Ergonomic Evaluation of Post Biomechanical Effects of Lifting Maximum Loads Using Male Subjects

The post biomechanical effects of performing lifting tasks using male subjects was investigated to know the body parts most disposed to pains and the degree of pains and injuries that occur as a result of lifting maximum loads. A field approach was adopted involving six industries performing different kinds of lifting tasks. A questionnaire showing a body discomfort chart was administered to 209 respondents. The data collected were analyzed using descriptive statistics to determine the mean and standard deviation while Kaiser’s rule of retaining factors were used in determining the most affected body parts predisposed to discomfort and to analyze workload assessments. High values were reported for thigh discomfort. Shoulder discomforts were significantly prevalent while most respondents reported discomforts in the mid to lower back regions. 51% of the respondents consider their work to be hard while 23% consider their work very hard. The average mass of materials lifted in the study is 32 kg. The average age, height and weight of subjects are 26.24 years, 169.59 cm and 65.08 kg respectively. Subjects involved in lifting maximum loads are prone to shoulder tendinitis and could suffer spinal kyphosis and spinal lordosis.


INTRODUCTION
Manual material handling such as lifting heavy loads still play an important role in the industrial and service sectors of any economy in the world irrespective of the growing advancement in mechanization and automation [1]. According to Triano and Selby [2], manual material handling (MMH) entails lifting, but also usually includes climbing, pushing, pulling and pivoting, all of which pose the risk of injury to the back. Any job that involves heavy labour or MMH may be classified as high risk. This is corroborated by Elfeturi [1] who suggested that MMH tasks should be designed to take into account several risk factors related to the task being handled. When a person involved in manual materials handling sustains an injury in the course of performing a lifting task, it often results in wastage of both time and material resources which usually has a multiplier effect(s) on the profit margin of his employer [3].
Biomechanics is a branch of ergonomics that deals with the motion undergone by the human body. It is the science of designing facilities, work place and systems to enhance the health, safety and comfort of the people using them [3]. According to Tichauer [4] and Hedge [5], biomechanics is the study of body movements and the mechanical forces at work in a particular body. In this field, the musculoskeletal system of the human body is viewed as a mechanical structure that can undergo certain motions and stresses. Biomechanical effects can be analyzed from joint kinematics and dynamics, giving basic understanding of what happens to the body in terms of mechanical load such as force and moment [6]. This is done using laws of physics and engineering concepts to describe the motion undergone by various body segments and the forces acting on those body parts during normal daily activities [7].
The objectives of ergonomics are those of achieving functional effectiveness of whatever physical equipment or facilities people use and of maintaining or enhancing human welfare or wellbeing (such as health, safety and satisfaction) by appropriate design of the equipment, facilities and environment [8].
The standards that are most widely used by ergonomist are ISO standard 11228-1 25 kg, Manual Material Handling (MMH) 27 kg and National Institute for Occupational Safety and Health (NIOSH) 23 kg as presented in Patenaude [9]. The standards determine the maximum weight that can be safely lifted by workers. According to Patenaude [9], the values need to be adjusted according to five main factors affecting worker's health and safety namely: lifting duration, lifting frequency, properties of the load, working environment and workers' posture. Although there are standards set to quantify the weight of the material that can be safely lifted, people involved in MMH still perform tasks involving lifting objects that are up to (and sometimes more than) two-third (2/3) of their total body weight by virtue of their occupation which is grossly un-ergonomic [6,10,11]. When the maximum load that is acceptable to the body is lifted, it results in a quantifiable strain, and stress acting on the spine. Depending on the posture of the person performing the lifting task, the torque and bending moments as well as the force acting on the body linkages during lifting can be determined using biomechanical models [6,10]. Lower Back Pain (LBP) has been identified as the most prominent of all the injuries related to lifting tasks. It has been reported that tasks involving lifting account for 33% of all workrelated causes of back pain [12]. Low back pain may be caused by an injury to the L5/S1 compression disc of the human spine when a heavy load is lifted and when bad lifting techniques are adopted while performing the task.
The aim of this work is to investigate the predisposition of male subjects involved in lifting maximum loads to discomfort and injuries and to determine the parts of the human musculoskeletal frame most affected by lifting such loads based on the lifting posture and lifting duration.

