What Is the Physics of the Human Body?

Human mechanics (human mechanics) is a science that uses mechanical principles to study maintaining and mastering the balance of the body, and how the body coordinates effectively when the body changes from one posture to another. It is based on the knowledge of human physiology, anatomy, and theoretical physics, and studies the structure, function, and movement laws of human moving organs to guide human protection and health. It is widely used in sports, dance, handling and weight bearing, medical, aviation and aerospace.

Human mechanics (human mechanics) is a science that uses mechanical principles to study maintaining and mastering the balance of the body, and how the body coordinates effectively when the body changes from one posture to another. It is based on the knowledge of human physiology, anatomy, and theoretical physics, and studies the structure, function, and movement laws of human moving organs to guide human protection and health. It is widely used in sports, dance, handling and weight bearing, medical, aviation and aerospace.

Chinese name

Human mechanics

Foreign name

human mechanics

Ergonomics definition

Human mechanics (human mechanics) is a science that uses mechanical principles to study maintaining and mastering the balance of the body, and how the body coordinates effectively when the body changes from one posture to another. It is based on the knowledge of human physiology, anatomy, and theoretical physics, and studies the structure, function, and movement laws of human moving organs to guide human protection and health. It is widely used in sports, dance, handling and weight bearing, medical, aviation and aerospace.

Human mechanics and physiology

Human mechanics is a discipline that studies human activity and ability to perform under various mechanical operating conditions. This discipline is based on the knowledge of human physiology, anatomy and theoretical physics, and studies the structure and function of human motion (active) organs, the laws of each joint and the entire body.

The human body has a well-functioning neuro-muscular-skeletal system. The following four physiological activities constitute the physiological basis of human mechanics, ensuring the free movement of human bodies and the smooth operation of mechanical operations.

The leverage of the musculoskeletal system

The first type of leverage (the fulcrum is between the point of action and the point of resistance) is used to maintain balance. The small resistance can be used to overcome the large resistance, and its mechanical efficiency can be greater than or less than 1. Occipital ring joints, pelvic thigh joints, knee and foot joints belong to this category. For example, the posterior cervical muscle pulls as the force, the head weight is the resistance, and the occipital ring joint is the fulcrum. Head posture is balanced. The second type of leverage (the resistance point is between the action point and the fulcrum) is a labor-saving lever with a mechanical efficiency greater than 1. Such a lever constitutes a person's toes. The ankle joint Achilles tendon is the acting force, and its gravity (resistance) falls on the ankle joint. The base of the toe is used as a fulcrum to adjust and maintain the balance of walking, running, and jumping. The third type is a laborious lever (the power point is between the resistance point and the fulcrum), and the power arm is shorter than the resistance arm. The knee, shoulder, and elbow joints fall into this category. For example, when holding a heavy object, the elbow joint is bent, the biceps brachii is used as the force, the hand is gravity, and the joint block is the fulcrum. When the biceps is contracted, bend the elbow joint to maintain a stable posture of the upper limbs.

Joint movement direction and angle

The direction and angle of each active part of the human body (mainly with the joint as the core) depends on the surface morphology of the joint. It determines the degree of freedom of joint displacement. Because the bones are in a fixed state, the joints have no more than three degrees of freedom (less than the robot). Different joints have different degrees of freedom (Table 1). A joint with more than one degree of freedom can enable the joint to complete its maximum possible direction of movement. If there are 3 degrees of freedom of the pelvis and mandible, the movements can be completed in up, down, left and right, and back and forth directions. The shoulder joint can perform three directions of movement on the human coordinate system: bending and stretching on the sagittal plane; adduction and abduction on the forehead; and rotation along the vertical axis. Each moving part of the human body has different moving directions and ranges.

