The Molecular Basis of Training Adaptation

It amazes me every time I ask the question to my athletes 'what happens in the body as a result of training that makes you fitter and faster?' No one seems to be able to give me a reasonable answer so I thought I might post a topic that might help explain this deep physiological mystery. Of course there are several components that make up performance but our performance potential is basically limited by our physiological capacity dictated by genetic predisposition. As endurance athletes we are typically limited by skeletal muscle parameters coupled with the cardiovascular system. You may have heard that world class athletes are the way they are because they were lucky enough to have good genes. This is partially true. The human genetic code is basically the same for everyone however some fortunate individuals express specific genes differently. Confused yet? Ill explain... The physiological system of the human body (and any living organism for that matter) is capable of adapting to it's environment. As such when a stimulus is applied (ie, training or running away from a dinosaur) the body does what it can to make sure that next time such a stressful event occurs it is better equipped to deal with it. If you want to understand the big picture you have to think small. Each cell of the body contains the entire genetic code and depending upon the cells role (eg. skeletal muscle, bone or red blood cell) it will express different genes within the genetic code. So each time the cell is stressed certain molecules called transcription factors stimulate certain genes. The primary role of a gene is to encode the sequence to make new proteins and it is the proteins that enhance the cells functional capacity. For example the contractile elements of skeletal muscle are made up of specific proteins that when assembled together form actin and myosin. Actin and myosin have their own specific sequences which is encoded into our genes. When we perform resistance exercise (I'll use this as an example instead of endurance training because its easier to visualize) we stress the muscle cells, activate transcription factors which then stimulate their specific target genes. These genes release the code for the proteins and the cellular machinery can then form these proteins together to form more functional equipment like actin and myosin. So if we repeatedly perform resistance exercise we are continually repeating this cellular process which with time results in more contractile proteins (actin and myosin) and thus bigger muscles. The same goes for endurance training except the proteins made are responsible for using oxygen to break down carbohydrate and fat for energy. So if this process is the same for everyone why haven't I got an Olympic cycling gold medal yet? I train just as hard as those guys! Well.. those guys are lucky because there are other process that display variance between individuals that dictate the upper limits of how much adaption should occur and these are basically set at a higher level for 'genetic freaks'. Without these boundaries we would otherwise from my previous example continually grow muscle and end up as some Hulk like creature with biceps so big we are unable to bend our elbows enough to get food into our own mouths. So.. train regularly to make sure you are continually stimulating new proteins but remember the triggers for these proteins are specific so your training must reflect the way you wish to adapt. Unfortunately there are many inhibiting pathways that regulate why endurance athletes with all of the hours of training they do don't stimulate muscle growth (which would possibly inhibit performance) as well as oxidative capacity. It's called specificity!!!