CHRISTOPHER B. COOPER, WILLIAM L. BEAVER, DAN M. COOPER
AND KARLMAN WASSERMAN

The V VO (alveolar CO2 output-alveolar 02 uptake) relationship ( V-slope) during increasing
work rate (r-amp) cycle ergometer exercise has two approximately linear components: a lower
component slope (S,) with a value of about 0-95 and a steeper, upper component (S2). We
examined the effect of muscle glycogen depletion (protocol 1) and the rate of increase in work
rate (ramp rate) without muscle glycogen depletion (protocol 2) on S1 and S2. In protocol 1,
ten healthy men with a mean age of 31 4 years (S.D. 6-2) were studied on each of 3 days (days
I and 3 were control days). They performed a ramp exercise test to maximum tolerance and
steady-state tests at rest, during unloaded pedalling and at two constant work rates below their
anaerobic threshold (AT). To deplete muscle glycogen before the test on day 2, the subjects
performed 2 h of very heavy cycle exercise on the preceding day and fasted overnight. Si was
reduced on day 2 (0 79 compared with 0 95, P < 0 001), as was the VC0 -VO slope derived
from steady-state measurements (0 81 compared with 0 99, P < 0 001), but AT and the slope
difference (S2 -S5) were unchanged. In protocol 2, seven healthy men with a mean age of 20 6
years (S.D. 2-4) performed ramp tests at three different rates of increasing work rate (1 5, 30 and
60 W min’), each ramp rate being performed twice in random sequence. The ramp rate did not
affect Si but S2 was steeper with the faster rates of work rate increase (127, 143 and 163,
respectively, P < 0 01). Our findings support the concept that the lower component of the Vslope
plot (below AT) represents muscle substrate respiratory quotient (RQ) while the
difference between Si and S2 reflects ‘excess CO2’ derived from bicarbonate buffering of lactic acid.