should be broader than a single static test suggests.
References
Bourne, M.N. et al. (2017). Impact of eccentric exercise on hamstring strain injury risk. BJSM, 51(18), 1364.
Ekstrand, J. et al. (2011). Hamstring muscle injuries in professional football. BJSM, 45(11), 975-979.
Chumanov, E.S. et al. (2012). Hamstrings are most susceptible to injury during the late swing phase of sprinting. Med Sci Sports Exerc, 44(5), 998-1005.
Al Attar, W.S.A. et al. (2017). Effect of injury prevention programs that include the Nordic hamstring exercise on hamstring injury incidence. Sports Med, 47(5), 907-916.
Mark Fisher
Founder, Swift Performance
Mark Fisher is the founder of Swift Performance and has spent 30 years designing and building athlete testing equipment used by elite sport programmes and universities worldwide. He has worked alongside researchers and PhD candidates across biomechanics, sprint mechanics, and strength science — developing the hardware and software they use to collect and analyse performance data. His writing comes from three decades at the intersection of applied sport science and precision measurement technology.
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