Impact of caffeine and protein on postexercise muscle glycogen synthesis

Med Sci Sports Exerc. 2012 Apr;44(4):692-700. doi: 10.1249/MSS.0b013e31823a40ef.


Background: Both protein and caffeine coingestion with CHO have been suggested to represent effective dietary strategies to further accelerate postexercise muscle glycogen synthesis in athletes.

Purpose: This study aimed to assess the effect of protein or caffeine coingestion on postexercise muscle glycogen synthesis rates when optimal amounts of CHO are ingested.

Methods: Fourteen male cyclists were studied on three different test days. Each test day started with a glycogen-depleting exercise session. This was followed by a 6-h recovery period, during which subjects received 1.2 g·kg⁻¹·h⁻¹ CHO, the same amount of CHO with 0.3 g·kg⁻¹·h⁻¹ of a protein plus leucine mixture (CHO + PRO), or 1.7 mg·kg⁻¹·h⁻¹ caffeine (CHO + CAF). All drinks were enriched with [U-¹³C₆]-labeled glucose to assess potential differences in the appearance rate of ingested glucose from the gut. Muscle biopsies were collected immediately after cessation of exercise and after 6 h of postexercise recovery.

Results: The plasma insulin response was higher in CHO + PRO compared with CHO and CHO + CAF (P < 0.01). Plasma glucose responses and glucose appearance rates did not differ between experiments. Muscle glycogen synthesis rates averaged 31 ± 4, 34 ± 4, and 31 ± 4 mmol·kg⁻¹ dry weight·h⁻¹ in CHO, CHO + PRO, and CHO + CAF, respectively (P = NS). In accordance, histochemical analyses did not show any differences between net changes in Type I and Type II muscle fiber glycogen content between experiments.

Conclusions: Coingestion of protein or caffeine does not further accelerate postexercise muscle glycogen synthesis when ample amounts of CHO (1.2 g·kg⁻¹·h⁻¹) are ingested.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Bicycling / physiology*
  • Blood Glucose / drug effects
  • Blood Glucose / metabolism
  • Blood Glucose / physiology
  • Caffeine / pharmacology*
  • Dietary Carbohydrates / administration & dosage
  • Dietary Carbohydrates / metabolism
  • Dietary Proteins / administration & dosage
  • Epinephrine / blood
  • Fatty Acids, Nonesterified / blood
  • Glycogen / biosynthesis*
  • Humans
  • Insulin / blood
  • Lactic Acid / blood
  • Leucine / administration & dosage
  • Male
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / metabolism*
  • Muscle, Skeletal / physiology
  • Norepinephrine / blood
  • Oxygen Consumption / drug effects
  • Oxygen Consumption / physiology
  • Young Adult


  • Blood Glucose
  • Dietary Carbohydrates
  • Dietary Proteins
  • Fatty Acids, Nonesterified
  • Insulin
  • Lactic Acid
  • Caffeine
  • Glycogen
  • Leucine
  • Norepinephrine
  • Epinephrine