Once again the fitness industry markets a catchy product, that grabs the attention of the masses, and this time it is the altitude training mask.
This mask limits the amount of oxygen you can take in while performing cardio based exercises...the result: you get tired very quickly because you can not deliver oxygen to the aerobic working muscles, thus giving you a less than stellar workout that is perceived as strenuous...it would be like trying to exercise with a major cold.
Your best bet is to increase your intensity naturally, run harder: breathe more, the whole concept of training is forced physiological adaptations, in this case building more mitochondria in muscle cells to uptake more oxygen, this happens by progressing exercises not regressing muscular ability with a mask.
On a pro side the participant in the photo said it has helped him regulate exercise induced asthma, this can be by limiting his production or maybe filtering atmospheric triggers. It may also aid in strengthening deep breathing muscles, but you are better off developing them by working harder to breath more.