Is it possible to consume up to 120 g of carbohydrates (CHO) per hour of exercise? - Part 1

Yes, according to research into the effects of intakes greater than 90 g/h proposed in several recent scientific papers. Test protocol has been via strict dietary interventions, or through constant daily work with elite cyclists. Results have stored interest in the endurance community, and there are several takeaways that you can use as part of your training and racing fuelling strategy.

It's now accepted that intakes greater than 90 g/h are possible to assimilate, obviously always with adequate Digestive System Training. With these amounts of CHO we can improve performance, recovery, metabolic adaptations and, by rebound, eating behaviour (with everything that goes into this: body composition, healthy habits, metabolic health, immune system, etc.). Of the many performance metrics the INSCYD PPD TEST establishes, fat and CHO combustion rates are particularly important. We know all this due to the field work and monitoring that we have done throughout this time in professional cyclists of the World Tour and Pro Team category, elite athletes and, also (yes, because they also represent a tremendous source of knowledge), in amateur athletes. All of them with different objectives, physiological and metabolic characteristics, situations and problems, etc. Sparing glycogen with improved power/pace at FatMax, coupled with the ability to absorb more CHO is an essential factor in endurance athletes performance.

With that in mind, let's take a look at a recent article published in the Nutrients First Quartile Magazine on the Effects of Intake of 120 g/h of HC on Exercise-Induced Muscle Damage after a Mountain Marathon

You can find it by clicking here: Viribay A, Arribalzaga S, Mielgo-Ayuso J, Castañeda-Babarro A, Seco-Calvo J, Urdampilleta A. Effects of 120 g/h of Carbohydrate Intake during a Mountain Marathon on Exercise-Induced Muscle Damage in Elite Runners. Nutrients. 2020; 12(5): 1367.

What were the results?

Since it was not a laboratory test, but a Mountain Marathon (a race), with all that this entails. They analysed the impact of an intake of 60, 90 and 120 g/h of CHO during the Marathon on different pre- and post-exercise biochemical variables, as well as different functional and performance tests. Let's focus on muscle damage and the internal load of exercise, quantified using the TRIMP.

Fig 1:

As described in Fig 1, the results we find are very promising. In different enzymes related to muscle damage and catabolism, such as Creatine Kinase (CK), Lactate Dehydrogenase (LDH), Glutamic-Oxalacetic Transaminase (GOT), Creatinine and Urea, the response was very different , depending on the parameter, in the 3 main groups (LOW = 60 g/h, CON = 90 g/h and EXP = 120 g/h). Specifically, significant differences were found in the change in the concentration of some muscle enzymes in the blood (remember that they are characteristic of muscle metabolism and their presence in the blood increases when there is damage to the membrane). Among them, CK, GOT and LDH are, especially the first, the enzymes most related to muscle damage itself. In this sense, it has been described that its kinetics increases between 24-72 hours after a very intense exercise that generates the muscle damage I am referring to. However, on this occasion the research team measure these parameters 24 hours after the Marathon.

Likewise, the exercise load of the athletes showed significant differences during the Marathon in the EXP group compared to LOW and CON, suggesting that the internal impact of the marathon was significantly lower in the group that consumed 120 g/h.

What can this say?

These results offer new evidence on the potential effect of GH intake not only on the performance of a test, but also on the reduction of its impact and, therefore, on recovery after exercise, something that is totally determinant in consecutive tests such as a Tour de France. This study was carried out by trail runners, with a strong eccentric component and, therefore, with a high muscular load that we know generates muscle damage in a higher dimension than other sports without said impact, such as those mentioned (cycling and cross country skiing).

Test subjects had less muscular and metabolic damage after ingesting an amount of CHO greater than 90 g/h, reduced internal load of exercise, which suggests less psycho-physical and metabolic stress after ingesting 120g/hr. In short, a better tolerance to effort and a lower repercussion of effort during a Marathon, improving post event recovery.

Explaining these results is complicated, especially with a methodology in which they did not measure different key aspects such as glycogen content or specific neuromuscular fatigue. One could hypothesize different lines of justification. In the first place, muscle damage seems to be related, among other factors, to low-frequency fatigue. This, in turn, is dependent on adequate muscle function and, specifically, on muscle contraction, which also depends on the correct functioning of membrane excitability and Excitation-Contraction (EC) coupling. In this first process, it has been shown that Glucose supplementation seems to play a determining role. Likewise, in the adequate function of the EC coupling and, specifically, of the availability of intracellular Calcium through its regulation by the Sarcoplasmic Reticulum, Glycogen seems to have a fundamental central role. A 20-25% decrease in intermyofibrillar glycogen by can limit the output of calcium from the sarcoplasmic reticulum by up to 10-15%, reducing muscle function and its ability to contract. If this inability to contract can generate fatigue and, in turn, be related to muscle damage, it could be clear that Intermyofibrillar Glycogen can also regulate these effects.

Although it has been shown that, with GH supplementation, is not depleted to a lesser extent than with a placebo, significant differences have been documented at 4h post-exercise, suggesting that GH intake may not have direct effect on this sub-location of Glycogen, which will be emptied as a priority due to its relationship with muscle contraction, but in its recovery. This could, in turn, be explained by a greater availability of Intermyofibrillar and/or Subsarcolemmal Glycogen that could help supply energy to the intermyofibrillar location.

In turn, the recovery, measured with the performance the next day, could improve directly through this protocol. We currently know that, although glycogen could be resynthesized after exercise to basal levels in about 36 hours with a diet high in CH (>8 g/kg/day), when there is muscle damage, this resynthesis is very limited, requiring up to 10 days. to return to baseline levels.

To Summarise

New studies are needed to confirm what was found in this intervention. It is clear that the intake of 120 g/h is possible in a sport as demanding, (both physically and at the gastrointestinal level), as Trail Running. For this, however, the training of the digestive system is essential. For the endurance athlete the high intake of CHO during exercise as an effective methodology not only to improve sports performance, but also to improve short and long-term recovery, as well as to maintain the integrity of muscle structures, reducing the factors related to muscle damage and metabolic load, which in turn translate into chronic inflammation in athletes. Taking this into account, this strategy could also preserve the health of athletes in the short term.

References:

• Viribay A, Arribalzaga S, Mielgo-Ayuso J, Castañeda-Babarro A, Seco-Calvo J, Urdampilleta A. Effects of 120 g/h of Carbohydrate Intake during a Mountain Marathon on Exercise-Induced Muscle Damage in Elite Runners. Nutrients. 2020; 12(5): 1367.