Isometric Muscular Strength of Agricultural Workers of Gujarat India

Selection of Subjects

The study was conducted in Gujarat state. India. Data were collected from 105 subjects (75 males and 30 females) from different communities. The subjects were randomly selected among healthy farm workers in the 18-62 years age group. All subjects were free from physical abnormalities and musculoskeletal problems. Table 1 presents the anthropometric data relevant to the male and female subjects included in the study.

Strength Parameters

Sixteen strength parameters considered relevant for the design of agricultural hand tools and equipment were selected for the study. These parameters were also recommended by the All India Coordinated Research Project (AICRP) on Ergonomics and Safety in Agriculture (ESA), India [13, 14]. The different measured strength parameters are presented in Table 2 and postures adopted during measurements of strength are presented in Figures 1-3.

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Measurement Setup

Sixteen strength parameters of male and female agricultural workers in different positions were measured in “force measurement setup” (Figure 1). A 2500 N load cell with digital load indicator (NovaTech, United Kingdom) was used to measure these push / pull parameters. The complete configuration of the measurement of human strength along with an anthropometer and other accessories was taken at each survey site for the survey work.

Procedure

A group of researchers composed of four qualified employees (two men and two women) with experience in measuring anthropometric dimensions and human strength parameters, collected the complete data from 105 subjects. Before obtaining the data, the male and female observer received enough practice to measure all the dimensions in a good posture and accurately. The subjects were acclimatized with the experimental protocol for proper and correct measurement. According to the strength data collection protocol, subjects had to reach their maximum strength within the first 2 seconds and then maintain maximum strength for the next 3 s [15, 16]. The readings were taken during the last 3 s of force application and the value of the mode of these readings was taken as the strength value for that particular test. During a preliminary test, it was observed that a certain stimulus in the form of light / sound is needed to guide the subjects in the application of the push / pull force for the desired period of time. Therefore, during the application of the force a 5 s timer was used with a red light signal and beeping sound. Subjects were asked to gently release the force applied to the handle when the red light went off and the beep signal stopped after 5 seconds. Three tests were performed with each subject. Subjects were given a 2 min resting period between two consecutive trials.

Analysis of the Data

From the raw data of the selected subjects, the minimum, maximum, mean and standard deviation (SD) values of 16 force parameters were calculated using Microsoft Excel software. For calculation of 5th percentile and 95th percentile values, the following standard equations given in the Anthropometric Source Book [17] were used:

5th percentile value

$$ e = \mathrm {m e a n} - 1. 6 4 5 \times \mathrm {S D} $$

95th percentile value

$$ e = \mathrm {m e a n} + 1. 6 4 5 \times \mathrm {S D} $$

Anthropometric Parameters of Agricultural Workers

Table 1 presents the mean and standard deviation for relevant anthropometric parameters of male and female agricultural workers. The mean age, stature and weight of male subjects were 39±75years, 1632±69 mm and 55.3±8.5 kg, respectively while the corresponding parameters for female subjects were 48±82years, 1521±68 mm and 48.8±8.6 kg. In general the male subjects were heavier and taller than female subjects.

Magnitude of Isometric Muscular Strength

Tables 3 and 4 presents the mean, standard deviation and 5th and 95th percentile values of push and pull strength of male and female agricultural workers. The forces exerted in push as well as pull mode by male subjects were expressively higher than by female subjects.

Hand strength: It is desirable to design the hand operated equipment considering ergonomical aspects like handle height, length of handle, handle inclination, so that maximum force can be exerted to operate with less effort, comfort and higher work output. The average value of push strength with both hands in standing posture for male and female workers is found to be 248.29 and 171.09 N respectively whereas pull strength in standing posture values are 232.40 and 141.75 N respectively which can be used in design of wheel hoe, lawn mower and manually operated push and pull equipment. For the design of joystick, gear shift lever and handle lever, the right hand push and pull strength data of male and female agricultural workers can be utilized which are found within the range of 49.74 to 96.53 N. The maximum value of 5th and 95th percentile of pull strength right hand in sitting posture are 68.78 and 124.28 N for male workers and 54.43 and 77.03 N for female workers and these are considered while designing of joystick, gearshift lever, handle lever, workplace design, etc. Leg and foot strength: Leg and foot operated equipment are also used in the agriculture like foot operated sprayer and foot operated tractor controls. The average value of right leg strength in sitting posture for male and female workers is 374.35 N and 280.66 N respectively and it can be used for the design purpose. The maximum foot strength of male and female agricultural workers is 285.18 and 249.96 N respectively, which is useful in the design of accelerator pedal and other foot-operated controls.

Torque strength: The mean value of torque strength of both hands in standing posture for male and female workers are found to be 209.93 and 117.72 N respectively which can be used in the design of manually operated equipment like chaff cutter and sugarcane crusher. Torque strength for both hand in standing and both hand in sitting are used in the design of manually operated equipment like chaff cutter, sugarcane crusher and design of control viz. steering. The 5th and 95th percentile values of torque strength of preferred hand in standing posture are 135.51& 231.39 N for male and 77.76& 103.92 N for female workers respectively and similarly in sitting posture are 207.87& 361.51 N for male and 166.49& 209.43 N for female workers respectively that should be considered in design of tractor or other vehicles steering. Design of knob control, sprayer lids and opening cover of service point, the mean value of hand grip torque for male is 48.17 N and for female 30.41 N respectively. These overall parameters can be used in the design / modification of hand controls and foot controls like clutch / brake within different workplaces of machines.