The effects of previous severe exercise upon the respiratory $$\dot V_{CO_2 } /\dot V_{O_2 }$$ exchange ratio as a predictor of maximum oxygen uptake

The present study examined the effect of previous severe exercise upon (i) respiratory exchange during maximal exercise, and (ii) the respiratory\(\dot V_{CO_2 } /\dot V_{O_2 }\) exchange ratio (R) as a predictor of maximum oxygen uptake (\(\dot V_{O_{2\max } }\))- Thirteen healthy males performed a progressive treadmill test to\(\dot V_{O_{2\max } }\): at rest (T1); after a 1 h run on the level treadmill at a speed corresponding 82.4±7.3% of their\(\dot V_{O_{2\max } }\) (T2); after 1 h recovery (T3); and after 24 h recovery (T4). Respiratory gases were continuously monitored. No changes in average work\(\dot V_{O_2 }\),\(\dot V_{O_{2\max } }\) or maximum heart rate were found between trials. Average work\(\dot V_{CO_2 }\) was lower in T2 (2.055±0.093 l·min⁻¹,p<0.001), T3 (2.080±0.087 l·min⁻¹,p<0.001) and T4 (2.337±0.154 l·min⁻¹, NS) compared with T1 (2.360±0.147 l·min⁻¹). This resulted in lower average R values in T2 (0.81±0.02,P<0.001), T3 (0.83±0.02,P<0.001) and T4 (0.94±0.02, NS) in relation to T1 (0.95±0.02). Analysis of the %\(\dot V_{O_{2\max } }\)/R relationship over the final 5 min of each test showed a shift to the left during T2 (p<0.001), T3 (p<0.001) and T4 (NS) compared with T1. As a result predictions of\(\dot V_{O_{2\max } }\) based on R (\(\dot V_{O_{2\max } }\)R) were similar to recorded\(\dot V_{O_{2\max } }\) in T1 (+0.6%) and T4 (+2.2%). But higher in T2 (+8.7%,p<0.001) and T3 (+6.9%,p<0.001). The present results show that previous severe exercise can significantly affect respiratory exchange at rest and during maximum incremental exercise, and by doing so can significantly influence predictions of\(\dot V_{O_{2\max } }\) based on R.