Arachidonic acid (AA) is an omega-6 polyunsaturated fatty acid found naturally in the phospholipids of cell membranes, especially in skeletal muscle. Its use in sports supplements, particularly for muscle growth and performance, is based on its role as a precursor to eicosanoids—signaling molecules that mediate inflammation and are thought to be involved in muscle hypertrophy signaling pathways.

Several small-scale human studies have investigated the effects of AA supplementation on muscle growth and strength. The most cited is a 2007 double-blind, placebo-controlled study (Journal of the International Society of Sports Nutrition) in which resistance-trained males supplementing with 1,000 mg/day AA for 50 days experienced greater increases in lean body mass, strength, and anaerobic power compared to placebo. The proposed mechanism is that AA increases the production of prostaglandins (notably PGE2 and PGF2α), which help initiate the muscle repair and growth process following exercise-induced muscle damage.

However, the body of evidence is limited and mixed; some studies have failed to find significant benefits. Most research also notes that excessive AA intake could have pro-inflammatory or negative cardiovascular effects, so caution is advised. While there is some scientific basis for AA's use in supporting muscle mass and strength, the overall level of evidence is moderate and further large-scale, long-term studies are needed.