Indian Journal of Occupational and Environmental Medicine Medknow Publications ISSN: 0973-2284 EISSN: 1998-3670 Vol. 10, Num. 1, 2006, pp. 19-23

Indian Journal of Occupational and Environmental Medicine, Vol. 10, No. 1, January-April, 2006, pp. 19-23

Original Article

Assessment of physiological strain in inland fishing activity

Biswas R, Samanta A

Department of Occupational Health, All India Institute of Hygiene and Public Health 110, Cittaranjan Avenue, Kolkata-700 073, India

Correspondence Address: A. Samanta, Department of Occupational Health, All India Institute of Hygiene and Public Health 110, Cittaranjan Avenue, Kolkata-700 073, India. E-mail: ergoraj@rediffmail.com

Code Number: oe06004

Abstract

Keywords: Cardiac strain, energy expense, heart rate, inland fishing, physiological strain, VO₂max

Introduction

Materials and Methods

Time and location

The study was conducted in two places of Hooghly district in West Bengal, viz., Chandannagar and Rishra, during the month of April-June 2001. The locations were selected meticulously - population of fishermen frequenting these areas - so that suitable follow-up studies could be undertaken.

Subjects

After selection of the sites, interactions were carried out with the fishermen at weekly intervals for a a period of one month, when the fishermen were motivated to cooperate as required by the design of the study. After a careful and repeated follow-up, a total of 10 professional fishermen were selected.

Description of the fishing task

A special fishing tackle, resembling a sieve, is used for fishing. This is made by mounting nets on circular or triangular bamboo frames and is called 'Bhasali' in local parlance.

Individual fishermen wade in knee- to waist-deep water and immerse this scoop net with a few strides in a bent position. The immersed entrapment is lifted, excess water is allowed to flow out, and the catches entrapped within the net are transferred to a container, usually strapped to the fisherman's waist.

Laboratory investigation

Maximal heart rate (HRmax) and maximal oxygen consumption (VO ₂ max) were measured in the laboratory using a maximal bicycle ergometry test[5] and expressed in beats. min ^-1 and ml. kg ^-1 min ^-1 respectively. Prediction equations for all the subjects were obtained in the form of linear regression using the initial, final and intermediate set of values of heart rate as the predictor variable and oxygen consumption as the criterion variable obtained during the test. Lowest heart rate recorded during a minimum rest period of 30 min in comfortable room temperature in the laboratory was considered as the resting heart rate (RHR). Heart rate reserve (HRR) of the subjects was obtained as the difference between the HR max and RHR and was also expressed in beats. min ^-1.

Field Investigation

In field working heart rate (WHR) was obtained in an unobtrusive way by means of lightweight telemetric equipment - Sports Tester PE 3000 (Polar Electro, Finland) at every 15-s interval. From these heart rates, oxygen consumption (VO) was predicted from VO ₂ = f (HR) relationship established in the laboratory test. Recovery heart rates were measured just after the cessation of work cycle.[6] Relative cost of work was determined in terms of relative aerobic strain (RAS) by expressing the VO as the percentage of maximal aerobic capacity (%VO ₂ max) of the subjects. Relative cardiac cost was obtained by expressing the WHR as the percentage of the heart rate reserve (%HRR) of the subjects. Net cardiac cost was obtained as the difference between WHR and RHR and expressed in beats/min. Perceived exertion was measured according to Borg's scale.[7] Corrected effective temperature (CET) was measured as an index of heat stress to ascertain the environmental heat load. Each fisherman was studied on a single day while he was regularly engaged in the task. The time for the study varied between 7 to 11 h for different study days. During the study, the fishermen maintained their normal pace of work, and no instructions were given to them to control their work pace and methods as it may interfere with the primary objective of the study.

Results

Physical and physiological characteristics of the subjects

Descriptive statistics of all the 10 fishermen studied is presented in the [Table - 1]. The mean age of the fishermen was 31.6±11.3 years, and work experience varied between 4 and 32 years. The mean BMI for the group was obtained to be 19.8±0.64 kg.m ^-2. It is apparent that the height and weight of the subjects are typical of the average populations from eastern India. Mean HRmax and VO ₂ max obtained in bicycler ergometry were 161± 8.1 beats. min ^-1sub and 38.8 ml. kg ^-1. min ^-1 respectively.

