The relationship between the ventilation and lactate thresholds following normal, low and high carbohydrate diets

Summary

Five men performed an incremental exercise test following a normal, low and high carbohydrate dietary regimen over a 7-day period, to examine the influence of an altered carbohydrate energy intake on the relationship between the ventilation (V _E T) and lactate (LaT) thresholds. V _E T and LaT were determined from the ventilatory equivalents for O₂ ($\dot V_E \cdot \dot V_{O_2^{ - 1} }$) and CO₂ ($\dot V_E \cdot \dot V_{O_2^{ - 1} }$) and the log-log transformation of the lactate (La) to power output relationship, respectively. The total duration of the incremental exercise test, carbon dioxide output ($\dot V_{CO_2 }$), respiratory exchange ratio, blood La values and arterialized venous partial pressure of CO₂ $(P_{CO_2 } )$ were reduced, and $\dot V_E \cdot \dot V_{O_2^{ - 1} }$, the slope of the $\dot V_E - \dot V_{CO_2 }$ relationship, blood β-hydroxybutyrate and pH were increased during the low carbohydrate trial compared with the other conditions. Total plasma protein and Na⁺, K⁺, and Cl⁻ were similar across conditions. LaT and V _E T were unaffected by the altered proportions of carbohydrate in the diets and occurred at a similar oxygen consumption (mean $\dot V_{O_2 }$ across trials was 1.98 L · min⁻¹ for V _E T and 2.01 L · min⁻¹ for LaT). A significant relationship (r=0.86) was observed for the $\dot V_{O_2 }$ that represented individual V _E T and LaT values. The increased $\dot V_E \cdot \dot V_{O_2^{ - 1} }$ and slope of the $\dot V_E - \dot V_{CO_2 }$ relationship could be accounted for by the lower $P_{CO_2 }$. It is concluded that alterations in carbohydrate energy intake do not produce an uncoupling of V _E T and LaT as has been reported previously.