Intense exercise can cause random bruising by straining a muscle enough to injure deep muscle tissue and rupture blood vessels, allowing blood to pool beneath the skin.
Notes on verification
Multiple independent, high-quality medical sources (Cleveland Clinic, Mayo Clinic, WebMD, AAOS) consistently confirm the physiological mechanism connecting muscle strain, blood vessel rupture, and bruising. [tier=silver indep_score=0.85 clusters=5 claim_tier=notable | kind=empirical eligibility=high (extractor: empirical/medium)]
Sources
- Random Bruising: 13 Possible Causes Excluding Obvious Injury (seed:health_and_medicine)
- https://my.clevelandclinic.org/health/diseases/22336-muscle-strains (corroboration)
- https://www.webmd.com/fitness-exercise/muscle-strain (corroboration)
- https://orthoinfo.aaos.org/en/diseases--conditions/muscle-strains-in-the-thigh/ (corroboration)
- https://www.mayoclinic.org/first-aid/first-aid-bruise/basics/art-20056663 (corroboration)
- https://www.livestrong.com/article/505433-bruised-legs-after-exercising/ (corroboration)