Intraworkout Carbohydrate Supplementation

If you have been around for a while, you have probably seen the trends of intraworkout carbohydrate supplements come and go, then come back again, disappear for a while and so on. One can make many an argument for intraworkout carbohydrate supplementation, some of which might include:

• Greater potential to accumulate volume,
• Greater strength,
• Greater muscle pumps,
• Lower perceived exertion,
• Greater resistance to fatigue,
• Greater enjoyment of training,
• More motivation,
• And less muscle protein breakdown.

 

… and so on. Today, we don’t want to get too caught up on hypothetical benefits, but rather, I want to provide the interested reader with a knowledge of the current evidence base relating to the use of carbohydrate supplements during resistance exercise.

According to both the 2008 and 2017 ISSN Position Stands on Nutrient Timing:

“Ingesting CHO alone or in combination with PRO during resistance exercise increases muscle glycogen, offsets muscle damage, and facilitates greater training adaptations after either acute or prolonged periods of supplementation with resistance training.”

Kerksick et al. 2008; Kerksick et al. 2017

We will discuss this again later on, but for now, I just want to plant it in your mind as an “opener” to what one might expect to gain from carbohydrate (CHO) supplementation. CHO supplementation does undoubtedly confer plenty of benefits to exercise performance, but a lot of these effects have been demonstrated in endurance exercise;

A 1999 study looking at the point at which highly trained cyclists reached volitional fatigue at 70% VO2max noted that the ingestion of an 8% CHO solution pre-exercise and every 15 mins throughout was associated with a 30% increase in time to exhaustion (+47 min) vs placebo (McConell et al. 1999).

However, what we must keep in mind is that this is endurance exercise, which is very different to resistance exercise. As I said, the majority of intraworkout CHO research has been based on endurance exercise, which makes sense due to its prolonged nature and high demand for energy/carbohydrate oxidation.

With this in mind, a 2000 study looked at the delivery of 1g/kg CHO pre- and 0.5g/kg CHO every 10 mins during the 40-minute resistance session, with the goal of determining changes in muscle glycogen content. This resulted in 49% less glycogen loss (Haff et al. 2000).

Now that we know this, we need to further explore what this actually means for training performance. It’s all very well to note a change in muscle glycogen content, but the question is “does that impact performance/adaptations?”.

 

Muscle Glycogen, Intraworkout Carbohydrate Supplementation & Resistance Training

Muscle glycogen can actually be stored in different locations, leading to different subtypes of muscle glycogen (Ørtenblad, Westerblad & Nielson 2013);

1. Subsarcolemmal (5-15%)
2. Intermyofibrillar (75%)
3. Intramyofibrillar (5%)

 

We needn’t dwell too much on that for now, but just be aware that glycogen can serve different functions depending on its location and this compartmentalisation is going to be different depending on fibre type too.

It has been demonstrated that resistance training can reduce muscle glycogen content by 24-40%, with greater decreases seen with higher repetition protocols (Knuiman et al. 2015). However, interestingly, a lot of the research looking at the resulting fatigue from low glycogen status in resistance training tends to look at this question from the perspective of pre-exercise carbohydrate restriction. I don’t think it is fair to consider those two things the same; glycogen depletion during exercise vs pre-exercise glycogen status achieved via nutritional changes.

There is mechanistic evidence suggesting that low glycogen availability did not attenuate the increases in ERK1/2 or p90 ribosomal S6 kinase phosphorylation (pathways involved in muscle growth) following 3 x 10 leg extensions with 70% 1RM (Creer et al. 1995). They did find an attenuated response in Akt phosphorylation and a non-significant attenuation of mTOR phosphorylation, both of which are also involved in the anabolic response. However, another study which demonstrated a similar attenuation of mTOR phosphorylation showed that this effect did not lead to a reduction in muscle protein synthesis (MPS), which is really what we wish to affect, as opposed to just mTOR in isolation (Camera et al. 1985). It is important to note, however, that there are methodological issues in that the study designs do not really reflect resistance training volumes used in the real world, which may be more likely to highlight the negative effects of low glycogen availability.

