We looked at the following paper for week 3 journal club:
Pritchett KL, Pritchett RC, Green JM et al. Comparisons of post-exercise chocolate milk and a commercial recovery beverage following cycling training on recovery and performance. JEP online 2011; 16(6): 29-39.
What was the aim of the paper?
The researchers wanted to compare the effects of chocolate milk to a commercial carbohydrate (CHO)/protein (PRO) drink after exercise. They hypothesised that because of similar CHO:PRO ratio of chocolate milk to the commercial drink, drinking chocolate milk for one week would be as effective in reducing markers of muscle damage (creatine kinase) and soreness compared to the commercial drink. They also believed that chocolate milk would be just as effective in enhancing time to exhaustion at 85% of VO2 max. The research was carried out by researchers at Central Washington University, The University of Alabama and The University of North Alabama.
What did the study involve?
This was a counterbalanced repeated-measures crossover design study. 10 recreationally trained cyclists completed two trials, each lasting one week, with a week between each trial. The first treatment period consisted of the participants receiving either a commercial drink (Endurox R4) or chocolate milk (Mayfeild, lowfat chocolate milk) based on the ACSM recommendation of 1g CHO/kg body weight immediately after exercise and 2 hours after. Participants self-reported training information and rating of perceived exertion (RPE). At the end of the week the participants completed a trial on the cycle erg at 85% of VO2 max until exhaustion. The researchers measured creatine kinase (CK) at baseline, before the test and around 24 hours after the last day of the trial. Heart rate was recorded every minute during the test and muscle soreness on one day of the treatment (the researchers did not state when) using an analogue scale. One week following the intervention, the participants repeated the second intervention period with the other drink. Food and training were monitored during the two periods to ensure that they were similar between the two.
What were the main results?
There were no significant differences between the two drinks for calorie, protein and carbohydrate, but there was a signficant difference in fat (chocolate milk 4.6gm and commercial drink 2.7gm). All participants preferred the taste of the chocolate milk. There were no significant differences in macronutrient intake, muscle soreness, RPE, CK and training between the two trials.
What can we take from it?
Although this study was an easy read, I agree with Matt that it did not really add anything to what we already know about the effects of drinks on recovery. The main point was that they did not use a control trial, which would have been easy to implement, with the athletes carrying out their usual diet and exercise. This would have allowed us to understand more about the effects of a commercial drink/chocolate drink on recovery. The authors do highlight in their discussion that a control trial was not used because it is well established that a post-exercise meal provides more benefit than nothing at all, but I think it would have helped to highlight this.
The repeated-measures crossover design of the study helped to eliminate any bias, so the researchers and participants were unaware of what they were drinking. Although it would have been quite easy to distinguish between the taste and consistency of the two drinks. I would have liked for the authors to explain how they randomised the participants. I was pleased to see that they had included a power calculation in the methods, which had indicated that they needed only six participants, but they used 10 to ensure sufficient statistical power.
There were large differences in daily dietary intake between the subjects for each trial, as indicated by the large standard deviations. This could have influenced the results. A final point that I have with the methods is that the results relied on the participants self-reporting their training programmes and diet during the two trials. They could have under or over-reported, which would have introduced bias.
The following points from the journal club comments are really interesting and sum up the research really well.
- It’s common for athletes of all levels across a wide range of sports to use chocolate shakes over the more common (and expensive) over-the-counter recovery powders and shakes.
- As the diets were matched and isocalorific over the two interventions, the results were fairly predictable.
- The recovery nutrition could possibly have been met by the subject habitual diet in-between each training session, and neither drink having an impact on recovery.
- I would have liked to see why the specific recovery beverage was chosen and how it compares to its competitors (i.e. energy, protein, carb, fat, like in table 2)
Overall, the research looked at a very popular recovery beverage (chocolate milk) but it would be good to see more research in this area.