Complexities of Carb Loading for Female Endurance Athletes

This Unknowntopic was especially interesting for me to explore academically, because I was researching this topic anyways to better understand how to carb load prior to my 50 mile race.  I had never done this before, and was nervous about trying something I had never tried before, for something so important.  However, I was armed with science!

Muscle glycogen is the preferred source of energy for an endurance event, and your body will utilize this first, before utilizing liver glycogen, or metabolizing glucose from carbohydrate ingestion during the race.  Your body converts glucose into glycogen which can be stored in the muscle, and is ideal for races more than 90 minutes in duration to improve performance.  While there are many studies that have been done on this topic, there are still unknowns.  For example, why do some carbohydrate loading regimes work better for some athletes?  Why does increased glycogen levels in the muscle not always translate into better performance? And the question to be examined more closely in this blog post – what does the research say about carb loading for women?

What Factors can Affect Muscle Glycogen Levels?
Part of the reason that there is not a direct correlation between increased muscle glycogen due to carbohydrate loading and performance, is that so many different factors can alter the outcome for why this may work for some athletes and not others.   Among these variants include the fitness and training of the athlete, the type of endurance event the athlete is prepping for, the diet consumed by the athlete prior to carb loading, the gender of the athlete, and the carbohydrate loading technique itself.  In addition, individual variants are common even when as many factors are controlled as possible, such as why such as some athletes increase muscle glycogen better than others using the same technique and when other factors are similar.  Initial research into carbohydrate loading advocated for a 6 day period before a race, with 3 days of glycogen depletion, followed by 3 days of taper and glycogen loading.  The theory behind this technique  it is thought that this was due to enhance muscle sensitivity to glycogen after being depleted, and that glycogen stores would be replenished at a higher concentration following depletion.  (Sedlock, D.A;  2008) Many endurance websites advocate for carb loading the night before, although research shows that  muscle glycogen can stay elevated for up to 5 days,  but optimally at 2-3 days can be assumed that it is at its peak.

Discrepancies in Research on Women and Carbohydrate Loading 
Research on women and carb loading effectiveness is not as supported as the results seen with the male athletes.  Some initial studies that began to study glycogen stores was a team led by M. A. Tarnopolsky in 1985 and they concluded that women were not able to increase their glycogen stores at similar levels as men, or even at all, in their article “Carbohydrate loading and metabolism during exercise in men and women” (Tarnopolsky et al., 1985)  However, more recent studies have criticized these earlier analysis and subsequent research by Walker et al. as flawed, in that the amount of carbohydrates the female athletes were ingesting were not at recommended levels, and in the subsequent study by Walker, the team did not measure men, despite making a comparative conclusion that women were not able to store glycogen in their muscles to the same extent.  The study by James et al. in 2001 titled “Muscle glycogen super compensation: absence of a gender-related difference” compared women and men, with women who were using birth control for at least two years, and all the athletes in their study consumed 9-12grams (on average 9.9 g CHO /kg), and found no discrepancy in percentage of glycogen storage, even accounting for different phases of women on their menstrual cycle, although they don’t discount that this may still play a factor in other athletes, as research indicates that during the luteal phase of the menstrual cycle, glycogen muscles stores can be up to 13% higher.  The authors of this study conclude: “Clearly, the view expressed in the scientific literature -Tarnopolsky et al. 1995; Walker et al. 2000) that exercise-trained women have a reduced capacity to accumulate supercompensation of muscle glycogen must be amended.” (James, et al. 2001) In addition, Tarnopolsky’s own subsequent research on muscle glycogen enhancements – though this study researched post exercise supplementation, but showed no gender differences, and they authors point out that this contradicted their previous hypothesis and more research should be done.  (Tarponsky, 1997).  Additionally, some journal articles summing up the literature on carb loading seem to erroneously report on conclusions researched about female athletes, which is common on running websites as well.  For example, a quote from an article by the University of Minnesota’s College of Education says: “Over time, men seem to increase their muscle glycogen storage much higher than women, whereas women increase their muscle glycogen about 13% when eating a high CHO diet for six days or more (Chen, 2008).” (Mueller, et al.) However, Chen’s article they cite is a study involving male athletes and does not conclude anything related to women’s muscle glycogen levels.

Conclusion
To conclude, carb loading can be a useful technique, and research indicates that when glycogen stores in the muscle are at maximal amount, this is likely to contribute to increased performance in an endurance event.   Women who utilize this technique should make sure to follow the proper guidelines and consume not less than 8.0 g·kg BM or even more – as some studies suggesting between 10-12g·kg BM to increase muscle glycogen stores to maximal capacity.   Women should be aware that there are conflicting studies about carb loading concerning female and male athletes, and that more research needs to be done on this topic.

Questions for Discussion 
What kinds of recommendations had you heard about carb loading for women that differed from men? Do you know of more recent research that supports either of these conclusions? What might be some strategies to push for including female athletes in more research studies?

References

Sedlock, D. A. (2008). The Latest on Carbohydrate Loading: A Practical Approach. Current Sports Medicine Reports7(4), 209–213. http://doi.org/10.1249/JSR.0b013e31817ef9cb

Tarnopolsky, M. A., Atkinson, S. A., Phillips, S. M., & Macdougall, J. D. (1995). Carbohydrate loading and metabolism during exercise in men and women. Journal of Applied Physiology (Bethesda, Md. : 1985)78(4), 1360–8.

Tarnopolsky, M. A., Bosman, M., Macdonald, J. R., Vandeputte, D., Martin, J., & Roy, B. D. (1997). Postexercise protein-carbohydrate and carbohydrate supplements increase muscle glycogen in men and women. Journal of Applied Physiology, 83(6), 1877–1883.

James, A., Lorraine, M., Cullen, D., Goodman, C., Dawson, B., Palmer, N., & Fournier, P. (2001). Muscle glycogen super compensation: absence of a gender-related difference. European Journal of Applied Physiology, 85(6), 533–538, pg. 537   http://doi.org/10.1007/s004210100499

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About Musings over Coffee

Fitness enthusiast. Love to travel, mess up recipes, ponder random things, get riled up about the news, all of which nearly always coinciding with one of my favorite things in the world: Coffee.
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