There should be some impact. Breathing under hypoxia will make lactic acid accumulate more, which is beneficial to improve the acid resistance and acid resistance of human body and improve the sports performance in normal state, but it also takes more time to recover from fatigue.
At least it can improve willpower, that is, tolerance under hypoxic breathing. Willpower is also one of the key factors to improve the level of exercise.
As for carbon dioxide poisoning, I personally don't think so, because this mask is breathable after all. When you inhale continuously, the outside air continuously dilutes the concentration of carbon dioxide in the mask, and when you exhale, the lung gas is discharged with the exhaust port of the mask. Because the mask is well sealed, almost only the vent is ventilated, so the airflow will be discharged from the vent. But the breathing smoothness is lower than that of those without masks.
In short, there are functions, but don't think that this is an artifact that will become stronger when worn. Personally, I think it is possible to improve the intensity of training. As long as there is enough exercise intensity, reasonable nutrition collocation and active rest and recovery, it is enough to achieve the purpose of fitness. There is no need to buy this mask, let alone choose this mask because the fitness effect is not ideal.
For reference only.