HIIT: hype or hope for all time-stuck gym rats?

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Exercise plays a vital role in staying healthy. However, many people struggle to make time to do so on a regular basis. We all have busy jobs, long commutes and maybe even a family to take care of. All of these factors place continuous demands on the limited 24 hours we have every day.
High-Intensity Interval Training (HIIT) is a type of interval training that combines short bursts of ‘go-all-out’ exercise with longer periods of rest or less intense exercise. There is no official time limit on a HIT session but they are usually short, tending not to exceed 30 minutes. This type of training is allegedly helping you achieve all the gains you would achieve from a steady state session that is 3 times as long, and probably not as exciting. Does this sound too good to be true?
What are the benefits of training?
Endurance training, HIIT or Low-Intensity Steady State (LISS), can assist with fat loss by creating a calorie deficit, as it increases the calories you burn. To lose weight, the energy balance is the number one factor, so essentially you need to eat fewer calories than you burn.
In addition to assisting with our fat loss goals, cardio training changes our bodies in a number of ways. It improves our cardiovascular health by making your heart stronger. Your heart rate tends to go down at rest because the heart needs to work less hard to pump your blood around the body. The wall of the heart muscle literally gets thicker to accommodate this.
During training, our veins dilate to allow more blood flow to the muscles, so that they can supply nutrients and oxygen and remove waste and CO2. This improves the elasticity of our veins. Finally, over time our blood and muscles will become more efficient at carrying and using oxygen, which will improve our overall performance. The maximum amount of oxygen your body can use at any given time is measured by a marker called VO2max, and this is considered an important marker for cardiovascular health. This statistic is usually better improved with HIIT than LISS – which isn’t strange as you’d be pushing your body to its limits more often with a HIT session than with LISS.
Intuitively, one might say that the more you practice the better you will become at any skill. There’s a common belief that there is a linear relationship between time practised and performance, and that experience creates excellence. Surely someone who spends an hour on the treadmill on a steady pace will be better than someone running a few sprints for 20 minutes, right?
Research actually indicates that HIIT is as effective and in some cases even slightly superior to LISS. Even though you are working for a shorter amount of time with HIIT, you are working harder, and closer to your optimal level of performance. The type of training is very different but the muscular adaptations, and as a result, the health benefits are very similar. How exactly these mechanisms work is still subject to debate but it is believed to be due to HIIT using different muscle fibres to LISS. There are roughly 2 types of muscle fibres: type 1 or slow twitch, and type 2 or fast twitch fibres. Type 1 fibres use mostly oxygen, are fuelled by fats and are very resistant to fatigue but can’t generate that much force. Type 2 fibres can produce a lot of force but are fatigued quickly. Type 2 fibres use carbohydrates as fuel and are often used for short bursts of explosive exercise. Our muscles always use a combination of both, but HIIT taps more into the type 2 fibres whereas LISS is more dependent on Type 1 fibres.
Furthermore, many people find HIIT a lot less boring than chipping away for hours on the treadmill. I am certainly guilty of this. I can’t help myself staring at the timer and wondering how time always flies except for when I’m on the treadmill. There’s something much more motivating seeing a timer clock down from 60 seconds rather than 60 minutes.
So should we all ditch LISS and go for HIIT?
There’s a time and place for any type of exercise depending on who you are and what your goal is. On some occasions, HIIT may not be the training for you. For example, if you’re very new to training and not quite comfortable with or able to reach that high intensity. Or maybe HIIT is your idea of hell and you’d much rather go for a run through your favourite park. Having said that, one doesn’t have to exclude either one or the other. You may opt for incorporating both by doing HIIT sessions during the week when you’re short on time, and a slightly more leisurely run in the park at the weekend for example.
Furthermore, it’s worth bearing in mind that HIIT is still cardio and does nothing for muscle gain and strength development. Muscle is another important factor in staying healthy and lean and is useful for most people. If I go for a relaxed 5K run in the morning I can still lift weights in the evening. However, if I do a HIIT session I can’t. HIIT is an intense form of exercise and requires more time to recover. This can be a negative if you are also working on building muscle and need to combine cardio with weight training. If this is the case then LISS might be the better choice for you, bearing in mind your overall goal.
The benefits of HIIT on cardiovascular health, performance and fat loss are very similar to LISS even though it only takes a fraction of the time. It’s perfect for people who are short on time but still want to make exercise part of their routine. If time is not an issue or you don’t enjoy HIIT, stick to your runs or rides. I’d always recommend choosing an exercise that you enjoy, works with your lifestyle and that you will be able to sustain. That may mean something different to you than it does to me and there’s nothing wrong with that!
Fancy trying your hand at one of our favourite HIIT workouts? Head to our Youtube channel!

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