. If your BMI drops below 18.5, you're at risk of becoming weaker and slower. WEIGHT LOST 5K 10K HALF-MARATHON MARATHON 900g 12.4 secs 25 secs 52 secs 1:45 2.3kg 31 secs 1:02 2:11 4:22 4.5kg

Weight Status Below 18.5 Under Weight 18.5 - 24.9 Normal 25.0 - 29.9 Overweight 30.0 and above Obese

successor, Usain Bolt, is not, but that is because he's 200ft tall and runs on wheels. How elite athletes' BMIs comparePaula RadcliffeHeight 5'7" Weight (kg) 54BMI 18.0 (Underweight) Haile GebrselassieHeight 5'4" Weight (kg) 56BMI 20.5 (Normal Weight

's not impossible. But a person who is overweight would be faster if he lost weight. Theoretically, a loss of about two pounds will increase speed by about a metre per minute of running. So if a runner runs a 5K in 20 minutes, a two-pound weight loss would make him

. GGWell, sure, it's not impossible. But a person who is overweight would be faster if he lost weight. Theoretically, a loss of about two pounds will increase speed by about a metre per minute of running. So if a runner runs a 5K in 20 minutes, a two

– and eat – to get the very best out of your body.Enduring Questions: What’s Your Ideal Weight? Start here - lock on to your weight-loss target by working out your ideal weight. GETTY IMAGESThe Basics To begin at the beginning – stick to simple healthy