Physiological strain in the fishing task

Physiological strain in scoop net fishing is expressed in [Table - 2]. The mean values for all the parameters calculated from the subjects' means indicated that the mean workday heart rate of the fishermen varied between 95 and 113 beats. min ^-1. Average net cardiac cost and relative cardiac cost was 31±3.7 beats. min ^-1sub and 36±3.9% respectively. The table also indicates that the fishermen have utilized 30 to 38% of their maximal aerobic power during fishing with an average oxygen uptake of 13.2±1.1 ml. kg ^-1. min ^-1 (range 11.1-15.1) that corresponded to an average energy expenditure of 3.3±0.4 kcal. min ^-1 . Recovery heart rate pattern indicates that the first minute recovery heart rate was only 93±6.3 beats. min ^-1sub , which is well below the recommended criteria[6] with a mean pulse deceleration index of -12.3 ± 4.3 beats. min ^-1. For two of the fishermen, the pulse deceleration index was above the recommended limit of -10 beats. Min ^-1.

For a cursory examination of the physical strain experienced by the fishermen, a 90-min averaged heart rate curve was constructed [Figure - 1] on the basis of mean heart rate of all the fishermen in each minute of the fishing period, which indicates the pattern of heart rate in the whole work shift. As displayed in the figure, the overall mean working heart rate was 41% higher than the mean resting heart rate although occasional peaks with 47% increment were also found. It is also noticeable from the figure that the periods of tachycardia (heart rate more than 100 beats. min ^-1) started at the 16th minute of fishing and continued throughout the whole shift and accounted for 53% of the total fishing period. It is also apparent from the figure that initially the heart rate increased from 91 to 109 beats.min ^-1 in the first 30 min of fishing period, after which it attained a more or less steady pattern.

For more detailed insight into the physical strain, the relative cardiac costs were divided into regular class intervals and plotted against time expressed as the percentage of the total working period [Figure - 2]. It can be seen from the figure that for most of the time in a workday, the physical strain remained below 50%, and for majority of the fishing period, the fishermen worked at a level of 31-40% of their heart rate reserve.

The average workload of the individual fishermen was also judged against various recommended indices of physical strain in relation to mean working heart rate, mean net cardiac cost and mean relative cardiac cost. The results are summarized in [Table - 3]. It can be observed from the table that for two fishermen (20%), the mean workday pulse exceeded the recommended limit of continuous work. In contrast, 70% of the mean net cardiac costs and 90% of the mean relative cardiac costs were higher than the accepted limit.

Duration of work periods exceeding cardiac strain limits was analyzed for individual fishermen as summarized in [Table - 4]. On an average, for 34.4% of the total work-period heart rates were above 110 beats. min ^-1sub and for 54.4% of the total work period, the net cardiac costs were higher than 30 beats. min-[1]. For 3% of the total duration of work, the relative cardiac costs of the fishermen were higher than 50%. It is also clear from the table that the fishermen did not respond equally during the work shift, as is evident from the range of the length of duration for which the recommended ranges were surpassed, particularly with respect to working heart rate and net cardiac costs.

Environmental conditions at the workplace are summarized in [Table - 5]. Mean CET at the workplace was obtained to be 29.3°C.

Discussion

Physical strain of the fishing task

Heart rate is the principal parameter monitored in the field. It not only permits the evaluation of circulatory strain imposed by the workloads of varying intensity[6] with minimal interference with the subject's freedom of motion and performance ability, but it also provides an integrated response to energy requirement and thermal and postural demand.[8] It is also suitable for field studies, as a number of recordings can be made during the whole work in contrast to the inconvenience of measuring oxygen consumption.[9]

Other than absolute heart rate, net cardiac costs and relative cardiac costs[10],[11] were derived as indices of cardiac strain. As heart rate response to one and the same work load is sensitive to many inter- and intra-individual influences,[12],[13] choice of these derived indices were made in this present study as they take into account the inter-individual differences.[14] Moreover, net cardiac cost, being related to resting heart rate, evaluates the work load strictly connected with the job; while the relative cardiac cost, taking into consideration both the resting and maximal heart rate of the subjects, gives best expression of the individual circulatory strain.[15],[16] Such a view also oriented the choice for 'limit for continuous work'[17] adjusted for male population and based on the resting pulse of the subjects. In this study, working oxygen consumptions were estimated from measured working heart rates as a general linear relationship exists between the parameters during standardized exercise as obtained in this study during laboratory examination; that corroborates well with earlier findings.[18] As this sort of estimation is reliable for all practical purposes of field investigation and is quite sensitive with a variation of ±15%,[18] estimated values were used to assess the relative degree of physical exertion by expressing the oxygen uptake as percentage of subject's maximal aerobic power. Responses were cross-examined against certain recommended criteria of physical strain, which allows a better evaluation of strain in relation to different parameters.

