title: Impact of caffeine and protein on postexercise muscle glycogen synthesis.
abstract: 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.
  
  
  OBJECTIVE
  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.
authors: Department of Human Movement Sciences, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre, Maastricht, The Netherlands.
authors: Milou
authors: M
authors: Beelen
authors: Janneau van
authors: Jv
authors: Kranenburg
authors: Joan M
authors: JM
authors: Senden
authors: Harm
authors: H
authors: Kuipers
authors: Luc J C van
authors: LJ
authors: Loon
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology*; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage; D004837:Epinephrine / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000096:biosynthesis*; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D007930:Leucine / Q000008:administration & dosage; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D002110:Caffeine; D006003:Glycogen; D007930:Leucine; D009638:Norepinephrine; D004837:Epinephrine