THE CLAIM
Working at a higher altitude forces the body to compensate by producing more hemoglobin (protein found in red blood cells that transport oxygen to tissues which fuel the body). The reason? The oxygen saturation levels in the blood are less at higher altitudes because the air is "thinner" as the elevation is increased. This forces the lungs and heart to also work harder which will strengthen them. Training at higher altitudes increases hemoglobin in the blood. This will generally translate in more energy production when competing at lower elevations. Oxygen is fuel. It's that simple.
The elevation masks that you may see football players and other athletes training with, are designed to simulate training at higher altitudes by restricting air causing the heart and lungs to work harder and increase efficiency. The masks use a valve system to reduce the amount of air entering the mask. This restricted air training method forces deeper breaths which increases lung and cardiovascular strength and efficiency. This is all designed to increase lung capacity and aerobic endurance.
THE RESEARCH
Restricted breathing and air that is thinner are separate issues for the body to adapt to. Atmospheric pressure is reduced at higher altitudes. This equates to total units of oxygen for a given area is reduced. In other words, the oxygen saturation levels are lessened at higher levels. The air is basically thinner, not necessarily restricted. The training results are different between altitude training and restricted training! It's common sense!! If the amount of oxygen per unit of air is less, it leads to less oxygen being transported to the working muscles which creates a greater demand on the heart and lungs to provide the oxygen. It's just like the business world... SUPPLY AND DEMAND. The demand is greater than the supply and therefore creates a greater need. This in turn creates the body (or people) to work harder to meet the demand.
When the body is exposed to higher elevations, it is forced to increase myoglobin/hemoglobin content and creates a vasoliation effect in the veins and arteries as well. This allows for the demand for higher oxygen to be met. When you return to a lower altitude, research shows the higher oxygen saturation levels increase performance. It's important to note though, that this is takes place over an extended period of time. Training at a higher altitude for one day or perhaps even a few days won't yield the desired results as the body needs time to adapt to the stimulus. This is something that will take weeks, even months to see noticeable results. Training in a gym with a mask restricting your breathing a couple times/week will yield the same benefit as covering your face with a pillow while trying to run on a treadmill!
To reap the benefit of altitude training, you will need to simulate lower oxygen saturation rather than restricted airflow!
Now back to the altitude training mask. I have simply found no solid research which will support the claims of the manufacturers. In fact I've found no research that training with the restricted breathing will increase hemoglobin. The masks simply restrict airflow to the lungs. It's no different than running a race with a snorkel and mask! (Actually there's a funny image right there!!!) In fact, may be worse than doing so! After speaking with a client who is a physician, she brought up a another valid point - is all the exhaled carbon dioxide expelled from the mask completely through the restricted valves before the next inhalation is taken? This posses another issue altogether. You are now inhaling carbon dioxide or waste instead of a fresh oxygen source.
Quite simply, endurance is more a matter of oxygen not necessarily air. Restricting air flow simply improves the strength of the heart and lungs but not the body's ability to produce more hemoglobin and make the body more efficient by creating a more oxygen dense delivery system when returning to perform at a lower altitude.
MY PERSONAL EXPERIENCE
I did the research AFTER I bought the masks... Yup, another impulse buy made by yours truly! After trying jumping rope, I nearly died after just 30 seconds! I completed 30 seconds on and 30 seconds off for just a few minutes. I thought I was going to die! The next workout, I thought I'd try something a little slower paced, I rode the stationary bike. Again, I found I had an extremely inefficient workout at best! In fact, the only thing I had to show for my experience was an extremely red face and a big zit on the end of my nose from the sweat and bacteria trapped in the mask... true story! I asked myself, why am I doing this? I am not a professional endurance athlete or someone who needs to improve cardiovascular performance! Perhaps an Olympian or professional athlete may reap some kind of benefit over the long term, but I'm personally skeptical.
CONCLUSION
No doubt, I had to work a lot harder while wearing the mask. My heart rate shot up quickly and I had labored breathing. However, if I just increase the resistance or workload I will receive the same response. I noticed my lactic acid threshold was lessened while wearing the mask. From a psychological point, I felt like a badass. I had the mask on, a baseball cap pulled down low and some motivating music with some heavy bass pounding through my headphones. Whether a placebo effect or not, I'm not sure but I felt I worked harder. But from a physiological perspective, I have found no real compelling evidence to support the elevation masks simulate training at a higher elevation. It is, in my opinion, the equivalent to training while having a stuffy nose, congested allergy day!