Basic characteristics of the labor process
Any professional activity is evaluated in terms of its impact on the worker's body. There are two main factors of the labor process:
- Physical workload. This parameter reflects the degree of physical exertion. The main "blow" during heavy labor is taken by the musculoskeletal system (MS). Functional systems that ensure muscular activity are also involved, primarily the cardiovascular and respiratory systems.
- Labor intensity. This characteristic describes the level of intellectual, sensory, or emotional load. During intense labor, the central nervous system (CNS) is subject to predominant impact.
Classification of physical work types
Physical labor is defined as the type of work in which the dominant load falls on the structures of the musculoskeletal system. In occupational hygiene, it is customary to divide physical work into categories depending on the volume of muscle mass involved in performing operational tasks:
- Local work. No more than 1/3 of the total body muscle mass is involved in the labor process. This type is characterized by the lowest overall energy expenditure levels.
- Regional work. Work operations require the participation of 1/3 to 2/3 of the worker's entire musculature.
- Global work. More than 2/3 of the muscle mass is involved in the process. This type of labor is associated with maximum levels of energy expenditure.
根据机体能量消耗的差异，专业人员将体力劳动的强度分为四级：轻度、中度、重度和极重度。
Hygienic regulation of energy expenditure
To preserve workers' health and prevent excessive fatigue, the maximum value of average shift energy expenditure is strictly regulated. These norms are calculated for a standard working shift lasting 7–8 hours:
- When performing global physical work, energy expenditure must not exceed 4.2 kcal/min.
- For regional work, a limit of 2.8 kcal/min is established.
- During local muscle work, the indicator is limited to 1.7 kcal/min.
Specifics and prevention of local work
Despite minimal overall energy expenditure, it is precisely during local physical work that pathological muscle strain most frequently develops. This paradox is easily explained: the entire biomechanical load is concentrated on an extremely limited number of muscles and muscle fibers, leading to their rapid local exhaustion.
To reduce the negative impact of heavy (global and regional) and local labor, comprehensive measures are introduced:
- Technical and technological: mechanization, automation of processes, and changes in technology to directly reduce physical exertion.
- Physiological regulation: strict control of work and rest time.
Special recommendations for local work: The most important task is to reduce the number of stereotyped movements and minimize static loads (since static loads fatigue muscles significantly faster than dynamic ones). This is achieved through the introduction of small mechanization tools (various clamps, pushers, automatic product turners). In addition, it is necessary to reduce the required physical effort when performing routine operations—for example, by replacing manual mechanical tool drives with electric ones.
The rule of thirds for classifying work: Local — up to 1/3, Regional — from 1/3 to 2/3, Global — more than 2/3 of muscles.
课堂与考试常见问题
What is the main difference between physical workload and labor intensity?
Physical workload reflects the physical load on the musculoskeletal and cardiopulmonary systems. Labor intensity characterizes the load on the central nervous system (attention, emotions, intellect).
Why is local work so dangerous if it burns minimal calories?
During local work (less than 1/3 of muscles involved), the entire production load falls on a microscopic number of muscle fibers. Because of this local overload, muscle strain rapidly develops.
What are the energy expenditure norms for different types of work per shift?
For global work, the norm is up to 4.2 kcal/min, for regional work — no more than 2.8 kcal/min, and for local work — a maximum of 1.7 kcal/min.
Which loads are more fatiguing for muscles: static or dynamic?
Static loads are much more fatiguing for the musculoskeletal system than dynamic ones, so their share in the workflow must be minimized.
该主题的其他拓展内容
- Methods for calculating energy expenditure in the workplace (chronometry and calorimetry).
- Specific occupational diseases of the musculoskeletal system during local labor.
- Ergonomic principles in the design of small mechanization tools.
- Criteria for assessing labor intensity (sensory, emotional, intellectual loads).
“第六章：劳动卫生与生理学基础”的其他主题
本资料由 WhiteCoat Pro 讲师根据医学院校教学大纲编写。仅供教育参考。