Low(er) Carb Crossfitters May be Missing Out | 11.1% vs. 4% Rep Increase With 6-8g/kg CHO in 12-Min Rohoi Benchmark

If there's one thing all crossfit WODs have in common it's their profoundly anaerobic, meaning glucose burning, nature

I don't care if you love or hate Crossfit. Why's that? "Liking" has nothing to do with science and science tells us that CrossFit is a highly demanding continuously glycogenolytic workout. In other words: while you will be burning fat, as well, the Crossfit workouts are mainly powered by glucose / glycogen.

Accordingly, scientists from the University of New Mexico, the California State and the Kennesaw State University speculated that with glucose / glycogen being the main energy resource crossfitters are using, adequate (or high) carbohydrate intakes may be "even more crucial to performance" for crossfitters than it is for other athletes.
Now, it is one thing to be able to show that an acute failure of glycogen repletion will acutely impair your performance. performance. It is a whole different thing, however, to assess the long(er)-term effect of the relatively low carbohydrate intake that's still prevalent in the world of crossfitters; a study addressing metabolic and performance variables following CHO manipulation during a CrossFit workout; a study as the one Escobar et al. have recently conducted.

In their 9-day experiment, the scientists investigated the effect of three consecutive days of high CHO intake (6-8 g/kg/day) during a period of training on CrossFit performance and corresponding metabolically-related variables in strength-trained individuals who have previously maintained a moderately-low CHO intake <6 g/kg/d.

The 12-minute Rahoi workout is used as a performance benchmark in the CrossFit community. It involves doing as many  rounds of the above box jump, thruster and bar facing burpee cycle (img from ifailedfran.com)

"CrossFit performance was measured in repetitions completed during a 12 minute CrossFit workout (Rahoi) performed on days 1, 5, and 9. From days 6- 8, the CHO group increased CHO intake from < 6 g/kg/day to 6-8 g/kg/day whereas the C group maintained their current intake of < 6 g/kg/day.

Subjects performed prescribed CrossFit workouts on days 6 and 7, followed by a day of rest prior to the final performance test on day 9. The present design was aimed to mimic a mid CrossFit-training period thereby investigating the effect of CHO intake and performance amidst a period of training.

During performance tests (days 1, 5, 9), in addition to repetitions completed, oxygen consumption (VO2), respiratory exchange ratio (RER), and blood lactate (BL) were measured" (Escobar. 2016).

As the authors point out, there was a main effect for time, meaning that both groups saw an increase in repetitions completed.
The data in Figure 1 tells you, however, "a more notable change was observed in the CHO group (+15.22; +10.9%) vs. that in the baseline sessions" (Escobar. 2016). That the difference didn't reach statistical significance is, as the scientists point out, possibly due to the large standard deviations and the small effect size (.354) in this 9-day study (you cannot expect a huge adaptational response within only what effectively were only 3 days, i.e. days 6-9 during which the subjects consumed their extra-carbs while training on day 6 and 7, rest on day 8 and the re-test on day 9).

Figure 1: Pre- vs. post changes in reps performed, Mean VO2 and respiratory exchange ratio (Escobar. 2016).

Needless to say that we cannot tell if the additional reps will translate to a more rapid adaptational response in form of strength or size gains. What is quite interesting, though, is that the high-CHO group improved their intra-workout fat burning rate (as evidenced by a lower RER) more than the subjects on the moderate carbohydrate diets. Diets of which common wisdom would tell you that their <6g/kg body weight CHO content should favor fatty acid oxidation compared to the 6-8g/kg high carbohydrate intake - that's also interesting, because, in a dietary isocaloric scenario, doing more reps and thus burning more calories at a slightly lower RER should promote not (as many of you  may fear) reduce fat loss. Eventually, future studies will have to show, though, whether this is "just" a transient performance increase due to better stocked glycogen stores or a training advantage that could give you the adaptational edge that makes the difference between "making gains" and "making outstanding gains" and thus, eventually, amateur- vs. pro-performance.

The number of studies on CrossFit has increased, but it doesn't match the 15-20x increase in interest Google Trends recorded from 2007 to today; below you will find a brief overview of recent and not so recent study results.

