Academic journal article Iranian Journal of Public Health

Changes in Back Compressive Force When Measuring Maximum Acceptable Weight of Lift in Iranian Male Students

Academic journal article Iranian Journal of Public Health

Changes in Back Compressive Force When Measuring Maximum Acceptable Weight of Lift in Iranian Male Students

Article excerpt

Introduction

There are several harmful factors at work environment that causes fatigue, burnout, and early exhaustion of individuals, and lead to the waste of time and money. Some of the occupational factors are responsible for the incidence of musculoskeletal problems. Manual Material Handling (MMH) tasks are one of the common occupational factors (1). In most industries, and even in non-occupational settings, manual handling and lifting of weights happens very frequently; each of these tasks have their own specific requirements, and such tasks are one of the important reasons for the incidence of low back pain (2). Low back pain and other musculoskeletal disorders caused by work, ranked the second after cardiovascular diseases, are among the most important and common diseases and cause of patients' referral to the physicians in Iran (3). Moreover, 85% of the population would suffer from back pain at some points in their life time. On the other hand, 25% of days off from the work are due to back pain (4).

In recent years, low back pain related to the job or career has become a major concern. In many studies conducted so far on different jobs and employees (such as posts staff, doctors, soldiers, construction workers and other groups) the prevalence of low back pain has been reported from 15% to 84% (5). Low back pain can reduce the functional performance and lead to absenteeism around the world and it imposes a huge economic burden on the individual, family, community, industry, and government. Until 10 years ago it was thought that the problem is limited to Western countries, however, since then the increased number of researches has found that low back pain is also a big problem in low and middle income countries as well (6). Low back pain can be caused by mechanical, ergonomic, personal, and social factors. Among the ergonomic and mechanical factors, we can note the followings: lack of adequate rest between the work shifts, doing work with hurry and top speed, improper body postures, high frequency and repetitive movements, and lifting or moving heavy objects. In addition, obesity, gender, age and other factors can be also introduced as the causes of low back pain (7). Based on the mentioned facts, back injuries associated with MMH tasks have been a rigid problem for both the person and the national economy. There are several different main types of the MMH tasks, such as lifting, holding, carrying, pushing, and pulling. Nearly 50% of back injuries occur when lifting objects, whereas only 9% occur when holding, throwing, or carrying objects. Therefore, as the most common MMH task associated with the prevalence of low back injuries is lifting tasks (8).

During lifting and bending forward, the trunk is placed in front of the lumbar spine and it leads to shear and compressive forces to be imposed on the disk. On the other hand, each person's tolerance of the load on the spine depends on different factors such as body posture, gender, age, the weight of the imposed load, and the individual anatomical changes (9). Many studies have examined the lifting task through using a biomechanical approach, which estimated the stresses incurred in the body while lifting materials. The Focus of these studies is primarily on the lower back, especially the L5/ S1 disc (10, 11). Accordance of the statistical data, between 85% and 95% of all disc herniations with a repeat equal proportion occur at the L4/L5 and L5/S1 levels, respectively (12). In all the methods designed for the assessment of the risk related to the lifting, the biomechanical factors are of great importance. Biomechanical factors in the work place, such as the workload, distance, and location of the workstations are effective in the prevalence of musculoskeletal disorders. Based on the previously conducted studies, the severity of the effects of each of these factors is quite variable and depends on the range of changes in the shear and compressive forces imposed on the lumbar discs and the incidence and prevalence of low back pain (13). …

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