The effects of short work vs. longer work periods within intermittent exercise on V̇o2p kinetics, muscle deoxygenation, and energy system contribution.

The effects of short work vs. longer work periods within intermittent exercise on V̇o2p kinetics, muscle deoxygenation, and energy system contribution.

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The effects of short work vs. longer work periods within intermittent exercise on V̇o2p kinetics, muscle deoxygenation, and energy system contribution.

Abstract
We examined the effects of inserting 3-s recovery periods during high-intensity cycling exercise at 25-s and 10-s intervals on pulmonary oxygen uptake (V̇o2p), muscle deoxygenation [deoxyhemoglobin (HHb)], their associated kinetics (τ), and energy system contributions. Eleven men (24 ± 3 yr) completed two trials of three cycling protocols: an 8-min continuous protocol (CONT) and two 8-min intermittent exercise protocols with work-to-rest periods of 25 s to 3 s (25INT) and 10 s to 3 s (10INT). Each protocol began with a step-transition from a 20-W baseline to a power output (PO) of 60% between lactate threshold and maximal V̇o2p (Δ60). This PO was maintained for 8 min in CONT, whereas 3-s periods of 20-W cycling were inserted every 10 s and 25 s after the transition to Δ60 in 10INT and 25INT, respectively. Breath-by-breath gas exchange measured by mass spectrometry and turbine and vastus lateralis [HHb] measured by near-infrared spectroscopy were recorded throughout. Arterialized-capillary lactate concentration ([Lac]) was obtained before and 2 min postexercise. The τV̇o2p was lowest (P < 0.05) for 10INT (24 ± 4 s) and 25INT (23 ± 5 s) compared with CONT (28 ± 4 s), whereas HHb kinetics did not differ (P > 0.05) between conditions. Postexercise [Lac] was lowest (P < 0.05) for 10INT (7.0 ± 1.7 mM), was higher for 25INT (10.3 ± 1.9 mM), and was greatest in CONT (14.3 ± 3.1 mM). Inserting 3-s recovery periods during heavy-intensity exercise speeded V̇o2p kinetics and reduced overall V̇o2p, suggesting an increased reliance on PCr-derived phosphorylation during the work period of INT compared with an identical PO performed continuously.
NEW & NOTEWORTHY
We report novel observations on the effects of differing heavy-intensity work durations between 3-s recovery periods on pulmonary oxygen uptake (V̇o2p) kinetics, muscle deoxygenation, and energy system contributions. Relative to continuous exercise, V̇o2p kinetics are faster in intermittent exercise, and increased frequency of 3-s recovery periods improves microvascular O2 delivery and reduces V̇o2p and arterialized-capillary lactate concentration. The metabolic burden of identical intensity work is altered when performed intermittently vs. continuously.
Practical Implication
Swim coaches should consider doing more short rest-periods within training, as it may provide similar power output and more PCr-derived phosphorylation.
Reference:
  1. McCrudden MC1, Keir DA1, Belfry GR2.  The effects of short work vs. longer work periods within intermittent exercise on V̇o2p kinetics, muscle deoxygenation, and energy system contribution. J Appl Physiol (1985). 2017 Jun 1;122(6):1435-1444. doi: 10.1152/japplphysiol.00514.2016. Epub 2017 Mar 23.

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