Discussion
HAD, IPF, respiratory and peripheral muscle function
To our knowledge, this is the first study to investigate the feasibility and potential efficacy of HIIT in the context of a circuit-based clinical PR programme for ILD and compare it with MICT. It demonstrated the feasibility of HIIT, in PR for patients with ILD and provided preliminary data on the exercise mode more likely to maintain benefits 6 months after programme completion. In addition, we identified the time of peak benefit and time course of subsequent deterioration.HIIT proved to be feasible and well tolerated but required closer supervision and careful instructions for patients to continue this mode of training than MICT. The attrition rate was higher in the HIIT group compared with the MICT group and more contact was needed in the 6-month period to ensure that the HIIT mode of training met the protocol requirements.The preliminary efficacy of HIIT over MICT was tested using random effects models. Their aim was to understand the average variation of the four key outcomes through time across groups to answer five main questions: (1) How do these measurements change over time? (2) Does the benefit differ between groups? (3) How sustainable is the benefit? (4) Does the attrition rate differ between groups? and (5) What is the influence of age? The study was primarily designed to compare the two treatment groups, but an exploratory analysis was performed to look for differences between clinical groups, although this resulted in small numbers in the subgroups.Contrary to our initial hypothesis, our data showed no evidence of greater benefit with HIIT compared with that achieved with MICT in exercise capacity, respiratory and peripheral muscle function or health status in the medium term. The study was designed as a pilot to test the potential for a trial of HIIT in a larger, definitive study, but we are forced to conclude that a study of the same design may not be worthwhile.At 2 months, both groups improved >34 m in the 6MWD, which is the reported minimal clinical important difference in patients with IPF,In addition to functional exercise capacity, patients improved quadriceps muscle strength post-PR but similarly, there was no difference between treatment groups. Age-adjusted results for quadriceps force were less variable than for 6MWD and benefits were well maintained above baseline in both groups. The modelling suggested that quadriceps force peaked a little later than other outcomes at 5.5 months in the MICT group and at 5 months at the HIIT group. Our results support the inclusion of strength training in ILD-PR programmes and suggest that it may explain why some studies showed greater improvement and maintenance in functional capacityRespiratory muscle strength was preserved at baseline (mean SNIP, MIP and MEP >70 cmHHealth status, as defined by the SGRQ-I and HAD Scale improved post-PR and was maintained at 8 months, but again, there was no evidence of superiority of HIIT over the MICT group (