High Intensity Interval Training (HIIT) is a common training method used to improve work capacity, anaerobic fitness & cardiovascular health. It is defined as periods of intense work followed by periods of rest or recovery that can be performed on various cardio equipment or be a part of your weights program via circuit training. Most general and athletic population use it in some format during their training week, but is it safe for everyone? This article addresses the safety and efficacy of HIIT in those with Coronary Artery Disease (CAD).
CAD affects 1.4 million Australians and refers to disorders of the coronary artery that cause disruption to blood flow. Although CAD can result in a heart attack, the development of plaque is the major issue, with a poor cardiometabolic profile and poor lifestyle choices exhibited (Shiraev et al., 2012). This highlights that if you live a healthy and balanced lifestyle you can significantly reduce the risk of developing CAD. The development of secondary conditions including hypertension, heart failure and Peripherovascular Disease means that cardiac rehabilitation needs to take a multi-centred approach that includes a tailored exercise and dietary program.
HIIT has been shown to be an effective and safe prescription in improving heart function and capacity in healthy individuals. Helgerud et al. (2007) showed that high intensity intervals were better at improving VO2max (overall fitness), while other studies have found HIIT to improve the overall functioning of the heart via the improvements in how much blood it can pump per beat (stroke volume) and how much blood can be pumped per minute (cardiac output) (Currie et al, 2014).
Is it Safe?
Many research papers have shown that HIIT is safe for people with CAD or for people performing a cardiac rehabilitation program, as it is for most, with 1 study performed by Rognmo et al. (2012) noting 2 non-fatal incidents over 23,182 hours of HIIT. This indicates that with the proper safety measures in place, HIIT can be a safe intervention and enjoyable exercise prescription. So what things need to be considered?
- Exercise screening – A thorough investigation prior to training, in which health risks, family history and associated injures or conditions are clearly identified by a qualified and experienced exercise physiologist or exercise scientist.
- Exercise assessment – Critical to highlight the feasibility and justification of implementing HIIT into your program performed by a qualified and experienced exercise physiologist or exercise scientist.
- Monitoring each session – This can come from subjective measures including Rate of Perceived Exertion (RPE), Shortness of Breath (SOB) and Pain scales. Other tools can include objective measures such as a heart rate monitor, however it is important to note that due to medications that lower the heart rate response to take pressure off the heart, this measure may be inaccurate.
- Tracking the progress – Regular monitoring of the clients HR, as a drop in HR with an increase in exercise intensity is a sign that the client is suffering a cardiac event.
How Do I Implement HIIT Into My Program?
After your initial appointment with your exercise physiologist or exercise scientist, they will then take you through all the variables and options to consider when performing this type of exercise. There are numerous training variables to consider including:
- Initial protocols: Helgerud et al. (2007) showed that a 15 seconds on/15 seconds off for 10 minutes is feasible with subsequent progressions of 1 minute on/1 minute off (Weston et al., 2014) and 2 minute on/2 minute off (Warburton et al., 2005).
- Duration of the interval: This should be the first point of progression (Heyward & Gibson, 2014) to increase the hearts ability to tolerate stress during a single bout.
- Increases in intensities: This can occur if the newly found duration is being tolerated as Moholdt et al. (2014) noticed greater changes in VO2max when HIIT was performed at 95%.
- Volume: Time spent per session and number of sessions can influence volume accrued at high intensity an initial total volume of 1 x 20 minute session per week (Currie et al. 2013), then gradually building up to a total volume of 60 minutes (Warburton et al. 2005) in 3 sessions are safe methods of progression.
The implementation of HIIT in CAD rehabilitation has been shown to be a safe form of programming with numerous benefits. This review highlights the importance of adequate pre-screening before any exercise regime to ensure that any exercise, particularly HIIT, can be performed safely. If you or someone you know is dealing with CAD, make sure you come on in to Absolute Health & Performance to ensure safe and effective exercise prescription for your long term health.
Written By Exercise Physiologist Adam Luther
Shiraev, T., Barclay, G. (2012). Evidence based exercise: clinical benefits of high intensity interval training. Journal of Australian Family Physician, 41(12), 960-962.
Helgerud, J., Hoydal, K., Wang, E., Karlsen, T., Berg, P., Bjrkass, M., Simonsen, T., Helgesen, C., Hjorth, N., Bach, R., & Hoff, J. (2007). Aerobic high-intensity intervals improve vo2max more than moderate training. Journal of Medicine & Science in Sports & Exercise, 39(4), 665-71.
Currie, K., Bailey, K., Jung, M., McKelvie, R., & MacDonald, M. (2014). Effects of resistance training combined with moderate-intensity endurance or low-volume high-intensity interval exercise on cardiovascular risk factors in patients with coronary artery disease. Journal of Science and Medicine in Sport,1-6.
Rognmo, O., Moholdt, T., Bakken, H., Hole, T., Molstad, P., Myhr, N., Grimsmo, J., & Wisloff, U. (2012). Cardiovascular risk of high versus moderate intensity aerobic exercise in coronary heart disease patients. Journal of Circulation, 126, 1436-1440
Weston, K., Wisloff, U., & Coombes, J. (2014). High-intensity interval training in patients with lifestyle-induced cardiometabolic disease: a systematic review and meta-analysis. British Journal of Sports Medicine, 48, 1227-1234.
Warburton, D., Mckenzie, D., Haykowsky, M., Taylor, A., Shoemaker, P., Ignaszewski, A., & Chan, S. (2005). Effectiveness of high-intensity interval training for the rehabilitation of patients with coronary artery disease. The American Journal of Cardiology, 95, 1080-1084.
Heyward, V., & Gibson, A. (2014). Advanced fitness assessment and exercise prescription (7th e.d.). USA: Human Kinetics.
Moholdt, T., Madssen, E., Rognmo, O., & Aamot, I. (2014). The higher the better? interval training intensity in coronary artery disease, Journal of Science and Medicine in Sport, 17, 506-510.
Currie, K., Dubberley, J., Mckelvie, R., & Macdonald, M. (2013). Low-volume, high-intensity interval training in patients with cad. Journal of Medicine & Science in Sports & Exercise, 1436-1442