The effect of adding caffeine to postexercise carbohydrate feeding on subsequent high-intensity interval-running capacity compared with carbohydrate alone


Journal Title (Medline/Pubmed accepted abbreviation): Int J Sport Nutr and Exerc Metab
Year: 2011
Volume: 21
Number:
Page Numbers: 410-416
doi (if applicable):

Summary of background and research design:

Background:Twice-daily training with morning and afternoon sessions separated by a 3- to 6-hour recovery period is a commonly used schedule for various sports. To maintain training intensity in the later sessions, it is necessary to promote maximal rates of muscle glycogen resynthesis. While carbohydrate (CHO) (1.2 g/kg body mass/hr) is commonly used, recent evidence showing that coingesting caffeine (CAF) (8 mg/kg body mass) with this feeding protocol increases glycogen resynthesis rates by 33% to 50% to 60 mmol/kg dry weight/hour.  

Hypothesis/Purpose: Coingestion of caffeine with CHO (CHO+CAF) during a 4-hour recovery period after glycogen-depleting exercise augments subsequent high-intensity interval-running capacity compared with ingesting CHO alone.

Subjects:Six recreationally active men (age, 21 ± 1 y; height, 1.78 ± 0.07 m; body mass, 74.5 ± 8.4 kg; maximal oxygen uptake [VO2max], 56 ± 1 mL/kg/min) volunteered for this study.

Experimental design: Randomized, double-blind, crossover 

Treatments and protocol:
All volunteers completed 3 experimental trials at least 7 days apart and at the same time of day. Following a glycogen-depleting run (5 min warm-up, 2 min intermittent runs from 90% to 60% VO2max [determined previously] with 2 min recovery at 50% VO2max at 10% grades to fatigue on a treadmill), they were randomized to replenishment for 4 hours with A) CHO only (1.2 g/kg body mass/hr), B) CHO + CAF (CHO protocol with 2 doses of 4 mg/kg CAF, one immediately after and another 2 hr after exercise), or C) water (WAT). After the recovery period, exercise capacity was tested (Loughborough Intermittent Shuttle Test, or LIST). Blood samples for glucose and lactate were collected at baseline, after glycogen-depleting exercise, during recovery period, and after exercise capacity testing. Heart rate was monitored continuously throughout the exercise.


Summary of research findings:
  • During the glycogen-depleting run, exercise times to exhaustion in the CHO, CHO+CAFF, and WAT trials were similar (P = .128).
    • Blood lactate levels were similar among groups (P =.220).
    • Average heart rates were not different among groups (P = .246).
  • During the recovery phase, blood glucose levels and gastrointestinal (GI) discomfort were higher in the CHO and CHO+CAF groups compared with WAT (P ≤ .005 for all).
    • Blood glucose and GI discomfort were similar in the CHO and CHO+CAF groups.
  • In the exercise capacity (LIST) assessment, total exercise times to exhaustion in the CHO, CHO+CAFF, and WAT trials were 32, 48, and 19 minutes, respectively.
    • Participants exercised significantly longer in the CHO+CAF trial than in the CHO (P = .044) and WAT (P = .001) trials.
  • After the exercise capacity phase, blood lactate was significantly increased in the CHO (preexercise, 1.3 mmol/L; postexercise, 4.4 mmol/L), CHO+CAFF (preexercise, 1.4 mmol/L; postexercise, 6.9 mmol/L), and WAT (preexercise, 1.4 mmol/L; postexercise, 7.6 mmol/L) trials, although there were no among-group differences (P = .443).

Interpretation of findings/Key practice applications:

CAF significantly increased the exercise capacity in volunteers following CHO and was not associated with any additional GI discomfort than that observed with CHO alone. While the authors speculate that, in part, some of the activity of CAF may be the result of its effects on the central nervous system, they did not assess any potential effects on lipid metabolism, and the authors acknowledge this as a shortcoming of the study. Additionally, it should be noted that longer-term effects on exercise capacity following such a glycogen replenishing schedule are unknown.


 

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