Carbohydrate Ingestion Increases Interstitial Glucose and Mitigates Neuromuscular Fatigue during Single-Leg Knee Extensions

INTRODUCTION

We aimed to investigate the neuromuscular contributions to enhanced fatigue resistance with carbohydrate (CHO) ingestion and to identify whether fatigue is associated with changes in interstitial glucose levels assessed using a continuous glucose monitor (CGM).

METHODS

Twelve healthy participants (six males, six females) performed isokinetic single-leg knee extensions (90°·s -1 ) at 20% of the maximal voluntary contraction (MVC) torque until MVC torque reached 60% of its initial value (i.e., task failure). Central and peripheral fatigue were evaluated every 15 min during the fatigue task using the interpolated twitch technique and electrically evoked torque. Using a single-blinded crossover design, participants ingested CHO (85 g sucrose per hour), or a placebo (PLA), at regular intervals during the fatigue task. Minute-by-minute interstitial glucose levels measured via CGM and whole blood glucose readings were obtained intermittently during the fatiguing task.

RESULTS

CHO ingestion increased time to task failure over PLA (113 ± 69 vs 81 ± 49 min, mean ± SD; P < 0.001) and was associated with higher glycemia as measured by CGM (106 ± 18 vs 88 ± 10 mg·dL -1 , P < 0.001) and whole blood glucose sampling (104 ± 17 vs 89 ± 10 mg·dL -1 , P < 0.001). When assessing the values in the CHO condition at a similar time point to those at task failure in the PLA condition (i.e., ~81 min), MVC torque, percentage voluntary activation, and 10 Hz torque were all better preserved in the CHO versus PLA condition ( P < 0.05).

CONCLUSIONS

Exogenous CHO intake mitigates neuromuscular fatigue at both the central and peripheral levels by raising glucose concentrations rather than by preventing hypoglycemia.

Carb-conscious: the role of carbohydrate intake in recovery from exercise

PURPOSE OF REVIEW

The present review summarized evidence on the role of carbohydrates in recovery from exercise within the context of acute and chronic effects on metabolism and performance.

RECENT FINDINGS

Recent studies demonstrate that, in contrast to recovery of muscle glycogen stores, the recovery of liver glycogen stores can be accelerated by the co-ingestion of fructose with glucose-based carbohydrates. Three recent studies suggest this can extend time-to-exhaustion during endurance exercise tests. However, periodically restricting carbohydrate intakes during recovery from some training sessions to slow the recovery of liver and muscle glycogen stores may, over time, result in a modest increase in the ability to oxidize fat during exercise in a fasted state. Whether this periodized strategy translates into a performance advantage in the fed state remains to be clearly demonstrated.

SUMMARY

To maximize recovery of glycogen stores and the capacity to perform in subsequent endurance exercise, athletes should consider ingesting at least 1.2 g carbohydrate per kilogram body mass per hour - for the first few hours of recovery - as a mixture of fructose and glucose-based carbohydrates. However, if a goal is increased capacity for fat oxidation, athletes should consider restricting carbohydrate intakes during recovery from some key training sessions.

VIDEO ABSTRACT

http://links.lww.com/COCN/A15.

Carbohydrate Hydrogel Products Do Not Improve Performance or Gastrointestinal Distress During Moderate-Intensity Endurance Exercise

The benefits of ingesting exogenous carbohydrate (CHO) during prolonged exercise performance are well established. A recent food technology innovation has seen sodium alginate and pectin included in solutions of multiple transportable CHO, to encapsulate them at pH levels found in the stomach. Marketing claims include enhanced gastric emptying and delivery of CHO to the muscle with less gastrointestinal distress, leading to better sports performance. Emerging literature around such claims was identified by searching electronic databases; inclusion criteria were randomized controlled trials investigating metabolic and/or exercise performance parameters during endurance exercise >1 hr, with CHO hydrogels versus traditional CHO fluids and/or noncaloric hydrogels. Limitations associated with the heterogeneity of exercise protocols and control comparisons are noted. To date, improvements in exercise performance/capacity have not been clearly demonstrated with ingestion of CHO hydrogels above traditional CHO fluids. Studies utilizing isotopic tracers demonstrate similar rates of exogenous CHO oxidation, and subjective ratings of gastrointestinal distress do not appear to be different. Overall, data do not support any metabolic or performance advantages to exogenous CHO delivery in hydrogel form over traditional CHO preparations; although, one study demonstrates a possible glycogen sparing effect. The authors note that the current literature has largely failed to investigate the conditions under which maximal CHO availability is needed; high-performance athletes undertaking prolonged events at high relative and absolute exercise intensities. Although investigations are needed to better target the testimonials provided about CHO hydrogels, current evidence suggests that they are similar in outcome and a benefit to traditional CHO sources.