Effect of blood pH on peripheral and central signals of perceived exertion.

Ten male subjects underwent exercise testing in three modes, arms (A), legs (L), and arms + legs (A + L), after ingesting 0.3 g X kg-1 body weight of either NaHCO3 to induce alkalosis or CaCO3 as a placebo (i.e., six exercise trials). Ratings of perceived exertion (RPE: Borg, 15-pt scale) for the arms (RPE-A), legs (RPE-L), chest (REP-C), and overall body (RPE-O) did not differ between acid-base conditions at 20, 40, or 60% VO2max for all three exercise modes. At 80% VO2max, 1) RPE-A was lower (P less than 0.01) during A; 2) RPE-L was lower (P less than 0.01) during L; and 3) RPE-A and RPE-L were lower (P less than 0.01) during A + L under the NaHCO3 as compared to the CaCO3 condition. Differences were not found for RPE-L during A or for RPE-A during L. RPE-C and RPE-O were lower (P less than 0.01) under NaHCO3 during A, L, and A + L. Blood acid-base, VO2, and cardiorespiratory responses were not differentially influenced by exercise mode. Blood pH was significantly higher under NaHCO3 than CaCO3 at pre-exercise and 80% VO2max. VO2, heart rate, and tidal volume did not differ between acid-base conditions at any exercise intensity. VE and respiratory rate did not differ between acid-base conditions at 20, 40, or 60% VO2max but were significantly lower under NaHCO3 at 80% VO2max. RPE-A and L were positively related to blood [H+], and RPE-C was positively related to VE for all exercise modes.