"It never gets easier, you just go faster." - Greg Lemond

Monday, July 2, 2012

A Quick Review of the Literature: Does caffeine enhance post-exercise recovery?


A very intriguing topic, often discussed in a wide range of magazines, from Men's Health, to Bicycling Magazine, to Runner's World.  As athletes we are constantly looking for methods to best refuel and rebuild our muscles after a difficult workout, and because caffeine has the ability to exert unique effects on metabolic machinery, it has constantly been a target for research.  One thing is fairly consistent throughout the literature, caffeine can improve exercise performance.  However, a quick google search revealed the above mainstream magazines touting the recovery-enhancing effects of caffeine, few of them addressed the fact that this is highly debated in the scientific literature (on a side note, the Bicycling magazine suggests incorporating 3.6 grams of caffeine per pound of body weight DO NOT DO THIS it is potentially lethal, I believe it is a type and they intended milligrams). 
            So, because I…  dislike overly simplistic one sided reporting of nutritional science, I have taken it upon myself to summarize recent scientific findings are available on the effects of caffeine on exercise recovery.  For the purpose of this summary is I will define recovery as increased glycogen synthesis, or increased activity of intracellular pathways associated with recovery, and finally altered secretion of hormones associated with the recovery process (insulin, IGF-1, testosterone, leptin, cortisol).
            Carbohydrates alone are not entirely sufficient to drive massive recovery when a person is near total glycogen depletion.  A plethora of data suggest that there is a platue on the efficiency of carbohydrates to fully drive recovery (1.2 grams of carbohydrates per kilogram of body weight per hour) as insulin levels will no longer increase, thus once carbohydrates are available in sufficient quantities, insulin levels tend  not increase further (1).  Similarly, and related, is the fact that once carbohydrates are available in sufficient quantities, muscle glycogen synthesis also plateaus.  Therefore, scientists have sought other nutritional strategies to further enhance muscle glycogen synthesis and/or muscle protein synthesis.  
            Although not universally supported (1), the addition of amino acids or protein to a carbohydrate rich recovery meal has been found to enhance insulin secretion, muscle protein synthesis, and in some cases also enhance muscle glycogen synthesis compared to carbohydrates alone (2-5).  Thus, this is the “Gold Standard” when it comes to recovery nutrition.  But I digress.
Interestingly, at rest, caffeine is known to have negative effects on glycemic control exerted by muscles (6, 7).  That is to say, caffeine diminishes the ability of muscles to respond to insulin signals to store glucose (carbohydrate).  However, this is at least partially abolished during and after exercise (6, 8, 9).  So then, does caffeine have a role in recovery?  In 2008, Pedersen and colleagues (10) said yes, and cited the fact that in their study they observed blood glucose levels to be elevated for a longer period of time in the group receiving carbohydrates + caffeine than compared to a group receiving only carbohydrates during the recovery phase.  This was further supported by their observation that glycogen synthesis rates were significantly higher in the carbohydrate + caffeine group 4 hours post exercise.  While the authors are unable to identify a mechanism for this observation, they speculate that this is achieved through increased intestinal glucose transport.  Based on this one result, indeed, there is some evidence to suggest caffeine may enhance recovery, if consumed with carbohydrates for 4 hours post exercise.  
However, this one study is somewhat of an outlier when looking at the entire breadth of work done on this topic.  In a more recent study performed based on the article published by Pedersen et al. using identical quantities of caffeine and carbohydrate, there was no difference in post-exercise blood glucose or insulin levels when comparing the group that received carbohydrates to the group that received carbohydrates + caffeine (11).  Furthermore, a study published in 2012 (perhaps the most complete study to date) which compared carbohydrates + caffeine, carbohydrates + protein, and carbohydrates alone, found that caffeine had no effect on muscle glycogen synthesis rates (12).  Furthermore, this study also investigated whether caffeine ingestion post-exercise increases intestinal sugar transport, and found that there was no change in the capacity of the intestines of their subjects (elite cyclists) to transport sugar (12).  
Indeed, these results are quite contradictory, and the positive results received much more attention from the media than did the negative/no effect results.  Perhaps one of the most overlooked differences between the 2012 study done by Beelen et al. and the 2008 Pedersen study, was the amount of carbohydrate supplied during the post-exercise window.  Study participants in Pedersen’s study received 1 gram of carbohydrates per kilogram of body weight per hour, while participants in the 2012 Beelen study received 1.2 grams of carbohydrates per kilogram body weight per hour.  This would indicate that athletes in the Pedersen study received a lower dosage of carbohydrate than those in the Beelen study.  Therefore, I believe this may be an explanation for the differences between these results.  
Further interpretation of these results can be that caffeine may enhance recovery when glucose (carbohydrates) are available in insufficient quantities.  I think that rarely do I consume the truly adequate amount of carbohydrates within the appropriate time frame to fully maximize glycogen synthesis (1.2 grams of carbohydrates per kilogram body weight per hour).  For me that would be approximately 80 grams of carbohydrates per hour.  Usually I grab a chocolate milk or Gatoraide that may contain roughly 60 grams of carbohydrates.  In this case, carbohydrates alone may be insufficient to fully maximize recovery, and coingestion of caffeine could have a beneficial effect.  However, if carbohydrates are available in sufficient quantities, I believe (IMHO) caffeine ingestion will NOT enhance recovery, and because of the known ways in which caffeine diminishes insulin action, there is too much risk it may hamper recovery.  
Overall, the rate at which glycogen is synthesized after a hard workout depends on a huge number of factors.  For example, length and duration of the workout, total hydration status (which can effect gastric emptying), the level of glycogen depletion, insulin sensitivity, as well as hormones, can all significantly effect rates of glycogen synthesis.  


