Abstract: This invention is related to the use of hydroxytyrosol (“HT”), or an olive juice extract containing hydroxytyrosol as an agent to improve muscle differentiation and thus improve or maintain the body's adaptation to exercise. It is also related to the use of hydroxytyrosol (“HT”), or an olive juice extract containing hydroxytyrosol as an agent to improve calcium signaling and to improve skeletal muscle contraction and relaxation. It also relates to pharmaceutical and nutraceutical compositions useful for conditions characterized by altered muscle differentiation especially under inflammatory conditions, such as delayed onset muscle soreness subsequent to strenuous exercise or sarcopenia.