No Time for Exercise? Try High-Intensity Interval Training (HIT)

2013-04-24T09:39:26+00:00 April 24th, 2013|Athlete Nutrition, Energy|

Gym man push-up strength pushup exercise with dumbbell

We all know that exercise is good for us, and we’ve heard that we should be getting 30 to 60 minutes per day most days of the week. But in today’s fast-paced world, where the demands of work, child care, and home maintenance seem to endlessly steal from our ever-shrinking depot of availability, finding the time to meet these recommendations can be quite a challenge.

What if there was a form of exercise that would allow you to reap the many health benefits of regular physical activity in just a quarter of the time? According to a recent review written by Australian researchers, high-intensity interval training (HIT) is a form of exercise that may do exactly that. Mounting evidence cited by the authors suggests that HIT is a time-efficient and effective alternative to traditional endurance exercise for boosting weight loss, aerobic stamina, and cardiovascular and metabolic health (1).

What is HIT?

HIT involves alternating intense bouts of exercise, ranging from 30 seconds to several minutes, with recovery periods spanning one to five minutes. For example, a cyclist might incorporate HIT by pedaling as fast as possible for 30 seconds against a strong resistance, lowering the resistance and leisurely cycling for 4 minutes, and then repeating this alternating schedule 4 to 6 times per session.

Such a training regimen adds up to about 20 to 25 minutes of exercise, which has shown substantial benefits when performed as few as three times per week (2). Just 2.5 hours of HIT completed over a total of 2 weeks has demonstrated benefits that are equivalent to 10.5 hours of continuous moderate exercise.

What are the benefits of HIT?

1.  Improved Body Composition

Many turn to traditional endurance exercise in the attempt to lose weight and improve their physical appearance, yet HIT may deliver even better results. HIT has been shown to reduce body fat, particularly abdominal fat (1, 3). In comparison with continuous moderate exercise, HIT increases energy expenditure and fat burning to a greater extent in the minutes and hours after a workout (1). This “after burn” is formally known as excess post-exercise oxygen consumption (EPOC) and reflects the body’s extra use of energy to replenish depleted fuel stores, and restore hormonal and other body systems to their pre-exercise state. (This is also prime time for consuming IsaLean Shake or IsaLean Pro to fuel greater muscle growth!)

In addition to increasing EPOC to a greater extent than traditional endurance exercise, HIT also promotes greater releases of growth hormone (4). This transient increase in growth hormone may be important during the post-workout period when muscles are primed for growth. During exercise, muscle damage occurs and muscle synthesis stops. Spikes of growth hormone promoted by HIT may quickly mitigate protein breakdown after exercise and serve as a signal for muscle growth (5).

HIT may also help preserve muscle mass in other ways. During long bouts of steady-state exercise, glycogen (the storage form of sugar) becomes depleted, and the body begins to break into its muscle reserves to get protein that can be used for energy. Because HIT relies on intervals of intense exercise broken up by intervals of more leisure, less intense exercise, muscle reserves are better preserved. Together, increases in growth hormone and the protection of muscle protein results in the preservation of muscle mass, which keeps metabolism running high and supports greater fat loss over the long term.

2.  Improved Cardiovascular Health

It is well known that several different markers of cardiovascular health—such as VO2 max, blood vessel wall elasticity, and blood pressure— can be improved by steady-state endurance training. HIT has also demonstrated equivalence or superiority over traditional endurance training in improving these markers (1). VO2 max is a measurement that determines the physical fitness of a person. It detects the maximum ability of the body to transport and use oxygen during exercise. The higher the VO2 max, the more efficiently a person can get oxygen to working muscle, and the more rapidly this oxygen can be used to power performance. Because the heart is a muscle that can be strengthened by exercise, HIT can improve the heart’s ability to contract, increasing the amount of blood and oxygen that can be pumped to muscle. HIT has been shown to increase VO2 max to an even greater extent than traditional endurance training (1).

