People talk about “fast twitch athletes” and “slow twitch athletes,” but does categorizing people this way hold any water? Are muscle fiber types relevant for performance? Can muscle fiber types change with training? On this episode of Science with Sergio, we discuss the paper Human Skeletal Muscle Fiber Type Classifications in an attempt to translate both the academic jargon and the bro science surrounding muscle fiber types into something useful. While most coaches and athletes aren’t going out to get their myosin heavy chains tested anytime soon, we can still improve our training by understanding what differentiates muscle fiber types and how that impacts the way that different athletes fatigue. If you're not already subscribed to our newsletter, head over to www.legionsc.com to get a weekly selection of training tips and our favorite articles. We run online workshops for coaches as well. Find out when our next workshop is here: https://legionsc.com/program-design-workshops These podcast are posted in video format on YouTube as well. Show Notes: [0:13] How should we think about muscle fiber types for athletes competing in the sport of fitness? Does thinking about "fast twitch" vs "slow twitch" athletes hold up? [11:11] Technical categorization of different muscle fiber types. What is the mechanism for fatigue in muscle fibers? [21:00] Production of lactate as a proxy for fast twitch vs slow twitch muscle fibers — and the difference in recovery between fast twitch and slow twitch. [36:50] How do muscle fiber types relate to recovery and potential for overtraining? [42:50] How muscle fiber types change over time in response to training. Why does training make muscle fibers more oxidative? [54:41] How should coaches and athletes use this information in the gym?