Effects of isocaloric carbohydrate vs. carbohydrate-protein supplements on cycling time to exhaustion


Journal Title (Medline/Pubmed accepted abbreviation): J. Strength Cond. Res.
Year: 2012
Volume: 26
Issue: 5
Page numbers: 1361-1365
 

Summary of Background and Research Design

Background: Tournaments, practices, and other events sometimes require athletes to perform maximally at several points during the same day.  Therefore, fast recovery is crucial.  Glycogen, or stored carbohydrates, is the first energy source to be used, but protein is critical for maintenance of muscle protein.
It has been established that consuming energy frequently/continuously (ex. every 30 minutes) throughout the recovery stage is more effective than consuming it in a single meal.

Hypothesis: Compared to a recovery beverage with only carbohydrates, a beverage with protein and carbohydrates will enable faster recovery, as determined by performance on exercise performed 3 hours later.

Subjects: Seven physically active men, age 27.9 ± 7.2 y

Experimental design: randomized, double-blinded, crossover trial

Treatments : CHO: 1.5 g carbohydrate (mixture of maltodextrin, fructose, and dextrose) per kg body weight
CHO-PRO: 1.2 g carbohydrate per kg body weight (mixture of dextrose, “complex carbohydrates”, fructose, and sucrose) and 0.3 g/kg body weight protein (whey)
Powder was mixed at 4.7 g per 1 oz. water.  Beverage was consumed at 0, 30, 60, 90, and 120 min after the first of two cycling bouts.  (The quantity of energy above is for the entire recovery session.)

Protocol : The participants were first evaluated for VO2max and maximal power output on a stationary bicycle.  In order to obtain a consistent amount of glycogen before the trials, participants did not exercise and their diet was regulated for 48 hours before the trial.  They then arrived at the laboratory in the morning after an overnight fast.  Participants cycled at 75% of their VO2max until they were unable to maintain the cadence of 80 revolutions per minute (about 20-25 minutes).  Time was noted.  Heart rate and perceived exertion were assessed every 2 min.  They then rested for 3 hours, during which they consumed one of the two treatments.  They then repeated the time-to-exhaustion test as before.  At least 1 week later, the participants returned and completed the protocol with the different treatment.
 

Summary of research findings
  • There was no significant difference between the time-to-exhaustion times during any of the trials, indicating that the CHO and CHO-PRO beverages aided in recovery to a similar extent.

Key practice applications

During a 3 hour recovery time in between exercise sessions, the addition of protein to a carbohydrate beverage did not appear to aid in restoring glycogen, calorie content being the same.

Limitations

  • There were no measurements of muscle glycogen stores, so it is not clear what the baseline muscle glycogen levels of the subjects were at start of each treatment or if the exercise caused similar muscle glycogen depletion before each treatment.
     
  • Aside from glycogen depletion, athletes can become fatigued in other ways. Protein in addition to carbohydrates may help in other regards.
     
  • Athletes usually do not exercise in the fasted state. The effects of macronutrients (CHO and protein) may have different effects on recovery when exercise occurs in the fed state.
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