Works Cited

1.         Howarth KR, Moreau NA, Phillips SM, Gibala MJ. Coingestion of protein with carbohydrate during recovery from endurance exercise stimulates skeletal muscle protein synthesis in humans. J Appl Physiol. 2009 Apr;106:1394-402.
2.         van Loon LJ, Saris WH, Kruijshoop M, Wagenmakers AJ. Maximizing postexercise muscle glycogen synthesis: carbohydrate supplementation and the application of amino acid or protein hydrolysate mixtures. Am J Clin Nutr. 2000 Jul;72:106-11.
3.         van Loon LJ, Saris WH, Verhagen H, Wagenmakers AJ. Plasma insulin responses after ingestion of different amino acid or protein mixtures with carbohydrate. Am J Clin Nutr. 2000 Jul;72:96-105.
4.         Berardi JM, Price TB, Noreen EE, Lemon PW. Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement. Med Sci Sports Exerc. 2006 Jun;38:1106-13.
5.         Ivy JL, Goforth HW, Jr., Damon BM, McCauley TR, Parsons EC, Price TB. Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. J Appl Physiol. 2002 Oct;93:1337-44.
6.         Thong FS, Derave W, Kiens B, Graham TE, Urso B, Wojtaszewski JF, Hansen BF, Richter EA. Caffeine-induced impairment of insulin action but not insulin signaling in human skeletal muscle is reduced by exercise. Diabetes. 2002 Mar;51:583-90.
7.         Robinson LE, Savani S, Battram DS, McLaren DH, Sathasivam P, Graham TE. Caffeine ingestion before an oral glucose tolerance test impairs blood glucose management in men with type 2 diabetes. J Nutr. 2004 Oct;134:2528-33.
8.         Yeo SE, Jentjens RL, Wallis GA, Jeukendrup AE. Caffeine increases exogenous carbohydrate oxidation during exercise. J Appl Physiol. 2005 Sep;99:844-50.
9.         Battram DS, Shearer J, Robinson D, Graham TE. Caffeine ingestion does not impede the resynthesis of proglycogen and macroglycogen after prolonged exercise and carbohydrate supplementation in humans. J Appl Physiol. 2004 Mar;96:943-50.
10.       Pedersen DJ, Lessard SJ, Coffey VG, Churchley EG, Wootton AM, Ng T, Watt MJ, Hawley JA. High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine. J Appl Physiol. 2008 Jul;105:7-13.
11.       Taylor C, Higham D, Close GL, Morton JP. The effect of adding caffeine to postexercise carbohydrate feeding on subsequent high-intensity interval-running capacity compared with carbohydrate alone. Int J Sport Nutr Exerc Metab.  Oct;21:410-6.
12.       Beelen M, Kranenburg J, Senden JM, Kuipers H, Loon LJ. Impact of caffeine and protein on postexercise muscle glycogen synthesis. Med Sci Sports Exerc.  Apr;44:692-700.

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