Does Carbohydrate Intake During Endurance Running Improve Performance? A Critical Review

Meta-Analysis of Carbohydrate Solution Intake during Prolonged Exercise in Adults: From the Last 45+ Years' Perspective

Carbohydrate (CHO) supplementation during prolonged exercise postpones fatigue. However, the optimum administration timing, dosage, type of CHO intake, and possible interaction of the ergogenic effect with athletes' cardiorespiratory fitness (CRF) are not clear. Ninety-six studies (from relevant databases based on predefined eligibility criteria) were selected for meta-analysis to investigate the acute effect of ≤20% CHO solutions on prolonged exercise performance. The between-subject standardized mean difference [SMD = ([mean post-value treatment group-mean post-value control group]/pooled variance)] was assessed. Overall, SMD [95% CI] of 0.43 [0.35, 0.51] was significant (p < 0.001). Subgroup analysis showed that SMD was reduced as the subjects' CRF level increased, with a 6-8% CHO solution composed of GL:FRU improving performance (exercise: 1-4 h); administration during the event led to a superior performance compared to administration before the exercise, with a 6-8% single-source CHO solution increasing performance in intermittent and 'stop and start' sports and an ~6% CHO solution appearing beneficial for 45-60 min exercises, but there were no significant differences between subjects' gender and age groups, varied CHO concentrations, doses, or types in the effect measurement. The evidence found was sound enough to support the hypothesis that CHO solutions, when ingested during endurance exercise, have ergogenic action and a possible crossover interaction with the subject's CRF.

Do Sex Differences in Physiology Confer a Female Advantage in Ultra-Endurance Sport?

Ultra-endurance has been defined as any exercise bout that exceeds 6 h. A number of exceptional, record-breaking performances by female athletes in ultra-endurance sport have roused speculation that they might be predisposed to success in such events. Indeed, while the male-to-female performance gap in traditional endurance sport (e.g., marathon) remains at ~ 10%, the disparity in ultra-endurance competition has been reported as low as 4% despite the markedly lower number of female participants. Moreover, females generally outperform males in extreme-distance swimming. The issue is complex, however, with many sports-specific considerations and caveats. This review summarizes the sex-based differences in physiological functions and draws attention to those which likely determine success in extreme exercise endeavors. The aim is to provide a balanced discussion of the female versus male predisposition to ultra-endurance sport. Herein, we discuss sex-based differences in muscle morphology and fatigability, respiratory-neuromechanical function, substrate utilization, oxygen utilization, gastrointestinal structure and function, and hormonal control. The literature indicates that while females exhibit numerous phenotypes that would be expected to confer an advantage in ultra-endurance competition (e.g., greater fatigue resistance, greater substrate efficiency, and lower energetic demands), they also exhibit several characteristics that unequivocally impinge on performance (e.g., lower O₂-carrying capacity, increased prevalence of GI distress, and sex-hormone effects on cellular function/injury risk). Crucially, the advantageous traits may only manifest as ergogenic in the extreme endurance events which, paradoxically, are those that females less often contest. The title question should be revisited in the coming years, when/if the number of female participants increases.

Addition of an Alginate Hydrogel to a Carbohydrate Beverage Enhances Gastric Emptying

PURPOSE

This study aimed to examine the effect of altering osmolality or adding sodium alginate and pectin to a concentrated carbohydrate (CHO) beverage on gastric-emptying (GE) rate.

METHODS

Boluses (500 mL) of three drinks were instilled double blind in eight healthy men while seated, GE was measured using the double sampling method for 90 min, and blood samples were collected regularly. Drinks consisted of glucose and fructose (MON; 1392 mOsmol·kg), maltodextrin and fructose (POLY; 727 mOsmol·kg), and maltodextrin, fructose, sodium alginate, and pectin (ENCAP; 732 mOsmol·kg) with each providing 180 g·L CHO (CHO ratio of 1:0.7 maltodextrin or glucose/fructose).

