Purpose and Methods: This study was designed to determine whether the physi
ological responses elicited during the run part of repeated bouts of cycle-
run exercise are similar to those required during the run segment of a cycl
e-run succession Thirteen male triathletes underwent four successive labora
tory trials: 1) an incremental treadmill test, 2) an incremental cycle test
, 3) 30 min of cycling followed by 20 min of running (C-R), and 4) five rep
eated bouts of 6 min of cycling and 4 min of running (X-CR). During the C-R
and X-CR trials, venous blood samples were obtained to measure lactate, ep
inephrine and norepinephrine concentrations. During all trials. ventilatory
data were collected every min using an automated breath-by-breath system.
Results: The results showed that 1) the cardiorespiratory responses observe
d during running were similar in the X-CR and C-R trials, 2) the lactate co
ncentration was similar in both trials, 3) the epinephrine concentration wa
s greater (277.9 +/- 11.9 vs 169.8 +/- 86.7 pg.mL(-1), P < 0.025) in X-CR t
han in C-R and 4) the norepinephrine concentration was similar in both tria
ls, except at the first cycle-run succession (T1) of X-CR. Conclusion: We c
oncluded that 1) multi-block training is a good method to stimulate the spe
cific adaptations required for the cycle-run succession. and particularly f
or the cycle-run transition, and 2) multi-block training seems to induce a
greater catecholaminergic response, which may be due to a combination of an
inherent effect of this type of training and the triathletes' relative lac
k of experience with it. In any case, the efficacy of the multi-block model
needs to be more thoroughly evaluated over the course of a longer-term tra
ining program.