The Big Book of Endurance Training and Racing
The best way to increase it is through running intervals such as 400-meter sprints. The normal protocol is to run as fast as you can for 400 meters, walk for a minute as you recover, and then repeat the process until you can’t run anymore.
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Today, occasional maximum effort sprints help increase energy levels, improve athletic performance, and minimize the effects of aging by promoting the release of testosterone and human growth hormone (these are beneficial for women as well as men). Once every 7-10 days, when energy and motivation levels are high, choose a simple, brief sprint worko
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Just what level, speed and intensity is ‘sustainable’ depends on the person and event. But it’s generally accepted that sustainable efforts in ultra-endurance events (over six hours’ duration) range between 50 to 75 per cent of your maximum heart rate.
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Recent research also shows that runners wishing to improve their speed should spend at least 80 per cent of their time at low intensity, so beneficial is it to heart, muscle, skeletal and neurological health.