Respiratory impedance has been studied as a possible countermeasure against fatigue during repeated
bouts of high-intensity exercise. By creating resistance during inspiration, an impedance threshold
device (ITD) decreases intrathoracic pressure and pulls more blood back to the heart, resulting in
increased stroke volume and cardiac output. This increased blood flow may enhance exercise recovery
by clearing metabolites and increasing tissue perfusion. PURPOSE: To examine the effects of breathing
with an ITD during recovery between repeated bouts of high-intensity exercise. METHODS: Eleven
participants (8 men, 3 women, 19-29 years-of-age) performed a total of 9, 20 s bouts of high-intensity
exercise interspersed with 3 min of active recovery on an electronic bicycle ergometer. Participants
were instructed to perform each exercise bout at an intensity that would elicit a rating of approximately
7 (very strong) on the Borg Category-Ratio scale of perceived exertion. The same exercise protocol was
performed on different days, with and without the ITD during recovery. RESULTS: As expected, the
exercise protocol significantly increased blood lactate (1.7 ± 0.2 mM pre-exercise vs. 11.5 ± 0.6 mM after
bout 9, p < .001). Ratings of perceived exertion also increased across exercise bouts (4.9 ± 0.4 after bout
1, 7.5 ± 0.2 after bout 5, and 9.0 ± 0.2 after bout 9, p < .001). Participants rated their perceived recovery
lower as the number of exercise bouts increased (p < .001). There were significant differences in peak
and mean power output, as well as total work between exercise bouts, with the highest values recorded
during the 9th bout (total work: 7434 ± 380 joules during bout 1, 8015 ± 266 J during bout 5, and 8391 ±
303 J during bout 9, p < .01). Thus, participants paced themselves during early bouts and gave a near
maximal effort during the last bout. However, results were not significantly different between the
control and ITD conditions. CONCLUSION: Use of an ITD during recovery periods between repeated, high
intensity exercise bouts that required pacing did not positively impact subsequent performance. Results
may be different if individuals perform repeated, high-intensity exercise that requires a maximal or near
maximal effort during each exercise bout rather than a pacing strategy.