Cardiac frequency throughout a working shift in coal miners

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Abstract
Despite the ever-increasing mechanization of industrial activities, coal mining still remains a physically demanding occupation as it is not always possible to extensively mechanize the extraction process. To estimate the physical effort necessary to sustain coal mining activities in a poorly-mechanized mine, cardiac frequency (ƒ/c) was measured throughout the working shift with a Sport-Tester PE3000 (Polar Electro OY. Finland) in a representative sample of 73 Asturian miners engaged in a full spectrum of underground work. The mean ± SD of the overallƒ/c values measured in miners working at the coal face (Group 1, 33 subjects, mean age 32·7 years, age range 21–48 years R was 106·5 ± 18·2 beats min−1. In other miners (Group 2, 40 subjects, mean age 34·6 years, age range 23–48 years) corresponding figures were 1031 ±177 beats-min−1 (pc Lbeats. Min−1) was not related to age, measured (treadmill) VO2 max nor VO2 max.kg body weight−1, while average working-shiftƒ c (%ƒ c max) was weakly related to age (r = 0·396, p2 max (r equals; 0·295, p < 0·05) and VO2max.kg body weight−1 (r= 0·352, pc (beats · min−1) was negatively related to age (r = 0·334, p < 0·05). Our study has provided the distribution of the overall ƒ c values likely to be found in subjects working in these poorly-mechanized mines. However, average working-shift ƒ c differs considerably from subject to subject and is largely unpredictable.