1. How does the nervous system adapt?
Sports training improves communication between the nervous system and the body’s muscles, leading to improved strength and athletic performance. People who do not exercise can only activate part of their muscle mass to perform any physical activity.
The adaptation of the nervous system to the training process occurs at the level of higher brain centers, at the nerve pathways between the brain and the spinal cord, at the level of reflex arcs, and at the very point of connection between a given nerve and the muscle it innervates.
The nervous system activates the muscles through so-called motor units. A motor unit is a neuron (nerve cell) together with all the muscle fibers it innervates. Like most physiological systems, motor units can become fatigued after prolonged exercise. With training, this fatigue effect is delayed more and more.
The brain also learns to activate more motor units, resulting in increased strength. In gym training, the early rapid increase in strength in beginners is not due to muscle hypertrophy, but to the activation of more motor units that have not been used up to that point.
When the body performs physical activity, the brain has to activate many motor units. In non-exercisers, the brain activates the motor units not all at once, but at small intervals, resulting in inefficient movement. Physical training improves the synchronization of this process, or in other words, the ability of the brain to activate the necessary number of motor units at the right time to obtain maximum force and efficiency of movement.
A 2003 study by the Cleveland Clinic Foundation, in Ohio, USA, provides an example of the importance of the nervous system in the training process. The study showed that just thinking about exercise can lead to an increase in strength. The researchers divided 30 healthy young men into 3 groups. For 15 minutes a day, 5 days a week for 12 weeks, the young people in the first group imagined that they were exercising the muscle that moves the little finger.
In the second group, they imagined that they were training the biceps muscle of the arm, and those in the third – were a control group, doing nothing. Participants in the first and second groups were asked to imagine the exercises as vividly and realistically as possible.
The strength of the participants was measured before and after the end of the “workouts”. After the end of the study, the youths in the first group (“exercising” their little finger) achieved an increase in strength of 53%, and those in the second group (“exercising” the biceps muscle) – 13.4%. The authors of the study hope that the results of their research will contribute to the development of treatment for patients with strokes, spinal cord injuries, and athletes with injuries.
They believe that anyone who has difficulty performing physical exercise can use mind training methods to maintain or improve muscle strength to some extent. Despite everything, a replacement for physical training has not yet been found as a method for improving sports performance and increasing muscle mass.
2. How do muscles adapt?
Based on structural, physiological, and biochemical criteria, several types of muscle fibers are distinguished.
Type I muscle fibers, also called red or slow-twitch, fatigue slowly and shorten slowly. They are suitable for making slow, long cuts. An example of such muscles are those of the back proper musculature and the intercostal muscles. In the muscles of athletes in sports where great endurance is required, there is a large percentage of such fibers.
Type IIb muscle fibers, also called white or fast-twitch, shorten faster and fatigue more quickly. Examples of such muscles are the extraocular muscles. Weight lifters, sprinters, and other speed athletes have a high percentage of such fibers in their muscles.
Type II muscle fibers, also called intermediate, represent a transition between the two aforementioned types. Middle-distance swimmers, 400-meter runners, and hockey players have a high percentage of such fibers in their muscles.
Although the amount of muscle fibers of each type is genetically determined, it is believed that they are plastic and can transform to some extent from one type to another, depending on the level and type of training.
Hypertrophy is caused by a net increase in the protein content of muscle (increased protein synthesis, decreased protein breakdown, or a combination of both). Protein synthesis increases immediately after heavy strength training and can remain elevated for up to 48 hours post-exercise. It depends on the availability of amino acids (the components of proteins that are obtained during the digestion of food) in the body, the time of intake of amino acids after training, the concentration of insulin in the body, testosterone, stretch hormone, and others.
Although free weight training is used to achieve muscle hypertrophy, strength training also increases muscle mass, but to a lesser extent. Aerobic training (running, jumping rope, cycling, etc.) almost does not lead to an increase in muscle mass. The simultaneous application of strength training and aerobic training leads to the hypertrophy of type IIa (intermediate) muscle fibers, but only strength training affects the level of type IIb (fast) fibers.
3. How does muscle metabolism change?
Regular strength and endurance training causes a variety of changes in muscle metabolism. During short workouts, muscles rely on their carbohydrate stores. Long endurance training results in the body using and breaking down more fat for energy and sparing carbohydrates. This pattern of changing the type of fuel used is an important mechanism by which athletes increase their endurance.
In contrast, strength training produces minimal changes in muscle metabolism. This is not surprising given the short time required to maintain maximal movement strength in strength sports. Athletes training in these sports rely on adaptation at the neuromuscular and structural level (activation of more motor units and muscle hypertrophy) rather than on changes in muscle metabolism.
It is important to note that strength training increases the body’s endurance to some extent, and endurance training can decrease strength gains. Athletes practicing sports requiring strength and endurance would improve their performance by practicing both types of training. However, those training in sports where strength is the most important component can compromise their performance if they mix strength training with endurance training.
4. How does the endocrine system adapt?
The classic endocrine changes that occur in the body with an increase in sports training are an increase in the level of hormones circulating in the blood, insulin being the main exception to this rule. Prolonged exercise leads to an increase in the capacity of glands such as the pituitary gland and the core of the adrenal gland (which produces adrenaline).
Training causes an increase in testosterone levels. Various factors affect the degree to which testosterone levels increase. For now, it is believed that the most important of these is the intensity of the training. Strength training with free weights produces a much greater increase in blood testosterone than training in endurance sports. Strength programs, in which exercise is performed at a moderate to heavy intensity, with small rest intervals, and which involve the largest volumes of muscle mass, produce the greatest increases in blood testosterone levels.
5. How do the cardiovascular and respiratory systems adapt?
Endurance training induces several adaptations in the body that allow an increase in the body’s maximum capacity to carry and use oxygen (VO2 max) and withstand high aerobic load. Coaches and athletes are aware of the importance of the body’s capacity to carry larger amounts of oxygen for sports such as running, cycling, and others, and apply numerous permitted and non-permitted methods to increase it.
The most key adaptations in the body increasing the endurance of the body are perhaps the adaptations in cardiac function and more specifically the increase in cardiac stroke volume (the amount of blood pushed by the heart in one beat) and cardiac output. To a lesser extent, the respiratory system adapts to physical exercises. According to some authors, it is considered the weak link in the system of transporting oxygen through the blood to the tissues.
However, it is generally accepted that both cardiac and respiratory muscles can become fatigued after heavy, prolonged exercise and reduce the body’s ability to carry oxygen, causing a serious decline in the body’s ability to perform aerobic exercise.
6. How is the musculoskeletal system adapted?
Bones adapt well to mechanical loading. Varied and intense physical activity increases bone size and strength, especially in childhood and adolescence, and helps preserve them as we age. In this way, practicing sports helps prevent fractures due to age-related bone weakness. Among the elderly, daily exercise is also extremely beneficial.
Compared to muscle tissue, adaptation processes in tendons and ligaments are much slower, due to their poorer blood supply. In general, they show a good level of adaptation to exercise as long as the period is long enough – weeks months, and years instead of days.
