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
3 x/week
Cycling, running, stair climbing, uphill brisk walking
A maximal sustainable workload for the prescribed duration or interval (unable to maintain a conversation uninterrupted).
30 min/session
Interval times
10 x 1 min*
1 min recovery
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).

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.

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
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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

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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