The aim of the present study was to investigate whether the changes in brea
thing pattern that frequently occur towards the end of exhaustive exercise
(i.e., increased breathing frequency, fb, with or without decreased tidal v
olume) may be caused by the respiratory work itself rather than by leg musc
le work. Eight healthy, trained subjects performed the following three sess
ions in random order: (A) two sequential cycling endurance tests at 78% pea
k O-2 consumption ((V) over dot O-2peak) to exhaustion (A1, A2); (B) isolat
ed, isocapnic hyperpnea (B1) at a minute ventilation ((V) over dot (E)) and
an exercise duration similar to that attained during a preliminary cycling
endurance test at 78% (V) over dot O-2peak followed by a cycling endurance
test at 78% (V) over dot O-2peak (B2); (C) isolated, isocapnic hyperpnea (
C1) at a (V) over dot (E) at least 20% higher than that of the preliminary
cycling test and the same exercise duration as the preliminary cycling test
, followed by a cycling endurance test at 78% (V) over dot O-2peak (C2). Ne
ither of the two isocapnic hyperventilation tasks (B1 or C1) affected eithe
r the breathing pattern or the endurance times of the subsequent cycling te
sts. Only cycling test A2 was significantly shorter [mean (SD) 26.5 (8.3) m
in] than tests A1 [41.0(9.0) min], B2 [41.9 (6.0) min], and C2 [42.0 (7.5)
min]. In addition, compared to test A1, only the breathing pattern of test
A2 was significantly different [i.e., (V) over dot (E): + 10.5 (7.6) 1 min(
-1), and fb: + 12.1(8.5) breaths min(-1)], in contrast to the breathing pat
terns of cycling tests B2 [(V) over dot (E): -2.5 (6.2) 1 min(-1), fb: + 0.
2 (3.6) breaths min(-1)] and C2 [(V) over dot (E): -3.0 (7.0) 1 min(-1) fb:
+ 0.6 (6.1) breaths min(-1)]. In summary, these results suggest that the c
hanges in breathing pattern that occur towards the end of an exhaustive exe
rcise test are a result of changes in the leg muscles rather than in the re
spiratory muscles themselves.