|Compared to liquid beverages, gels have the advantage of causing lower GI stress, when significant quantities of CHOs are consumed during exercise. Bars, can be held in the cheek pouch and chewed during critical phases of a race.|
As a seasoned student of the SuppVersity you will know that certain paradox involved with regard to the duration / type of exercise. Short exercise durations, for example, shouldn't require large CHO boluses, long duration exercise, on the other hand, is fueled mostly by fat - so why should you supplement with carbohydrates, anyway?
I promise to answer this and other questions in the following paragraphs, but before I do so, I would like to point out that there is as of now no evidence that the much-praised "fat adaptation" increases the exercise performance to an "Olympia" level. Carbohydrate supplements, on the other hand, are still part of the regular supplementation regimen for the 99% of the top athletes.
That being said, the human physiology dictates that the use of carbohydrate supplements during aerobic workouts that last less than 60 minutes is useless, because muscle glycogen is generally not limiting to performance when exercise durations are less than ~60 minutes.
It should not work for short duration exercise, but it still does
Interestingly, 16 out of 23 studies, Trent Stellingwerff and Gregory R. Cox from the Canadian Sport Institute-Pacific and the Australian Institute of Sport reviewed for their recent paper in Applied Physiology have found that carbohydrate supplementation and/or oral (mouth) exposure to carbohydrate can improve performance of tasks less than 1 hour in duration:
This effect of CHO mouth-washing to improve performance in events from 30-60min has now been replicated in several other performance studies (10 of 13 studies) using both cycling and running interventions and with both sweet (sucrose) and non-sweet (maltodextrin) caloric CHO sources,as compared to 5 non-caloric artificial sweetener placebo trials showing no performance enhancing effects.
"In 2004 a seminal paper was published showing that a carbohydrate mouth-wash (swirling 25ml of a 6% CHO beverage (only ~1.5g of CHO in 25ml [6.4% maltodextrin solution (CHO)]) around in the mouth for ~10 sec, every 7.5min) significantly improved time trial (TT) performance [in seven male and two female endurance cyclists] by ~3% (Carter et al. 2004a)." (Stellingwerff & Cox. 2014)
You won't fully deplete your muscular glyocogen levels
during short duration resistance training (Haff. 2003)
Studies evaluating the effects on perceived exertion (Fares et al. 2011) found similar benefits all of which support the idea that the effect does not occur in the musculature, but rather in the head.
"All these findings have been mechanistically supported with a functional magnetic resonance brain imaging study showing that CHO mouth-washing from both sweet tasting glucose and non-sweet maltodextrin can stimulate the brain areas of the insula/frontal operculum, orbitofrontal cortex and striatum, which are involved with brain centers responsible for reward and motor control (Chambers et al. 2009). Interestingly, if the mouth (oral receptors) and GI tract is by-passed by CHO infusion straight into the blood stream then 1h cycling TT performance was unaltered as compared to no CHO supplementation (Carter et al. 2004b)." (Stellingwerff & Cox. 2014)
Figure 1: Hard to believe, but true - In 2010 Pottier et al. observed that CHO mouth-rinsing, but not CHO ingestion increases the 1h high intensity time-trial performance in trained subjects.
So what do you do to benefit during short-duration (<60) minute workouts? To benefit during short duration exercise exercise (<1h) ~1.5g of high GI carbohydrates (30g/h total = max) consumed or used as a mouth-wash in servings of 25ml for 5 to 10 sec every 8 to 10 min of exercise will do the trick. Since it can be difficult to actually drink / mouth-wash with CHO during critical phases of the race, Stellingwerff and Cox suggest "placing a sports confectionary in the cheek cavity" as a more practical option for some athletes.It should be obvious that the physiological, or rater intra-muscular benefits of carbohydrate supplements increases with the exercise duration.
CHO supplementation during exercise that lasts 60 minutes or longer
In view of the fact that it is 100% logical and well established by studies by Coyle et al. (Coyle 1992a; Coyle 1992b) that the intake of carbohydrate (glucose alone, and glucose + fructose blends) can significantly improve prolonged endurance capacity and performance (>60min of exercise (Jeukendrup 2010)).
|Figure 2: Overview of the performance increases in the 50 studies Stellingwerff & Cox reviewed (2014)|
Glucose + fructose - the combination advantage
As a SuppVersity reader you've previously heard about the benefits of combining glucose and fructose in your intra-workout beverage. It is thus only logical that most commercially available formulas are mixtures glucose + fructose (GLU:FRU) or maltodextrin + fructose - so-called "multi-transportable CHOs". The advantage of using both glucose and fructose is that the carbohydrates will be absorbed via SGLT1 and GLUT5 intestinal transporters.
|Comparison of single vs. mutliple CHO sources (CHO, carbohydrate; FRU, fruc- tose; GLU, glucose; Perf, performance; P, placebo; TT, time-trial; TTE, time to exhaustion; Signif, Significant; SUC, sucrose; Stellingwerff & Cox. 2014)|
|Specifically during long(er) duration exercise, when the carbohydrate consumption can exceed 60g/h there is a significant performance increase with multi- vs. single source carbohydrate supplements (Stellingwerff & Cox. 2014)|
Now an increase in carbohydrate oxidation alone does not sound like something you would aim for as an endurance athlete. In practice, increases in carbohydrate oxidation have yet been shown to increase the performance during prolonged exercise bouts compared to isocaloric glucose-only beverages. (Currell et al. 2008; Triplett et al. 2010; O'Brien et al. 2011; O'Brien et al. 2013).
