Inclusion criteria:
Participants must be selected from among female athletes in the youth age group (16 to 18 years old).
Having at least 2 years of professional and competitive experience in water polo and membership in teams in the country's first division league.
Participants must be members of the national championship team in the under-20 age group in the year of the study.
Not having any musculoskeletal injuries (such as muscle tears or shoulder or knee injuries) that would prevent you from performing strenuous exercise or physical tests.
Absence of chronic metabolic (such as diabetes), cardiovascular, respiratory, or inflammatory diseases that would affect physiological responses to training and supplementation.
No use of specific medications and supplements: No use of any anti-inflammatory drugs (steroidal or non-steroidal), antibiotics, orthogenic supplements (such as creatine or beta-alanine), or synthetic antioxidants during the past 3 months until the end of the study period.
Commitment to attend training sessions according to the team schedule, such that the percentage of training attendance during the study period is at least 85% (based on the average attendance of 87 ± 11% mentioned in the main text).
Completion of an informed consent form by the participant (or legal guardian if under 18 years of age) after receiving full explanations about the research objectives and process.
Exclusion criteria:
Absence of more than 15% of training sessions or failure to complete the 8-week training intervention period.
Failure to comply with the supplementation protocol: Failure to regularly take L-arginine and spirulina supplements according to the study instructions (such as forgetting more than 20% of the prescribed doses).
Any acute injury during the study that prevents the participant from continuing with training or testing, or acute illness (such as severe flu or viral infections) that requires rest or medication.
Dietary or medication changes: Sudden and significant changes in diet, initiation of specific diets (such as ketogenic or vegan diets), or initiation of new medications that may interfere with study variables (such as inflammatory or hormonal markers).
Unwillingness or inability to provide blood or saliva samples at designated times (pre-test, mid-test, or post-test).
The willingness of the participant to leave the study at any point in time without having to provide a reason.
Performing strenuous exercise outside of the team's training program or participating in informal competitions that affect training load and oxidative stress.