Watts Doc #37: Your Fast Twitch Fibers Probably As Aerobic As Your Slow Twitch

Empirical Cycling Podcast · Watts Doc #37: Your Fast Twitch Fibers Probably As Aerobic As Your Slow Twitch

Does your training zone determine the fiber type used? Does fiber type determine aerobic or anaerobic pathways, carbs or fats? We answer these questions by looking at evidence and concepts that show that fast twitch fibers can be just as aerobically capable as slow twitch fibers, nearly as good at burning fats, and why that might be. We dissect a paper on elite cross-country skiers, and another paper on whether or not fast twitch fibers had been recruited at relatively low intensity. In-depth discussion follows on fiber type distribution, muscle mass recruitment and force availability, why endurance athletes defy the expected metabolic properties of fast twitch fibers, and why these expectations may have started with cats.
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Show Notes
XC Skiers paper
The Muscle Fiber Profiles, Mitochondrial Content, and Enzyme Activities of the Exceptionally Well-Trained Arm and Leg Muscles of Elite Cross-Country Skiers

Ramp test muscle recruitment paper
Progressive metabolite changes in individual human muscle fibers with increasing work rates

Figure 2 from XC ski paper, showing HAD and CS activity of arm and leg muscle samples against MHC1 proportion in those samples.

Figure showing metabolite changes at rest and after ramp test stages to 2 below LT (t2), 3 above LT (t3), and to exhaustion (t4).