REF-321 · Sadeghi S, Newman C & Cortes DH, 2018 · PeerJ, · Paper · PubMed

Change in skeletal muscle stiffness after running competition is dependent on both running distance and recovery time: a pilot study

SWE of 8 leg muscles in 22 runners before and after races of 3-5, 10-13 or 26+ miles: 67% of muscles trended SOFTER immediately after the race; race distance affected biceps femoris, vastus lateralis and semitendinosus stiffness, recovery time affected the soleus

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

Participants

n=22 healthy individuals (age 23 ± 5 years), convenience sample, in three race categories: short distance (9 subjects, 3-5 miles), middle distance (10 subjects, 10-13 miles), long distance (3 subjects, 26+ miles)

Protocol

Shear modulus by a custom Focused Comb-Push Ultrasound Shear Elastography (F-CUSE) method, both legs, 8 muscles: rectus femoris, vastus lateralis, vastus medialis, soleus, lateral and medial gastrocnemius, biceps femoris, semitendinosus
Measured before and after the race
Linear mixed model with recovery time and running distance as fixed variables and shear modulus as the dependent variable

Key Results

Recovery time had a significant effect on the soleus (p = 0.05)
Running distance had a considerable effect on the biceps femoris (p = 0.02), vastus lateralis (p < 0.01) and semitendinosus (p = 0.02)
67% of muscles showed a DECREASING stiffness trend from before the race to immediately after
Authors: preliminary results; SWE could potentially quantify changes in muscle mechanical properties as a way to measure recovery in runners

Mechanism

Immediately after a running race most muscles measured were softer, not stiffer — consistent with the endurance direction seen after an ultra (Andonian 2016 REF-313) rather than the eccentric-DOMS stiffening seen at 24-96 h after downhill running (Kong 2018 REF-317).

Inference, not tested: distance mattered for the hamstrings and vastus lateralis, and time-since-race for the soleus, so different muscles carry the race differently; the pilot design cannot say which muscle recovers slowest.

Practical Application

Pilot (n=22): after races from 3-5 to 26+ miles, 67% of the 8 leg muscles measured trended softer immediately post-race; race distance influenced biceps femoris, vastus lateralis and semitendinosus stiffness, and recovery time influenced the soleus — the running load lands muscle by muscle, not uniformly
The distance effect on the hamstrings and vastus lateralis is the dose-response signal in this study; the soleus is the muscle whose stiffness related to how long after the race it was measured
Inference, not tested: recovery planning after long races may need to be muscle-specific (hamstrings and quads for distance, calves for time), but the study has one post-race measurement and only 3 runners in the long-distance group, so it cannot give timelines
Not from this paper; the base's own practice: treat the long-run/race recovery window as longer than the short-race one — this study supports a distance effect on stiffness but gives no durations

Limitations

Small, unequal groups (9 / 10 / 3 per distance category); convenience sampling
Running only — cycling may differ (less eccentric component)
Single post-race measurement — no longitudinal recovery tracking
How this entry was checked and changed
Content correction 2026-09-27
"Longer distance = greater and more prolonged stiffness changes" -> the abstract shows a distance effect on three muscles; "more prolonged" is not shown (one post-race measurement); reworded.
"Soleus is the slowest-recovering muscle" -> the abstract: recovery time had a significant effect on the soleus; no ranking of recovery speed; reworded.
Limitations "n=7-8 per group" -> 9 / 10 / 3 per the abstract; Sport "cycling, running" -> running; Tier annotated from the abstract (healthy individuals, 23 ± 5 y).