Compositions herein increased creatine retention and/or glycogen storage in muscle. A composition comprises creatine or its derivative and a carbohydrate or its derivative. The carbohydrate is in an amount by weight which is greater than the amount of creatine. The amount of carbohydrate and the amount of creatine are effective for increasing creatine retention and/or glycogen storage in muscle. The compositions may be in the form of a pharmaceutical or a dietary supplement and are intended for use in the human or animal body. Other compositions comprise creatine or an active derivative together with insulin or an active derivative. The amount of creatine and the amount of insulin are effective for increasing creatine retention and/or glycogen storage in muscle. The compositions including creatine and insulin may further contain a carbohydrate or its derivative. A method of increasing creatine retention in a human or animal body comprises causing an increase in blood plasma creatine concentration and causing a substantially simultaneous increase in blood plasma insulin concentration. A method of increasing glycogen storage in a human or animal body comprises causing an increase in blood plasma creatine carbohydrate concentration and causing a substantially simultaneous increase in blood plasma creatine concentration. The compositions to increase the creatine retention and/or glycogen storage in the muscle are administered by injection or ingestion.