Effects of exercise on muscle and muscle performance

2021-06-10 03:24 PM

In old age, many people become sedentary, so their muscles atrophy a lot. In these cases, however, muscle training can increase muscle strength by more than 100 percent.

The importance of maximal resistance training. One of the key principles of muscle growth during exercise is the following: Muscles that do not function under load, even when they are performed in the last hours, increase slightly in strength. At the other extreme, muscles that contract more than 50% of maximum force will develop strength quickly even if contractions are performed only a few times per day. Using this principle, muscle-building experiments have shown that 6 near-maximal contractions performed 3 times a week for optimal muscle strength gains without creating chronic fatigue. for muscle.

Figure. Approximate performance of resistance training in increasing muscle strength over 10 weeks

The upper curve in the figure shows the approximate percentage increase in muscle strength achievable in a young adult who was not previously trained with this resistance training program, indicating that muscle strength Corn increased by about 30% in the first 6-8 weeks but remained mostly the same after that time.

Along with the increase in strength comes an approximately equal proportion increase in muscle mass, which is known as hypertrophy.

In old age, many people become sedentary, so their muscles atrophy a lot. In these cases, however, muscle training can increase muscle strength by more than 100 percent.

Muscle hypertrophy

The average size of a person's muscle is determined to a large extent by genetics plus the level of testosterone secretion, which, in men, causes significantly larger muscle than in women. With exercise, muscles can become enlarged, perhaps by 30-60%. Most of this hypertrophy results from an increase in the diameter of the muscle fibres rather than an increase in the number of fibres.

However, a very small number of large muscle fibres are thought to divide along their entire length to form entirely new fibres, thereby increasing the number of thin fibres.

Changes occurring within the hypertrophic muscle fibre include (1) an increase in the number of fibroblasts, commensurate with the degree of hypertrophy; (2) up to 120% increase in mitochondrial enzymes; (3) an approximately 60 to 80 % increase in the components of the phosphagen system, including ATP and phosphocreatine; (4) a large 50% increase in glycogen stores; and (5) a 75-100 % increase in triglyceride (fat) stores. Because of all these changes, the capacities of both aerobic and anaerobic metabolic systems are increased, especially increasing the oxidation efficiency and maximum efficiency of the metabolic system. oxidizing as much as 45%.

Fast and slow-twitch fibres

In humans, all muscles have a ratio of fast-twitch and slow-twitch fibres

different. For example, the abs have superiority in fast-twitch fibres, which have the power to contract quickly and strongly of the type used in dance. In contrast, the soleus muscles have a high predominance of slow-twitch fibres and are therefore utilized to a greater extent for prolonged calf muscle activity.

The basic differences between fast-twitch and slow-twitch muscle fibres are as follows:

1. Fast-twitch fibres are about 2 times larger in diameter than slow-twitch fibres.

2. The enzymes that promote the release of energy from the phosphagen and glycogen-lactic acid energy systems in the fast-twitch fibres are 2-3 times as active in the slow-twitch fibres, thus making maximum strength achievable in the slow-twitch fibres. very short time spans with fast-shrink yarns about twice that of slow-shrink yarns.

3. Slow-twitch fibres are mainly held for endurance, especially for aerobic energy generation. They have more mitochondria than fast-twitch fibres. In addition, they contain significant amounts of myoglobin, a haemoglobin-like protein that binds oxygen in muscle fibres; myoglobin, in addition, increases the rate of oxygen diffusion throughout the fibre by the oxygen shuttle from one myoglobin molecule to the next. In addition, enzymes of the aerobic metabolic system are significantly more active in slow-twitch fibres than in fast-twitch fibres.

4. The number of large capillaries in the vicinity of slow-twitch fibres is greater than in the vicinity of fast-twitch fibres.

In a nutshell, fast-twitch yarns can deliver peak total energy for a few seconds to a minute or so. In contrast, slow-twitch fibres provide endurance, providing muscle contraction strength that lasts for minutes to hours.

Genetic differences among athletes in fast-twitch and slow-twitch fibres

Some people have significantly more fast-twitch fibres than slow-twitch fibres, and others more than slow-twitch fibres, a factor that can determine some range of athletic ability of different individuals. Athletic training has not been shown to change the relative ratios of fast-twitch and slow-twitch fibres; however, one athlete may be more interested in developing one type of athletic skill than another. Instead, the relative ratios of fast-twitch and slow-twitch fibres seem to be determined almost entirely by genetics, thereby helping to determine the athletic zone that is best for individuals: some people appear to be born to be long-distance runners, while others are born to sprint and jump. For example, the following values ​​have been recorded for the ratio of fast to slow fibres in the quadriceps of different types of athletes:

 

Fast-shrink yarn

Slow-shrink yarn

Marathon

18

82

Swimming

26

74

Average in the south

55

45

Weightlifting

55

45

High jump

63

37

Jump far

63

37