The main point of this blog-post is to bring the attention to the nutritional strategies for purposefully training with low muscle glycogen through altering the availability of carbohydrates in the diet and clarify important differences with LCHF/ketogenic diets (Figure 1).
Figure 1. Training with low muscle glycogen and LCHF/ketogenic diets are not the same.
What is skeletal muscle glycogen?
Skeletal muscle glycogen is the form of carbohydrate storage in skeletal muscles and it is the main fuel source for ‘fast’, high quality, energy production for muscle contraction. Muscle glycogen is very limited when compared to the body fat stores and used quickly during moderate and high intensity exercise.
Skeletal muscle glycogen a dual role: a source of energy and a switch for muscle adaptation.
While the muscle glycogen stores allow for sustained high intensity exercise they don’t only work as a fuel source. When this ‘fuel tank’ is running low, it triggers signals to drive specific metabolic adaptations that are beneficial for endurance capacity (Figure 2).
Figure 2. Very simplified and exaggerated schematic of the relationship between the muscle glycogen content and muscle metabolic response increasing adaptations for endurance exercise. The chronic/intermittent lower muscle glycogen content would be reflected in increased mitochondrial content in muscle (and a plethora of other adaptations). For these adaptations to take place, weeks of months of repeated treatment are needed.
This means that after a glycogen depleting session, not replenishing with carbohydrates can have beneficial metabolic effects through increasing the time during which the muscle is adapting to a given training session. If done repeatedly over time this intervention can be reflected in enhanced muscular metabolic adaptations, that include -but are not limited to- increased markers of mitochondrial content and fat utilisation.
This idea, present in the muscle physiology literature for some years, was pushed through to the sports performance world through a very elegant study by Bengt Saltin’s group published in 2006 (1). Subsequently others and us (3, 4, 6) have done further research showing that indeed, there are enhanced metabolic adaptations to these type of interventions in humans.
Importantly, a recent study in competitive triathletes have shown that a specific way of training with reduced muscle glycogen in selected sessions, can in fact enhance adaptation to exercise and improve endurance performance (5). While there is still a lot of work to be done in this area, the current findings point towards them being effective interventions (7).
So, should you not be having carbohydrates after your hard (or moderate) training sessions? Is then LCHF or ketogenic diets the way to go?
First of all it is important to remark that there should be no ‘absolutes’ when it comes to nutritional interventions. A balanced approach that contemplates each individual’s situation and aims, is essential. Moreover, it is important to highlight that what it can be beneficial for certain periods of training (e.g. involving long easy training sessions), might not be the best for others (e.g. involving high intensity intervals), or what can work during a training period might not be the best approach for competition. Like training load and intensity, nutrition should be periodised to match the metabolic demands of exercise in specific phases of training.
What it also essential to consider is that for optimal performance all energetic systems maximising metabolic flexibility (the capacity to switch between the use of carbohydrate and fat) is probably the most important factor. Training with selected session on a stat of low muscle glycogen content does not equal to being chronically exposed to low carbohydrate availability. Sticking to low carbohydrate, high-fat diets, can impair the capacity of doing high intensity work and have a harmful effect on performance (2, 8). While this has not been directly tested for the case of ketogenic diets (or similar), these simply represent an extreme of high-fat diets. Therefore, while holding back from carbs after training can be beneficial, it should be balanced out with more traditional interventions as per the traditional sports nutrition guidelines. You probably don’t want to miss that break-away, get dropped on the climb, or lose on the final sprint!
What is the best way to try to do these type of interventions? When you should someone try to do it?
While these interventions have great potential, they pose risks if not done properly. For an intervention to be successful it is crucial to know the macronutrient (CHO, protein and fat) and the energy content of the food to be ingested as well as the right timing of ingestion. The plan should also be synchronised with the specific training plan of each athlete. Importantly care should be taken that energy intake is not be reduced because of changing the macronutrient composition intake or timing of food ingestion.
This all requires a great deal of knowledge of sports nutrition. Provided its complexity, it is probably advisable to only try to do this treatment guided by a trained, experienced, up-to-date (and forward thinking!) sports dietician only when reaching a very high level of competition and all the basics of training and nutrition are covered. This can take years of dedication!
Be wise and think of the things that give you the biggest amount in return for each unit of energy, time and resources spent. Training purposefully with low muscle glycogen is probably not on top of the list.
In conclusion, training purposefully with low muscle glycogen content it is not the same as LCHF/ketogenic diets. This type of interventions have a great potential for competitive athletes but they can be complex, involve risks and require a vast knowledge of sports nutrition. To ensure effectiveness of these treatments, all the basics of training and nutrition should be covered first. These treatments should be attempted together with supervision of a trained, forward-thinking and up to date sports dietician or equivalent professional.
1. Hansen AK, Fischer CP, Plomgaard P, Andersen JL, Saltin B, and Pedersen BK. Skeletal muscle adaptation: training twice every second day vs. training once daily. Journal of Applied Physiology 98: 93-99, 2005.
2. Havemann L, West S, Goedecke J, Macdonald I, Gibson ASC, Noakes T, and Lambert E. Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance. Journal of Applied Physiology 100: 194-202, 2006.
3. Hawley JA, and Morton JP. Ramping up the signal: promoting endurance training adaptation in skeletal muscle by nutritional manipulation. Clinical and Experimental Pharmacology and Physiology 41: 608-613, 2014.
4. Lane SC, Camera DM, Lassiter DG, Areta JL, Bird SR, Yeo WK, Jeacocke NA, Krook A, Zierath JR, and Burke LM. Effects of sleeping with reduced carbohydrate availability on acute training responses. Journal of Applied Physiology 119: 643-655, 2015.
5. Marquet L-A, Brisswalter J, Louis J, Tiollier E, Burke LM, Hawley JA, and Hausswirth C. Enhanced Endurance Performance by Periodization of CHO Intake:" Sleep Low" Strategy. Medicine and science in sports and exercise 2016.
6. Psilander N, Frank P, Flockhart M, and Sahlin K. Exercise with low glycogen increases PGC-1α gene expression in human skeletal muscle. European journal of applied physiology 113: 951-963, 2013.
7. Stellingwerff T. Case study: nutrition and training periodization in three elite marathon runners. Int J Sport Nutr Exerc Metab 22: 392-400, 2012.
8. Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, and Burke LM. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. American Journal of Physiology-Endocrinology and Metabolism 290: E380-E388, 2006.