Introduction: Functional capacity, also termed maximal oxygen consumption (VO₂max), or aerobic fitness, has been shown to be an independent risk factor for all-cause and cardiovascular disease mortality. The cardiopulmonary exercise test (CPET) is the golden standard for assessing the functional capacity of the patient and it is becoming the integral part of the growing number of recommendations and guidelines. (1, 2) While high-intensity interval training (HIIT) would seem to be more effective than other types of training in improving cardiac performance and function (3), the time course of functional adaptations to this training in ST-elevation myocardial infarction and non-ST-elevation myocardial infarction patients is still unknown. Therefore, the aim was to assess the progressive cardiopulmonary improvements throughout the process of 12 weeks of individually-prescribed HIIT training.

Patients and Methods: 16 STEMI and NSTEMI patients (age 58 ± 10 years; VO₂max 19 ± 5.3 ml min^-1 kg^-1) underwent 12 weeks of supervised cycling HIIT (4x4 min at 85-95% of HRmax) 3 times per week. Functional capacity (VO₂max) and all cardiopulmonary parameters ware assessed by means of the incremental cardiopulmonary test to exhaustion (CPET) every 4 throughout the training program. Individual training zones were prescribed and adjusted according to the parameters obtained in CPET.

Results: Peak VO₂ increased significantly by 8% (19.2 ± 5.1 vs 20.8 ± 5.0 mil min-1 kg-1, P=.002) across the group already after 4 weeks of training. In the same timepoint, anaerobic threshold (AT) and respiratory compensation point (RCP) significantly improved by 15% (12.4 ± 3.1 vs 14.3 ± 3.0 mil min-1 kg-1, P<.001) and 19% (15.5 ± 4.2 vs 18.6 ± 4.3 mil min-1 kg-1, P<.001), respectively. The absolute improvement in VO2peak at the end of the 12-week training was 32% (19.2 ± 5.1 vs 25.5 ± 4.9 mil min-1 kg-1, P<.001)

Conclusion: 4 weeks of HIIT are enough to induce significant functional adaptations like VO2max, VO2 at AT and RCP in STEMI and NSTEMI patients provided that patients are trained at the same in terms of volume, but at individually tailored intensity. Moreover, across 12 weeks of training, HIIT has proven to be effective training method in increasing functional capacity as well as exercise tolerance in STEMI and NSTEMI patients.