The ancient "super food", spirulina contains high levels of essential amino acids, fatty acids (linoleic acid, F-linolenic acid, and palmitic acid), selenium, and vitamins C and E. As well, it contains a powerful combination of other antioxidants.
 
In a recent double bind, placebo controlled study published in Medicine & Science in Sports & Exercise, scientists examined the effect of spirulina supplementation on exercise performance, metabolism, and blood antioxidants before and after exercise. The subjects involved were 9 moderately trained men who ingested 2000 mg of spirulina or a placebo 3 times daily (before meals) for four weeks. Each subject ran on a treadmill at 70%-75% of their VO2max for 2 hours and then at 95% VO2max to exhaustion. The researchers reported a significant increase in the time to exhaustion at 95% VO2max, implying that spirulina may boost anaerobic (or high intensity) performance. Under aerobic conditions (during 2 hr run at 70-75% max), subjects who received spirulina burned about 11% more fat. As well, the authors reported higher antioxidant levels at rest and 24 h after exercise in subjects who received spirulina supplementation.

Reference:
Kalafati M, Jamurtas AZ, Nikolaidis MG, Paschalis V, Theodorou AA, Sakellariou GK, Koutedakis Y, Kouretas D. Ergogenic and antioxidant effects of spirulina supplementation in humans. Med Sci Sports Exerc. 2010 Jan;42(1):142-51.