Muscle strength and energy

Muscle activity (three forms of contraction, relaxation, maintaining tension, which robots do not have) consumes energy. The greater the amount of activity (intensity), the more muscle masses are involved in the activity, and the more energy is consumed. For example, compared with quietness, the human body has more muscle groups involved in maintaining a standing posture, and the energy metabolism rate is sometimes higher than 22% of the quiet state. The increase in energy metabolism rate is accompanied by an increase in a series of physiological functions (breathing cycle and heat production, etc.). When overload or severely impaired human activity (for example, the pressure suit is in a pressurized state), muscle force and energy consumption increase excessively, and there will also be a material metabolic disorder, which promotes fatigue (robots do not have). Therefore, labor saving and energy saving are important ergonomic preventive measures.

Posture (or posture) adjustment control

Under normal conditions, the brain regulates and controls the working state of the musculoskeletal system (relevant muscle groups participate in activities), and complete various voluntary movements; at the same time, under the combined adjustment control of the brain-cerebellum-balance organs, it passes through the various muscle groups Work to stabilize posture or posture. For example, when the human body is sitting, standing, walking, or running, it keeps the human body from deviating from the center of gravity (the animal's center of gravity is different from the human body) through the coordinated work of the complex neuro-muscular-skeletal system and balancing organs, so as to achieve the proper body position or posture. . In mechanical operations, only by adopting effective human mechanical operation methods or protective measures, can satisfactory effects be achieved through the same mechanism as described above. Obviously, robots do not have this kind of complex and sensitive regulation and control system.

Main research fields of human mechanics

Competitive sports

(I) Study the relationship between movement structure and motor function

Structure determines function is the basic view of mechanics. In human movement, studying the overall and local movement structure, muscle distribution and activity forms, coordination and development of various organ systems is the biomechanical basis of the study of sports function, and also the basic task of sports biomechanics theory and practical research.

(Two) study the mechanics of human movement technology

Investigate the biomechanical structure and function of human movement techniques, study the biomechanical principles of human movement techniques in physical education, reveal the mechanical rationality of movement structures and the mechanical regularity of sports techniques, and better guide physical education and sports training .

(3) Research on optimization of sports technology

Based on the biomechanical diagnosis of athletes' technical movements, a reasonable technical movement structure that complies with the principles of biomechanics is proposed, the best technical movement scheme is established, and training schemes for improving technical movements are sought to improve the scientific level of sports training.

(D) research, design and improve sports equipment

In sports, both the human body movement and the equipment movement are the result of the interaction between the human body and the outside world or sports equipment. Therefore, researching, designing and improving sports equipment to conform to the principles of biomechanics can create conditions for the continuous improvement of sports performance. In addition, the development of fitness equipment and sports products provides a wealth of research topics for the application of sports biomechanics.

(5) Study the causes and preventive measures of sports injuries

By studying the biomechanical analysis of the human movement system and the biomechanical analysis of the exercise technology, on the one hand, it can reveal the unified clinical treatment of the morphological structure and exercise function of the exercise system and rehabilitation of human efficacy and mutual restraint, so as to establish a reasonable exercise technology To prevent damage to the motor system. On the other hand, it can reveal the effects of different sports actions on the local body load, find out the mechanical and biological reasons for the injury of the sports system, and take reasonable technical actions and preventive measures to avoid sports injuries or choose a reasonable biomechanical rehabilitation means.

(6) Provide biomechanical parameters for athlete selection

Investigate the biomechanical characteristics of various sports techniques, and construct the requirements of human body shape and functional quality that must be satisfied to complete the action. Taking the impact of the inertia parameters of the human body on the motor function as an example, jumpers require relatively lower limbs. However, when the length of the lower limbs is equal, the ratio of the length of the thigh to the length of the calf should be considered. Obviously, the thigh is shorter and the calf is shorter. Long is more suitable for sports.

Clinical and Rehabilitation

(I) Application of human mechanics in clinical treatment

The musculoskeletal system is an important organ that maintains the macrostructure of the human body. The biomechanics of the musculoskeletal system is the study of the relationship between the forces, torques and corresponding deformations caused by the musculoskeletal system's movement under physiological and pathological conditions. Human mechanics research can better understand the physiological load patterns of the human musculoskeletal system, help us analyze abnormal mechanical patterns and mechanical abnormalities under pathological conditions, and guide the development of treatment plans and the design of musculoskeletal orthopedic implants.

