To evaluate the difference of ventilatory and gas exchange response differences between arm and leg exercise, six healthy young men underwent ramp exercise testing at a rate of 15 W·min
−1 on a cycle ergometer separately under either spontaneous (SPNT) or fixed (FIX) breathing modes, respectively. Controlled breathing was defined as a breathing frequency (
fb; 30 breaths·min
−1) which was neither equal to, nor a multiple of, cranking frequency (50 rev·min
−1) to prevent coupling of locomotion and respiratory movement, i.e., so-called locomotor-respiratory coupling (LRC). Breath-by-breath oxygen uptake (V
O2), ventilation (V
E), CO
2 output (V
CO2), tidal volume (V
T),
fb and end-tidal P
CO2 (P
ETCO
2) were determined using a computerized metabolic cart.
Arm exercise engendered a higher level of V
O2 at each work rate than leg exercise under both FIX and SPNT conditions. However, FIX did not notably affect the V
O2 response during either arm or leg exercise at each work rate compared to SPNT. During SPNT a significantly higher
fb and lower P
ETCO
2 during arm exercise was found compared with leg exercise up to a
fb of 30 breaths·min
−1 while V
E and V
T were nearly the same. During fixed breathing when
fb was fixed at a higher rate than during SPNT, a significantly lower P
ETCO
2 was observed during both exercise modes. These results suggest that: 1) FIX breathing does not affect the V
O2 response during either arm or leg exercise even when non-synchronization between limb locomotion movement and breathing rate was adopted; 2) at a
fb of 30 breaths·min
−1 FIX breathing induced a hyperventilation resulting in a lower P
ETCO
2 which was not associated with the metabolic rate during either arm or leg exercise, showing that V
E during only leg exercise under the FIX condition was significantly higher than under the SPNT condition.
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