Health & beauty
Exercise myths
Introduction
There's a lot of misleading information about exercise - we separate out the fact from the fiction.
There are many myths about exercise, and they often relate to how well it burns fat and kilojoules (calories). Even fitness professionals get the facts wrong sometimes.
In this report we take a look at 10 common exercise myths, and give you the real facts.
How much and how often?
Myth: "Exercising three times a week is enough."
There's a lot of conflicting advice about the amount of exercise you need to do to get results, ranging from 'anything is better than nothing' to 'over an hour a day, every day'.
There's a bit of truth in both extremes and everything in between, and it also depends on what you mean by 'get results'. For example:
- If you go for a 30- to 40-minute brisk walk, you can temporarily reduce blood sugar, triglycerides and blood pressure levels. So in that sense, just one session can be beneficial.
- People who've lost a great deal of weight (20kg or more) seem to require 60 to 90 minutes of moderate to vigorous exercise every day to maintain that weight loss.
Sport and Recreation New Zealand (SPARC) and Ministry of Health guidelines recommend 30 minutes of moderate exercise most days. The 30 minutes can comprise several sessions of at least 10 minutes each.
For greater health and fitness benefits, consider three or four sessions of vigorous exercise each week for at least 30 minutes each time, in addition to the moderate exercise listed above. Exercise should be continuous, and hard enough to make you puff - where it's difficult to talk in full sentences without taking a breath. Your heart rate should be about 70-85 percent of its maximum (which is 220 beats per minute, minus your age).
Finally, for good all-round physical health, you might consider including two or three resistance or strength training (weightlifting) sessions per week, as well as a flexibility and balance program (such as yoga or Pilates, or even just some gentle stretching), in your exercise routine.
Bottom line:
Anything is better than nothing, but for good health exercise moderately for at least 30 minutes a day on five or more days a week.
Myth: "I just ate a 1200 kilojoule chocolate bar. Walking burns 1200 kilojoules per hour, so if I walk for about an hour, I'll burn off the chocolate."
If you look up most exercise and kilojoule tables, they'll tell you that a 68kg person walking for one hour at a moderate speed of 5 to 6km/h burns between 1000 and 1250 kilojoules.
They don't usually remind you that by sitting around doing nothing or pottering about, you'd also burn some kilojoules - maybe up to 580.
In other words, they give 'gross' energy expenditure per unit of time, not 'net' expenditure (the amount above and beyond what you'd normally expend).
Assuming the chocolate is surplus to your daily energy needs and you want to burn off an extra 1200 kilojoules, you'll need to do 1200 'net' kilojoules of exercise.
Researchers have worked out that the net kilojoules burned walking in this situation would be about 750 kilojoules per hour.
This means more than 1.5 hours of walking to burn off the chocolate. And eating it took you ... how long?
Bottom line:
Calculating energy expenditure based on gross rather than net kilojoule burn overestimates the contribution of exercise to total daily expenditure.
How hard?
Myth: "No pain, no gain."
The old 'exercise as punishment' philosophy - that it has to hurt to do you good - has just about disappeared from exercise lore, though for some people puffing, sweating or messing up their hairdo constitutes pain.
So, does higher-intensity exercise have any advantages over lower-intensity?
In terms of basic health benefits, just meeting the minimum recommendations (see How much and how often?) will provide many health benefits. However, vigorous exercise can provide extra protection against heart disease. It can also help with overall fitness and kilojoule burning.
Bottom line:
Exercise shouldn't hurt, but exerting yourself a little can improve your fitness.
Myth: "Low-intensity exercise is better for fat burning."
The idea is that if you exercise at low intensity (around 50 to 60 percent of your maximum heart rate) you burn more fat than if you exercise at a higher heart rate (such as the 70 to 85 percent recommended for improving fitness).
Unfortunately it's not entirely true. You do burn more fat as a percentage of the total energy you burn when exercising at low intensity - it accounts for almost all the fuel your body uses. But you burn more actual fat per minute and a lot more total kilojoules at higher intensities.
The advantage of low-intensity exercise, especially for people who aren't terribly fit, is that it's less tiring and puts less strain on the body so you can exercise for a longer period of time. In the end it's the total kilojoules burnt that count - so for maximum weight loss you can either get puffing or just keep going for longer.
