An Evaluation of the Effectiveness of Exercise Training-Based Cardiac Rehabilitation to Improve Aerobic Fitness

On intake to exercise-training based cardiac rehabilitation, an incremental CPET is performed to identify V̇O2peak and establish baseline exercise capacity. In individuals who provide a symptom-free and maximal effort, V̇O2peak provides a reasonable estimate of the maximal ability of the body to take up, transport, and utilize O2 and the ceiling of aerobic capacity. However, in those unaccustomed to exhaustive exercise, such an effort is challenging to obtain. In clinical atmospheres, CPET testing is commonly symptom-limited due to breathlessness and fatigue. Thus, many patients voluntarily terminate exercise before reaching their maximal physiological limit of O2 delivery and utilization. As a result, the measured V̇O2peak is lower than V̇O2max and the patient’s true aerobic capacity may be underestimated. Therefore, V̇O2peak may not be the best metric to evaluate exercise capacity and effectiveness in cardiac rehab populations. During a routine CPET, most individuals cross two metabolic boundaries as they ascend towards peak effort. At these boundaries, muscle metabolism changes in a way that alters cellular and physiological homeostasis and prompts compensatory adjustments of the cardiorespiratory support system. These “adjustments” may be observed in measured gas exchange and ventilatory response profiles and are identified as two thresholds. The first, the estimated lactate threshold, signifies the onset of blood lactate accumulation and the second, the respiratory compensation point is the onset of metabolic acidosis. Improving these thresholds makes daily activities easier; therefore, the LT and RCP may be equally or more informative in the assessment of patients\u27 aerobic fitness before and after exercise training