During shorter (~1 h) activity bouts, ingestion of carbohydrates would not be expected to enhance performance because glycogen depletion would be unlikely to limit performance capacity and euglycemia would be maintained without exogenous carbohydrate ingestion [8
]. However, numerous investigations typically involving highly trained endurance athletes running or cycling after periods of significant fasting have provided evidence supporting enhanced performance and mood or lowered perceived exertion during exercise lasting ~1 h with CE ingestion or mouth rinse, without confirmation of the mechanisms responsible for these changes. The aims of this study were to determine if similar ergogenic properties would be exhibited in non-fasted recreational exercisers.
The results of this study support our first hypothesis that CE consumption during 50 min of sub-maximal exercise would not result in improved WAnT
performance compared to NCE or W (Figure ). Ball et al. [5
] found carbohydrate ingestion during 50 min of high intensity cycling resulted in 6.5% higher mean power and 5.8% higher peak power during a subsequent WAnT
versus ingesting an artificially-sweetened placebo. The similarity in protocols makes comparing the results between the current and Ball et al. [5
] studies favorable with 3 factors taken into consideration.
The first is that the 50 min sub-maximal exercise intensity was prescribed at a more moderate intensity level that could be completed by our highly active but non-competitive level recreational exercisers. It is possible that our contrasting finding of no impact of carbohydrate consumption on performance was due to the lower relative intensity level of the sub-maximal exercise portion of our protocol, which resulted in 15 beats per min lower mean HR than was exhibited for the participants in the Ball et al. [5
] study. However, mean sub-maximal exercise RPEs in the Ball et al. [5
] study were only 5.0
1.0 (carbohydrate trial) and 5.6
1.1(placebo trial), and our participants reported the overall difficulty of the trials was higher than their normal workouts (Table ).
A second difference in our methodology and that of Ball et al. [5
] was that our protocol incorporated 3 sets of WAnT
versus a single WAnT
to assess performance. The primary rationale for incorporating WAnT
as a performance measure was that variability in pacing strategies for our recreational exercisers would make it difficult to interpret more aerobically-based time trial tests that have been most commonly used to assess performance differences in the past. However, repeated WAnT
have been established to be a stable measure, particularly if a practice session is provided [33
] and allowed for direct comparison to the results of the Ball et al. [5
] study. The additional two WAnT
were used to ensure fatigue late in exercise, as we anticipated our sub-maximal exercise bout would be comparatively less intense based on average heart rate than that of Ball et al. [5
]. We predicted if CE ingestion exhibited a protective effect and delayed fatigue, the effects would be more likely to be manifested with repeated versus a single WAnT
. Carbohydrate ingestion during ~1 h of intermittent high intensity exercise has also been shown to improve multiple forms of anaerobic performance tests late in exercise including 20–m sprint time [12
], vertical jump height [13
], and shuttle running to fatigue [12
] for recreational athletes.
A third consideration when comparing our findings was that of the competitive cyclists in Ball et al. [5
] were that Ball et al.’s participants fasted for 12 h prior to exercise. In contrast, in the present study and others [21
] a pre-activity meal was consumed within 2 to 4 hours before the start of exercise. All of the studies that included pre-activity meals found no increase in performance with carbohydrate consumption or mouth rinse during activity. Pre-feeding provides contrasting results (i.e. no improvement versus improvement) compared to nearly all published investigations incorporating fasted participants in exercise lasting 1 h or less. The findings of the present study using recreational exercisers supports the position of Desbrow et al. [21
] who studied highly trained cyclists, and found that mixed-nutrient feeding within a few hours prior to testing mitigated most ergogenic effects of carbohydrate ingestion during exercise of ~1 hour in duration. As long as gastrointestinal distress is not a concern, a pre-exercise meal is recommended for athletes, and beginning exercise in a fasted state is discouraged [34
]. In light of our findings and those of others who included a pre-activity meal in their study design, as well as in keeping with the recommendations for athletes by most sport nutrition related organizations [34
], the impact of including a meal or snack in a reasonable time frame prior to exercise warrants further discussion.
In addition to performance improvement, Ball et al. [5
] found significantly lower mean RPEs for competitive cyclists consuming a CE versus a placebo. Although blood glucose was not measured in their investigation, the authors speculated the differences in RPE for their cyclists possibly stemmed from higher levels of blood glucose maintenance with carbohydrate ingestion versus placebo [5
]. In our investigation, CE resulted in higher blood glucose levels at the end of sub-maximal cycling, but normal blood glucose levels were observed for NCE or W treatments. Sweetness, whether from caloric or non-caloric sources, did not result in statistical differences in perceived exertion (Figure ) or POMS responses (Table ) in comparison to each other or W.
Authors of other studies have suggested that improved mood and lower perceived exertion associated with carbohydrate ingestion or mouth rinse may be mediated through central neural mechanisms [5
]. Functional magnetic resonance imaging has revealed that sucrose, delivered in small doses of fluid to the mouth, results in reward center activation in the brain that is not exhibited with the artificial sweetener sucralose [35
]. Similar results have also been found for other forms of less sweet carbohydrate sources such as maltodextrin and glucose compared to saccharin [14
]. Artificial sweeteners do not elicit the same response as carbohydrates whether participants are fed [35
] or fasted [14
]. Obvious technical limitations of functional MRI make it difficult to determine if physical activity alters these responses, but under the exercise conditions of the present investigation, the addition of caloric sweeteners do not appear to provide an affective domain advantage. If these unidentified oral receptors are responsible for lessened perception of fatigue, it is plausible that their impact is mitigated by carbohydrate presence in the gastrointestinal tract, or changes in blood glucose or glycogen concentration levels in liver or muscle tissue following a pre-exercise meal.
Perhaps part of the reason the mood of our participants was not affected by the CE treatment is because our participants had preconceived notions regarding the efficacy of sport beverages (Table ). While regularly physically active, our participants were neither competitive nor elite endurance athletes, who have been shown to have strong convictions that CE can improve performance [36
]. In one study, following a 40-km time trial with water ingestion only, competitive cyclists were split into 2 cohorts with 1 group being told they were going to consume a CE and the other group being told they were receiving a carbohydrate-free artificially sweetened beverage. In actuality, half of the cyclists in each group received a placebo, and the other half received a CE. The group informed that they were receiving CE improved their average power output by 4.3% during a second time trial compared to baseline whereas the group informed that they were receiving a carbohydrate-free artificially flavored beverage increased their power output by only 0.5%, even though half of the individuals in both groups actually received a CE [36
Differences between the participants in the present study and competitive endurance athletes featured in other studies [36
] may be related to exposure of competitive athletes to literature promoting the importance of CE for performance. It is also probable that most participants in the current investigation were unlikely to have had experiences in which they felt a lack of exogenous carbohydrates hindered exercise performance in comparison to the competitive endurance athletes used in other investigations. These factors may have given our participants a different subjective bias concerning mood and perceived exertion, in contrast to those of trained endurance athletes who frequently consume CE.