Exercise won't just help you maintain a healthy weight, it could be the single most important step you can take for your mental and physical health, and the best way possible to keep the effects of ageing under control.
Exercise can reduce your risk of stroke, type 2 diabetes and some cancers by up to 50 per cent, and lower your risk of early death by nearly a third.
It can also cut your risk of osteoarthritis by up to 83 per cent, boost mood and sleep quality and reduce your risk of depression and dementia.
The official recommendation is to be active daily, with at least two-and-a-half hours of physical activity a week. But a recent report from the British Heart Foundation found that 44 per cent of adults never exercise. The good news is it's never too early or too late to start.
Use these tests to check whether you're as fit as you should be for your age, right up to your 80s - the experts then explain what you can do to improve your fitness, whatever your age.
Even youngsters need to check their fitness! You should be at your physical peak in your twenties - but be warned, the ageing process kicks in at 25, as you start to lose muscle mass at up to 1 per cent a year.
Challenge: Beep test
This involves running between two points, getting faster as you progress. The aim is to keep going for as long as possible. This is a widely accepted test of cardiovascular fitness. Download a Beep Test app on your mobile phone (it's free), then set two markers exactly 20 m apart. Start the app and jog gently to the first marker, jog back when you hear the beep, then back to the first marker, aiming to arrive at each marker in time for the beep. The test starts comfortably slowly, but with each minute, the beeps get closer together.
When you can no longer reach the marker before you hear the beep, stop and check your score. A good score is level 10-11, excellent is 12-13. If you can reach only level 5 (or less), you could certainly benefit from getting regular exercise into your life.
Your exercise aim:
"This is a crucial decade for building good exercise habits, muscle mass and bone density - which fall away in later life - while you have time and optimal health," says physiotherapist Sammy Margo.
She recommends experimenting with a range of sports and exercise classes: "Aim for at least five 40-minute sessions, mixing cardiovascular work with strength training.
"Repeat the test every three months, with the aim of improving your result each time."
For many women, this decade is dominated by pregnancy and young motherhood, and hormonal changes can throw up problems. "I see an increasing number of pregnancy-related back pain problems from women who have lived sedentary lives," warns physiotherapist Sammy Margo.
However, men and women who are active could be at risk of over-use injuries in this decade, says Dr Mark Hamer, an exercise physiologist at University College London. This includes damage to the cartilage which cushions the joints.
The challenge: Fun run
Try to run 1.5km in nine minutes for a woman, eight for a man; this puts you well into the top 50 per cent for your age group.
A study by the Cooper Institute in Dallas, Texas, showed that the speed you can run a mile by the age of 40 could become a spooky prediction of your risk of heart disease years later. If you take longer than ten minutes (12 minutes for women), you have a 30 per cent greater risk of developing and dying from heart disease in 30 years' time.
Your exercise aim:
Keeping fit now means working harder than in your 20s. Take time to find a sport or activity you enjoy and which you can fit around the other demands on your time (cycle to work; book an exercise class three evenings a week).
Make activity part of your life - stand instead of sitting, take stairs not lifts, never stand still on an escalator and pay attention to your posture.
As well as doing at least two-and-a-half hours exercise a week, Sammy Margo recommends speeding up your mile: start by walking fast, break into jogging intervals as your fitness increases, then run when you can.
This is the decade of the triple whammy: hormonal decline, gravity pulling everything south and as the reduction in muscle mass accelerates, your metabolism slows - because muscle burns more fat as fuel. As a result, we put on weight.
Challenge: Step test
This is a step-up exercise - you will need a high step that's 12 in above the ground. Warm up for ten minutes by marching on the spot swinging your arms, then start a stopwatch and simply step up on to the step and off again, one foot at a time, for three minutes.
It's an easy rhythm to get into, but you may find it a help to do it with a metronome or a mobile app that provides beeps at set times - try Interval Timer or Seconds Timer, both free from iTunes, set to 24 beeps per minute (one step up, one down, per beep.)
For a less high-tech alternative, you could count the seconds in your head saying: 'One elephant (up), two elephant (down),' for example.
At the end of the three minutes, measure your heart-rate by counting the pulse in your wrist. In your 40s to 60s, men's should be 90 to 95 or less per minute and women's 95 to 100 or less. "This test seems simple, but it is a great measure of fitness, balance, agility and rhythm," says Sammy Margo.
Your exercise aim:
"This is a challenging decade as most people are torn between the demands of young children and ageing parents," says Sammy Margo, "but it is important to integrate activity into every opportunity throughout the day to hold back the effects of ageing".
She recommends including stretching and flexibility exercises in your regimen, too.
A study last month, in the British Journal of Sports Medicine, found that men in their 40s who do 30 minutes of physical activity - irrespective of its intensity - six days a week, have a 40 per cent lower risk of dying from any cause before 70.
The researchers found that boosting physical activity levels in this decade is as good for your health as giving up smoking. Strength training (working with weights, or performing exercises such as squats and lunges) is also increasingly important now.
"The only way to boost your metabolic rate is to prevent muscle depletion by strength training," says Dr Miriam Nelson, professor of nutrition and a specialist in physical activity at Tufts University, Massachusetts, who conducted a study of 40 post-menopausal women, encouraging them to follow a programme of strength training twice a week for 30 minutes.
