The effect of induced alkalosis and prolonged submaximal cycling on central and peripheral control of maximal voluntary contraction of the knee extensors

This study was designed to determine if inducing alkalosis would alter central voluntary activation ratio (CAR) and muscle fibre conduction velocity (MFCV) after 50 minutes of high‐intensity cycling. Seven highly trained male cyclists (mean ± SD age and VO 2max 32 ± 7years 62 ± 8 ml.kg −1 .min −1 ) ingested capsules containing either CaCO 3 (placebo) or NaHCO 3 (0.3 g kg‐1 body mass) in six equal doses over a 2‐h period on two separate occasions, commencing 3 h prior to exercise. Subjects performed 3 x 7 s maximal voluntary contraction (MVC) of the knee extensors whilst determining CAR by superimposing electrical stimulation both pre‐ingestion and post‐exercise, followed by a 50 s MVC in which MFCV was assessed. Plasma pH, blood base excess and plasma HCO 3 were significantly (p<0.01) higher during the NaHCO 3 trial. There was a significant (p<0.05) increase in MFCV during the 50s MVC for the NaHCO 3 trial post cycle (5.1 ± 0.4 vs 4.2 ± 0.4 m.s −1 ) whilst the electromyographic amplitude and force remained the same. CAR was significantly (p<0.05) less post cycle for NaHCO 3 than placebo (89.6 ± 10.7 vs 94.4 ± 7.7 %). During the cycle, VO 2 , respiratory exchange ratio, rating of perceived exertion, lactate and heart rate were the same between treatments. These data indicate that inducing alkalosis increased MFCV from a likely increase in intramuscular pH which resulted in a compensatory reduction in central voluntary activation.