Perhaps the best form of exercise for weight loss, it's easy to do, free and will make you feel good thanks to the release of endorphins, while it will also hugely benefit the heart and lungs. Those training for marathons or 10km runs, they should seek specific advice, however for general training, most people should be running at least three times a week with their heart rate at 70-75 per cent of its maximum.
Running on grass is the best surface possible, and machines will also cushion impact to an extent. Road running is the hardest form of running and comes with the highest risk of injury but, if you are running road races - such as marathons - you will need to run on pavements to train. You can replicate road-running conditions, to an extent, on a machine by setting the gradient to 1.5 degrees.
What it works: heart, lungs, legs and stamina.
There is a high risk of injury to knees, shins and backs among other things because of the impact of pounding the pavement. Running can shorten muscles, too, unless you stretch properly before and afterwards.