"After a year their bodies had become 15 to 20 years younger," she says, "and all the participants regained bone density instead of losing it, as women normally do at that age."
Find a good strength and conditioning exercise class (circuit training or kettlebells for instance).
This can be a decade of unfamiliar aches and pains. Even someone with previously healthy blood pressure may notice their readings creeping up, as ageing arteries stiffen.
But exercise can help. Studies from the American Heart Association show that regular physical activity (30 minutes most days of the week) can cut high blood pressure risk by a fifth compared with people who exercise for less than one hour a week.
Challenge: Sit/rise test
Stand in front of a mirror in comfortable clothes with your shoes off. Simply lower yourself into a cross-legged sitting position on the floor without using your hands for support or kneeling on the way down, then return to a standing position without using your hands, knees or arms for support.
Score your efforts out of ten, subtracting one point every time you have to use a hand or knee for support, and half a point every time you lose balance or wobble. Aim to score eight or above.
In a study in the European Journal of Preventive Cardiology last year, researchers found that people aged between 50 and 80 who scored less than eight were twice as likely to die within the next six years compared with people with perfect scores.
In fact, they found every point increase in the test is linked to a 21 per cent decrease in mortality from all causes. Be warned - this test may take practice, and is not recommended for anyone with arthritic knees.
Your exercise aim:
Aim to achieve the recommended two-and-a-half hours' activity a week in any way you can. Consider investing in a pedometer and reaching at least 10,000 steps per day.
You don't have to join a gym. Studies show exercise such as cycling, swimming, dancing and even mowing the lawn can be as effective at lowering blood pressure as medication.
"Weight-bearing exercise (performed standing up) will help reduce bone loss as you age, as well as increasing your metabolism," says Sammy Margo.
The National Osteoporosis Society recommends short exercise sessions which 'jolt' the skeleton - e.g., running or jumping - to strengthen bones. A recent study in the Journal of Sport and Health Science found that women burned more calories during the dance-fitness class Zumba compared with salsa dancing, though both offer a great boost to cardiovascular fitness and psychological well-being.
In your 60s, wear and tear on your joints may become more apparent. Studies show one in three people over 60 suffer a fall each year, and, according to Sammy Margo, muscle weakness and impaired balance are factors.
Challenge: Chair test
Sit comfortably on a dining room chair, your feet firmly on the ground. Set a stopwatch, or use the secondhand on your watch, and simply stand without using your hands or arms for support, then sit again gently as many times as you can in 30 seconds. Healthy women in their 60s should be able to achieve at least 12 and men 14.
If you find this easy, progress to a softer, lower easy-chair which demands greater strength and balance to get up from and down without support, and see how many times you can get up and down out of the chair in 30 seconds. The targets are the same as above.
Your exercise aim:
Adapting a workout routine for the 60s may mean curtailing aerobic exercise that jars and stresses the joints. So replace long runs with shorter jogging stints, cycling or power-walking and swimming. Strength training is still important, as are stretching and balance. If you are new to exercise ask at your local health centre about age-specific classes; aquarobics is an excellent gentle workout.
Aim to practise the test once every day and watch your score improve. Being able to perform regular squats like this - i.e. rising up and down from a chair without using your hands - keeps the muscles of the thighs and buttocks strong and is the key to maintaining independence in older age.
"Lose this ability, and you won't be able to get on and off the loo by yourself," Sammy Margo warns.
"If you are a keen gardener, don't underestimate how fantastic the activity is for the strength of your arms, legs and overall stamina."
Specialists agree it's never too late for exercise and activity to make a difference. "You can rejuvenate 20 years of lost strength through physical activity," says Dawn Skelton, an exercise physiologist and professor of ageing and health at Glasgow Caledonian University. Even if you have been inactive for many decades, gentle activity now can reverse the decline.
Challenge: Up and go
Measure a 3m distance and place a dining room chair at one end. Ask a friend to stand at the other end with a stopwatch.
Sit yourself comfortably on the chair, get the friend to start the timer, then get up, walk the distance, walk back and sit down again. The clock stops the moment your bottom hits the chair.
A score of 12 seconds or less is excellent, if you score 13 to 20 seconds your balance could be impaired, 20 seconds plus could indicate problems with mobility.
Your exercise aim:
Vicky Johnston, a physiotherapist, recommends practising this at every opportunity. "If you're watching TV, get up every time the ads come on, and lower yourself slowly when you sit back down, to work your muscles against gravity.
"If you slump back with an audible 'oof', you've not controlled your descent," she says.
"Do something that gets you breathing a little more deeply than normal - for ten minutes three times a day, five days a week. Try marching on the spot while you're washing up or getting off the bus one stop earlier."
She also advises regular balance work - either through tai chi classes, or single leg stands.
"Balancing involves co-ordination of the muscles in the ankles and hips; this will make you more stable on uneven ground, or on a moving bus."
Protect your knees by strengthening the thigh muscles. Sitting on a chair, straighten your legs in front of you, hold for five seconds and then slowly return to the starting point. Repeat 12 to 15 times.
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