The physiology of being in shape: adaptation at its best

AMAA Journal, Spring-Summer, 2009 by Edward H. Nessel

Every person who engages in prolonged vigorous movement realizes that with continuous training something happens over time that allows the body to withstand increasingly-demanding physical challenges. What would have sunk your ship in stormy seas just a few weeks ago now presents with calmer water towards your destination. This destination is what every serious athlete and dedicated exercise participant should be striving for throughout their training experience: to be in the kind of shape that allows for a positive adaptive transformation to occur that matches the physical potential Nature has granted each of us, and then a little more. Climbing the formidable mountain of being in shape should be the goal of everyone wanting to be labeled an athlete.

Getting in "shape" is neither easy to attain nor to explain. As you know, the human body is a wondrous machine with complicated systems able to produce great quantities of energy both quickly and over extended periods of time. This permits the body to adapt to whatever is physically challenging it, and enlarge its capacity to handle increasingly more vigorous exercise. Unlike an automobile engine which has the exact parts needed to produce a certain amount of predicted energy and power, the human body's components can be made to produce more by having them induced more through use of specific physiologic protocols over time. In every instance of adapting to exercise, three main elements, the holy grails of athletic training as 1 see it, are brought into the picture and must be addressed to a greater or lesser extent depending upon the venue and sport. These elements are endurance, strength, and power. Following the correct pathway to physiologic condition is like a professional concert or jazz musician mastering the three main woodwind instruments in proper order: clarinet, saxophone, and flute. The athlete should build endurance, then go for increased strength, and finally work to capture power.

Endurance

Endurance is where it all starts if the coach/trainer and athlete correctly approach getting in shape. It takes the greatest amount of time and the most effort to develop all the physiological changes the body needs to build endurance. It is not a simple goal; it is an ongoing process. When speaking of endurance, we must include both the muscular and cardiorespiratory systems. In dealing with muscular tissue, endurance becomes specific to individual muscle groups. When dealing with cardio-respiratory endurance, we speak more of the body as a whole and its ability to sustain extended vigorous physical exercise. This becomes the more important aspect of physical fitness. If physical condition is suspect and fatigue sets in too quickly, muscular strength diminishes, as does neuromuscular coordination, concentration, and alertness. To prevent this and to correctly train the athlete, we need to increase the mechanisms required to harvest and utilize energy supplies for prolonged bouts of movement and to concomitantly increase the distribution of nutrients and oxygen throughout the body to sustain total body involvement.

Although fast-twitch muscle fibers are usually larger in size than slow-twitch, slow-twitch fibers can become up to 22% larger than fast-twitch fibers with effective endurance training. What this causes, however, is increased development of endurance fibers at the expense of pure power. Even the subtype of fast-twitch fibers (Fiia), which has more oxidative capacity than the absolute all-out fast twitch fibers (Fiib), develops more with endurance training. Consequently, the athlete ends up sacrificing all-out power for enhanced endurance.

Specificity of training will enhance one ability at the cost of another. A sprinter who trains mostly endurance will cause some fast twitch fibers to switch over to fire more slowly; this will lessen power and all-out speed, but will add the ability to perform longer. Along with the change in fiber type, a second adaptation occurs: an increase of more than 15% in the number of capillaries innervating muscle fibers which allows for greater exchange of O2 and CO2, heat, wastes, and nutrients between the blood and active muscle tissue. This is an important adaptation; the muscles are then able to contract more efficiently over an extended period of time to delay fatigue.

A third muscular adaptation to endurance training is the increased formation of the iron-containing protein, myoglobin. With appropriate aerobic training, muscle myoglobin can be increased in situ by up to 80%, allowing for a much better oxygen supply.

The fourth adaptation to aerobic training is an increased number of muscle mitochondria, allowing for increased energy production throughout the working muscles. Again, specificity of training: only those muscles being called upon regularly will produce more mitochondria. This is the goal of much of our training: work the main muscle groups needed to power the athlete through the event's requirements, but don't ignore the ancillary groups that can be used to support the whole body through various movements. Total body development is key to superior athletic performance.