CARDIAC FREQUENCY THROUGHOUT A WORKING SHIFT IN COAL-MINERS

Despite the ever-increasing mechanization of industrial activities, co al mining still remains a physically demanding occupation as it is not always possible to extensively mechanize the extraction process. To e stimate the physical effort necessary to sustain coal mining activitie s in a poorly-mechanized mine, cardiac frequency (f(c)) was measured t hroughout 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 overall f(c) values measured in miners working at the coal face (Group 1, 33 s ubjects, mean age 32.7 years, age range 21-48 years) 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 103.1 +/- 17 .7 beats.min(-1) (p < 0.05). Subjects' average working shift f(c) (bea ts.min(-1)) was not related to age, measured (treadmill) VO2 max nor V O2 max.kg body weight(-1), while average working-shift f(c) (% f(c) ma x) was weakly related to age (r = 0.396, p < 0.05), VO2 max (r = -0.29 5, p < 0.05) and VO2 max.kg body weight(-1) (r = -0.352, p < 0.05). Wo rking-shift peak f(c) (beats.min(-1)) was negatively related to age (r = -0.334, p < 0.05). Our study has provided the distribution of the o verall f(c) values likely to be found in subjects working in these poo rly-mechanized mines. However, average working-shift f(c) differs cons iderably from subject to subject and is largely unpredictable.