Role of Ionic Buffering in the Relationship between Recovery and Fatigability



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Purpose: This study aimed to characterize the role of ionic buffering capacity, as measured by non-metabolic expired carbon dioxide (nm-V ̇CO2), in the relationship between recovery and performance fatigability. Methods: Twenty healthy adults (men, n=9, age =44.7±13.9 years; women, n=11, age=50.3±11.1 years) completed peak cardiopulmonary exercise (CPET) and submaximal constant work rate tests (CWRT) on the cycle ergometer on separate days before and after a vigorous, 4-week aerobic exercise training (AET) regimen. Each test was followed by 10-minutes of passive recovery and an endurance test at 70% of the peak watts attained during the CPET. Performance fatigability was measured by the endurance test durations following both the peak CPET (End1) and CWRT (End2), peak CPET time (pk-Time), and peak CPET watts (pk-Watts). Metabolic indices were total V ̇CO2 (t-V ̇CO2), metabolic V ̇CO2 (m-V ̇CO2), and non-metabolic V ̇CO2 (nm-V ̇CO2), and recovery capacity indices were V ̇O2 and V ̇CO2 off-kinetic oxidative response index (ORI). Data were analyzed using paired t-tests, correlations, and regressions and compared before and after AET. Results: Significant improvements in recovery (V ̇O2 -off ORI 7.48±7.52 ml/s, p<0.001 and V ̇CO2-off ORI 4.11±5.05 ml/s, p<0.001) and performance fatigability measures (End 1 265±337 s ; End2 321±392 s ; pk-Time 63±40 s, p<0.001; pk-Watts 24±19, p<0.001) were observed after AET, along with significant increases in t-V ̇CO2 (1512±2225 ml, p<0.01) and nm-V ̇CO2 (608 ± 666 ml, p<0.001). However, a significant change in m-V ̇CO2 (904±2255 ml, p=0.089) was not observed. Relationships between measures of recovery and PF measures were observed, although the strengths of the relationships were diminished (pk-Time, pk-Watts) or became non-significant (End1, End2) after controlling the analyses for the effect of nm-V ̇CO2. Conclusion: The current study suggests that ionic buffering capacity may moderate the relationship between recovery and performance fatigability. These results could have implications regarding AET induced buffering dynamics and its role in fatigue resistance when performing physical activities above moderate intensities.