Bottom line:
Low-intensity exercise is great for beginners, while exercising at higher intensities helps you get fitter and burn more total energy in a given amount of time.
Walk, run or swim
Myth: "Walking one kilometre burns the same kilojoules as running one kilometre."
What's amazing about this myth is that it has persisted for so long. Scientists have known for years that it's not true, but you'll still hear it touted as fact by any number of health and fitness industry professionals.
A version of it even features on lists of exercise myths - except that the 'myth' is that 'running a mile burns more kilojoules than walking a mile' - which is actually true.
Walking is an extremely efficient way for humans to move around. With straight-ish legs and a reasonably level centre of gravity, you're bit like a bunch of swinging pendulums with good momentum, especially when you include your arms.
Running requires a lot more energy than walking. You're effectively jumping from one foot to the other, raising and lowering your centre of gravity far more than walking - more like a bouncing ball than pendulums.
In fact running consumes around 40 to 50 percent more gross kilojoules, or twice as many net kilojoules, per kilometre than walking - at least up to a certain walking speed. (See the 'walking-off-a-chocolate-bar' myth for the difference between net and gross kilojoules.)
At speeds over 8km per hour, walking burns more kilojoules than running at the same speed because it's more inefficient and difficult.
If speed's not your thing, the good news is that it doesn't matter how fast you run: it's the distance that matters. So running a kilometre slowly burns as many kilojoules as running a kilometre quickly.
However, as running burns twice as many net kilojoules per kilometre as walking, if you run twice as fast as you walk, you'll get twice as far and therefore burn four times as many net kilojoules in the same amount of time.
Bottom line:
Running burns twice as many net kilojoules per kilometre as walking.
Myth: "Swimming isn't a good way to lose weight."
Media reports in recent years have suggested that people who swim for exercise don't lose weight, or even that they gain weight.
There are several possible explanations for these findings:
- One study found that swimmers gained weight (though not a significant amount) while walkers and cyclists lost weight. Kilojoules weren't restricted (so the swimmers may have eaten more) and exercise intensity wasn't monitored or controlled. This one study seems to be cited over and over again, giving the impression that the evidence is based on lots of different sources.
- Another study found that people who exercised in cold (20°C) water ate more afterwards than people who exercised in neutral (33°C) water. So swimming in cold water may stimulate the appetite, possibly resulting in weight gain if kilojoules aren't restricted.
- If you swim pretty slowly - essentially floating, with minimal propulsion - you're likely to expend less effort than if walking or cycling.
- Swimming without changing energy intake might mean that you're building muscle and losing fat, so your weight may not change much - though your clothes may become looser.
- Finally, you might get tired out from swimming and laze around the rest of the day. Improving your 'efficiency', through stroke correction lessons, for example, can help prevent strains, injuries and fatigue caused by poor technique.
If you're very heavy swimming can be a great way to start exercising because your weight is supported and it works all parts of the body (especially if you include some work with a kickboard and flippers).
It's possible to lose as much weight swimming as walking or cycling - you just have to do it fast enough (you might need to take your pulse regularly to help you determine how hard you're working).
Bottom line:
Swimming can help you lose weight, as long as you go fast enough and long enough. Just watch your diet as well.
Kilojoule and burn cardio machines
While it's tempting to believe the kilojoule-burn figures clocked up on the stair climber, treadmill or exercise bike, you could be fooling yourself.
Some machines don't ask for your weight, and base their calculations on a weight of 70kg. If you are heavier or lighter than this, you'll be burning more or fewer kilojoules than what is claimed on the display.
All machines assume you're using the correct technique for the exercise, but it's easy to (perhaps unwittingly) expend less effort than assumed. Common energy-saving errors in technique include:
- Holding onto the bars of a treadmill or step machine to support your weight, instead of swinging your arms
- Leaning forward and/or taking baby steps on the step machine
- Not using the swinging handles to exercise your upper body on the elliptical cross-trainer.
The other problem is that some machines give you gross kilojoule burn rather than net kilojoule burn figures. (See the 'walking-off-a-chocolate-bar' myth for more about net and gross kilojoule burn.)
Metabolism
Myth: "Your metabolism increases after exercise, so you burn more kilojoules even though you've stopped exercising."
