Adaptations in capillary density during multi-week Zone 2 blocks are often cited as a key benefit of this type of training, but what if the actual increase in capillary density is minimal compared to the perceived benefits, and the real adaptation is actually in the increased myoglobin levels and enhanced oxygen delivery to the muscles.
If this were the case, would it change how we structure our Zone 2 blocks, and would we need to incorporate more high-intensity intervals to specifically target the increase in myoglobin levels.
Furthermore, if capillary density is not the primary adaptation, would this mean that the traditional 4-6 week Zone 2 block is too long and that shorter blocks with more frequent high-intensity intervals would be more effective in inducing the desired adaptations.
Additionally, what role do other cellular adaptations, such as increased mitochondrial density and enhanced Krebs cycle function, play in the overall increase in endurance performance, and are these adaptations more closely linked to the increase in myoglobin levels rather than capillary density.
Is it possible that the increase in capillary density is actually a secondary adaptation that occurs in response to the increased oxygen demand created by the enhanced myoglobin levels and mitochondrial function, rather than a primary adaptation that drives the increase in endurance performance.
If so, would this change how we measure the effectiveness of our training, and would we need to focus more on the increases in myoglobin levels and mitochondrial function rather than the increase in capillary density.
Also, are there any studies that have investigated the relationship between capillary density, myoglobin levels, and endurance performance, and what do the results of these studies suggest about the relative importance of these different adaptations.
Lastly, what are the implications of these findings for the design of Zone 2 blocks, and would it be more effective to incorporate a mix of high-intensity intervals and low-intensity steady-state training to target the different adaptations, rather than relying solely on Zone 2 training.