On 8 January 2013, British journalist and television presenter, Andy Marr, suffered a stroke following a strenuous workout on a rowing machine. He was 53, not overweight and exercised regularly. There have been several reports of other high-profile individuals having a heart attack or stroke while exercising. 

It’s a scary thought to think that doing the one thing we’ve been told to do to prevent a heart attack or stroke - exercise - may actually be the thing that kills us. In a 2012 study from the Norwegian University, 4,846 high-risk patients with coronary heart disease, participated in a study comparing high-intensity versus moderate-intensity aerobic exercise. The high-intensity exercise involved interval training, which is a training method whereby you alternate periods of high and low intensity. The moderate intensity exercise consisted of walking or jogging. The moderate-intensity group exercised for a total of 129,456 hours, while the high-intensity group exercised for a total of 46,364 hours. The high-intensity group exercised for much less time because the activity is much more strenuous. 

In those 4,846 patients with coronary heart disease, for all those hours of exercise, only one patient had a fatal cardiac arrest and that was in the moderate-intensity exercise group. Two people had nonfatal cardiac arrests and they were in the high-intensity group. 

These findings demonstrate that there is very little chance of having a cardiac arrest during exercise, including high-intensity exercise, even in high-risk coronary heart disease patients. The study in fact, states that high-intensity interval training of shorter duration appears to be safe and better tolerated than moderate-intensity continuous exercise. This research, and other case studies of people having a heart attack or stroke during exercise, demonstrates that exercise is not the sole way to prevent heart attack or stroke. Other likely contributors to heart disease include poor diet, lack of quality sleep, smoking, lack of regular movement throughout the day, stress and mental illness. Therefore, these issues must be addressed in addition to exercise. 

So what should you do?

• If you don’t currently exercise, you should start. The risks associated with not exercising greatly outweigh the risks associated with exercising. One risk that comes with exercise is injury. Ensure you workout at a level you are competent at to avoid injury, because the greatest risk factor for injury, is previous injury. 

• Participate in regular high-intensity interval training classes but only at the movement competence and load you are capable of. If you are just starting out, you likely don’t have great movement patterns or are capable of working at a high-level for very long. Don’t go jumping around and working out beyond your level of competence if you can’t control your movements. 

• Practice the foundations of movement - squat, lunge, bend, brace, push up and pull up. Practice them in their simpler foundations before graduating to jumping and more complex strength moves. 

• Exercise until you can’t hold yourself together any longer. Just because someone says you’ve got 50 push ups, 60 seconds of skipping or a 20 minute jog, doesn’t mean you have to push through and complete that. If you can competently hold yourself together with good form during the exercise, then yes. But if you can’t, you should stop. A good trainer is one that will recognise this and set a target for you based on your level of movement competence and aerobic capability. Instead, aim for as many push ups as you can with good form up to 50, good quality skipping up to 60 seconds, or a jog with correct technique walking when you need to. Twenty minutes of walk/jog with good technique is better than twenty minutes of plodding along poorly. 

• Do some moderate-intensity activity. Don’t start with too much. Start with just 10 minutes of walking and jog when you can. Alternatively, if you like to ride, go for a ride. Build your way up to an hour. Research from the University of Sydney found that moderate-intensity continuous exercise was more effective at achieving fat loss, particularly the fat that surrounds the organs (visceral fat), than high-intensity interval training. High-intensity interval training was still effective at achieving fat loss, but moderate-intensity continuous exercise, particularly when performed for an hour, created a fat-furnace effect. 

What is high-intensity training (HIT)?

When people refer to high-intensity training, they are usually referring to high-intensity interval training. That’s a short bout of exercise, usually 10 seconds to 2 minutes, followed by a rest period. For example, a typical high-intensity interval training (HIIT) session might consist of 20 seconds of exercise followed by 10 seconds of rest. Another session might be 90 seconds of exercise and 30 seconds of rest. That’s quite an advanced version and a simpler version for a beginner would be to swap that - 30 seconds of exercise and 90 seconds of rest. The interval component comes in because you’re not working continuously - you’re working in intervals. 

What does high-intensity training do to your body?

A 2011 study published in the Journal of Obesity found that high-intensity interval training is more effective at reducing fat just beneath the skin (subcutaneous fat) and abdominal fat. In addition, it also burns more calories (in less time), it continues to burn calories after you’ve finished exercising, improves your fitness (including your ability to complete moderate-intensity continuous exercise), strengthens your heart and lungs, increases mitochondria (the energy factory in your cells), and improves strength. 

The research cited in this article demonstrates that high intensity interval training is better at reducing sub-cutaneous fat while moderate-intensity continuous exercise is more effective at reducing visceral fat. High-intensity interval training may actually be safer for beginners as well as high-risk patients with coronary heart disease, if the periods of high-intensity are reduced and periods of rest or low-intensity are increased. 

Both types of exercise are good for you so long as you workout at your level of competence. For best results, both should be incorporated into a weekly training regime. To reduce your risk of coronary heart disease you should also address diet, sleep, stress and any indication of mental illness.

What are your experiences with high-intensity interval training?

Leave your answer to that question in the comments section below.