REF-322 · Pieters D, Witvrouw E, Steyaert A, Vanden Bossche L, Schuermans J, Freitas S & Wezenbeek E, 2025 · Journal of Strength and Conditioning Research, · Paper · PubMed

The Time-Course of Hamstring Muscle Passive Stiffness and Perceived Tightness After Strenuous Exercise

After prone leg curls to exhaustion in 24 subjects, semitendinosus stiffness peaked at 48 h (+9.7%) and was back to baseline at 96 h, while perceived hamstring tightness peaked at 24 h: feel and tissue did not follow the same time course

Blimited evidenceMeasured on recreational to trained athletesWritten before October 2026, being re-checked

Participants

n=24 subjects (training status not given in the abstract)

Protocol

Prone leg-curl exercise until full exhaustion
At 6 time points (baseline, 0, 24, 48, 72 and 96 h post-exercise): passive stiffness of each hamstring head by shear-wave elastography, and perceived overall hamstring tightness on a numeric rating scale
Mixed models; α = 0.05

Key Results

Semimembranosus and biceps femoris long head: no significant change in stiffness over time (p > 0.05)
Semitendinosus shear modulus increased significantly, reaching its maximum at 48 h (+9.7%, p = 0.012), then decreased significantly (−7.8%, p = 0.024) to baseline level by 96 h
Perceived hamstring tightness peaked at 24 h (p < 0.001), decreased significantly between 24 and 48 h (p = 0.036), and normalised by 96 h (p < 0.001)
The time course of perceived tightness did not follow the localised passive stiffness — the authors advise caution when designing training and recovery programmes from either alone

Mechanism

Only one of the three hamstring heads (semitendinosus) stiffened measurably, and it did so a day after the athlete felt tightest. Inference, not tested here: perception seems to track an earlier, more global signal (soreness, pain) while the tissue change in the semitendinosus builds and resolves more slowly; the abstract does not explain why the semitendinosus alone responded, and says nothing about its fiber composition.

Practical Application

In 24 subjects after leg curls to exhaustion, the semitendinosus was stiffest at 48 h (+9.7%) and back to baseline only at 96 h, whereas the hamstrings FELT tightest at 24 h and already less tight by 48 h — the day the athlete feels better is the day the tissue measure peaks
The other two hamstring heads did not stiffen at all, so a "tight hamstring" feeling is not a read-out of hamstring stiffness in general
Inference, not tested: perceived readiness at 48 h after a heavy hamstring session can overstate tissue recovery; the study measured no performance or injury outcome
96 h to tissue normalisation matches the 4-day passive-stiffness elevation after downhill running in Kong 2018 REF-317
Not from this paper; the base's own practice: after an unaccustomed, exhaustive eccentric hamstring session, do not schedule maximal sprinting inside 72-96 h on the strength of "feels fine"

Limitations

Isolated leg-curl exercise — not whole-body training
Training status not stated in the abstract (active, not elite, per the original entry)
Hamstrings only — quadriceps and calves may differ; no performance outcome
How this entry was checked and changed
Why this level

regraded 2026-09-27 from A-: uncontrolled pre-post, n=24

Content correction 2026-09-27
"Semitendinosus (most Type II-fiber dominant of the hamstrings) ... consistent with Lievens fiber type findings" -> not in the abstract; relabelled as untested speculation.
"Validates HRV paradox principle" removed (not from this paper); scheduling advice labelled as house practice.
Tier 4-5 (Elite) -> Tier 1-2 (abstract: "subjects"; entry's own limitations: active, not elite); Level A- -> B (uncontrolled pre-post, n=24).