Thursday, 30 October 2014

High-Intensity Interval Training (HIIT)

 The popularity of HIIT among the general public has increased over the past 5-10 years. This article defines HIIT, and outlines the benefits and exercise recommendations.

What is HIIT?
HIIT describes physical exercise that is characterised by brief, intermittent bouts of vigorous activity, interspersed by periods of rest or low-intensity exercise (Gibala, Little, MacDonald & Hawley, 2012). It refers to exercise training sessions that are relatively brief consisting of ≤10 min of intense exercise within a training session lasting ≤30 min including warm-up, recovery periods between intervals and cool down  such that the total weekly exercise and training time commitment is reduced compared with current public health guidelines (Gillen & Gibala, 2014). Whereas, Moderate Intensity Continuous Training (MICT) refers to physical exercise performed in a continuous, steady-state manner for a prolonged period of time (>30 minutes).

Why use HIIT over MICT?  
Recent evidence from relatively small, short-term studies suggests that HIIT may be as effective as traditional MICT to induce physiological remodelling, which in turn may be associated with improved health markers, despite a reduced time commitment (Gillen & Gibala, 2014). HIIT induces similar or superior improvements in cardiorespiratory fitness (CRF) compared to MICT in sedentary individuals (Tjønna et al., 2013; Gibala et al., 2012) and a number of clinical populations (CVD, lifestyle-induced cardiometabolic disease and obese individuals) (Guiraud et al., 2012; Weston, Wisløff & Coombes, 2014). This is important, as CRF is a strong predictor of mortality (Blair et al., 1996). Moreover, recent evidence suggests that HIIT is perceived to be more enjoyable than MICT (Bartlett et al. 2011).

A recent meta-analysis has identified that HIIT has more physiological benefits (blood pressure, blood lipids, insulin sensitivity, glycaemic control and endothelial function) than MICT in patients with lifestyle-induced cardiometabolic disease. Including HIIT in a training programme implies that greater health-enhancing benefits could be gained in less time, making HIIT a more time efficient and attractive option (Weston et al., 2014).

Protocol Recommendations for HIIT
Frequency
3 x/week
Modality
Cycling, running, stair climbing, uphill brisk walking
Intensity
A maximal sustainable workload for the prescribed duration or interval (unable to maintain a conversation uninterrupted).
Duration
30 min/session
Interval times
10 x 1 min*
1 min recovery
Warm-up/cool-down
5 min @ low-intensity

* Longer duration intervals can also be undertaken (i.e. 1-4 minutes).
You may decide to incorporate one HIIT session per week in combination with MICT. For optimal health benefits, it is recommended resistance and flexibility programs be performed in conjunction with a cardiovascular program. Little is known about the chronic (long-term) effects of HIIT (Gillen & Gibala, 2014).

Exercise Precautions
As with the initiation of any new exercise program, it is important to undergo proper screening procedures (Gillen & Gibala, 2014). HIIT may require initial supervision in untrained and high-risk individuals (Kessler et al., 2012). It may also be prudent to include a preconditioning phase of training consisting of traditional MICT prior to initiating HIIT (e.g. 20–30 min per session, a few times per week for several weeks) to avoid excessive orthopaedic stress (American College of Sports Medicine, 2014). It has been shown that a baseline level of fitness is a cardioprotectant and reduces the risks associated with exercise-induced ischemic events (Thompson et al. 2007).

References
American College of Sports Medicine. (2014). ACSM’s guidelines for exercise testing and prescription (9th ed.). Baltimore, MD & Philadelphia, PA: Lippincott Williams & Wilkins.

Australian Bureau of Statistics 2011-2012. Physical activity and health. http://www.health.gov.au/internet/main/publishing.nsf/Content/health-pubhlth-strateg-active-evidence.htm

Bartlett, J. D., Close, G.L., MacLaren, D.P., Gregson, W., Drust, B., & Morton, J. P. (2011). High-intensity interval running is perceived to be more enjoyable than moderate-intensity
continuous exercise: implications for exercise adherence. Journal of Sport Sciences, 29, 547–553. doi: 10.1080/02640414.2010.545427

Blair, S. N., Kampert, J. B., Kohl, H. W., Barlow, C. E., Macera, C. A., Paffenbarger, R. S. & Gibbons, L. W. (1996). Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women. JAMA, 276(3), 205–210.

Buchheit, M. & Laursen, P. B. (2013). High-intensity interval training, solutions to the programming puzzle part II: anaerobic energy, neuromuscular load and practical applications. Sports Medicine, 43, 927–954. doi: 10.1007/s40279-013-0066-5

Gibala, M. J., Little, J. P., MacDonald, M. J., & Hawley, J. A. (2012). Physiological adaptations to low-volume, high-intensity interval training in health and disease. Journal of Physiology, 590(5), 1077–1084. doi: 10.1113/jphysiol.2011.224725

Gillen, J. B., & Gibala, M. J. (2014). Is high-intensity interval training a time-efficient exercise
strategy to improve health and fitness? Applied Physiology, Nutrition and Metabolism, 39, 409–412. doi: 10.1139/apnm-2013-0187

Guiraud, T., Nigam, A., Gremeaux, V., Meyer, P., Juneau, M., & Bosquet, L. (2012). High-intensity interval training in cardiac rehabilitation. Sports Medicine, 42(7), 587-605. doi: 10.2165/11631910-000000000-00000

Kessler, H. S., Sisson, S. B., & Short, K. R. (2012). The potential for high-intensity interval training to reduce cardiometabolic disease risk. Sports Medicine, 42(6), 489-509. doi: 10.2165/11630910-000000000-00000

Strasser, B. (2013). Physical activity in obesity and metabolic syndrome. Annals of the New York Academy of Sciences, 1281, 141-159. doi: 10.1111/j.1749-6632.2012.06785.x
Thompson, P. D., Franklin, B.A., Balady, G. J., Blair, S. N., Corrado, D., Estes, N. A. M., … 

Costa, F. (2007). Exercise and acute cardiovascular events placing the risks into perspective: a scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism and the Council on Clinical Cardiology. Circulation, 115(17), 2358–2368. doi:10.1161/CIRCULATIONAHA.107.181485

Tjønna, A. E., Leinan, I. M., Bartnes, A. T., Jenssen, B. M., Gibala, M. J., Winett, R. A., Wisløff, U. (2013). Low- and high-volume of intensive endurance training significantly improves maximal oxygen uptake after 10-weeks of training in healthy men. PLoS ONE 8(5), e65382. doi: 10.1371/journal.pone.0065382

Trost, S.G., Owen, N., Baurman, A.E., Sallis, J.F., & Brown, W. (2002). Correlates of adults’ participation in physical activity: review and update. Medicine and Science in Sport and Exercise, 34(12), 1996–2001. doi: 10.1097/00005768-200212000-00020

Weston, K. S., Wisløff, U., & Coombes, J. S. (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. doi: 10.1136/bjsports-2013-092576