Abstract
Purpose: To determine whether a carbohydrate mouth rinse can alter self-paced exercise performance independently of a high degree of thermal and cardiovascular strain.Methods: Eight endurance-trained males performed two 40-km cycling time trials in 35°C, 60% RH while swilling a 20-ml bolus of 6.5% maltodextrin (CHO) or a color- and taste-matched placebo (PLA) every 5 km. Heart rate, power output, rectal temperature (Tre), and mean skin temperature (Tsk) were recorded continuously; cardiac output, oxygen uptake (VO2), mean arterial pressure (MAP), and perceived exertion (RPE) were measured every 10 min.Results: Performance time and mean power output were similar between treatments, averaging 63.9 ± 3.2 and 64.3 ± 2.8 min, and 251 ± 23 and 242 ± 18 W in CHO and PLA, respectively. Power output, stroke volume, cardiac output, MAP, and VO2 decreased during both trials, increasing slightly or remaining stable during a final 2-km end-spurt. Tre, Tsk, heart rate, and RPE increased throughout exercise similarly with both treatments. Changes in RPE correlated with those in Tre (P < 0.005) and heart rate (P < 0.001).Conclusions: These findings suggest that carbohydrate mouth rinsing does not improve ~1-h time trial performance in hot-humid conditions, possibly due to a failure in down-regulating RPE, which may be influenced more by severe thermal and cardiovascular strain.
Highlights
During prolonged exercise (≥90 min) in temperate conditions, carbohydrate ingestion increases time to fatigue by maintaining a high rate of carbohydrate oxidation and sparing muscle glycogen (Coyle et al, 1986; Tsintzas et al, 1996)
Performance of shorter-duration exercise (∼1 h) is improved by carbohydrate ingestion in both temperate and hot (Below et al, 1995) conditions; Carbohydrate Rinsing and Cycling Performance the ergogenic effect may be of non-metabolic origin, as performance improvements have been observed despite similar carbohydrate availability (Carter et al, 2004b), glycogen oxidation rates (Hawley et al, 1997; McConell et al, 2000), and muscle glycogen storage (Bosch et al, 1996; Hawley et al, 1997)
Central fatigue, defined as a progressive reduction in voluntary muscle activation (Gandevia, 2001), may be delayed by carbohydrate ingestion via stimulation of oral carbohydrate receptors, activating brain regions associated with motivation and pleasure, and affecting behavior and possibly exercise performance (Carter et al, 2004a)
Summary
During prolonged exercise (≥90 min) in temperate conditions, carbohydrate ingestion increases time to fatigue by maintaining a high rate of carbohydrate oxidation and sparing muscle glycogen (Coyle et al, 1986; Tsintzas et al, 1996). Use of a carbohydrate mouth rinse, which isolates a potential central effect, results in improved endurance performance by 1.9–11.6% (Jeukendrup, 2013), characterized by higher running speed (Rollo et al, 2008, 2010) and cycling power output (Carter et al, 2004a; Chambers et al, 2009; Pottier et al, 2010; Fares and Kayser, 2011; Lane et al, 2013), despite similar heart rates and ratings of perceived exertion (RPE). Some studies report no effect of carbohydrate mouth rinsing on performance (Whitham and McKinney, 2007; Beelen et al, 2009)
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