How To Train With Restricted Carbohydrate Availability (RCA)

The previous article covered restricting carbohydrate availability (RCA) as a means to become more efficient at using fat while cycling.

This can be beneficial for long races/events, by delaying the depletion of carbohydrate (‘glycogen’) stores, which can be exhausted in as little as 1.5H. A further, lesser-known benefit is that it can also help to improve the lactate threshold (and similarly your threshold power/FTP/Critical Power) by reducing production of lactate (and associated fatiguing metabolites) at a given power output. 

This article addresses the practical side of RCA training: how to do it, when to do it and what to avoid.

How to use RCA

So, there are three main ways to do this:

• The ‘overnight fasting’ method involves training in the morning, before you have eaten or drunk anything that contains any carbohydrates. Liver glycogen stores and blood glucose levels drop gradually overnight, and will usually be below baseline when beginning training in the morning. 

• The ‘twice daily’ method involves training twice in one day, consuming minimal carbohydrates between sessions. The first session depletes muscle glycogen stores, meaning the second session is conducted with lowered muscle glycogen levels.

• A combination of the first two methods, which we’ll call the ‘sleep low’ strategy, where the evening before the RCA session, a high-intensity training session is completed which depletes muscle glycogen stores. Carbohydrate intake is then restricted after that session meaning these stores are not replenished. The RCA session is then conducted in the morning after an overnight fast, meaning the RCA session is started with low muscle and liver glycogen and blood glucose.

  Possibly an obvious point, but in all cases, you should avoid eating or drinking carbohydrates during the RCA session.

The evidence supporting the second and third methods is stronger than the evidence supporting the ‘overnight fasting’ method. Nevertheless, there is research that does suggest that overnight fasting might be beneficial over the longer term (1,2), and many athletes and coaches do use this type of RCA training (either intentionally, or accidentally!) with seemingly good results. Often the science follows the practice, so when you see a lot of top coaches and athletes doing something, it can be a sign that it works (although not always of course!).

In our view, if you’re really wanting to get the biggest benefits possible from RCA training, we’d recommend either the twice daily or the sleep low strategies. However, if you happen to be training in the morning, and you don’t mind doing the session fasted, then our view is ‘why not’?! We’ve never seen any evidence that the overnight fasting method will be detrimental (provided you combine this with the right kind of training session and refuel well afterwards - see below). So if it’s convenient to do, then it might be worth including within your training. That said, if you really dislike training in the morning before breakfast, then the evidence is probably not strong enough to warrant using the overnight fasted method.

Does it matter what kind of training session I do?

The short answer to this is YES!

Nutrition and training are two sides of the same coin. Just in the same way you need to pick the right training intensity to stimulate certain adaptations, you also need to select the right substrate availability (i.e. nutrition) in order for those adaptations to be optimally stimulated.

Much of the early research actually found no performance benefits from RCA training (3,4). However, that appears to have been because these studies asked participants to complete all training sessions with RCA, including interval sessions. Intervals are almost entirely fuelled by carbohydrates, and in these studies, participants often could not complete intervals properly with RCA, potentially explaining the lack of performance benefit. [Note, this is also a reason why you shouldn’t chronically restrict your daily carbohydrate intake by following e.g. a high-fat, low-carb diet].

More recent research has looked at using RCA only with lower intensity training (zones 1-3 within the classic Coggan zones), with positive effects (5-7).  These training zones stimulate adaptations that are very closely aligned with those from RCA training. Furthermore, given that these zones are relatively low-intensity, they can be completed to a high quality despite having RCA.

So, in short, RCA training should only be used with low intensity training, where the objective is to improve aerobic capacity and fat oxidation/lactate threshold.

How long to train with RCA?

This really depends on your existing ability to use fats as fuel, and how hard you are riding. I’d recommend starting conservatively, perhaps beginning with 30-60 mins, and build up from there depending on how you feel.

Some people are able to train for many hours without eating. However, I wouldn’t advocate doing RCA training for longer than 3 hours, because this will impact your total daily energy and carbohydrate intake (with there being fewer hours in the day when you can actually eat!). This may in turn impact subsequent training in the week and increase your risk of illness and injury, if you are under-fuelled.

RCA training frequency

While there’s no scientific research directly looking at this, most researchers and coaches agree that it shouldn’t be performed more than twice per week. 

