Effects of Exercise on the Muscles
How are muscles affected by exercise?
As a sweeping generalisation: Muscles develop through exercise and the more stress placed upon the muscles during the exercise (within their limits) the more they develop.
How do they develop through exercise?
The reason they develop is because they undergo muscle hyper trophy. This is the scientific name given to the process where muscles grow and increase in size. Muscle hypertrophy occurs when muscles and in particular muscle fibres are stressed to their limit during exercise and they experience a ‘microtrauma’. This is where a small number of the fibres become damaged (this should not be confused with a muscle strain or tear). The body then repairs this microtrauma, but instead of repairing back to its original condition the body overdoes it to ensure that the same micro injury cannot occur again, thus making the muscle bigger and stronger. For example, when performing weight lifting if an individual places their muscles under the most stress that they can take then they becomes damaged and sore. As the body repairs the affected muscles they overcompensate, making the fibres bigger and stronger, thus allowing them to lift the same amount next time but easier. If this is constantly occurring then the individuals muscles begin to grow and develop.
Do all exercises affect muscles in the same manner?
Not all exercises will affect all the muscles in the same way. As different exercises will utilise different fibres within the muscles. Aerobic exercises incorporate slow twitch fibres (Type I) as they are based around low levels of muscular exertion but over a sustained period of time. The muscles are not required to contract near their maximal strength or speed. Anaerobic exercises, on the other hand, utilise fast twitch fibres (Type II) as they incorporate short bursts of high intensity exercises that cannot be sustained for long periods as they require muscles to contract close to their maximum contractile strength. Aerobic exercise relies more on a mixture of fat, protein and carbohydrates for energy. While anaerobic relies on ATP or glucose. Where the energy is obtained from greatly determines how long an exercise can occur for. Aerobic produces little lactic acid, while Anaerobic produces a lot. The production of lactic acid can inhibit the generation of ATP within that given muscle and potentially prevent performance from continuing if there is too high a concentration within the muscle cells. Long term exercising programmes aimed at anaerobic exercise can lead to neovascularization within the muscles. This increases the muscles ability to remove waste products from their cells and allow contractions to till occur. If the level of training is sufficient the body can begin to use the removed lactic acid within other muscles as a source of energy.
DMOS is often a short term side effect of exercise, why?
A short term affect of exercising on the muscles could be delayed muscle soreness onset (DMOS). DMOS is the pain or discomfort that an individual can experience within their muscles 1 to 3 days after exercising and can last for as long as 3 days. The precise cause of DMOS is still unknown although some individuals have attempted to relate it to the presence of lactic acid, however the wider held belief is that it could be a result of the type of contraction undertaken during exercise. It has been suggested (Roth, S. January 2006) that individuals who undertake more eccentric contractions within their exercises will suffer more severe DMOS than those undertaking a higher proportion of concentric contractions. Another potential explanation is that the pain is caused during the regeneration stage (as the muscles repair microtrauma) as opposed to the damaging of muscle cells (Yu, J., Carlsson, L. & Thornell, L.E. 2004). As the muscle undertakes muscle hypertrophy the cells swell and put pressure on nerves and arteries, thus resulting in mild soreness or pain.