REF-327 · Coale AT, Pittman SC, Dorsey CB, Chowdry F & Berkoff DJ, 2025 · Journal of Ultrasound, · Paper · PubMed
The effect of repetitive exercise on tensile changes in the infraspinatus muscle evaluated with ultrasound elastography
In 10 healthy subjects, infraspinatus strain went 0.5 (baseline) → 0.7 immediately after a standardized exercise bout → 0.6 at day 1 → 0.4 at day 2: stiffness took up to 48 h to return within 10% of baseline and then overshot to softer than baseline
Participants
n=10 healthy subjects (average age 23.7)
Protocol
Baseline ultrasound elastography scan, a standardized exercise program, a post-exercise scan, then daily scans until results returned to within 10% of baseline
Elastography measured around the infraspinatus tendon; the deltoid used as the baseline standard
Summary statistics, t-tests and regression
Key Results
Average strain: 0.5 at baseline, 0.7 immediately post-exercise, 0.6 at day 1, 0.4 at day 2
Statistically significant differences between every time point: baseline → post +0.24 (p < 0.0001); post → day 1 −0.14 (p < 0.0001); day 1 → day 2 −0.15 (p < 0.0001); baseline → day 2 −0.05 (p < 0.005)
Infraspinatus stiffness increased immediately after exercise and took up to 48 h to return within 10% of baseline
At day 2 there was an "overcorrection": the infraspinatus remained softer than baseline
Mechanism
Stiffness peaked immediately after the bout, resolved over two days, and at day 2 had passed below the starting level. Inference, not tested: the overshoot into a softer-than-baseline state is the same direction as the endurance "softening" seen after long races (Andonian 2016 REF-313, Sadeghi 2018 REF-321) — whether it marks vulnerability, remodelling or simply measurement noise in a 10-person sample is not something this study can say.
Practical Application
In 10 healthy subjects a single rotator-cuff exercise bout raised infraspinatus strain from 0.5 to 0.7 (+0.24; about +40%), and it took until day 2 to be back within 10% of baseline — at which point the muscle read softer than baseline (0.4)
Not from this paper (cross-entry comparison): the 48-h return to baseline here is consistent with the 48-h return seen after eccentric elbow flexion (Cheng 2026 REF-320) and the 48-h elevation after submaximal trunk work (Brandl 2024 REF-324); other protocols in the base run longer (96 h after downhill running, Kong 2018 REF-317) — the window depends on the load, not on a fixed "48-h rule"
Inference, not tested: a day-2 overshoot into softer tissue may be a period when the muscle behaves differently from baseline; the study measured no injury or performance outcome, so "injuries happen 2-3 days after hard training" is not something it shows
Not from this paper; the base's own practice: daily tracking of an individual's stiffness curve (myotonometry or elastography where available) can show when that athlete's tissue is back to their own baseline
Limitations
Rotator cuff — not locomotor muscles; upper-body exercise only
Very small sample (n=10); no control group
Single exercise bout
How this entry was checked and changed
Content correction 2026-09-27
Added the abstract's step changes (+0.24, −0.14, −0.15, −0.05) with their p-values.
"48h recovery timeline consistent across all studies in this section" -> other entries show 96 h (Kong 2018, Pieters 2025); reworded to the specific comparisons. "This overshoot explains why some injuries occur 2-3 days after hard training" -> no injury outcome; relabelled as untested inference.