Speaking of gains, can you even make gains on CrossFit or will you just injure yourself? Well, even though the number of studies on CrossFit has been continuously increasing over the decade, what we can tell for sure is this:

• CrossFit-based high-intensity power training improves maximal aerobic fitness and body composition -- in Smith et al. 2013, for example, the male and female subjects lost 4% body fat (from 22%) and 3% (from 26%), respectively, while significantly improving their VO2max - irrespective of their baseline fitness level
• CrossFit workouts are injury-prone - not more injury prone than O-lifting, though -- that's at least what Hak et al. (2013) found; in their 2013 paper they report an injury rate of 3.1 per 1000 hours trained [shoulder (1.18 per 1000 hours training | Summitt. 2016) and spine injuries predominate] - a result that is "similar to that reported in the literature for sports such as Olympic weight-lifting, power-lifting and gymnastics [but] lower than competitive contact sports such as rugby union and rugby league" (Hak. 2013); more recently, Weisenthal, et al. (2014) reported injury rates of approximately 20%, with men being more prone to injuries than women (leave your ego at the door, boys!)
• CrossFit is so successful, because it's motivating -- Katie Heinrich et al. (2014) confirmed that two years ago in a study that compared a CrossFit™ workout to a classic aerobic + resistance training combination and found the former workout to keep people on track, i.e. they maintained their exercise enjoyment and were more likely to intend to continue after the 8-week intervention; and, more recently, Eather et al. (2016) showed that teens love it (rather the teen version), too - a satisfaction score ranging from 4.2 to 4.6 out of 5 points ain't bad, for sure
• CrossFit is not more taxing than running -- at least if we measure "taxing" by the oxidative stress that's generated during a workout, a measure of which Kliszczewicz, et al. (2015) have recently shown that they are similar for treadmill running and crossfitting

Now, this is not a CrossFit advertisment-article, so, I would like to remind you that, even if you're not CrossFitting, an increased or at least adequate carbohydrate intake will have scientifically proven benefits for athletes from various other sports - with the "optimal" intake depending on the pecularities of the sports / training and individual (Jeukendrup. 2014; Pöchmüller. 2016).
References:

• Eather, Narelle, Philip James Morgan, and David Revalds Lubans. "Improving health-related fitness in adolescents: the CrossFit Teens™ randomised controlled trial." Journal of sports sciences 34.3 (2016): 209-223.
• Escobar, Kurt A., Jacobo Morales, and Trisha A. VanDusseldorp. "The Effect of a Moderately-low and High Carbohydrate Intake on Crossfit Performance." International Journal of Exercise Science 9.4 (2016): 8.
• Hak, Paul Taro, Emil Hodzovic, and Ben Hickey. "The nature and prevalence of injury during CrossFit training." Journal of strength and conditioning research/National Strength & Conditioning Association (2013).
• Heinrich, Katie M., et al. "High-intensity compared to moderate-intensity training for exercise initiation, enjoyment, adherence, and intentions: an intervention study." BMC Public Health 14.1 (2014): 1.
• Jeukendrup, Asker. "A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Medicine 44.1 (2014): 25-33.
• Kliszczewicz, Brian, et al. "Acute Exercise and Oxidative Stress: CrossFit™ vs. Treadmill Bout." Journal of human kinetics 47.1 (2015): 81-90.
• Pöchmüller, Martin, et al. "A systematic review and meta-analysis of carbohydrate benefits associated with randomized controlled competition-based performance trials." Journal of the International Society of Sports Nutrition 13.1 (2016): 27.
• Smith, Michael M., et al. "Crossfit-based high-intensity power training improves maximal aerobic fitness and body composition." The Journal of Strength & Conditioning Research 27.11 (2013): 3159-3172.
• Summitt, Ryan J., et al. "Shoulder injuries in individuals who participate in crossfit training." Sports Health: A Multidisciplinary Approach (2016): 1941738116666073.
• Weisenthal, Benjamin M., et al. "Injury rate and patterns among CrossFit athletes." Orthopaedic journal of sports medicine 2.4 (2014): 2325967114531177.