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It is with great pleasure that the Cardiopulmonary Physical Therapy Journal publishes an invited paper on the effectiveness of and practical suggestions for interval training in patients with chronic obstructive pulmonary disease.1 This paper makes a significant contribution to cardiopulmonary physical therapy for areas of further research as well as for immediate clinical practice related to exercise prescription. In fact, the paper highlights an area of intersection between research and practice of exercise prescription that deserves more attention.
Empirical research can only inform us of the mean trend of a sample; whereas in clinical practice we are interested in an effect on one particular person–the patient who is seeking our suggested interventions. Estimated effects in a particular study reflect the mean and variance of the sample being studied; in clinical practice, we are estimating a particular effect on a particular person based on several indicators. Researchers must select inclusion and exclusion criteria that help produce a sample that represents the population in which they anticipate an effect and to which they want to generalize. Clinicians, in making decisions about exercise prescription, must make informed decisions based on the empirical evidence (generated by empirical studies and inductive reasoning); but must vet the empirical evidence through a process of deductive reasoning as they take general understanding and apply it very specifically to a case.
Kortianou and colleagues have captured this balance in the following paper.1 Despite the fact that mean effects of interval training that have not been demonstrated to be superior to continuous training in patients with COPD, the authors appropriately use deductive reasoning. The expected benefits of interval training are based on accumulating a higher intensity of exercise for longer durations, leading to greater total work. In past studies in patients with COPD, the total work between interval training and continuous training were not different. Hence, the superiority of interval training has not actually been tested in these studies. The authors then rightly refer to studies that demonstrate improved tolerance of interval training–lending support to the hypothesis that these patients can accomplish greater total work. With greater total work it is hypothesized that patients would gain greater improvements. This is a major consideration for the interpretation of studies on interval training in patients with COPD, for the development of additional studies, and when considering incorporation of interval training in the exercise prescription of patients with COPD.
Kortianou and colleagues also suggest that interval training may have a unique role to play in the training of two particular subpopulations of patients with COPD.1 They ask us to consider the benefits for these two groups based on the two proposed mechanisms. The two subpopulations include: (1) those with known ventilatory limitation prevents sustained exercise, and (2) those with known peripheral muscle dysfunction. As we continue to develop our understanding in this area we should attempt to delineate at least one of the rationales outlined by Kortianou and colleagues as the reason to study or prescribe interval training. To do this, we need to determine whether ventilation or peripheral muscles are the primary limitation to sustained work. I suspect that with improved understanding of these issues we will develop greater specificity of prescription parameters in these two groups of patients, as well as improved estimation of benefits to be expected from interval training interventions. One step would be to analyze responder subgroups in future interval training studies.2