What is the impact of polyphasic sleep on testosterone?
Polyphasic sleep has not been researched well
All similar questions need to be answered in theoretical. Beyond Dr Stampi, nobody did any good physiological research over polyphasic sleep. Stampi did not measure testosterone levels. The polyphasic schedule is untenable. Without strict lab supervision, it cannot be sustained and it cannot run naturally via entrainment. As such it is very hard to study. Moreover, it is not even too interesting to study. Scientists like simple models. Polyphasic sleep induces chaotic changes in the circadian cycle. Those are hard to interpret.
Modelling polyphasic sleep
Imagine studying hydrodynamic properties of a ship in a water tank. To understand the behavior of the ship, it may be useful to observe the impact of various types of waves. Good understanding will come from simple experiments with various wave types. Circadian variable ripples are too chaotic for a good study. It is as if studying the ship in a tank while throwing dozens of rocks into water simultaneously. The behavior of waves would be unpredictable. Naturally, we can always give the ship the ultimate test by exposing it to a volley of chaotic storm waves. This test will not benefit modeling as much as polyphasic sleep attempts do not advance the science of sleep.
Polyphasic sleep and testosterone
All questions about the impact of Uberman on testosterone can only be answered in theoretical by someone who understands endocrinology.
The hallmark of polyphasic sleep is sleep deprivation. Sleep deprivation affects the function of the brain. In terms of modelling, the impact of sleep deprivation can also be chaotic, however, it has been studied pretty well. Brain malfunction in sleep deprivation can be compared to kicking a computer. It is hard to predict how the software running on the computer will respond to a kick. In case of sleep deprivation, some things are more predictable. In the chaos of polyphasic sleep, hormones may go haywire. However, due to the fact that sleep deprivation leads to a stress response and tipping the metabolism in the catabolic direction, we might guess that the level of testosterone in polyphasic sleep would dip. This would then be a nightmare for body builders. In the end, in conditions of chaos, the outcome can depend on the person, context, timing, and other factors. I would not be surprised if polyphasic bloggers have already reported an increase in testosterone instead (assuming testosterone is good). If you Google patiently, perhaps you will find some claims to that effect.
Whatever the answer, it should not affect you assuming you will never attempt the unhealthy practice of polyphasic sleep.