The Most Effective Way to Lose Fat – High-Intensity Interval Training

Did you know that the influence of traditional slow, long-duration aerobic activity of low to moderate intensity (as in brisk walking or jogging) in causing fat is negligible?1-3

New emerging evidence now hints towards high-intensity interval training (HIIT) – the New Kid on the Block – may be a much more effective and quicker way to induce fat loss. Some of the evidence being reported is so strong that previous recommendations of walking and slow jogging as measures to fight obesity is now be frowned upon by most researchers and fitness professionals.

In addition to causing fat loss, there are numerous other benefits of HIIT – increased aerobic and anaerobic capacity, improved power and strength components, improved glucose tolerance and insulin sensitivity.

What Is HIIT?

Intense exercise with an all out effort for a short time followed by low intensity exercise or rest for another fixed time with repetition of these cycles is what constitutes HIIT. This can be done using any piece of aerobic equipment like a spinning bike, rower or a treadmill.

The most famous protocol utilized by researchers has been the Wingate Protocol which includes an all out effort for 30 seconds followed by a 4 min. rest4. This cycle is ideally repeated 4-6 times during the sessions. Alternate day sessions are recommended for 2 to 6 weeks.

Other protocols utilize an 8second/12second or 12second/24 second splits.

Other methods of HIIT include sprint interval training (SIT), activities like swimming or rowing, incorporating athletic training using agility drill exercises or plyometric moves combined with resistance training or weightlifting exercises.

The latest craze, CrossFit, with an almost cult-like following, is an HIIT protocol with exercises done against time – back to back and, thus, involving no rest at all.

What HIIT Does for You

HIIT causes prominent immediate as well as longer term effects on the human physiology.

Immediate effects can be summarized as follows:

• Cardiovascular effects: increased heart rate to almost 90% of maximal heart rate1.

• Metabolic effects: increased blood glucose5;6, increased plasma glycerol and plasma lactate levels1, significant increase in secretions of catecholamines hormones like epinephrine (adrenaline) and norepinephrine 7;8, cortisol9 and growth hormone10.

The effects of all these changes brought about by HIIT are complex – increased blood glucose for almost 5 to 30 minutes post workout can prevent hypoglycaemic attacks in patients of type 1 diabetes mellitus. Thus, after a prolonged exercise stint, a short sprint – by preventing further fall and in fact, elevating blood glucose – can avoid hypoglycaemic episodes.

Elevated growth hormone levels after a bout of HIIT are beneficial in maintaining as well as improving lean muscle mass.

Significantly elevated levels of catecholamines after HIIT have quite an important influence on the fat loss as discussed below.

Chronic effects of HIIT can be summarized as follows:

  • Increased aerobic fitness11; different HIIT protocols have shown an increase in VO2 max. varying from 6% to a whopping 41%12;13
  • Increased anaerobic fitness
  • Increased skeletal muscles utilization of fat as fuel for exercise
  • Favourable effects on glucose metabolism with decrease in insulin levels as well as increased sensitivity to insulin.

How Does HIIT Cause Fat Loss?

Outlined below are some of the mechanisms responsible for the fat loss associated with HIIT.

  1. Elevated levels of fat oxidation and energy expenditure during exercise session
  2. Elevated levels of post-exercise oxygen consumption (PEOC) – meaning you keep burning calories for hours after you are done with the exercise session
  3. Increased mobilization of fatty acids (FAs) due to increased catecholamine (adrenaline and noradrenaline) secretion induced by HIIT and increased utilization of these FAs by enhanced skeletal muscles utilization of FAs caused by HIIT14
  4. Suppression of appetite1;15


Initial research evidence strongly supports the idea that HIIT is indeed the most effective way of inducing fat loss – both subcutaneous and abdominal. Thus in addition to being an effective tool for fighting obesity, other benefits of HIIT – improvement in fitness and health parameters – make it equally important, if not more, for enhancing sports performance improving overall health.

What’s even more amazing is that it is a very ‘time-efficient’ method of training – as little as 10 min. every alternate day can bring about amazing results over as little as 2 weeks.

