NSAIDs for training soreness

Non-selective NSAIDs inhibit cyclooxygenase-1 and cyclooxygenase-2, blocking the conversion of arachidonic acid to PGH2 and therefore the downstream prostaglandins (PGE2, PGI2) and thromboxane. PGE2 sensitises peripheral nociceptors and drives the vasodilation and plasma extravasation of an inflammatory response. Block it and pain, swelling, and warmth all fall. This is one of the best-characterised drug mechanisms in medicine, which is why the mechanism axis on this audit scores near the top of the index.

The catch is that prostaglandins are not only pain molecules. PGE2 and PGF2alpha rise after mechanical loading and participate in the signalling that follows it: satellite cell proliferation and differentiation, fibroblast activity in tendon, and osteoblast behaviour in bone. Post-exercise inflammation is a construction order, not an error message. Blocking the signal blocks part of the response you were training to provoke.

COX-1 is the other half of the safety story. It maintains gastric mucosal prostaglandins (hence GI erosion and bleeding), platelet thromboxane A2 (hence impaired aggregation), and renal prostaglandins that preserve glomerular perfusion when circulating volume is low.

That renal detail deserves emphasis for athletes specifically. A dehydrated athlete in a hot endurance event is in exactly the state where renal prostaglandins are doing the work of maintaining filtration. Adding an NSAID removes that compensation. NSAID use plus dehydration plus prolonged endurance load is a well-documented route to acute kidney injury, and it becomes considerably worse in combination with hyponatraemia.

Trappe et al. 2002 gave 1200 mg/day of ibuprofen or acetaminophen after eccentric exercise and found the normal post-exercise rise in muscle protein synthesis was abolished. Mackey et al. 2007 found indomethacin blunted the satellite cell response to eccentric loading. Both are mechanistic studies with small samples, and both point the same way.

Lilja et al. 2018 took it to a training outcome: eight weeks of resistance training in young adults, high-dose ibuprofen (1200 mg/day) versus low-dose aspirin, with smaller gains in muscle volume and strength in the ibuprofen group. Small n, single trial, and consistent with the mechanism, which is the combination that should raise concern without settling the matter.

Bone is where the orthopaedic literature is most anxious. Multiple reviews associate NSAID exposure with delayed union and higher nonunion rates, with the strongest concern in stress fracture, spinal fusion, and paediatric patients. The evidence is largely observational and confounded by why people were taking analgesia in the first place, and the field genuinely disagrees about how strong the effect is at short courses and modest doses. That disagreement is real and should not be flattened in either direction.

On the outcome athletes actually care about: NSAIDs reliably reduce reported soreness and do not reliably speed the return of force. Feeling recovered while not being recovered is a specific and dangerous combination, because the pain that would have modulated your next session has been removed while the tissue's actual state has not changed.

Where NSAIDs are entirely legitimate: acute painful conditions under clinical guidance, defined inflammatory disease, and post-operative protocols decided by a surgeon who has weighed exactly this tradeoff.