There is an upper limit to the oxygen consumed during exercise requiring maximal effort.  The upper limit is defined as maximal oxygen uptake (VO2max).  "The maximum rate at which an individual can take up and utilize oxygen while breathing air at sea level." Astrand & Rodahl, 1986).  This can be backed up by an experiment performed by McArdle, Katch and Katch (1996).  Maximal oxygen uptake (VO2max) is reached while running up hills of increasing gradient.  VO2max occurs in which a further increase in exercise intensity is not accompanied by an additional increase in oxygen uptake.  "The VO2max value quantitatively expresses a person's capacity for aerobic resynthesis of ATP.  As such, it is an important factor in determining one's ability to sustain high intensity exercise for longer than 4 or 5 minutes."  McArdle et al (1996).
            
Results.
            
Table 1.
            
Exercise Intensity	Respiratory Rate	Tidal Volume	Oxygen Uptake.
            
Rest (100)	12.7	478	250.
            
125	12.9	577	315.
            
150	13.1	670	375.
            
175	13.3	760	436.
            
The table shows the increases of respiratory rate, tidal volume, and oxygen uptake for each exercise intensity during each exercise bout.
            
Table 2.
            
	20.9%O2	16% O2	10% O2	6.5% O2.
            
	Rest/Ex	Rest/Ex	Rest/Ex	Rest/Ex.
            
Alv PO2 mmHG	101.7/111.1	77.1/80.4	48.2/46.8	30.6/30.5.
            
Art O2 content (a) ml/100ml	19.5/19.5	19.0/18.9	17.0/16.2	12.7/10.4.
            
Venous O2 content (v) ml/100ml	14.5/8.9	14.1/8.5	12.7/7.3	9.6/4.8.
            
a-v diff O2 (ml/100ml) 	5.0/10.6	4.9/10.4	4.3/8.9	3.1/5.6.
            
Cardiac Output (l/min)	5.01/9.3	5.1/9.5	5.6/10.7	7.3/14.
            
VO2 (ml/min)	250/972	252/979	222/956	215/826.
            
The table shows all the results of how the body is affected in many ways by the increase of height above sea level, during rest and exercise.
            
Discussion.
            
Respiratory rate and tidal volume both constitute ventilation, when occurred with incremental exercise as both increase because the rate of inspired and expired air increases.  This can be viewed in table 1.  These respiratory physiological functions are easily measured with a Spirometer.