RESULTS

Time to empty half of the ingested bolus was faster for ENCAP (21 ± 9 min) than for POLY (37 ± 8 min); both were faster than MON (51 ± 15 min). There were main effects for time and drink in addition to an interaction effect for the volume of test drink remaining in the stomach over the 90 min period, but there were no differences between MON and POLY at any time point. ENCAP had a smaller volume of the test drink in the stomach than MON at 30 min (193 ± 62 vs 323 ± 54 mL), which remained less up to 60 min (93 ± 37 vs 210 ± 88 mL). There was a smaller volume of the drink remaining in the stomach in ENCAP compared with POLY 20 min (242 ± 73 vs 318 ± 47 mL) and 30 min (193 ± 62 vs 304 ± 40 mL) after ingestion. Although there was a main effect of time, there was no effect of drink or an interaction effect on serum glucose, insulin or nonesterified fatty acid concentrations.

CONCLUSION

The addition of sodium alginate and pectin to a CHO beverage enhances early GE rate but did not affect serum glucose, insulin, or nonesterified fatty acid concentration at rest.

Effect of protein and carbohydrate solutions on running performance and cognitive function in female recreational runners

This study compared the effects of a carbohydrate–electrolyte–protein solution (CEPS, 2% protein plus 4% carbohydrate), carbohydrate–electrolyte solution (CES, 6% carbohydrate), and noncaloric sweetened placebo (PLA) on both 21-km running performance and cognitive function. Eleven female recreational endurance runners performed a 21-km time-trial running on three occasions, separated by at least 28 days. In a randomized cross-over design, they ingested CEPS, CES, or PLA at a rate of 150 mL every 2.5 km with no time feedback. A cognitive function test was performed before and after the run. Participants ingested approximately 24 g/h carbohydrate plus 12 g/h protein in CEPS trial, and 36 g/h carbohydrate in CES trial during each 21-km trial. Time to complete the time-trial was slightly shorter (P < 0.05) during CES (129.6 ± 8.8 min) than PLA (134.6 ± 11.5 min), with no differences between CEPS and the other two trials. The CEPS trial showed higher composite of visual motor speed than the PLA trial (P < 0.05). In conclusion, CES feedings might improve 21-km time-trial performance in female recreational runners compared with a PLA. However, adding protein to the CES provided no additional time-trial performance benefit. CEPS feeding during prolonged exercise could benefit visual motor speed compared to PLA alone, but no differences in the performance of the other cognitive function tests were found.

Nutrition behaviors, perceptions, and beliefs of recent marathon finishers

OBJECTIVES

To describe the nutrition behaviors, perceptions, and beliefs of marathoners.

METHODS

A survey-based study was conducted with 422 recent marathon finishers (199 men, 223 women). Participants reported their running background, demographics, diets followed, supplements used, and food/fluid intake during their most recent marathon (median 7 days prior), as well as beliefs about hydration, fueling, and sources of nutrition information.

RESULTS

Median finishing times were 3:53 (3:26-4:35) and 4:25 (3:50-4:59) h:min for men and women during their most recent marathon. Most participants (66.1%) reported typically following a moderate-carbohydrate, moderate-fat diet, while 66.4% carbohydrate-loaded prior to their most recent marathon. Among 139 participants following a specific diet over the past year, the most common were vegetarian/vegan/pescatarian (n = 39), Paleolithic (n = 16), gluten-free (n = 15), and low-carbohydrate (n = 12). Roughly 35% of participants took a supplement intended to improve running performance over the past month. Women were more likely to follow specific diets (39.0% vs. 26.1%), while men were more likely to recently use performance-enhancing supplements (40.2% vs. 30.0%). Most participants (68.3%) indicated they were likely or very likely to rely on a structured plan to determine fluid intake, and 75% were confident in their ability to hydrate. At least 35.6% of participants thought they could improve marathon performance by 8% or more with nutrition interventions. Scientific journals ranked as the most reliable source of nutrition information, while running coaches ranked as the most likely source to be utilized.

CONCLUSIONS

Findings from this investigation, such as diets and supplements utilized by marathoners, can be used by practitioners and researchers alike to improve the dissemination of scientifically-based information on nutrition and marathon running.