Effects of Anthropometry Variations on Physiological Parameters of Heart Rate, Oxygen Consumption, Aerobic Power While Performing Manual Operation at Fixed Vice Height

This study investigated the effect of fixed height standing-workstation on different people with diverse anthropometry dimensions. Measurements of some anthropometric and physiological parameters are carried out as bases for the calculation of body mass index (BMI) and the determination of the maximum heart rate (HR max ) and aerobic power (VO 2 max) of individual subject while performing manual cutting operation with hacksaw on fixed vice height of 940 mm. Twenty subjects (S1 to S20) parted 2 mm thick square-pipe of 25 mm × 25 mm. Each subject carried out cutting operation in 5 replicates and their physiological parameters during activities are measured to determine their expended energy (EE) and oxygen consumption rate (VO 2 ). The results showed that subject S4 with BMI of 20.76 kg/m 2 has maximum cutting rate of 5.33 stroke/s, while subject S8 with BMI of 23.39 kg/m 2 has minimum cutting rate of 0.92 stroke/s. There was a statistically significant effect on the interaction between BMI, EE and Cutting rate, with F = 827.54, P = 0.000, R 2 = 0.967 and S = 1.749 units. Subject S11 was discovered to have VO 2 (28.54 l/min) and VO 2 max (24.36 ml/min/kg), with highest value of EE (2.94


Introduction
Presently, technical products, such as some basic hand held tools and many workstations, where daily activities are being carried out are being designed/layout conventionally with a focus primarily on their functional and aesthetic aspects with little or no consideration about end users. This is often true in developing nations, where little or no priority is given to anthropometry variations of the citizens. As observed by [1] "Powered hand tools are the most common hand held industrial products found in many industrial work situations, yet non-powered hand tools such as hammers, screwdrivers, wrenches, hacksaws, pliers, etc. still have its own importance in different industries and daily life situations".
Poor design/layout of manually (hand) operated tools/equipment and their usage for a long time may lead to much energy input with less work actualization, causing early hand fatigue and different hand and arm related musculoskeletal disorder. Several studies have suggested ergonomics criteria for hand tool design relevant in terms of biomechanical and physiological stress [2]. Ergonomic interventions are increasingly used to reduce labour turnover rates, lower costs, increase revenue and accomplish more work with a little work force [3].
Sawing is a process wherein a narrow slit is cut into the workpiece by a tool consisting of a series of narrowly spaced teeth, called a saw blade. Sawing is used to separate work parts into two or more pieces, or to cut off an unwanted section of a part [4]. These processes are often called cut-off operations and since many manufacturing projects require cut-off operations at some point in the production sequence, sawing is an important manufacturing process.
As presented by [4] "basically, sawing is a simple process: As the blade moves past the work, each tooth takes a cut. Depending on the thickness or diameter of the work, the number of teeth cutting at one time varies from two to ten or more. Sawing is one of the most economical means of cutting metal. The saw cut (kerf) is narrow and relatively few chips are produced in making a cut. Therefore, only minimal power is used in removing large amounts of waste metal".
A hacksaw is a fine-tooth saw with a blade under tension in a frame, used for cutting materials such as metal. Hacksawing involves a linear reciprocating motion of the saw against the workpiece. This method of sawing is often used in cut-off operations. Cutting takes place only on the forward stroke of the saw blade. Because of this intermittent cutting action, hacksawing is less efficient than other sawing methods. Hacksawing can be done manually or with a power hacksaw [4]. Handheld hacksaws consist of a metal frame with a handle, and For manual handling operation design, the strength of the joint and muscle is of importance to guide the design of workspace or equipment to reduce work related injuries, and furthermore to help in personnel selection to increase work efficiency [5]. Based on the study conducted by [6] on wrist positions and movements among female operators in a repetitive, non-forceful industrial quality-control work during a physical examination, they concluded that the high prevalence of disorders in the wrists/hands among the operators may resulted from repetitiveness and high speeds.
As reported by [7] that a tool should be adapted to the task rather than having the worker adapt to a general-purpose tool. Care also needs to be taken to include design features so as to reduce the existing limitations in hand tools. It is evident that the use of hand held industrial products can lead to accidents, overexertion, injuries and discomfort when poorly designed or badly used [8].
[9] submitted that, muscular forces are required to perform the physical work, that is, to hold and move the load from one point to another. Muscular activities (muscle contraction and extension) during physical work require energy. Supplying the demanded energy creates loads on the cardiovascular system (heart and blood vessels) and respiratory system. The heart must pump faster to deliver the increased oxygen demand through blood vessels to the involved muscles. [9] and [10] submitted that volume of oxygen intakes (VO 2 ) and aerobic power Energy expenditure (EE) is defined as the amount of work done by a body in kilocalories per minute. The EE of a man or woman over a whole day is often divided into different components, which can be individually determined [9].
The relativity of manual hacksawing is paramount among the road side welders, plumbers, as well as in technical workshops in academic and research institutions in Nigeria. Experience has it that, more often, holding device (vices) height is always fixed depending on artisans' preference. However, this study investigates the effect of anthropometry variations on some physiological parameters: heart rate; oxygen consumption; aerobic power; energy expended by the subjects during cutting operation, cutting rate and tool management (wear rate).

