Sarcopenia is the decrease in skeletal muscle mass and muscular function that occurs with aging. The underlying mechanisms of sarcopenia include anabolic resistance, which is defined as a poor muscle protein synthetic response to previously effective stimuli such as nutrients and exercise. Among the nutrients that humans ingest, amino acids directly trigger the synthesis of muscle proteins. The essential amino acid leucine, in particular, functions as a stimulatory signal. Leucine-enriched essential amino acids help overcome anabolic resistance in elderly individuals to effectively stimulate muscle protein synthesis. Long-term intake of leucine-enriched essential amino acids has a synergistic effect with exercise to increase skeletal muscle mass, strength, and walking speed in elderly individuals, and can be an effective countermeasure to sarcopenia.