Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely consumed among athletes worldwide in relation to muscle injury and soreness. This presentation aims to provide an overview of studies investigating their effect on skeletal muscle adaptation, including the repair processes in injured muscle, adaptation to unaccustomed and/or resistance exercise and training. Muscle injury occurs in diverse situations and the nature of muscle injuries varies significantly, from classical muscle strain injuries to contusion and overload injuries. Strain injuries occur at the interphase between the muscle fibres and connective tissue most often in the myotendinuous junction, whereas contusion or overload injury can damage both myofibres and intramuscular connective tissue. It is important to distinguish between types of muscle injury -and to keep in mind that unaccustomed (voluntary) exercise does not necessarily lead to muscle damage or injury, at least not to the muscle fibres per se. Likewise, delayed onset muscle soreness (DOMS) following unaccustomed exercise can occur in the presence or absence of actual damage to the muscle fibres. Investigations into the potential of NSAIDs to alleviate DOMS in exercised muscles are numerous, and the outcomes are inconsistent, with roughly equal numbers finding no effect of NSAIDs on DOMS or a significant attenuation of DOMS. -NSAID effects on cells responsible for muscle repair -satellite cells A population of muscle stem cells, known as satellite cells, is well recognised as being indispensable for the repair of skeletal muscle. The evidence, at least from animal studies, for an inhibiting effect of NSAID action on satellite cells is convincing (Bondesen 2004, 2006) and in addition, human studies have shown a reduction of satellite cell numbers 8 days after exercise by NSAIDs (Mackey 2007, Mikkelsen 2009). -NSAIDs and muscle adaptation without injury -protein synthesis & hypertrophy A blunting of the muscle hypertrophy response to overloading has been reported in animals treated with NSAIDs. In humans, NSAID ingestion has been reported to suppress the protein synthesis response to a single bout of exercise in young individuals (Trappe 2002), whereas NSAIDs appear to have positive effects on training induced hypertrophy and strength gains in elderly (Trappe 2011). Accordingly, it is possible that the influence of NSAIDs on muscle adaptation is different between young and old individuals, which may relate to the chronic level of systemic inflammatory markers. In summary, evidence exists for a negative influence by NSAIDs on cellular activity during muscle repair, mainly comprising the muscle stem cell population (satellite cells), and as regards muscle protein balance and hypertrophy discrepant results may relate to differences in chronic inflammatory state.