Similar to my point above, that’s because doing more than two sessions per week might lead to insufficient total energy and carbohydrate intake over the course of the day or week, which might impact your ability to complete subsequent training, and increase your risk of illness or injury.

Does carb-loading before a race mitigate the impacts of RCA training?

No, once you have trained for a consistent period of time with RCA, you should be better adapted at using fats for fuel, even when you are well fuelled with carbohydrates.

Bonus tips for optimising RCA Training

1. Take a snack or energy drink with you… So you can refuel if you need to and/or want to ride for longer.

2. Have a caffeinated drink before heading out… Training with RCA can feel harder than training with high carbohydrate availability. Having caffeine around 30-60mins before can make the session feel a little easier. Just make sure you avoid sugary drinks, or adding sugar or milk to tea/coffee. Sugar-free sweetener and unsweetened plant milks like soya or almond milk, which contain minimal carbohydrates, can be substituted instead.

3. To improve muscular endurance and optimally boost lactate threshold, try adding some low-cadence zone 3 intervals to your RCA session to promote aerobic adaptations within Type IIa muscle fibres… These efforts, being at a low cadence, require the muscles to produce high forces (or torques), which increases the activation of Type IIa fibres. These fibres tend to favour carbohydrates for fuel, so doing these low-cadence efforts with RCA will help increase aerobic efficiency in these fibres specifically.

4. Avoid RCA during a recovery ride... That’s because the goal of a recovery session is to promote recovery. These sessions should stimulate blood flow to the muscles, without adding any additional training stress or fatigue. That’s in conflict with RCA training, which adds an additional training stress.

5. Avoid RCA if you are ill… That’s because limiting carbohydrates can compromise your immune system, and might mean it takes longer for your illness to shift.

6. Make sure you refuel well afterwards… Training fasted can acutely induce a fairly large energy deficit, where you are burning considerably more calories than you are consuming, particularly if your ride is quite long. However, this is something we generally want to avoid over the longer term (e.g. over a period of several days), and we want to ensure you are taking on enough fuel to adapt to the training, and to perform your high-intensity training sessions well. We therefore recommend making sure you consume a meal or snack that’s high in carbohydrates within 30-minutes of finishing your RCA ride. This is the period of time in which your muscles will be most receptive carbohydrates, helping to replenish your muscle glycogen stores more effectively.

References

1) Van Proeyen, K., Szlufcik, K., Nielens, H., Ramaekers, M., & Hespel, P. (2011). Beneficial metabolic adaptations due to endurance exercise training in the fasted state. Journal of applied physiology, 110(1), 236-245.

2) Aird, T. P., Davies, R. W., & Carson, B. P. (2018). Effects of fasted vs fed‐state exercise on performance and post‐exercise metabolism: A systematic review and meta‐analysis. Scandinavian journal of medicine & science in sports, 28(5), 1476-1493.

3)    Yeo, W. K., Paton, C. D., Garnham, A. P., Burke, L. M., Carey, A. L., & Hawley, J. A. (2008). Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. Journal of Applied Physiology, 105(5), 1462-1470.

4)    Hulston, C. J., Venables, M. C., Mann, C. H., Martin, C., Philp, A., Baar, K., & Jeukendrup, A. E. (2010). Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Medicine & Science in Sports & Exercise, 42(11), 2046-2055.

5)    Lane, S. C., Camera, D. M., Lassiter, D. G., Areta, J. L., Bird, S. R., Yeo, W. K., ... & Hawley, J. A. (2015). Effects of sleeping with reduced carbohydrate availability on acute training responses. Journal of Applied Physiology, 119(6), 643-655.

6)    Marquet, L. A., Hausswirth, C., Molle, O., Hawley, J. A., Burke, L. M., Tiollier, E., & Brisswalter, J. (2016). Periodization of carbohydrate intake: short-term effect on performance. Nutrients, 8(12), 755.

7)    Marquet, L. A., Brisswalter, J., Louis, J., Tiollier, E., Burke, L. M., Hawley, J. A., & Hausswirth, C. (2016). Enhanced endurance performance by periodization of carbohydrate intake: “sleep low” strategy. Medicine & Science in Sports & Exercise, 48(4), 663-672.

8) Bennett, S., Tiollier, E., Brocherie, F., Owens, D. J., Morton, J. P., & Louis, J. (2021). Three weeks of a home-based “sleep low-train low” intervention improves functional threshold power in trained cyclists: A feasibility study. PLoS One, 16(12), e0260959.