xactly wrote:I'm trying to confirm that San Millan's definition of Zone 2 is 60 - 70% of your max heart rate. Peter Attia talks about keeping track of his Zone 2 workouts by using watts and FTP, not heart rate. And San Millan talks about a Zone 6, which I have never seen before in conjunction with heart rate monitoring.
I don't think San Millán uses heart rate, per se, to define his zones. From this Training Peaks article
Skeletal muscle is composed of 2 kinds of muscle fibers- Type I, also known as slow twitch, and Type II, or fast twitch. Fast twitch fibers are also divided in two subgroups called Type IIa and IIb. Muscle fiber contraction obeys a sequential recruitment pattern where Type I muscle fibers are the first ones to be recruited. As exercise intensity increases muscle contractile demands increase and Type I muscle fibers cannot sustain the necessary demand. Type IIa muscle fibers kick in and eventually as intensity keeps increasing Type IIb will finally be recruited. Simply put, slow twitch fibers are used at slower speeds and fast twitch at faster speeds. Each muscle fiber has different biochemical properties and thus different behaviors during exercise and competition. Type I muscle fibers have the highest mitochondrial density and capacity and therefore are very efficient at utilizing fat for energy purposes. Type IIa fibers have a lower mitochondrial density and a higher capacity to utilize glucose. Type IIb muscle fibers have a little mitochondrial density and a very high capacity to use glucose as well as ATP stored in these fibers for instant anaerobic energy. Therefore, each exercise intensity implies different metabolic responses and muscle fiber recruitment patterns which also corresponds to different training zones [see above]
Thus type of muscle and type of muscle metabolism seem to define the zones.
So, [from the 2018 paper Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals]
here is an example showing the crossover into zone 2, defined as "the point at which their mitochondria are no longer able to meet the energy output requirement at blood lactate increases"
and in this 2015 presentation slide deck: Sports Performance testing in the Cyclist: where are we in 2015 and how does it apply to the recreational athlete?
, he shows the 'Crossover Point' at which the athlete transitions from zone 2 into zone 3.
In this case, a heart rate for a particular athlete is shown, but I don't think you can generalize from that.
I did find this article Training Center: Why heart rate shouldn't be ignored
which suggests that, once you've developed a lactate utilization profile and correlated it with heart rates, you can use heart rate as a proxy to define your zone. And you might also be able to use disciplined time trial type tests to develop approximate zones.
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