title: Effect of aging on changes in plasma potassium during exercise.
abstract: BACKGROUND
  Exercising skeletal muscle releases large amounts of potassium into plasma. beta-adrenergic receptors enhance reuptake of potassium into muscle. Since beta-adrenergic responses decline with aging in many tissues, the elderly might be predisposed to hyperkalemia during exercise.
  
  
  METHODS
  Venous plasma potassium (K+) was measured during graded bicycle exercise (30 W initial workload with 3-minute 30 W increments) in 18 healthy young men (24.0 +/- 2.9 yrs; mean +/- SD), 18 healthy untrained elderly men (70.0 +/- 3.6 yrs), and 7 elderly master athletes (70.0 +/- 4.6 yrs). Subjects exercised to exhaustion.
  
  
  RESULTS
  Exercise times and maximal oxygen uptake were: young (N = 14; 19.6 +/- 4.4 min, 42.1 +/- 3.8 ml/kg/min), elderly (N = 13; 11.7 +/- 1.9 min, 26.6 +/- 8.0 ml/kg/min), elderly master athletes (N = 6; 16.8 +/- 2.4 min, 40.2 +/- 10.2 ml/kg/min). The rate of increase in K+ was greater in both elderly (89 +/- 59 mumol/l/min) and elderly master athletes (88 +/- 26) compared with healthy young men (60 +/- 30), p < .05. Despite this greater rate of increase, the elderly group did not achieve higher maximal K+ concentrations than the young because of the much shorter duration of exercise in the elderly group. For subjects performing a maximal exercise test, the maximal increase in K+ was similar in the elderly (1.15 +/- 0.91), but significantly greater in elderly master athletes (1.70 +/- 0.31), compared with healthy young men (1.31 +/- 0.45).
  
  
  CONCLUSIONS
  Changes in K+ during short-lasting exercise are similar in untrained healthy elderly men compared with healthy young men, but elderly master athletes have greater changes in K+ during exercise. The greater rate of increase in potassium in healthy and athletic subjects supports the hypothesis of an age-related impairment of the beta 2-adrenergic process that mediates potassium flux into skeletal muscle.
authors.affiliation: Stanford University School of Medicine, Palo Alto, California.
authors.forename: G A
authors.initials: GA
authors.lastname: Ford
authors.forename: T F
authors.initials: TF
authors.lastname: Blaschke
authors.forename: R
authors.initials: R
authors.lastname: Wiswell
authors.forename: B B
authors.initials: BB
authors.lastname: Hoffman
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000097:blood*; D015444:Exercise; D006801:Humans; D008297:Male; D010809:Physical Fitness; D011188:Potassium / Q000097:blood*
chemical_list: D011188:Potassium