Taking L-arginine supplements while doing intense interval training won’t make highly trained female handball players any faster or stronger in short sprints than training alone.

A double-blind, placebo-controlled RCT with 30–40 highly trained female handball players randomly assigned to either L-arginine supplementation (0.05–0.1 g/kg/day) or placebo, both groups performing identical high-intensity interval training for 8 weeks, with anaerobic power (e.g., Wingate test) and 20-meter sprint times measured pre- and post-intervention.

A within-subject crossover trial where each highly trained female handball player undergoes two 8-week phases: one with L-arginine supplementation and one with placebo, separated by a washout period, with anaerobic power and sprint speed measured at the end of each phase under identical training conditions.

A prospective cohort study tracking highly trained female handball players who self-select into L-arginine supplementation or no-supplement groups while all perform the same HIIT program for 8 weeks, measuring changes in anaerobic power and sprint speed.

A retrospective analysis comparing past L-arginine supplement use among female handball players who showed significant vs. minimal improvement in anaerobic power or sprint speed after 8 weeks of HIIT.

A series of individual case reports tracking changes in anaerobic power and sprint speed in highly trained female handball players before and after 8 weeks of L-arginine supplementation combined with HIIT.