PLASMA K-TRAINED AND SPRINT-TRAINED SUBJECTS( CHANGES DURING INTENSE EXERCISE IN ENDURANCE)

Active muscle releases K+, and the plasma K+ concentration is conseque ntly raised during exercise. K+ is removed by the Na,K pump, and train ing may influence the number of pumps. The plasma K+ concentration was therefore studied in five endurance-trained (ET) and six sprint-train ed (ST) subjects during and after 1 min of exhausting treadmill runnin g. Non-exhausting bouts of exercise at either lower speed or of shorte r duration were also carried out. Blood samples were taken from a cath eter in the femoral vein before and at frequent intervals after exerci se. The pre-exercise venous plasma [K+] was (mean +/- SEM) 3.68 +/- 0. 10 mmol 1(-1) (ET) and 3.88 +/- 0.06 mmol 1(-1) (ST). One minute of ex hausting exercise was sustained at 5.27 +/- 0.08 m s(-1) (ET) and 5.59 +/- 0.06 m s(-1) (ST) and caused the plasma K+ concentration to rise by 4.4 +/- 0.3 (ET) and 4.7 +/- 0.3 mmol 1(-1) (ST; ns) respectively. Three minutes after exercise the K+ concentration was 0.48 +/- 0.08 mm ol 1(-1) (ST) and 0.50 +/- 0.07 mmol 1(-1) (ST) below the pre-exercise value. During the following 6 min of recovery, the value was unchange d for the ET subjects, while a 0.32 +/- 0.06 mmol 1(-1) rise was seen for the ST subjects. Exercise at reduced intensity or of reduced durat ion resulted in smaller changes in the K+ concentration both during ex ercise and in the post-exercise recovery, and for each subject the low est: post-exercise K+ concentration was therefore inversely related to the peak K+ concentration during exercise. For a given peak K+ concen tration, the ST subjects had higher plasma K+ concentrations than the ET subjects in the recovery period, suggesting that the two groups of subjects may regulate the K+ concentration differently after exercise.