RECURRENT HEAT EXPOSURE - EFFECTS ON LEVELS OF PLASMA AND URINARY SODIUM AND POTASSIUM IN RESTING AND EXERCISING MEN

Authors:
  • RFR Francesconi
    R Francesconi
  • JMJ Maher
    J Maher
  • GBG Bynum
    G Bynum
  • JMJ Mason
    J Mason
Google Scholar
  • 1 January 1977
    • journal article
    • research article
    • Vol. 48  (5) , 399-404
    • PMID:880177
Abstract
Heat acclimatization was induced in a group of healthy young men by walking on a treadmill (5.6 km/h; 49.degree. C/27.degree. C, dry/wet bulb; 90 min/day; 7 d [days]) and confirmed by observing significantly reduced final rectal temperatures and heart rates on the 7th day of exercise in the heat. A 2nd group of men, paired for maximal O2 consumption and body weight, remained sedentary under identical environmental conditions. While the mild exercise combined with the severe heat conditions induced significant hyperkalemia (P < 0.02, minimal significance) on both the 1st and final days, there did occur an attenuated response with significantly (P < 0.01) reduced plasma K+ after 45 min on the 7th day when compared with 1st day levels. No significant inter- or intragroup differences in plasma Na+ levels were found although the Na+ content of 24 h urine samples showed that men exercising in the heat retained an increased ability to conserve Na+, while sedentary individuals consistently displayed increased excretion of Na+. Even the mild exercise described herein effected hyperkalemia at each sampling time, but the level of hyperkalemia was attenuated after acclimatization, and while Na+ was conserved in the exercising men, no such adaptive processes occurred in sedentary individuals.