An important indicator of cardiovascular health is blood vessel wall elasticity, often referred to as endothelial function; the better the endothelial function, the greater the capacity of the blood vessel to expand or contract when necessary. Unhealthy arteries tend to be harder and less flexible. HIT has also demonstrated improvement in endothelial function and in reduction of blood pressure (1).

In addition to increasing VO2 max, improving endothelial function, and lowering blood pressure, HIT may help lower total cholesterol and LDL cholesterol (the “bad” cholesterol), while also increasing blood levels of HDL cholesterol (the “good” cholesterol) when combined with a balanced diet. Improved levels of cholesterol, as well as better blood pressure and endothelial function, can lead to reduced cardiovascular disease risk.

3.  Improved Metabolic Health

Another well-known benefit of regular exercise is improved blood sugar control. Exercising muscle has a high demand for sugar as a fuel source. The more intense the exercise, the more muscle relies on sugar from the bloodstream and stored forms of sugar (glycogen) for energy. HIT has been shown to be effective in reducing blood sugar, and has also been shown to improve insulin sensitivity (1).

As a gatekeeper of sugar’s entry into body cells, the hormone insulin has a primary role in keeping blood sugar levels within a healthy range. Resistance to insulin ultimately leads to high blood sugar levels and impaired energy production. The ability of HIT to enhance insulin sensitivity helps ensure the delivery of sugar to the cells that need it as well as proper blood sugar control.

4.  Improved Aerobic Stamina and Exercise Performance

Although steady-state endurance training is notorious for improving aerobic stamina and conditioning, studies show that HIT is also an effective exercise strategy for achieving this goal. Not only does HIT increase VO2 max, it also increases time to exhaustion during exercise. In one study, the length of time that a group of eight athletes were able to cycle at 80 percent VO2 max nearly doubled—from 26 minutes to 51 minutes—after undergoing six HIT sessions over two weeks (6).

Another factor that contributes to endurance performance is the ability of the muscle to store sugar as glycogen. Glycogen is used for energy as exercise progresses. There is a limit to the amount of glycogen that each person can store, but HIT has been shown to increase this amount (1, 2, 7). HIT also causes muscle to lower the rate at which it uses glycogen for energy, resulting in a greater reliance on the use of fat for fuel. Increasing and preserving energy stores in the form of glycogen will extend time to exhaustion, ultimately improving exercise performance (1, 2, 7).

HIT is for (Almost) Everyone

Most people can benefit from HIT. Studies have shown that it is safe and effective for those with health conditions such as diabetes and cardiovascular disease, and offers numerous advantages for healthy people simply looking to save time or switch up their workouts (1). Even professional endurance athletes are using HIT to improve performance by incorporating it alongside traditional endurance exercise in a comprehensive training program.

HIT is a fun way to break up the monotony of conventional workouts, and according to the Australian researchers, may even be easier to stick to than traditional endurance training. HIT can yield substantial health and fitness benefits with minimal time commitments, making it the perfect prescription for those who don’t have 30 to 60 minutes every day to meet the current exercise recommendations. However, before starting HIT or any other exercise program, a consultation with a person’s physician is advised to determine if appropriate.


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. Gibala MJ. High-intensity interval training: a time-efficient strategy for health promotion? Curr Sports Med Rep. 2007 Jul;6(4):211-3. Review.

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

4. Pritzlaff CJ et al. Impact of acute exercise intensity on pulsatile growth hormone release in men. J Appl Physiol. 1999 Aug;87(2):498-504.

5. Post-exercise hypertrophic adaptations: A re-examination of the hormone hypothesis and its applicability to resistance training program design. J Strength Cond Res. 2013 Feb 25. [Epub ahead of print]

6. Burgomaster KA, et al. Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol. 2005 Jun;98(6):1985-90. Epub 2005 Feb 10.

7. 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 Apr;36(2):58-63.