A Comparison of Cardiac Strain among D r i l l e r s o f Tw o D i f f e r e n t A g e G r o u p s i n Underground Manual Coal Mines in India:Ratnadeep SAHA, et al. Department of Physiology, Universal College of Medical Sciences, NepalCardiac strain was evaluated in terms of working heart rate (WHR), relative cardiac cost (RCC), net cardiac cost (NCC) and other recovery indices among six younger (mean age 34.2 ± 2.7 yr) and sixteen older (mean age 48.9 ± 5.4 yr) drillers working in a manual underground coal mine over two spells of work. The mean WHR was within the range of 117-132 beats / min with corresponding mean relative cardiac cost between 44-48% of heart rate reserve for the younger group and 53-55% for their older counterparts. The mean NCC was above 50 beats/min for both age groups. It was seen that the workers surpassed the recommended limits of cardiac strain indices. The intensity of workload indicates the job to be "heavy" to "extremely heavy" in accordance with the heaviness scales based on WHR, NCC and recovery heart rates. Heat stress prevailing in the workplace in terms of effective temperature (ET) and wet bulb globe temperature (WBGT), was above the recommended limits as per the guidelines proposed by WHO and ACGIH. High physiological demands of the job which requires predominate static muscular exertions coupled with high heat stress were found to hinder the recovery process and may prove deleterious particularly for the older workers. Therefore, in the present context, the need of ergonomic interventions for job organization and quick reparation of environmental condition are strongly indicted. (J Occup Health 2008; 50: 512-520) Field Study

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Thirty-nine healthy carriers (23-57 years of age) were investigated in underground manual coal mines in West Bengal, India during two different work spells of a single work shift. We compared physiological strain of workers <40 and > or =40 years of age. For both groups, mean heart rate was 124-133 beats/min, with a mean corresponding relative cardiac cost of 50-66%. Maximum aerobic capacities were estimated indirectly, following a standard step test protocol. Average oxygen consumption was 1.07-1.1 l/min, with an energy expenditure of 5.35-5.5 kcal/min among both age groups. Acceptable levels of physiological strain were well encroached, and older workers faced the maximum burden. The tasks studied were heavy to very heavy in nature. The weight of load carriage at a spontaneously chosen speed and the prevailing environmental conditions merit serious attention. There is extreme need of ergonomic interventions in reducing the postural load and musculoskeletal discomforts in this population.

physiological workload underground trammer coal mine aerobic capacityThe authors are grateful to the managerial authorities of various mines of Eastern Coalfield for providing necessary facilities for conducting this study. The authors also express their gratitude to the miners who volunteered for the study against various odds.Correspondence and requests for offprints should be sent to

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