Materials and Methods
The consents of 20 engineering students of Federal College of Agriculture, Moor Plantation Ibadan are obtained before the commencement of the measurements and the experiment. The relative anthropometry measurements are carried out by using standard anthropometric measurement techniques. Some physiological parameters, at resting state before the cutting operation and after each cutting operation such as heart rate, body temperature, and blood pressure are measured. Alongside with these, the vice height was measured (940 mm). The object for experiment is mild steel material of 25 mm square pipe, having 2 mm thickness. This is work piece considered for being cut; it was the same across all 5 replicates cut by each subject. The profiles of blades are determined before and after 5 replicate cutting through, so that relative amount of wear can be easily determined.

Methods
In this study, for proper monitoring of needed data, questionnaire was developed for the subjects, age ranged from 16 to 22 years. All relative anthropometry data measured are: stature (overall height), arm length, hand width (thumb in- was used to measure heart rate and blood pressure, while analogue thermometer (AGARY FEVER CЄ0197 1/10˚C), was used to measure body temperature.
The energy expenditure was determined by using [11] formula which is: where, EE = Energy expenditure and HR = measured heart rate after a task is performed.
The maximum heart rate (HR max ) of each subject was determined by using [12] Oxygen consumption rate (VO 2 ) is calculated using the relationship presented by [9] [13] and [14], which are: where: Y = predicted oxygen consumption; X = measured heart rate.
Aerobic power (VO 2 max) was obtained using equation created by a group of researchers to estimate VO 2 max in ml/min/kg as presented by [15]. The equation shows the relationship as follows: where HR rest = heart rate at rest. The profiles of saw blades (18 TPI/BD SANDFLEX BI-METAL) was determined by using black paint on the teeth of three (3) randomly selected blades and were dragged on white cardboard to ascertain the relative number of teeth on average peculiar to the blade type and to determine the missing teeth after cutting operation by each subject.

Data Analysis
The collected data from measured anthropometry parameters, calculated heart rates, expended energies and aerobic powers of the subjects was analyzed statis-

Anthropometry Parameters
The results on descriptive statistics of selected anthropometric measurements of 20 subjects, age ranged 16 to 21 years are presented in Table 1 is most pronounced in leg length compared to the remaining measured parameters, however this is contrary to (whole stature) height. This could justify the fact that height does not necessarily predict the leg length (Table 1).   Figure 1. Relationship between heart rate at rest and heart rate after cutting operation.

Relationship between Heart Rates before and after Cutting Operations
differences is recorded across all participants in heart rate at rest (HRrest) and heart rate after cutting operation (HRactivity). The histogram bars corresponded to subject 8, showed major variation in between rest and activity heart rates when compared with the other subjects ( Figure 1). From    Table 4, presents estimation of maximum heart rate (HR max ), aerobic power  As presented in Figure 2, also in Table 5 time. This follows the same trend as subjects S18 and S20 ( Figure 2 and Table   4).

Estimated Physiological Parameters and Their Relationship to Some Operational Parameters
The relationship between EE and Tool Wear Rate in one-way analysis of variance, was statistically significant F = 45.87, P = 0.000 at 0.05 level ( Table 5).
The R 2 and S indicate that, the EE explains 54.69% of the variation in the Tool Wear Rate and the remaining 45.31% is not explained which means that the rest Figure 2. Relationship of physiological parameter, operational parameter and tool management.

Conclusions
Generally from the anthropometric analysis results coefficient of variations of the measured parameters indicated normally distributed data (<10) except for hand-width with and without thumb. Leg length has highest level of skewness to the negative side with value of −84% and the hand-width without thumb is positively skewed, with highest value of 62%.
From the study conducted the results evidently assert that BMI, VO 2 and EE have effects on cutting time, cutting rate and tool wear rate.
Body Mass Indexes (BMI) showed significant effects on interactions with EE, cutting rate, and wear rate at α = 5%. Based on stated hypothesis, null hypothesis was rejected.
It is evident that anthropometry variations have effects on physiological responses of individual subjects as well as tool management with F = 827.54, P = 0.000 and the R 2 value of 0.967.
The proper matching of machine requirements with the human capabilities is basically necessary for optimum performance, it was observed that subjects S3 and S5 expended the same energy of 1.22 kcal/min, but different wear rates: cutting time of 2.91 teeth/s:48.18 s and 6.25 teeth/s:17.28s respectively. It could be deduced from this that the increase in wear rates of the tool is relatively corresponding to decrease in cutting time by the subjects, as the same is applicable to subjects S18 and S20.
The main contribution from this investigative study is that it serves as eye opener into hazardous effect of fixed-vice height on manual hack-sawing users, which may be unnoticed by many. Areas of biomechanics are more needful area of attention for comprehensive information, as the scope of the work did not address the area.