Acute Physiological Responses to High-Intensity Interval Exercise in Patients with Coronary Artery Disease

Purpose Time spent closer to maximal effort during exercise is a potent stimulus for cardiorespiratory adaptations. The primary purpose was to determine which high-intensity interval exercise (HIIE) protocol provided the greatest physiological stimulus by comparing time spent >= 90% peak oxygen consumption ((V) over dotO(2)peak) and heart rate reserve (HRR) in patients with coronary artery disease (CAD) in response to 3 HIIE protocols and the exercise standard of care, moderate-intensity continuous exercise (MICE). A secondary purpose was to assess protocol preference. Methods Fifteen patients with CAD (6 females, 67 +/- 6 years) underwent measurements of (V) over dotO(2) and heart rate during MICE and three HIIE protocols all performed on a treadmill. The HIIE protocols included one with long intervals (4 x 4-min), short intervals (10 x 1-min), and an adapted version of the 4 x 4 [Toronto Rehabilitation Institute Protocol, (TRIP)]. Time spent >= 90% (V) over dotO(2)peak and HRR were compared. Results Time spent >= 90% (V) over dotO(2)peak was higher during 4 x 4 (6.3 +/- 8.4 min) vs. MICE (1.7 +/- 3.9 min; P = 0.001), while time spent >= 90% HRR was higher during 4 x 4 (6.0 +/- 5.3 min) vs. MICE (0.1 +/- 0.2 min; P < 0.001) and 10 x 1 (0.7 +/- 0.8 min; P = 0.016). TRIP had similar responses as 10 x 1 and MICE. The 10 x 1 was the most preferred protocol and the 4 x 4 was the least preferred protocol. Conclusion Longer intervals (4 x 4) provided the greatest physiological stimulus compared to the exercise standard of care and shorter intervals. However, this protocol was least preferred which may impact exercise adherence. Although the physiological stimulus is important to maximize training adaptations, exercise preferences and attitudes should be considered.