'Training at higher altitudes, if possible, can also help increase lung capacity.;
Source:
http://www.wikihow.com/Increase-Your-Lung-CapacitySo define a relatively uniform control group which will train at normal altitude, and an experiment group which will train at high altitude.
Then, each day, each of the participants has to fully inhale, then fully exhale into a balloon. Measure the diameter of the balloons using string. If overall the experiment group balloons have larger diameters after a given amount of time than the control groups do, then you could say the results indicated that training at high altitude appears to increase lung capacity.
Another test you could do with the same groups is to test resting/working heart rate. Lower heart rate in the experiment group would indicate that high altitude training reduces workload of the heart.
Body fat could be another one.
Just remember to say that the experiment would need to be repeated several times to confirm the results.
Also comment on the groups. Talk about the size of groups, relative ages, fitness level etc.