A February 2026 paper published in PLOS One has tightened the picture of where marathon running actually damages the hamstring, and the answer is more localised than the post-race ache might suggest. The study combined MRI-based T2 mapping with self-reported pain scoring across a cohort of recreational marathon finishers and concluded that the distal and middle sites of the biarticular hamstring muscles take significantly more damage than the proximal site, with the elevated T2 signal still present three days after race day and broadly resolved by day eight. The proximal site stayed essentially unchanged across the same window.
The pattern matters because it points at the part of the hamstring that does the most braking work during the late swing phase of the marathon stride. The biarticular hamstrings — the long head of biceps femoris, semitendinosus and semimembranosus — span both the hip and the knee, and eccentric loading on these muscles is what slows the lower leg before foot strike. In a marathon, an athlete repeats that braking cycle around 30,000 times. The new paper argues that the distal and middle portions of those muscles sit at the mechanical hot spot of that workload, and that is where the inflammatory and structural markers concentrate.
A companion result from a broader 2026 PLOS One survey, published earlier in the same window, found that 24.2 per cent of marathon participants reported hamstring pain or stiffness in the days following the race. The prevalence was higher in male runners, in the 30-to-34 age bracket, in first-time marathon finishers, in athletes who reported significant weekly mileage during training and in those who layered other aerobic work — cycling, rowing, cross-trainer sessions — on top of their running plan. The link to additional aerobic cross-training is the surprise of the survey: it is plausibly a fatigue-accumulation signal rather than a direct mechanism, but it is consistent enough across sub-groups to be worth noting.
For runners building toward a late-spring or summer marathon, the practical reading is straightforward. Hamstring damage is concentrated in regions that respond well to specific eccentric strength work — Nordic hamstring curls, single-leg Romanian deadlifts and high-velocity bridge variations — and several sports-medicine groups have argued for years that those exercises should be in a standard marathon strength plan. The new MRI evidence is the clearest mechanistic case yet that those regions are the ones doing the damage-incurring work, and that a four-to-eight week pre-race window of progressive eccentric loading is a reasonable injury-prevention investment.
The recovery side of the picture is equally useful. Because the damage is concentrated and resolves on a roughly eight-day timeline, the paper supports something experienced coaches have long recommended: the hamstrings, not the quads, are usually the limiting tissue in the first ten days after a marathon, and post-race plans should respect that. Light walking and easy cycling are well-tolerated within 72 hours; longer easy runs are usually fine by day five to seven; and any return to faster work — strides, tempo, even brisk uphill walking — is best delayed until the second post-race week. Coaches working with athletes targeting back-to-back autumn marathons should plan a hamstring-protected ten-day block rather than a flat ten-day rest, the paper's authors suggest.