ObjectiveTo examine the efficacy of naproxen sodium for exercise-induced dysfunction, muscle injury, and soreness.DesignDouble-blind crossover.SettingCommunity.ParticipantsEight young adult, healthy males.InterventionsTen sets of seven to 10 eccentric actions with each quadriceps femoris with a load equal to 85% of the eccentric one repetition maximum (IRM) followed by 10 days of naproxen sodium or placebo.Main Outcome MeasuresConcentric IRM; cross-sectional area (CSA) and spin-spin relaxation time (T2) of quadriceps femoris, and subjective rating of thigh soreness pre- and 1,4, and 10 days postexercise; subjective rating of ability to sleep or perform morning activities daily during recovery.ResultsConcentric IRM was reduced by (p= 0.0001) 41% day 1 of recovery; by day 4 of recovery, it had increased (p= 0.0145) to 24% below baseline in the drug trial, but did not change for the placebo trial. By day 10 of recovery, concentric IRM was 16 and 26% below (p= 0.0001) baseline for the drug and placebo trials, respectively. Quadriceps femoris CSA and T2were increased (p≤ 0.0250) after exercise, with the greatest (p= 0.0008) responses evident on day 4 of recovery. At this time, each variable showed greater increases (p≤ 0.0129) for the placebo than for the drug trial 8 vs. 5 and 26 vs. 15%, respectively). The CSA of the quadriceps femoris showing an elevated T2was 27 and 37% greater (p≤ 0.0085) for the placebo than for the drug trial. on days 1 and 4 of recovery, respectively. The percentage of quadriceps femoris CSA with an elevated T2(40%) was 1/3 greater (p≤ 0.0138) for the placebo than for the drug trial on these days. Thigh soreness was lower (day 4,p= 0.0087) and the ability to sleep or perform morning activities was less (p≤ 0.0030) compromised (days 3 and 4) during recovery in the drug trial.ConclusionsThe results suggest that naproxen sodium improved recovery after eccentrically biased exercise, probably by attenuating expression of the inflammatory response to muscle injury.