METHODOLOGY
A field approach was adopted because of the nature of the research work. In order to collect relevant data for this work, different small scale industries (SMEs) -pallet, drinks depots, block moulding, cement depots, poultry feed depots and sachet water packaging industry -where manual lifting tasks are performed were visited. Only male worker seen in the locations visited were sampled as subjects in the study. The frequency of loading and lifting postures was observed at the various sites where the questionnaires were administered. Work postures were analyzed using Ovako Working Postures Assessment System (OWAS) as adopted in [13]. Snapshots of the workers were taken as they performed various lifting tasks and the most frequent postures assumed while lifting were observed. The summary of tasks studied is presented in Table 1.
A well-structured questionnaire adapted from Lin et al. [6] (Fig. 1) was administered on subjects after performed lifting tasks at the various locations visited and relevant data collected. This was to assess the post biomechanical effects of performing occupational lifting tasks on the subjects. The questionnaire contains a body discomfort chart and an overall workload assessment scale. It was also used to obtain other basic data such as age, height, and weight. The weight of the various materials lifted and lifting posture of the subjects were also obtained. Each subject was asked to rate the degree of discomfort for each listed body part as a result of performing the type of task being studied. Illiterate workers posed a great challenge during the field trip. This was however taken care of by educating them in their local dialect. The data obtained in the study was analyzed using Statistical Package for the Social Sciences (SPSS) version 17 to determine the mean, standard deviation as well as standard error of the age, height and weight of the subjects. Principal component factor analysis procedures were used to analyze the body discomfort scale (stress analysis). Kaiser's rule of retaining factors with eigen values larger than 1.00 was used.

Fig. 1. A whole body discomfort questionnaire used in the research
Source: Adapted from Lin et al. [6]

RESULTS AND DISCUSSION
The descriptive statistics shows the means and standard deviation for the twenty six variables on the body discomfort scale. From the descriptive information in Table 2 it is obvious that the mid to low back region of the body is the most stressed body part among these subjects that performed lifting tasks in the locations visited in this study with the highest mean value of 2.58. This is followed closely by discomforts reported in the right shoulder and the thighs with mean values of 1.33, 1.25 (right thigh) and 1.24 (left thigh) respectively. This agrees with the work of Arjmand and Shirazi [12] that tasks involving lifting account for 33% of all work-related causes of back pain [12].
The principal component communalities extracted range from 0.465 to 0.908 revealing an obvious variance in the response of all the subjects to these variables related to their body discomfort as presented in Table 2. The communalities show how much of the variance in the variables has been accounted for by the extracted factors. For instance, over 90.08% of the variance in right upper arm is accounted for while 46.5% in buttocks is accounted for. Eight factors were extracted using Kaiser's rule of retaining factors with eigen values larger than 1.00. The eigen values for eight principal components were retained. The scree plot of the eigen values against the components number shows support for Kaiser's rule opting for eight factors as can be seen in Fig. 2. A look at the scree plot shows that eight among the twenty six variables have eigen values greater than one.   A look at the workload rating by the subjects for the tasks they performed in Table 3 reveals that 51% of them consider their workload to be HARD while 23.44% opted for VERY HARD. It thus follows that their unemployment status and other economic factors might have compelled them to be performing occupational tasks that most of them refer to as "hard work".
From Table 4, it can be seen that the average age, height and weight of subjects that participated in the study are 26.24 years, 169.59 cm and 65.08 kg respectively. The average weight of the materials lifted in the study is 32 kg which is above the ergonomic standards discussed earlier. It can be seen that the average weight of material lifted in this research is about half the weight of the person that lifted it instead of Load ≤ 1 / 3 weight of subject.
In summary, with the right shoulder as the second most stressed part of the body among the subjects used in this research beside the mid to lower back, there is no gain saying that these subjects are also predisposed to shoulder tendinitis (a medical disorder that may evoke due to work tasks involving repetitive arm movements) as reported in [14]. In addition, a work posture involving elevated arms may accelerate degeneration of shoulder tendons through impairment of circulation due to static tension and humeral compression against the coracoacromial arch [14].

CONCLUSION
The results of this study show that the level of body discomfort is dependent on the nature of the lifting task(s). However, the lifting posture employed when performing the task as well as the frequency of lift are also seen to determine the body parts that will likely experience more discomfort. Other factors can be identified as lifting duration, properties of the load, working environment, physiological factors (stature, height, weight of subject), psychological factors (like economic pressure) etc. The results of this study implies that people performing lifting tasks in the locations investigated in this research are predisposed to lower back pain and lower back injury. Repeated stress on the shoulder predisposes respondents to shoulder tendinitis. This can be ameliorated by rest, medication and corticosteroid injection. The connection between lower back pain and spinal kyphosis and spinal lordosis is inconclusive and is still a subject of research.
All tasks involving weights above the set ergonomic standards must be redesigned to incorporate engineering controls. Similarly, worker selection criteria should be used to identify workers who can perform potentially stressful lifting tasks without significantly increasing their risk of work-related injury. Those selection criteria, however, must be based on research studies, empirical observations, or theoretical considerations that include job-related strength testing and/or aerobic capacity testing. It is also necessary to employ the procedures of Job severity Index (JSI) when allocating manual lifting tasks to employees in industries.