Low doses of caffeine reduce heart rate during submaximal cycle ergometry

Table 2 Respiratory and metabolic values during submaximal and maximal exercise

% of VO_2max	30	45	63	Peak VO₂
V_E (L·min^-1)
PLA	28.0 ± 2.3	41.5 ± 2.4	56.6 ± 3.4	129.0 ± 15.8
1.5	28.6 ± 3.0	42.7 ± 3.8	59.3 ± 5.3	129.1 ± 13.4
3.0	28.5 ± 2.4	42.0 ± 3.2	59.5 ± 6.0	127.1 ± 12.3
Bf (breaths·min^-1)
PLA	19.3 ± 2.8	21.3 ± 2.8	23.5 ± 4.1	41.0 ± 8.3
1.5	18.7 ± 3.1	20.8 ± 3.2	23.2 ± 4.4	38.8 ± 6.0
3.0	18.0 ± 2.6	20.0 ± 3.3*	23.3 ± 4.1	38.9 ± 6.7
V_T (L·breath^-1)
PLA	1.55 ± 0.23	2.02 ± 0.27	2.50 ± 0.41	3.21 ± 0.36
1.5	1.63 ± 0.27	2.13 ± 0.28	2.64 ± 0.36	3.38 ± 0.31
3.0	1.67 ± 0.19	2.22 ± 0.42	2.63 ± 0.41	3.32 ± 0.36
VO₂(ml·kg^-1·min^-1)
PLA	14.9 ± 1.6	22.6 ± 2.4	31.0 ± 3.3	49.7 ± 4.4
1.5	14.8 ± 0.9	22.7 ± 1.7	31.4 ± 2.7	50.7 ± 5.6
3.0	15.2 ± 1.0	23.0 ± 2.1	31.9 ± 3.2	50.3 ± 4.1
RER
PLA	0.85 ± 0.04	0.90 ± 0.02	0.94 ± 0.03	1.21 ± 0.05
1.5	0.86 ± 0.05	0.92 ± 0.03	0.96 ± 0.04	1.18 ± 0.06
3.0	0.82 ± 0.06	0.88 ± 0.05^*†	0.93 ± 0.03^†	1.16 ± 0.06^*†
RPE
PLA	8.4 ± 1.3	11.7 ± 1.5	13.8 ± 0.9	19.0 ± 0.6
1.5	8.2 ± 1.3	11.0 ± 0.7	13.4 ± 1.0	19.1 ± 0.6
3.0	7.9 ± 1.1	11.3 ± 1.2	13.4 ± 1.0	19.3 ± 0.6

Values listed as mean ± SD. V_E, ventilation; Bf, breathing frequency; V_T, tidal volume; VO₂, oxygen consumption; RER, respiratory exchange ratio; RPE, rating of perceived exertion. PLA, placebo; 1.5 and 3.0 represent dose of caffeine in mg·kg body weight^-1.
* Significantly different from placebo (p < 0.05).
^† Significantly different from 1.5 caffeine in mg·kg body weight^-1. (p < 0.05).

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