Spero Karas, MD, assistant professor of orthopaedics in the division of sports medicine at Emory University, says that testosterone, the male hormone responsible for muscle growth, maxes out between the ages of 16 and 18. It reaches a plateau during the 20s and then begins to decline. As a result, muscle building after the adolescent years can be challenging, he says.
Entry into neural tissues in general is mediated by the secondary creatine transporter (CrT-2) known as SLC6A10,[186] which is the same transporter that is active in a male’s testicles.[145] CrT-2 belongs to the family of SLC6 transporters that act to move solutes across the membrane by coupling transport with sodium and chloride.[187][188] Genetic deletions in the 16p11.2 region, which encodes both SLC6A8[189] and SLC6A10[186] can result in severe mental retardation in humans and is one of the causes of “Creatine Deficiency Syndrome.” Creatine Deficiency Syndrome is not only caused by lack creatine transporter expression, however, as creatine synthesis is also critical for neural function.[190].[189] Retardation caused by defective creatine synthesis[31] can be reversed with creatine supplementation and dietary changes.[191]
Using too much weight, too soon; always start lower than your expected ability and work your way up that first workout. If your form suffers, you are swinging the weight, or using momentum, this indicates you may be using too much weight. Greater momentum increases the potential for injury and reduces the effectiveness to the muscle group being targeted.