and maintain a reasonable pace, you still only have about 2,000 calories worth of glycogen stored in your muscles – enough to get most runners to about mile 18 or 20," he says. "As glycogen reserves are used up and fatty acid metabolism increases, your heart

P20 Once A Day (£18.45 for 200ml from chemistdirect.co.uk). If you have fair skin or a family history of melanoma, consider sun protective clothing and avoid midday runs. You should also have a coffee before you go, advise dermatologists from

Rusko. Lie down for 10 minutes at the same time each day (morning is best), and record your heart rate. Stand up and note your heart rate again after 15, 90 and 120 seconds. Well-rested athletes demonstrate consistency between measurements. But Rusko

, and associating to actually focus on the feeling," says Lewis. To associate, start from the head and work down, assessing each area or group of muscles. "Keep your pace in line with the information you gain from your body monitoring, from heart rate to basic

P20 Once A Day (£18.45 for 200ml from chemistdirect.co.uk). If you have fair skin or a family history of melanoma, consider sun protective clothing and avoid midday runs. You should also have a coffee before you go, advise dermatologists from

of Running Well (£14.99, amazon.co.uk). "Working backwards from your goal, incorporating all the other stuff in life you have to fit around your training – from kids to work – will help you identify what is realistic in your specific time frame." Get it down

, and associating to actually focus on the feeling," says Lewis. To associate, start from the head and work down, assessing each area or group of muscles. "Keep your pace in line with the information you gain from your body monitoring, from heart rate to basic