Physiological Adaptations to Physical Activity

A few of the effects of exercise have been mentioned, already. But, there are others that are worth noting. As the body is subjected to regular exercise, it will adapt accordingly. And, the adaptations will always be specific to the type of exercise being done.

The following variables affect the rate of adaptation to various types of physical activity:

1. Age:

The older an individual, the slower the rate of response. This is directly related to hormone release rates and blood circulatory responses.

2. Gender:

In general, males experience a quicker rate of adaptation to physical activity. This is primarily related to hormonal response differences, where testosterone increases the muscles response to physical activity.

3. Rest and Recovery:

If an individual experiences minimal recovery time following activity, their body will not be allowed sufficient time to regenerate fuel, and repair broken down tissues. This will result in the body entering a catabolic state instead of an anabolic state. Sleep is also vital in the recovery process, as it is during deep sleep cycles that the body rebuilds, regenerates and growths new tissue.

4. Nutrition

Correct nutrition will aid the body in regenerating fuel reserves as well as repairing broken down tissue.

5. Genetics

Certain individuals respond more effectively to certain types of physical activity. This is determined by their hormonal response to physical activity, their muscle fibre type ratio as well as their lean muscle mass.

6. Previous Conditioning

If an individual has previously reached a certain level of conditioning, they will generally return to that level at a faster rate than a previously sedentary individual. This is what is loosely termed “muscle memory”. It is not directly related to the muscle, but rather the nervous system, which “learns” adaptation responses.

Adaptation to Endurance Training

With oxygen being the most important part of this type of training, it is understandable that most of the adaptations will revolve around oxygen delivery to the working muscles, and oxygen use within the muscles. We have already made mention of an increase in capillarisation of the alveoli. And, the same will occur in the muscles, allowing for greater delivery of fuels and oxygen, as well as waste removal. A further adaptation happens within the cells. The use of fuels and oxygen to create energy occurs in the mitochondria in the muscle cells. To enable the muscles to create more energy, and to do so more efficiently, there is an increase in the mitochondrial content responsible for this chain of reactions. Also, there is an increase in the water stored in the muscles. This is both for fuel storage and waste management, as well as for temperature regulation.

Adaptations to endurance training take approximately 12 weeks to manifest.

Adaptation to Flexibility Training

This adaptation is two-fold. With regular stretching, as well as regular exercise, the first of these adaptations is noticed. This is a decrease in adhesion between muscle fibres. This decrease in adhesion allows the fibres to move more freely, within the muscle, which will lead to the muscles being able to pass through an extended range of motion. The second of the notable adaptations happens as a direct result of correct flexibility training, and stretching. When a warmed muscle is stretched, the elastin component of the fibres (the flexible, pliable and elastic portion) can be forced to increased length. This allows the muscle, over time, to allow for an increased range of motion. If this is done at a rate that is too rapid, or to muscles that have not been sufficiently warmed up, the result is over stretching of the collagen component of the muscle fibres (the more plastic, rigid component). Since this part of the fibre is largely responsible for the resting tone of the muscle, over stretching, and increasing the length of this aspect will result in a “loose” muscle tone. While this may seem like a good thing for overall flexibility, it can be rather disastrous for things like balance, force generation, and even injury prevention. This is because activities all require some level of resting tension, in the muscles.

Adaptations to flexibility training take approximately 5 days to 2 weeks to manifest.

Adaptation to Strength Training

To understand the adaptations to strength exercise, first we need to confirm where strength comes from. As much as it is from the muscle fibres themselves, it is even more from the neural stimulation. When first starting a strength training program, the neural system is not accustomed to it. As a result, only a few muscle fibres are recruited for contractions. As a result, the force generated is less. With training, the nerve impulse can be more effective transmitted through the acetyl-choline (an increase in volume of the neurotransmitter is stored in the vesicles), and the muscle fibres become more sensitive to stimulation. This increased sensitivity results in a greater number of muscle fibres contracting, and hence a greater force being applied. Also, the fibres themselves become thicker and stronger, through training (which we have already touched on). This means that each fibre becomes capable of greater force production. When these two adaptations are paired together, a far greater increase in in force production is noticed. In other words, there is a larger increase in strength.

The adaptations to strength training take an average of 8 weeks to manifest.

The following responses occur at varying rates. The rate of response is dependent on the type of training being undertaken, as well as other variable mentioned earlier.

Contractile Rate

As already mentioned, adaptations will be specific to the training being done. This is also true of the speed of the contractions. If the exercise being done use slower contractions (such as standard body-building type exercises) will cause the muscles to contract at slower rates. To cause adaptation to faster contractions, exercises that use faster contractions are needed in training. This lends more to power training, and plyometrics. These types of exercises rely more on high speed contractions, as well as stimulating greater force generation (as seen in strength adaptations). These higher speed contractions are more likely to lead to what is known as sarcomeric hypertrophy. This means that the muscle fibres themselves become thicker, and this is what causes the visually notable increase in muscle size.


Increases in water, blood and mitochondrial content, in response to endurance type training, will increase the overall volume in the muscle. Because of this, slower, higher volume type training will lead to what is known as sarcoplasmic hypertrophy. This is an apparent increase in muscle size, caused chiefly by the increase in liquid volume within the muscle.

Fibre Recruitment

Another result of adapting to exercise is what is referred to as up-recruitment, or down-recruitment of muscle fibres. If we look back to the discussion of the 3 types of muscle fibres, we remember that the different types of fibres contract at different rates, and have noticeable characteristics that differ between the different types. But, in response to training, these fibres can take on the characteristics of the fibre on either side of them, in terms of type. In other words, type IIa fibres can adapt to behave more like type I fibres, in response to endurance training, or they can adapt to be more like type IIb fibres, in response to strength and power training. The other fibres can do the same. But, it is worth mentioning that the adaptations will be towards what we can call the adjacent type of fibres (type I – type IIa, type IIa – type IIb).