Carbs Before and During High-Intensity Training Don't Improve Performance, New Study Finds
New findings question the benefits of carbs for high-intensity interval exercise.
The study "No Effects of Carbohydrate Ingestion on Muscle Metabolism or Performance During Short-Duration High-Intensity Intermittent Exercise" (PMID: 39308061) investigates the impact of carbohydrate supplementation on muscle metabolism and performance during high-intensity intermittent exercise.
Study Overview
The research aimed to determine whether carbohydrate ingestion influences muscle glycogen depletion and performance in short-duration high-intensity intermittent exercise, which is common in sports like ice hockey and racquet sports.
Key Points
Methodology Overview
Participant Preparation: Eleven moderately to well-trained young males participated in the study, undergoing two experimental conditions: carbohydrate (CHO) supplementation and placebo (PLA).
Breakfast: On each experimental day, participants consumed a standardised breakfast approximately one hour before arriving at the laboratory. This breakfast consisted of oats, skimmed milk, raisins, sugar, and juice, providing about 1.5 g of carbohydrates per kilogram of body mass. This meal was consumed three hours before the start of the high-intensity intermittent exercise protocol.
Experimental Design
Study Structure: The study followed a randomised, double-blinded, counterbalanced crossover design involving two experimental conditions: carbohydrate (CHO) supplementation and placebo (PLA). Each participant underwent both conditions on separate days.
Intra-Workout Carbohydrate Drink
Carbohydrate Supplementation: During the exercise sessions, participants ingested carbohydrate drinks continuously. The supplementation provided approximately 55g/h of carbohydrates during three periods of high-intensity intermittent exercise (EX1-EX3). This was designed to assess the effects of carbohydrate ingestion on muscle metabolism and performance.
Exercise Protocol
High-Intensity Intermittent Exercise: The exercise regimen included three periods, each comprising ten 45-second cycling bouts at an intensity of approximately 100%−105% of the participants' maximum wattage (Wmax), interspersed with 135 seconds of passive recovery. There were also 20-minute recovery periods between each exercise session.
Data Collection
Muscle Biopsies and Blood Sampling: Muscle biopsies were taken from the vastus lateralis muscle at baseline and immediately before and after the final exercise period (EX3). Blood samples were collected at baseline and after each exercise period to monitor changes in blood glucose and insulin levels.
Performance Assessments
Repeated Sprint Tests: Participants underwent repeated sprint tests before and after each exercise period to evaluate changes in sprint performance and muscle function.
This comprehensive methodology aimed to provide insights into how carbohydrate ingestion affects muscle metabolism and performance during short-duration high-intensity intermittent exercises. The study's design ensures that results apply to real-world athletic scenarios where athletes might consume carbohydrates during competition.
Related
Findings
There were no significant differences in muscle glycogen breakdown between the CHO and PLA conditions (p=0.683).
Repeated sprint ability declined by approximately 9% after exercise, with no differences between CHO and PLA (p=0.971).
Blood glucose concentrations were significantly higher in the CHO condition post-exercise compared to PLA (5.3 vs. 4.1 mmol/L, p<0.001), along with elevated plasma insulin levels in the CHO condition.
Conclusion: Despite higher blood glucose and insulin levels with carbohydrate ingestion, there were no beneficial effects on muscle glycogen depletion or sprint performance during short-duration high-intensity intermittent exercise.