I'm feeling quite pleased with myself - apparently, I have the fitness level of a 30-year-old, when I'm actually 10 years older. This was the judgement of a new free online tool, the National Fitness Test, which assesses your strength, aerobic fitness, flexibility and 'shape' (weight, height and body measurements), giving you an individual score for each component as well as an overall 'age'. I was faring even better (a sprightly 27) until I completed the flexibility element of the test, for which my result read: 'Crikey, you're stiff. I don't know how you put your socks on in the morning!'

The National Fitness Test is the brainchild of Dave Reddin, a fitness trainer for the Rugby World Cup squad and a consultant to Team GB. "I wanted to show people how easy it is to take control of your fitness and get a fair assessment that is relative to age and sex," he says.

The fact that the test is home-based and requires little more than a tape measure, a computer (visual and written instructions appear on the screen as and when you need them), a watch with a second hand, and a set of weighing scales certainly make it accessible to all and maximises its appeal. But is the test valid?

Well, the aerobic fitness side of things is addressed using a four-minute step test - you simply step up and down a step of measured height to a designated rhythm (provided as a sound clip) and record your heart rate before, immediately afterwards, and then a minute later. Reddin took elements from two existing well-validated fitness tests - the Harvard Step Test (above) and Canadian Home Fitness Test - to create this simple protocol. "The combination of resting heart rate, the heart rate achieved after four minutes of exertion and your ability to recover within a minute are used to give a 'fitness index' or score,' he explains.

The step test is what's known as a 'submaximal' test - in other words, it doesn't require you to reach exhaustion. "In submaximal testing, fitness isn't being directly measured but estimated using the heart rate response," explains Steve Hunter, an exercise physiologist at South Bank University. "Recovery heart rate is generally a good measure of cardiorespiratory fitness and with repeated tests, a quicker recovery provides indirect evidence of an improvement in fitness level."

While Hunter concedes that step tests are easy to administer, he points out that they carry a risk of tripping and, he says, can lead to an underestimation of fitness levels if the legs are weak. He suggests the Rockport Walking Test (above) - a one-mile walk (ideally on a smooth, level surface) as briskly as you can manage. Time taken to complete the mile, along with age, heart rate at the end of the test, and gender, are used to estimate 'VO2 max' - or maximal aerobic capacity - widely seen as a 'gold standard' measure of fitness. "This test demonstrates good reliability in test/re-test measurements and offers an indication of improvement," he says.

If you want a true measure of your aerobic fitness, you'll need to don a nose clip and breathing tube while you run yourself ragged on a laboratory treadmill (a crash mat is handily placed at the back, in case you go flying off). Such tests are the norm for serious athletes, but there are also 'field-based' maximal tests that can give you a good estimate without necessitating costly lab visits.

"The Multistage Shuttle Test [or bleep test, above] is one of the most accurate and reliable, showing a strong correlation with measured VO2 max," says Hunter. "However, it involves a large amount of stopping and turning, often at some speed, so I would not recommend it for the masses. It's best suited to young, active individuals, particularly those involved in team sports that require change of direction."

A slightly less daunting alternative is the Cooper Test - a 12-minute run in which you cover as great a distance as you can, or the 1.5-Mile Run, in which you aim to complete the distance as fast as possible. Hunter says such tests are useful for fit, healthy, active people but may be too challenging for the general 'apparently healthy' population.

Reddin has incorporated the 1.5-Mile Run into his 'Park Fitness Test', one of the forthcoming additions to the National Fitness Test website, geared towards fitter people. But he believes that for the general public, the idea of having to go out and run, or measure a distance, could be off-putting. "The idea with the home-based test was to appeal to the greatest number of people and get as many of them as possible to give it a go," he says. "Many people know they're unfit - this gives them a chance to try the test without even having to tell anyone or leave their own home. It's a great awareness tool."

My one gripe about the National Fitness Test is that when calculating your overall fitness score and 'age,' equal weighting is given to aerobic fitness, flexibility, strength and shape. While these are important components of fitness, it's aerobic fitness that is the real key when it comes to heart health, disease prevention and combating obesity. And this observation has nothing to do with the fact that I ranked 'poor' in both strength and flexibility …

Whatever fitness test you're undertaking, you need to follow the instructions to the letter if you are to get meaningful results. The disadvantage with a home test is there isn't anyone watching you and it's possible to cheat or do things slightly wrong. (For example, the National Fitness Test uses the 'plank' exercise, above, to assess strength. And while I, of course, executed mine with perfect posture, it would be easy to do it badly and still score highly by holding the position for a long time.) Recruiting a friend or partner to help with timing and technique is a good idea.

It's also worth bearing in mind that unless you intend to repeat any fitness test in the future, the results merely provide a snapshot of where you are now. "In terms of making tests reliable and repeatable, it is essential that the methods followed are precisely the same on each occasion," says Hunter. "For example, carry out the test at the same time of day, and if outside, try to do it when the environmental conditions are the same or as similar as possible to that of previous tests. Otherwise, you may mask the effects - positive or negative - of your training programme."

Hunter recommends repeating tests every six-12 weeks. "Don't be tempted to repeat them too frequently, because it can be discouraging if you don't see any improvement," he says.

Useful links

For information on how to do the Cooper, Rockport and Multistage Fitness Tests, and for general information on fitness testing, visit brianmac.co.uk.

Sam Murphy's website is at sam-murphy.co.uk. Click on 'News and Events' to find out how to do the 1.5-Mile Run Test and see how your score compares to others of the same age and gender.