If we take a look at long distance running, I will have to introduce you to a legendary coach: Arthur Lydiard. He invented the term ”˜jogging’ and got famous for his strategies to achieve peak performance in long distance running events. When the runners started to run longer distances, they got more efficient and achieved a better endurance. LSD (Long Slow Distance) improves your peripheral adaptations, which means increased capillary density, more myoglobin, more mitochondrias, better use of free fatty acids as fuel and larger glycogen stores. Also there are probably some neural adaptations that make running more efficient. Training at slow speeds has only very little effect on VO2 maximum.
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