In the cardiovascular field, the prevention and treatment of various cardiovascular diseases has become a hot issue of global concern. Common cardiovascular diseases such as atherosclerosis, aneurysms, and acute thrombosis are closely related to the hydrodynamic phenomena in the human blood circulation system. Biomechanics, especially research carried out with the help of modern computer simulation technology and in vitro cytomechanical loading technology, provides research on the pathogenesis of cardiovascular disease, the development of personalized treatment plans, and the design of vascular implants / interventions with hemodynamic optimization Theoretical basis and technical means.

(Two) the application of human mechanics in rehabilitation engineering

It is the main task of rehabilitation engineering in rehabilitation medicine to use engineering methods and methods to recover the disabled and promote their functional recovery, reconstruction or compensation. Among them, human mechanics plays a very important role. It is mainly manifested in two aspects:

First, the measurement and analysis of the biomechanical characteristics of physical disorders is an important basis for the design of rehabilitation aids. In order for rehabilitation aids to reach their design goals, the characteristics of obstacles need to be effectively measured and evaluated first, and biomechanical characteristics are one of the important indicators of the physiological system, and therefore also an important basis for the design of rehabilitation accessories.

Second, the biomechanical interaction between the human body and the assistive device is an important factor in the optimal design of the rehabilitation assistive device. In order to compensate, replace or repair the physical obstacles of disabled people, rehabilitation aids must interact with the human body, and biomechanical factors have an important influence in this interaction process.

Aerospace and other special fields

In special fields such as aerospace, human beings face long-term or short-term weightlessness or overweight environments. In this special environment, the major postgraduates of human mechanics in the aerospace power environment have physiological changes and their protective measures. It belongs to both the special environmental physiology category and the biomechanics category.

(I) Impact of positive acceleration on the human body:

When the fighter plane flies in circles, heel-followers, half-followers, and dive-out, the pilot's head faces the center of the circle and is subject to centripetal acceleration from the foot to the head, while the inertial centrifugal force acts on the human body in the opposite direction. The pilot is subjected to a constant positive acceleration (+ Gz). The main effects are as follows:

Circulatory system: changes in blood pressure, lower blood pressure above the heart level, increased blood pressure below the heart level, changes in blood distribution, etc.

Respiratory system: Increased weight of thorax and diaphragm, increased respiratory muscle load, laborious inhalation, prolonged inhalation time, and even apnea. Lung ventilation is low, and arterial oxygen saturation is reduced.

Visual function: arterial pressure at the eye level decreases, blurred vision, reduced vision, and loss of central vision.

Brain function: The blood circulation disorder in the brain causes temporary blurring or even loss.

(Two) the impact of weightlessness on the human body

Weightlessness is a special environmental factor encountered in aerospace, and it will have a significant impact on the human musculoskeletal system, cardiovascular system, and immune system.

During long-term and repeated space flights, progressive and cumulative changes in bone and calcium metabolism will lead to decreased bone density and redistribution of bone mineral salts. Bone loss caused by weightlessness and the negative balance of calcium and phosphorus metabolism are difficult to recover after return, and injuries such as fractures may occur, affecting the health of the astronauts.

The disappearance of gravity load will lead to the obvious atrophy of human skeletal muscles, especially anti-gravity muscles, accompanied by changes in muscle fiber types, metabolic patterns and muscle contraction functions. The occurrence of weightless muscle atrophy not only affects the astronaut's orbital flight time and work efficiency, but also seriously affects the astronaut's ability to adapt after returning to ground.

Weightlessness has a wide range of effects on the human cardiovascular system, mainly manifested by poor endurance after spaceflight. Although the reduction of blood volume is the main reason and necessary condition for the change of cardiovascular disorders after flight, it is not the only reason, and sometimes it is not even necessary. Changes in the function of the arterial system may play an important role in the occurrence of astronauts' endurance caused by spaceflight.