There are several reasons for muscle pain, one of which can be attributed to one degree or another to physiological, and all the others to pathological. Muscle pain often occurs 1-2 days after training in athletes and people who are engaged in physical exercises after a long break or have moved to a new level of exertion. Muscle soreness can occur after a workout when the athlete is performing a strength program for the first time, when performing unfamiliar exercises that involve muscles that normally do not work, when working with increased loads, or if the exercise focuses on the eccentric phase. In addition, muscle pain is experienced by beginners who expose themselves to high loads without appropriate adaptation. Super-intensive training techniques, such as supersets (two exercises performed one after the other, without a break) and forced repetitions also contribute to the occurrence of muscle pain after training.
This condition is called crepature, and the pain is due to microtraumas and inflammation in the muscles, and not, as was mistakenly believed earlier, due to lactic acid.
Causes of delayed pain
Crepature is characterized by muscle soreness some time after exercise (8-48 hours). Delayed-onset muscle pain occurs if the increase in exercise load exceeds 10% of normal.
The fact that exercise causes damage is due to two main mechanisms: impaired metabolic function and mechanical rupture of the muscle cell. The metabolic mechanism of muscle damage works during prolonged submaximal activity until complete exhaustion, which is often present in bodybuilding techniques. Direct strain on the muscles, especially during the eccentric contraction phase, can cause muscle damage, which can later lead to metabolic changes. One of the most noticeable types of damage is a rupture of the muscle cell membrane (for example, swelling of the mitochondria, damage to the plasma membrane, violation of myofibrillary components, sacrolemma rupture).
In comparison with concentric contraction, eccentric contraction generates muscle tension, selectively deactivates slow-twitch muscle fibers, and increases the activation of fast-twitch motor units. Athletes who use the eccentric method without a sufficient amount of strength training or without adapting the connective tissue suffer from discomfort and muscle damage. An eccentric contraction generates more heat during the same workout compared to a concentric contraction. Elevated temperatures can damage the structural and functional components of the muscle cell.
The cause of delayed muscle pain is considered to be ruptures in the area of Z-plates (actin-binding protein). Muscle overexertion during exercise causes an overload of the Z-line, causing deformation or rupture, accompanying disorganization of the adjacent threads (Friden 1981). The body responds to the overload with a protective response-inflammation, and activation of immune cells. Studies have found that macrophages contribute to the formation of prostaglandins in large quantities, which cause a feeling of pain. Histamine and potassium can also irritate free nerve endings in the muscles.
Both mechanisms of muscle damage are associated with muscle fibers that experience light exercise , which is expressed in increased levels of the creatine kinase enzyme, a marker of muscle damage, for a period of time up to 48 hours after a training session. Discomfort occurs within the first 24-48 hours after exercise is completed, and this is why this type of discomfort is called delayed-onset muscle soreness syndrome.. However, usually the muscle fibers quickly return to their original state; however, in the case of severe tension, the muscle is injured. Thus, a training session that is too intense or intense can result in a dull aching sensation along with painful sensitivity and stiffness that can last up to seven days.
Muscle biopsy results
Studies of athletes ‘ muscle fibers using muscle biopsies conducted by the Laboratory of Fundamental Problems of the Theory of Physical and Technical Training of Athletes at the Research Institute of Sports showed that the cause of pain is as follows. In an untrained person, myofibrils of different lengths are present in muscle fibers: short and long. During eccentric exercises, short myofibrils are torn. With regular training, the myofibrils inside the muscle fibers become the same length, and severe pain no longer occurs, but eventually stops altogether. Thus, the presence of lactic acid is not crucial. Pain is always a consequence of the destruction of muscle fibers or their tears, for example, as a result of injury.