Sorry to say this but the Bruce protocol in a lab might look cool but it is garbage. For peak performance, you need unobstructed mouth and nose. You should exhale forcefully through the mouth and then air comes back in mechanically while inhaling through both mouth and nose. When obstructed that pattern is not as efficient. Outtake hits a wall, intake is limited. Treadmills are also bad for performance because they are too rigid and slow you down. It is much better to use the Cooper test while running a proper running track. All you need to do is to accurately measure the distance covered in 12 minutes. My VO2 max is currently at ~50 and I have been running for 25 years. It is tough to sustain a high VO2 max for many years unless you always run. It might be more beneficial for that metric to avoid inhaling toxic chemicals (air pollution, perfumes, etc) Use the following simple calculator to find your VO2 max after running a specific distance in 12 minutes https://runbundle.com/tools/vo2-max-calculators/cooper-test

After many years, I decided to quit using gyms for exercise. That includes home gyms as well. It has to be open air. More oxygen, less fatigue, better results. Vigorous exercise in a closed space is a very bad idea. Poor ventilation, filthy AC filters, floor mats off gassing, toxic disinfectants and cleaning chemicals. Running, swimming, hiking, walking and street workouts are great and more than enough. However gyms can be fun as social places but they are not as healthy as people think.