Blue green algae, particularly species like Spirulina and Aphanizomenon flos-aquae (AFA), have been marketed as exercise and athletic aids due to their rich content of protein, vitamins, minerals, and antioxidant compounds such as phycocyanin. The scientific evidence for these claims is limited but not entirely absent. A few small clinical trials and animal studies have investigated Spirulina supplementation in athletes and found modest improvements in certain indices, such as increased exercise endurance, reduced oxidative stress, and decreased markers of muscle damage after strenuous activity. For example, some studies have reported that Spirulina supplementation may increase time to fatigue in cycling or running, possibly due to its antioxidant properties or its effect on fat oxidation.

However, these studies are generally small, short-term, and sometimes lack rigorous controls. The improvements observed are modest and not universally replicated. Reviews of the literature typically conclude that while there is some scientific basis for the use of blue green algae as an exercise aid, the quality and consistency of the evidence is low, and more robust, well-designed clinical trials are needed to make definitive recommendations. The evidence is stronger for Spirulina than for other blue green algae. Thus, while the use of blue green algae as an athletic or exercise aid is based on some scientific findings, the support is currently weak to moderate at best.