Bonus! Not only have you just burned off 1600 kilojoules doing aerobics, but you'll keep burning kilojoules for hours afterwards. Better still, the less fit you are, the slower you recover and therefore the more you burn.
Experts call it excess post-exercise oxygen consumption (EPOC), whereby increased metabolism means consuming more oxygen, which in turn burns kilojoules. And while it's not entirely bunkum, one extra biscuit could wipe out that kilojoule debt - and then some.
Most people who are aware of this post-exercise metabolic increase probably overestimate the degree of extra energy burned. And the small amounts involved could well be negated by moving less throughout the day and/or eating slightly more as a 'reward' for exercising.
For any sort of meaningful EPOC effect, you have to exercise long and hard. Low or moderate-intensity exercise - walking or slow jogging, say - would have little to no effect. Even at higher intensities you need to exercise for almost an hour for any appreciable increase in metabolism. Experts argue the level required would be intolerable for the average person, and only serious athletes would be capable of sustaining the required intensity for long enough.
Bottom line:
Any increase in metabolic rate after exercising is likely to be fairly insignificant for the average athlete.
Myth: "You burn more fat if you exercise on an empty stomach."
The theory goes that if you don't eat before exercising your body has to use fat as fuel because there's hardly any sugar to burn. And if you want to lose weight it stands to reason that burning off fat is a good thing.
There's nothing wrong with the basic theory - evidence shows that more fat is burnt after longer fasting conditions than in the few hours after eating, when carbohydrate is the preferred fuel. But in fact it's the total amount of energy burned that's the issue, not whether it's fat or carbohydrate.
You may find that without eating you get tired and don't exercise as hard as you would if you'd eaten beforehand - and therefore you'll burn less total energy.
Depending on how hard and how long you intend to exercise and whether exhaustion might affect your speed and endurance, it may be better to have some fruit, yoghurt or toast at least half an hour before exercising, as well as a drink to help prevent dehydration, and have the rest of your meal afterwards.
Bottom line:
Eating before exercise may help by giving you more energy for a better workout, and it's total energy burn that counts.
Other myths
Myth: "You should stretch before exercising."
While it's important to warm up before exercise, especially if you've just got out of bed or are about to undertake strenuous exercise, there's no good evidence that 'stretching' does much good.
By stretching they mean static stretches to pull at particular muscle and ligament groups, like hamstrings, calf muscles, Achilles tendons and so on. Warming up, on the other hand, is doing the basic moves of your exercise (running, swimming, cycling, playing soccer) at a low intensity.
Proponents of stretching say it prevents injuries and muscle soreness and improves performance. However, reviews of many studies have found there's no beneficial effect on reducing the chances of injury and soreness, and there are contradictory findings on performance - some find it helps, some find it hinders, some find no effect.
Stretching is still useful to help maintain or increase flexibility and can improve performance in the long term, so do it another time - while you're watching TV, for example.
Bottom line:
Stretching before exercise doesn't appear to help reduce muscle soreness or risk of injury.
Myth: "I'm slim and healthy, I don't need to exercise."
Even if you're slim and seem to be healthy, if you are inactive you're probably not as healthy as you could be. Studies have also found that people who are 'fat and fit' - that is, who are overweight but do regular exercise - are healthier than people who don't exercise, and therefore likely to live longer.
Meeting the minimum exercise recommendations can go a long way to achieving good health. Benefits include:
- Normal blood pressure
- Healthy cholesterol levels
- Lower levels of anxiety and depression
- Stronger bones and better balance (particularly important for older people otherwise at risk of osteoporosis)
- Weight management
- Good cardio-respiratory fitness, muscular strength and flexibility
- General self-esteem and psychological wellbeing.
Bottom line:
Exercise contributes to good overall physical and mental health - it's not just about body weight.
Think you're too old to exercise?
Some people think if they've led a pretty inactive life, there's no point taking up exercise at an older age - that it may do more harm than good. But studies have shown there are many benefits to taking up and continuing exercise well into old age.
Among the key benefits are maintaining independence through greater muscular strength, aerobic fitness and stability (balance), as well as stronger bones. Walking and (supervised) resistance training are particularly recommended.
This report was first published by the Australian Consumers' Association, CHOICE.