Putting the Physiology Back in Physiotherapy

Measures of excess [Formula: see text]CO2 and recovery [Formula: see text]CO2 as indices of performance fatigability during exercise: a pilot study

BACKGROUND

The 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 ([Formula: see text]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.

METHODS

Cross-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 ([Formula: see text]O2) and [Formula: see text]CO2 on- and off-kinetics (transition constant and oxidative response index), excess-[Formula: see text]CO2, and performance fatigability severity scores (PFSS) were measured. Data were analyzed using regression analyses.

RESULTS

All 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-[Formula: see text]CO2 accounted for 61% of the variability in performance fatigability as measured by [Formula: see text]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, [Formula: see text]CO2 -off ORI accounted for 70% (R2=0.695; y = 1.390x - 11.984, 95% CI [0.331, 2.449]) and [Formula: see text]CO2 -off Kt for 73% of the variability in performance fatigability measured by [Formula: see text]O2 on-kinetic ORI (ml/s) (R2=0.730; y = 1.818x - 13.639, 95% CI [0.548, 3.087]).

CONCLUSION

The findings of this study suggest that utilizing [Formula: see text]CO2 measures may be a viable and useful addition or alternative to [Formula: see text]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.

Carbon Dioxide Expiration and Performance Fatigability Following Aerobic Exercise Training: A Longitudinal, Observational, Pilot Study

Purpose

This study examined the influence of aerobic exercise training (AET) on components of carbon dioxide expiration (VCO2), cardiorespiratory function, and fatigability.

Methods

Twenty healthy adults completed peak cardiopulmonary exercise (CPX) and submaximal tests before and after a vigorous, 4-week AET regimen. Each test was followed by a 10-min recovery and endurance test at 70% of peak wattage attained during CPX. Fatigability was assessed using testing durations and power output. Respiratory buffering (excess VCO2) and non-buffering (metabolic VCO2) were calculated. Data were analyzed for significance (p<0.05) using regressions and paired t-tests.

Results

Significant improvements in all measures of fatigability were observed after AET. A significant increase in excess VCO2 was observed, though not in metabolic VCO2. Excess VCO2 was strongly predictive of fatigability measures.

Conclusion

Significant decreases in fatigability are often observed in clinical populations such as obstructive or restrictive lung disease or pulmonary hypertension following AET, even when peak cardiorespiratory function does not appear to adapt. Decreases in fatigability appear to predict longevity with no yet identified mechanism. These results suggest that respiratory buffering and metabolic components of VCO2 may adapt independently to AET, introducing foundational plausibility for an influence of respiratory buffering adaptation to AET on fatigability status.