Weight Loss: Understanding Muscles and Growth Patterns for More Efficient Scientific Exercise

The human body has approximately 500 muscles, widely distributed throughout. In adults, muscles account for about 40% of body weight, with the limbs having the largest and most developed muscles, making up about 80% of the total muscle mass. The proportion and size of muscles in the human body depend primarily on age, sex, training level, and the type of exercise.

Muscles are divided into voluntary and involuntary muscles. Voluntary muscles are attached to the skeletal frame and are therefore also called "skeletal muscles." The muscles commonly referred to, such as the pectoralis major, latissimus dorsi, rectus abdominis, and quadriceps femoris, refer to skeletal muscles. Skeletal muscles are controlled by will and produce voluntary movements, such as walking, running, jumping, throwing, pushing, and pulling. Involuntary muscles, on the other hand, are not controlled by will and contract rhythmically on their own. For example, the muscles of internal organs such as the stomach, intestines, blood vessels, and bladder are involuntary muscles.

The heart muscle is also an involuntary muscle, but its "automatic rhythmicity" and contractile force are much stronger and more pronounced compared to gastrointestinal peristalsis. Therefore, physiology and anatomy call it "cardiac muscle" to distinguish it from other involuntary muscles.

II. Muscle Characteristics in Adolescents and Children Within the human body, new life is constantly being created, while death is also occurring continuously. This is specifically manifested in the relationship between anabolism and catabolism in metabolism. When anabolism is dominant (anabolism is higher than catabolism), life is vigorous, and the body's tissues and organs continuously grow and develop, allowing a person to develop from infancy to maturity. When catabolism is dominant (catabolism is higher than anabolism), the functions of the body's tissues and organs begin to decline, and a person gradually ages. When anabolism and catabolism tend to balance, it is middle age. Thus, the contradiction between anabolism and catabolism in the human body is the driving force behind human growth and development. From the perspective of the longitudinal system of human life, a person goes through infancy, childhood, adolescence, youth, middle age, and old age from birth to death. While the standards for dividing life's ages vary slightly from country to country, based on the laws of human growth and development and the characteristics of morphology, function, physiology, and psychology, age periods are roughly divided as follows: infancy (from birth to 1 year old), childhood (3-12 years old, preschool children 3-6 years old), adolescence (13-17 years old), youth (18-35 years old), middle age (36-59 years old), and old age (60 years and above).

(I) Characteristics of Growth and Development in Children and Adolescents The growth of a person from small to large, from short to tall, and from light to heavy is the result of the continuous proliferation of cells and the continuous increase of intercellular matrix. This is the quantitative change process of the human body, called growth. The continuous differentiation of human cells and organs, the gradual maturation of functions, and the gradual perfection of morphology constitute the qualitative change of the human body, called development. Extensive data from both domestic and international sources demonstrate a close relationship between growth and development and age. The characteristics and rate of growth and development differ across different age groups.

Throughout a person's life, the rate of growth and development varies, exhibiting a wave-like pattern, encompassing both quantitative and qualitative changes; it has both stages and continuity. Analysis of data from a 1979 survey of children (7-17 years old) in my country shows that both height and weight increase with age. Height: For males, 7-10 years old, the annual increase is 4-5 cm, with an average increase of 4.68 cm. The fastest growth occurs between 11-14 years old, with an annual increase of 5-7 cm, averaging 5.98 cm. The growth rate slows down after age 15. The maximum increase is at age 12, at 6.6 cm. For females, 7-9 years old, the annual increase is 4-6 cm, with an average increase of 5.67 cm. The rapid growth period is between 10-12 years old, with an annual increase of 5.33 cm, and the maximum increase is at age 11, at 5.9 cm. Growth rate slows down after age 13. Weight: For males, from 7 to 10 years old, the annual weight gain is 1-3 kg, with an average increase of 2.3 kg. The rate of increase accelerates from 11 to 14 years old, with an annual increase of 3-6 kg, with an average increase of 4.63 kg. The rate of increase slows down after age 15, with the maximum increase occurring at age 13, at 5.5 kg. For females, from 7 to 9 years old, the annual weight gain is 1-3 kg, with an average increase of 2.4 kg. The period of rapid growth is from 10 to 12 years old, with an annual increase of 3-5 kg, with an average increase of 3.9 kg. The maximum increase occurs at age 11, at 4.4 kg. A relatively high rate of increase is maintained for 1-2 years after age 13, after which the rate of increase gradually slows down.

As shown in Table 4-2, growth and development accelerate around age 11, entering the rapid growth period of puberty. During the rapid growth period of puberty, the peak growth in height and weight for boys is around 12-13 years old, and for girls around 11 years old. After the peak, there is a sustained period of significant growth, followed by a rapid slowdown. Analyzing the magnitude of growth: For height, boys grow 23.9 cm in the four years from 11 to 14 years old, averaging 5.98 cm per year, while in the seven years from 15 to 21 years old, they only grow 7 cm, averaging only 1 cm per year. This means the growth in the first four years is 3.41 times that of the subsequent seven years, and the growth rate in the first four years is 6 times that of the subsequent seven years. For girls, the growth in height is 15.8 cm in the four years from 11 to 14 years old, averaging 3.9 cm per year, while in the seven years from 15 to 21 years old, they only grow 2.6 cm, averaging only 0.37 cm per year. This means the growth in the first four years is 6 times that of the subsequent seven years, and the growth rate in the first four years is 10.5 times that of the subsequent seven years. It is evident that the period from 11 to 14 years old is an extremely important period for human growth and development. The speed and quality of growth and development during this age group directly affect the size and robustness of the adult physique.