Measures of excess dot{mathrm{V}} CO2 and recovery dot{mathrm{V}} CO2 as indices of performance fatigability during exercise: a pilot study

Abstract

BackgroundThe severity of performance fatigability and the capacity to recover from activity are profoundly influenced by skeletal muscle energetics, specifically the ability to buffer fatigue-inducing ions produced from anaerobic metabolism. Mechanisms responsible for buffering these ions result in the production of excess carbon dioxide (CO2) that can be measured as expired CO2 ( dot{mathrm{V}} CO2) during cardiopulmonary exercise testing (CPET). The primary objective of this study was to assess the feasibility of select assessment procedures for use in planning and carrying out interventional studies, which are larger interventional studies investigating the relationships between CO2 expiration, measured during and after both CPET and submaximal exercise testing, and performance fatigability.MethodsCross-sectional, pilot study design. Seven healthy subjects (30.7±5.1 years; 5 females) completed a peak CPET and constant work-rate test (CWRT) on separate days, each followed by a 10-min recovery then 10-min walk test. Oxygen consumption ( dot{mathrm{V}} O2) and dot{mathrm{V}} CO2 on- and off-kinetics (transition constant and oxidative response index), excess- dot{mathrm{V}} CO2, and performance fatigability severity scores (PFSS) were measured. Data were analyzed using regression analyses.ResultsAll subjects that met the inclusion/exclusion criteria and consented to participate in the study completed all exercise testing sessions with no adverse events. All testing procedures were carried out successfully and outcome measures were obtained, as intended, without adverse events. Excess- dot{mathrm{V}} CO2 accounted for 61% of the variability in performance fatigability as measured by dot{mathrm{V}} O2 on-kinetic ORI (ml/s) (R2=0.614; y = 8.474x − 4.379, 95% CI [0.748, 16.200]) and 62% of the variability as measured by PFSS (R2=0.619; y = − 0.096x + 1.267, 95% CI [−0.183, −0.009]). During CPET, dot{mathrm{V}} CO2 -off ORI accounted for 70% (R2=0.695; y = 1.390x − 11.984, 95% CI [0.331, 2.449]) and dot{mathrm{V}} CO2 -off Kt for 73% of the variability in performance fatigability measured by dot{mathrm{V}} O2 on-kinetic ORI (ml/s) (R2=0.730; y = 1.818x − 13.639, 95% CI [0.548, 3.087]).ConclusionThe findings of this study suggest that utilizing dot{mathrm{V}} CO2 measures may be a viable and useful addition or alternative to dot{mathrm{V}} O2 measures, warranting further study. While the current protocol appeared to be satisfactory, for obtaining select cardiopulmonary and performance fatigability measures as intended, modifications to the current protocol to consider in subsequent, larger studies may include use of an alternate mode or measure to enable control of work rate constancy during performance fatigability testing following initial CPET.