Introduction: Adoption of physical activity (PA) consistent with current guidelines does not improve maximal cardiorespiratory fitness (mCRF; V˙O2peak) beyond the error of measurement for approximately 30% of adults. Whether PA improves measures of exercise tolerance at submaximal levels (submaximal cardiorespiratory fitness [sCRF]) independent of change in mCRF is unknown. Here we assessed the relationship between exercise-induced changes in mCRF and sCRF.
Methods: Twenty-five physically inactive men 30-60 yrs old (mean ± SD = 44.3 ± 9.1 yr) completed 4 wk of supervised exercise consisting of 30 min of exercise, five times per week at 65% mCRF. mCRF was assessed using a maximal treadmill test. sCRF was measured as follows: 1) exercise tolerance, the distance traveled during a 12-min time trial on a treadmill, and 2) change in heart rate (HR) at submaximal work rates during the maximal treadmill test. Daily PA was measured by accelerometry at baseline and 4 wk.
Results: mCRF (P = 0.009) and both measures of sCRF (P < 0.001) improved at 4 wk. No change in measures of daily PA was observed at 4-wk compared with baseline (P > 0.05). No association was observed between exercise-induced change in mCRF and change in either measure of sCRF (P > 0.05) after exercise training. In the group of participants who did not improve mCRF beyond the measurement error (n = 13, or 52%), we observed a significant improvement in both measures of sCRF (P < 0.001). Among these 13 individuals, all improved in at least one measure of sCRF.
Conclusion: Exercise-induced improvements in mCRF were not associated with improvements in either measure of sCRF. Improvements in submaximal measures of cardiorespiratory fitness are observed in the absence of change in mCRF. Measures of sCRF capture peripheral adaptations to exercise not captured by measures of mCRF alone.