The physical strain of the present inland fishing task in terms of heart rate could be compared with the tasks related with apple farming[15] and dairy farming works.[19] The relative aerobic strain in the scoop net fishing varied between 30 and 38% of VO ₂max, which compared with the values obtained for different types of coastal fishing tasks, viz., hand line, long line and net fishing but was lower than the strain of fishing with a Danish-seine.[2] Values of energy cost are also comparable with some aspects of agricultural works, stone cutting, textile and jute mill works. [20],[21],[22],[23],[24],[25],[26],[27],[28]

Analysis of work activities

The average length of the total duration of fishing period was 93.4±3.5 min, during which the fishermen made 7 to 11 fishing attempts. Wading, stooping and catch-handling are the main activities noted. Observations on these tasks indicate the presence of predominant static components in the whole work that comprises bending postures during fishing, and static contractions of arms during holding and cleaning the entrapment and collecting the entrapped fishes. Static muscular contractions were also required during prolonged standing and wading in water to adjust postural disequilibrium. Besides, every time the fisherman bent his trunk to dip his entrapment in water, a new cycle is initiated that ends in sorting and collecting the catch. This cyclic pattern of work (with average cycle time of 10 min) represents a nonsteady work phase that might prevent the workers from full recovery in between successive work cycles. The recovery pattern of the fishermen revealed that although the recovery heart rates were well within the recommended range, the pulse deceleration index was higher than the recommended range of -10 beats. min ^-1sub[6] which may be due to the predominant static load of the work.

Environmental conditions

Environmental conditions of the workplaces of the fishing jobs are shown in [Table - 5], comprising dry bulb, wet bulb and globe temperature along with wind velocity. For the purpose of evaluation of the environmental heat load, the CET is considered. The present findings indicated that the work output of the fishermen was 198 kcal.hr ^-1sub at an average CET of 84.7°F. This level of energy expense in relation to environmental heat load could be considered well within the acceptable level of energy expense within the 'prescriptive zone.'[25],[26] Furthermore, the total working time (90-101 min) was also much less than the work pattern for the industrial workers (480 min). So from these results, it could be suggested that the actual prevailing temperature in the workplace was not a threat to the health of the fishermen.

Heaviness of the task

The physiological gradations of different activities have been proposed by different researchers in the field of work physiology and ergonomics from time to time. They are either based on the monitoring of some principal parameters like heart rate both during work[18] and recovery,[6],[27] energy cost[28] or on some derived parameters like net cardiac cost.[11] Based on these scales of heaviness, it appeared that fishing with scoop net represented a work of moderate intensity.

Rationalization of the fishing tasks

The knowledge of acceptable workload is of great practical importance in the field of work physiology in order to rationalize a task because often the workload for a particular task is so heavy that it imposes undue physiological strain on the workers and results in fatigue that leads to gradual decrement of work capacity. A number of earlier studies have attempted to establish an optimal work rate limit expressed in terms of relative aerobic strain (%VO _2max) appropriate for specific occupational tasks . For a relatively homogenous group of individuals, the average value of this parameter therefore may be considered as the reasonable upper limit for continuous work stretching over several hours. This assumption is also equally applicable for Indian workers.[29] It was found during the study that the fishermen maintained their usual pace of work without any compromise with the actual usual length of work shift and on average have utilized 34% of their VO₂max, which is not only lower than the recommended level for Indians,[29] but also lower than the acceptable level of 41 and 45% for a mixed dynamic and static work[30] and self-paced sustained physical work of 1-2 hours' duration[31] respectively. It was established that the heart rate in terms of relative cardiac cost is also an equally reliable measure to rationalize the physiological workload since the later showed better correlation with the relative aerobic strain.[19] In the present study, the average value of relative cardiac cost was around 36%, which is almost similar to the value of the acceptable level of relative aerobic strain for Indians.[29] Furthermore, as the inland fishing task as investigated in the present study represents a work stretching much less than 480 min, as with industrial operations, the acceptable limit for the fishermen engaged in different fishing tasks could be set on a higher side than that set for different tasks spanning 8 h. From these facts, it therefore seems to indicate that the workload of the fishermen was within the acceptable limit.

Conclusion

Acknowledgment

References

Copyright 2006 - Indian Journal of Occupational and Environmental Medicine

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