Table 4: Changes in Expired ventilation (${\dot{V}}_E$ ) and Heart rate (f_H) at rest and during incremental exercise at the three CO₂ levels.

		Air (n=8)	3% CO2 (n=8)	6% CO2 (n=8)
${\dot{V}}_E$ (l/min)	Rest	8.8 ± 1.1	14.9 ± 0.8*	26.5 ± 4.3*†
	30% ${\dot{V}}_{O_{2\max }}$	19.1 ± 3.0	29.9 ± 6.0*	45.8 ± 11.5*†
	45% ${\dot{V}}_{O_{2\max }}$	30.6 ± 7.4	41.1 ± 10.0*	62.7 ± 13.2*†
	60% ${\dot{V}}_{O_{2\max }}$	41.7 ± 6.7	58.0 ± 10.0*	75.9 ± 15.6*†
	80% ${\dot{V}}_{O_{2\max }}$	68.6 ± 14.7	87.8 ± 13.1*	94.1 ± 21.1*†
	90% ${\dot{V}}_{O_{2\max }}$	85.7 ± 14.7	104.3 ± 17.4*	108.3 ± 22.8*†
	Max	109.9 ± 22.3	125.5 ± 22.3*	118.8 ± 23.7
fH(beats/min)	Rest	71.9 ± 9.2	75.6 ± 7.7	82.0 ± 10.9*
	30% ${\dot{V}}_{O_{2\max }}$	98.0 ± 9.4	97.1 ± 7.5	103.4 ± 6.2
	45% ${\dot{V}}_{O_{2\max }}$	113.9 ± 6.7	112.5 ± 6.8	123.1 ± 6.9*†
	60% ${\dot{V}}_{O_{2\max }}$	133.6 ± 13.6	134.6 ± 12.2	142.0 ± 12.1
	80% ${\dot{V}}_{O_{2\max }}$	166.0 ± 9.6	165.1 ± 8.9	163.1 ± 11.1
	90% ${\dot{V}}_{O_{2\max }}$	176.9 ± 7.5	175.4 ± 8.2	172.1 ± 9.4
	Max	185.3 ± 8.5	182.8 ± 7.8	177.1 ± 7.0

Values are means ± SD. *P<0.05 vs Air. ^†P<0.05 vs 3% CO₂ .