High intensity interval training (HIIT)

Aerobic exercise has numerous benefits for high-risk populations and such benefits, especially weight loss, are amplified with high intensity interval training (HIIT).

• high intensity interval training involves repeatedly exercising at a high intensity for 30 seconds to several minutes, separated by 1-5 minutes of recovery (either no or low intensity exercise)
• HIIT is associated with increased patient compliance and improved cardiovascular and metabolic outcomes and is suitable for implementation in both healthy and 'at risk' populations
• as some types of exercise are contraindicated in certain patient populations and HIIT is a complex concept for those unfamiliar to exercise, some patients may require specific assessment or instruction before commencing a HIIT program

Aerobic exercise has a marked impact on cardiovascular disease risk

• benefits include improved serum lipid profiles, blood pressure and inflammatory markers as well as reduced risk of stroke, acute coronary syndrome and overall cardiovascular mortality
• aerobic exercise is effective in the prevention and management of insulin resistance and type 2 diabetes mellitus (T2DM)
• 30 minutes of moderate exercise five times per week (the basis of most exercise prescription guidelines) reduced all cause mortality by 19% versus no activity

High Intensity Interval Training (HIIT)

• high intensity interval training (HIIT) involves repeatedly exercising at a high intensity for 30 seconds to several minutes, separated by 1-5 minutes of recovery (either no or low intensity exercise)
• the most common HIIT intervention used in studies is the Wingate Protocol developed in the 1970s
  • involves 30 seconds of cycling at maximum effort (at an intensity of over 90% of maximal oxygen uptake, also known as 90% of VO2 max) separated by 4 minutes of recovery, repeated 4-6 times per session, with three sessions per week
    • results in only 2-3 minutes of exercise at maximum intensity and 15-25 minutes of low intensity exercise per session, making it a time efficient method of exercise
    • less demanding protocols may be utilised for sedentary, overweight patients, which is important to remember considering the target patient population for exercise as prevention and management of cardiovascular and metabolic disease
• Timmons regime
  • Jamie Timmons, professor of ageing biology at the University of Birmingham, is a proponent of a few short bursts of flat-out intensity. In a BBC Horizon programme in February 2012, he put Michael J. Mosley on an exercise bike regime consisting of three bursts of about 2 minutes gentle pedalling followed by 20 seconds of cycling flat-out. This was done three times a week for a total of 3 minutes of intense exercise per week, plus some warm-up and recovery time. Measurable health benefits were reported, including significantly improved insulin sensitivity (2)

HIIT vs continuous moderate exercise (CME)

• HIIT has been shown to significantly reduce subcutaneous fat, especially abdominal fat, as well as total body mass, and to improve VO2 max (a marker of physical fitness) and insulin sensitivity
  • in comparison with CME
    • HIIT burns more calories and increases postexercise fat oxidation and energy expenditure more than steady-state exercise
    • HIIT decreased total cholesterol and LDL-cholesterol, while increasing HDL-cholesterol and VO2 max more than CME
    • there is study evidence that fat loss was significantly increased after HIIT, while fat loss did not change in CME patients versus controls, ie. there was no difference in fat loss between subjects carrying out CME and the inactive subjects (3)
    • increased exercise energy expenditure (such as with HIIT) as assessed by metabolic equivalents (METs) has been shown to result in a reduced risk of cardiovascular events in both males and females, and decrease all cause mortality (4)
    • benefits of vigorous intensity exercise surpass those of moderate intensity exercise, even when the latter is performed for a longer duration to equalise total work performed (5)

HIIT effects in high risk populations

• in patients with cardiovascular disease, HIIT has been shown to be superior to CME in reducing blood pressure, improving endothelial function, lipid profiles, VO2 max, left ventricular and overall myocardial function, as well as reversing left ventricular remodelling in heart failure patients
• patients with metabolic syndrome who carry out HIIT have been demonstrated to have improved endothelial function, insulin signalling, blood glucose and lipogenesis
• studies carried out in T2DM patients demonstrated reduced blood glucose and increased mitochondrial capacity and GLUT4 expression after only 2 weeks of three 20 minute sessions of HIIT per week, and have been shown to significantly improve glucose tolerance at 6 months with no such changes in CME subjects (1)
• HIIT programs are not only effective, but are also safe
• HIIT has been used effectively in patients with diabetes, stable angina, heart failure and after myocardial infarct, as well as postcardiac stenting and coronary artery grafting
• Rognmo et al examined the use of high versus moderate intensity exercise in coronary heart disease patients (6):
  • all patients performed continuous exercise at 60-70% HRpeak on some days and high-intensity interval training on other days. Interval training involved four 4-min intervals at 85-95% HRpeak preceded by a 10-min warm-up and interspersed with 3-min intervals at 50-70% HRpeak
  • approximately 129 000 patient-hours of exercise occurred during moderate intensity sessions and 46 000 patient-hours during high-intensity sessions. No MIs were reported. Only three cardiac arrests were reported; one fatal with moderate intensity exercise and two nonfatal with high-intensity exercise. Although the rate of cardiac arrest was greater with high intensity (1:23 000) than moderate intensity (1:129 000), the absolute number of cardiac arrests was low
  • Rognmo and colleagues demonstrated that CHD patients can safely perform high-intensity interval exercise during supervised cardiac rehabilitation. Although there was a higher rate of cardiac arrest on high-versusmoderate intensity days, the number of events was low and the authors stated "..Considering the significant cardiovascular adaptations associated with high-intensity exercise, such exercise should be considered among patients with coronary heart disease..."

Reference:

• (1)Shiraev T, Barclay G. Evidence based exercise - clinical benefits of high intensity interval training.Aust Fam Physician. 2012 Dec;41(12):960-2.
• (2) How To Get Fit With 3 Minutes Of Exercise A Week: BBC Doc Tries "HIT". Medical News Today. 6 March 2012.
• (3) Trapp EG, Chisholm DJ, Freund J, Boutcher SH. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. Int J Obes (Lond) 2008;32:684-91.
• (4) Lollgen H, Bockenhoff A, Knapp G. Physical activity and all-cause mortality: an updated meta-analysis with different intensity categories. Int J Sports Med 2009;30:213-24.
• (5) Swain DP, Franklin BA. Comparison of cardioprotective benefits of vigorous versus moderate intensity exercise. Am J Cardiol 2006;97:141-7.
• (6) Rognmo O, Moholdt T, Bakken H, et al. Cardiovascular risk of high- versus moderate-intensity aerobic exercise in coronary heart disease patients. Circulation 2012;126:1436-40.