We do have limited evidence to suggest that carbohydrate ingestion prior to resistance exercise can enhance performance, but this effect was shown in the context of two sessions performed on the one day (with the performance boosted during the second session), but it would be an extrapolation to say that is purely a glycogen availability related effect, as we do have evidence from the same author to suggest that even in the presence of greater depletion of muscle glycogen (up to 49% less, as discussed previously, there are no differences in isokinetic muscle strength (Haff et al. 1999; Haff et al. 2000).

Furthermore, there is conflicting evidence that would suggest no benefit to CHO supplementation during resistance exercise, with one of the multiple studies assessing this effect during squats at 85% 1RM performed to volitional failure with 0.3g/kg CHO showing no significant increase in repetitions performed, volume load or total work (Kulik et al. 2008).

From a perceived exertion perspective, it has been noted that during a 2-hour session, supplementation with a 10ml/kg CHO solution (6% CHO) produced no attenuation of RPE, other than for whole body RPE during the back squat and upright row (Utter et al. 2005).

As a summary of this, the ISSN 2017 position stand suggests:

“Carbohydrate ingestion throughout resistance exercise (e.g., 3-6 sets of 8-12 repetition maximum [RM] using multiple exercises targeting all major muscle groups) has been shown to promote euglycemia and higher glycogen stores. Consuming carbohydrate solely or in combination with protein during resistance exercise increases muscle glycogen stores, ameliorates muscle damage, and facilitates greater acute and chronic training adaptations.”

However, I would just add that this conclusion seems to be somewhat confusing to me, as there did not seem to be evidence discussed in their position stand that would lead to such a clear-cut conclusion, although there is evidence to suggest that CHO and essential amino acid (EAA) supplementation combined can reduce markers of muscle damage and increase muscle cross-sectional area (CSA) (Bird et al. 2006). But, it remains to be elucidated whether this is an effect that could be attained purely through EAAs.

 

Intraworkout Carbohydrate Supplementation Pragmatic Considerations

It would be remiss of me to finish off this short article without running over some of the considerations beyond just the adaptations themselves.

Firstly, for a lot of you, dietary adherence is probably one of your biggest barriers to progress, especially if you are dieting. Consumption of intraworkout carbohydrate drinks can have two major downsides for someone in a caloric deficit:

1. Satiety – You are very unlikely to be as full after a liquid carbohydrate source vs the same amount of carbohydrates from oats, potatoes or fruit.

2. Nutrition – Carbohydrate powders are essentially just carbohydrates. We already know that many popular diets can leave one with inadequate micronutrition, so it’s probably not the greatest idea to exacerbate that by consuming a big chunk of your carbohydrates from a source void of vitamins, minerals, phytonutrients and other bioactive compounds.

Personally, my recommendation would be to simply give it a try yourself. Run the experiment. Realistically, it probably only matters to you if it affects the results that you or your clients get from training, so while the research might point you in the right direction, it is useless if the effects do not play out in the real world. If I was you, I would simply supplement with 40-60g CHO for 12 weeks and see if it impacts your strength, accumulation of volume, perceived exertion, perceived recovery, muscle soreness, motivation to train, endurance during the session etc.. If you notice a positive effect, then why not keep going with it. On the other hand, if you are concerned that you are missing out on a very meaningful performance boost by not having carbohydrates during your workout, I wouldn’t be too worried.

Just remember that while intraworkout carbohydrate supplementation may be glycogen-sparing, it’s important to keep in mind that it is your nutrition over a daily/weekly period that will be the ultimate determinant of glycogen levels/replenishment. Therefore, comments noted from research regarding glycogen-sparing effects need to be viewed in the context of a real-world setting; if someone is consuming 400g of carbohydrates daily, they are going to have greater glycogen levels than someone who consumes 200g, regardless of whether they use intraworkout carbohydrate supplementation or not. So as always, keep this information in context!

If you don’t have your diet set up correctly, then it really does not make sense to spend your time focusing on intraworkout carbohydrate supplementation. If you need specific help with your diet, then it may make sense for you to reach out and enquire about online coaching. If you want to learn how to coach people to better nutrition, then consider becoming a certified nutrition coach!