So how much does it take during long(er) 1-2h+ exercise: You've already learned that glucose + fructose mixtures should be preferred to carbohydrate supplements with only one type of CHO. While 30-60g/h, which is the amount of carbohydrates that is currently suggested by the American College of Sport Medicine (ACSM 2000; Sawka, Burke et al. 2007) appears to be be enough for exercise durations ranging from 60-120 minutes, recent evidence suggests that hard exercise bouts which last longer than 2h require up tp 90g/h or carbohydrate solutions with a CHO content of >8%.Needless to say that there is still research to be done with respect to individual influencing variables of carbohydrate requirements. The currently available evidence, for example, is largely based on results from runners and cyclists. Two other factors / issues that come to mind are...
- the dose-response relationship, which appears to be capped at 75g/h - at least according to a large-scale multi-center study by Smith et al. (Smith. 2013) who found that their subjects, endurance trained cyclists or triathletes experienced significant performance increases, with increasing amounts of carbohydrates (0, 10, 20, 30, 40, 50,
60, 70, 80, 90, 100, 110 and 120g of CHO/h) during a 2h constant load ride.
The optimal amount for performance (+4.7%) was 78g/h, with a range of 68 to 88g/h. However, even at 10g/h, a 1.0% increase in performance was observed, showing even a small amount of carbohydrate has the potential to positively impact performance.
- the optimal mix of glucose, dextrose, fructose, maltodextrin or other "special" carbohydrates - needless to say that waxy maize, hydroxypropyl distarches (learn more) or the expensive fast absorbing highly insulinogenic patented carbohydrate source Vitargo come to mind, when we are talking about finding the optimal mix of different carbohydrate sources - a mix, by the way, of which you can safely assume that it will differ according to the physiological demands of the workout and the exercise duration.
One thing we shouldn't forget, though, is that next to optimal performance, optimal GI tolerance, i.e. the absence of bloating, diarrhea & co would be an important criteria the "optimal" carbohydrate blend would have to meet.
Figure 4: CHO suppl. ameliorates testosterone reductions in 800m runners (de Sousa. 2010)
- Carter, J., Jeukendrup, A.E., Mundel, T., and Jones, D.A. (2003). Carbohydrate supplementation improves moderate and high-intensity exercise in the heat. Pflügers Archiv : European journal of physiology446: 211-9.
- Carter, J.M., Jeukendrup, A.E., and Jones, D.A. (2004a). The effect of carbohydrate mouth rinse on 1-h cycle time trial performance. Medicine and science in sports and exercise36: 2107-11.
- Carter, J.M., Jeukendrup, A.E., Mann, C.H., and Jones, D.A. (2004b). The effect of glucose infusion on glucose kinetics during a 1-h time trial. Medicine and science in sports and exercise36: 1543-50.
- Chambers, E.S., Bridge, M.W., and Jones, D.A. (2009). Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity. The Journal of physiology587: 1779-94.
- de Sousa, Maysa Vieira, et al. (2010). Effects of carbohydrate supplementation on competitive runners undergoing overload training followed by a session of intermittent exercise." European journal of applied physiology 109.3: 507-516.
- Fares, E.J. and Kayser, B. (2011). Carbohydrate mouthrinse effects on exercise capacity in pre- and postprandial States. J Nutr Metab2011: 385962.
- Pottier, Andries, et al. (2010). Mouth rinse but not ingestion of a carbohydrate solution improves 1‐h cycle time trial performance" Scandinavian journal of medicine & science in sports 20.1: 105-111.
- Sawka, M.N., Burke, L.M., Eichner, E.R., Maughan, R.J., Montain, S.J., and Stachenfeld, N.S. (2007). American College of Sports Medicine position stand. Exerciseand fluid replacement. Medicine and science in sports and exercise39: 377-90.
- Smith, JohnEric W., et al. (2013). Curvilinear dose-response relationship of carbohydrate (0-120 g/h) and performance." Med Sci Sports Exerc 45.2: 336-341.
- Stellingwerff, T., & Cox, G. R. (2014). Systematic Review: Carbohydrate Supplementation on Exercise Performance or Capacity of Varying Durations. Applied Physiology, Nutrition, and Metabolism (2014). Ahead of Print.
- Zhao, Can, et al. (2014). Effects of carbohydrate supplements on exercise-induced menstrual dysfunction and ovarian subcellular structural changes in rats." Journal of Sport and Health Science 3.3: 189-195.