Amby Burfoot is Executive Editor of Runner's World USA, and the 1968 Boston Marathon winner Imagine that there was an exercise programme that could guarantee to get you in shape with only three identical 30-minute exercise sessions per week. I

1.041 50 1.128 60 1.222 70 1.324 80 1.494 Click here to use Ray Fair's age-and-pace calculator

on treadmills, not of cyclists. No one can say exactly how the two differ, but they do. The triathlon legend Mark Allen has lived in those narrow spaces. Allen is the fastest runner ever to win six Hawaii Ironman Triathlons. In 1989, he closed with a 2:40:04

. 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

of the participants running a 62-mile race consumed 14,000 millilitres of liquid; another who ran only 26 miles, drank only 280 millilitres. The latter runner, not surprisingly, showed the most loss of vascular fluid, resulting in thickened blood plasma and impaired

."NUTRITIONPass on the extra carbsBread, bagels, pasta, potatoes and pancakes - you just can't get enough, right? Wrong, says sports nutritionist Nancy Clark, author of Nancy Clark's Food Guide for New Runners (£12.95, Meyer & Meyer Sport). Running two or three miles