Can you HIT it? The risks and benefits of high-intensity interval training

Vanilla exercise is passé. Fitness fan-atics are putting some Shades of Grey into their workouts, opting for short, sharp, punishing regimes that promise to get you twice as fit in half the time of a regular gym session. HIIT (high-intensity interval training) sessions can last for just 20 minutes. Spend 30 seconds pushing your body and metabolism out of its comfort zone by working out as hard as you can — say, by sprinting — then recover with lighter exercise, such as jogging, for 20 seconds before powering up again. And again and again.

Studies have shown that within months, even weeks, the body’s systems can adapt positively to the increases in stress and as a result fitness improves enormously. Research suggests that these regimes can help to reduce blood sugar levels and offset Type 2 diabetes, as well as improving strength, endurance and muscle tone. So no more excuses for those previously claiming to be ‘too busy’ to work out.

And yet, despite the evidence, controversy is now clouding this intense exercise phenomenon. With the BBC presenter Andrew Marr’s revelation that he believes his recent stroke was linked to intense interval training on a rowing machine, there is a fear that HIIT can cause more harm than good, because what all variations of these workouts share (some focus on strength, others on cardio) is that they are punishing to the extreme. So you have to be reasonably fit to begin with in order to try them safely. This, say experts, is where some people are going wrong. ‘These types of sessions are not suitable for everyone,’ says Greg Whyte, professor of applied sport and exercise science at Liverpool John Moores University. ‘You need to have a good fitness background before you even take part. Pushing yourself to those limits is strongly inadvisable if you are in any way unfit or have underlying problems.’

People mistakenly think that because they last for just a few minutes, these workouts are an easy option. Don’t be fooled. Steve Barrett, a personal trainer who has worked with leading athletes, says, ‘They should leave you feeling as if you literally couldn’t do anything more.’ And that degree of effort, says Dr Dominic Micklewright, director of the sport, performance and fatigue research unit at the University of Essex, can mean ‘there is almost certainly an increased risk of injury among untrained people with this sort of approach’. Couple intense workouts with minimal calorie intake or fasting and you could find yourself suffering more for your fitness than you imagined; with blood sugar levels too low to sustain you through these workouts, headaches, muscle weakness and nausea or feeling faint could result.

None of this means that, as long as you are fit enough, the high-intensity approach should be avoided. Barrett uses it with some of his fitter clients and says it should be employed two to four times a week, in addition to run-of-the-mill activities such as steady running, cycling or swimming. And most experts agree that, if you build up to it, interval training of some sort is essential for fitness progression, but that a watered-down version of HIIT is more appropriate for the masses. Exercise scientists at McMaster University in Canada recently tried a ‘gentler’ version of a HIIT schedule, involving a minute of effort followed by a minute of easy recovery repeated ten times over 20 minutes, on a group including some previously unfit volunteers. All displayed remarkable improvements in overall health and fitness after several weeks. ‘With any exercise, the key thing is to feel like you’ve worked hard, but not to the point that you are in extreme physical discomfort or pain,’ says Barrett. ‘You do need to push yourself harder in order to progress, but it should be effort that is just within the realms of your ability. Always listen to your body.’

NUMBER CRUNCHING How much is too much at your age

TWENTIES

Maintaining strong bones is important during this decade, but your focus should be on developing good all-round habits. Flexibility, strength and endurance capacities all peak in your twenties so make the most of your athletic prowess before children and career take full hold.

Best workouts Mix up the intensity of cardio workouts and include some HIIT sessions as you get fitter. Add weights or body-pump classes to tone muscle. Set goals while you have the fitness and time to train for them — run a 5km race or a marathon, enter a triathlon or outdoor swimming event.

Do Build up your cardio to 45-60 minutes at a time. Try at least two resistance sessions a week.

Don’t Push yourself hard every day. Overexerting the body will not deliver optimum results and can lead to symptoms of chronic overtraining — colds and viruses, fatigue and injuries. Take days out between workouts to rest.

THIRTIES

Since your heart and lung capacities, which enable you to exercise aerobically, start a downward trend from your late-twenties, it’s important to keep up the running, swimming and aerobics. Regular aerobic exercise can also help with hormone regulation and increase the possibility of conception.

Best workouts Body-weight circuits are another of the big trends for 2013 and represent a general move away from complicated equipment and fancy resistance aids to using your own body weight to help gain strength via old-fashioned moves such as press-ups, pull-ups and squat thrusts.

Do Schedule in active recovery days when you walk, cycle or take part in a mind-body activity to allow your body to recover from the strain.

Don’t Sit down too much. Even if you are a gym-goer, the chances are you spend too much time in the parked position. A recent American study revealed that women who exercise regularly spend as much time sitting down as those who never pull on a pair of trainers. Professor Lynette Craft, a preventative medicine expert who led the research, found that while many gym-goers met or exceeded the recommended 150 minutes of physical activity a week, in reality only a fraction of their days were spent being active. Walk up stairs, stand to talk on the phone and move as much as you can to avoid the dreaded middle-age fitness slump.

FORTIES

Years spent hunched over a desk can lead to posture problems and back pain. Rounded shoulders can also age you, so best to deal with them before it’s too late. And then there’s the pull of Mother Nature with gravity, hormones, and the slowing of your metabolism as lean muscle mass begins to decrease and body fat increases. Yet with children and a career it can be difficult to squeeze everything in.

Best workouts Pilates and yoga help with postural issues, but so can walking — walk everywhere you can. And studies have shown that climbing stairs several times a day is a great way to tone buttocks and offset diabetes. Indoor rowing is also a time-efficient workout for this age group as it does everything in one, gobbling 600 calories in an hour, and every stroke requires you to work the muscles in your calves, upper legs, buttocks, core, upper back and arms.