We have two basic types of muscle fibers, slowtwitch and fast twitch.
我们每个人有两种基本的肌肉纤维，慢抽搐和快抽搐肌纤维。
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Too much distance work can convert fast twitch muscle fibres into slowtwitch fibres and can actually decrease an athlete's speed over time.
太多的长途运动会造成快肌纤维转换成慢肌纤维，并随着时间的推移，逐渐减慢运动员的速度。
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Your distance runs, of course, produce aerobic gains, including increased blood volume and capillarization, enhanced mitochondrial density and size, and improved slow-twitch fiber development.