Thus, time constraint as the major excuse of not exercise now gets thrown out of the window! So, beware before you say – I don’t have the time to exercise – might just not work anymore and it might even make you look like a fool!


(1)  Boutcher SH. High-intensity intermittent exercise and fat loss. J Obes 2011; 2011:868305.

(2)  Shaw K, Gennat H, O’Rourke P, Del MC. Exercise for overweight or obesity. Cochrane Database Syst Rev 2006;(4):CD003817.

(3)  Wu T, Gao X, Chen M, van Dam RM. Long-term effectiveness of diet-plus-exercise interventions vs. diet-only interventions for weight loss: a meta-analysis. Obes Rev 2009; 10(3):313-323.

(4)  Gibala MJ, McGee SL. Metabolic adaptations to short-term high-intensity interval training: a little pain for a lot of gain? Exerc Sport Sci Rev 2008; 36(2):58-63.

(5)  Vincent S, Berthon P, Zouhal H, Moussa E, Catheline M, Bentue-Ferrer D et al. Plasma glucose, insulin and catecholamine responses to a Wingate test in physically active women and men. Eur J Appl Physiol 2004; 91(1):15-21.

(6)  Gaitanos GC, Williams C, Boobis LH, Brooks S. Human muscle metabolism during intermittent maximal exercise. J Appl Physiol 1993; 75(2):712-719.

(7)  Trapp EG, Chisholm DJ, Boutcher SH. Metabolic response of trained and untrained women during high-intensity intermittent cycle exercise. Am J Physiol Regul Integr Comp Physiol 2007; 293(6):R2370-R2375.

(8)  Bracken RM, Linnane DM, Brooks S. Plasma catecholamine and nephrine responses to brief intermittent maximal intensity exercise. Amino Acids 2009; 36(2):209-217.

(9)  Hoffman JR, Falk B, Radom-Isaac S, Weinstein Y, Magazanik A, Wang Y et al. The effect of environmental temperature on testosterone and cortisol responses to high intensity, intermittent exercise in humans. Eur J Appl Physiol Occup Physiol 1997; 75(1):83-87.

(10)  Nevill ME, Holmyard DJ, Hall GM, Allsop P, van OA, Burrin JM et al. Growth hormone responses to treadmill sprinting in sprint- and endurance-trained athletes. Eur J Appl Physiol Occup Physiol 1996; 72(5-6):460-467.

(11)  Whyte LJ, Gill JM, Cathcart AJ. Effect of 2 weeks of sprint interval training on health-related outcomes in sedentary overweight/obese men. Metabolism 2010; 59(10):1421-1428.

(12)  Helgerud J, Hoydal K, Wang E, Karlsen T, Berg P, Bjerkaas M et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc 2007; 39(4):665-671.

(13)  Mourier A, Gautier JF, De KE, Bigard AX, Villette JM, Garnier JP et al. Mobilization of visceral adipose tissue related to the improvement in insulin sensitivity in response to physical training in NIDDM. Effects of branched-chain amino acid supplements. Diabetes Care 1997; 20(3):385-391.

(14)  Burgomaster KA, Hughes SC, Heigenhauser GJ, Bradwell SN, Gibala MJ. Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol 2005; 98(6):1985-1990.

(15)  Bilski J, Teleglów A, Zahradnik-Bilska J, Dembinski A, Warzecha Z. Effects of Exercise on Appetite and Food Intake Regulation. Med Sport 2009; 13(2):82-94.

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Dr. Deepak S Hiwale

Dr. Deepak S Hiwale, a.k.a "The Fitness Doc" specializes in sports medicine in addition to being an elite personal trainer. He currently runs an elite personal training company in West London. As a sports injury and fitness writer-presenter, he tries to disseminate as much knowledge as possible for the benefit of all. MBBS (University of Pune); MSC, Sports and Exercise Medicine (University of Glasgow); Diploma in Personal Training (YMCA Dip. PT, London).

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