PUT your left hand on your chest under your shirt and you'll feel it throbbing – your heart, the body organ we most take for granted, but the one on which all else depends: if it stops, so do you.
When we exercise, our heart works harder, pumping more blood to help take the strain. The heart is a big muscle and like any muscle, exercise is good for it – but also like any muscle, you don't want to overstrain it.
Heart-rate monitors – HRMs for short – are a good way of checking how your heart is going. They're not essential, but they are a useful training tool.
You can wear the latest models on your wrist like a watch and, courtesy of modern GPS technology, they have morphed into devices that don't just tell you how much you're exercising, they also let you know where you are if you're in unfamiliar territory.
And while we don't actually need technological devices to tell us how hard we're working – your breathing rate will do that; or where we are – a local map would do – the new HRMs can be pretty handy, and even a bit addictive.
The new models offer a range of services to help you negotiate tough challenges, such as mountain climbing by acting like a kind of hi-tech sherpa.
We tested the newly launched Fenix from leading maker Garmin, its first GPS wrist-watch for "serious mountaineers and outdoor discoverers".
We found it a godsend during a tough 900-metre, misty ascent of the Maamturk mountains in Connemara, where we were grateful for its inbuilt ABC (altimeter, barometer, compass).
But think before you buy. With all these devices, the more money you fork out the more features you'll be treated to, but first it's worth checking on what you actually need your chosen gizmo for.
Most monitors use a chest strap to transmit heart-rate information continuously to a wrist-watch, with a display you can glance at to monitor your progress.
Strapless monitors with finger sensors are also available – these give accurate, but not constant, readings.
Heart-rate monitors are great for gym work and running but are not necessarily suited to all exercises.
For example, during rowing the strap may come off, or for swimming make sure they're waterproof.
And for those of us who – ahem – tend to keep a little too much within our comfort zone (so what's wrong with being comfortable during exercise?) having a monitor means you can't cheat and convince yourself or your fitness buddies you're really pushing yourself to the limit.
You can't fool technology, so your pesky HRM may publicly out you as having a heartbeat barely moving past sleep levels.
So why bother? Because knowing how fast your heart is beating allows you to structure your training, building up and down gradually and keeping an eye on your overall fitness.
But first you need to work out your maximum healthy heart rate by subtracting your age from a set number – 226 for women, 220 for men. So if you're a 26-year-old woman, your maximum heart rate is about 200 beats per minute.
Then you can use your heart monitor to decide what kind of exercise is best for you.
If you want to lose weight and burn fat, aim for longer periods at 60-70pc of capacity.
But it's better if you can work between 70-80pc of your maximum, as this builds aerobic stamina.
Continuously work higher than that (80-90pc) and you could be ready for the next Olympics.
Mountain guides from across Europe helped with the design of the Fenix, and it's also good for running as it helps you map terrain and find your position and altitude.
You can then plan routes, monitor your progress and compare notes with others in the growing online workout community.
Do we need all this technology? Not necessarily, but it's a useful addition to your workout kit that lets you know how you're doing – and checks on the most important muscle you've got.
WE TRIED: Heart-rate monitors
DID IT WORK? Kept us on training target, and stopped us from getting lost
PLUSES: Combination of a personal trainer and a GPS
MINUSES: No longer being able to fake it!
COST: The Garmin Fenix is one of the best, and it’s at about €430.
Basic heart monitors cost between €40 and €120.
CONTACT: JDM stores nationally and Great Outdoors, Chatham Street, Dublin
Health & Living