- Katharina Butsch
- Apr 20
- 6 min read
Updated: May 4
The right energy supply for top training performance
Most endurance athletes among you can probably tell a thing or two about it - bonking... Not only is bonking no fun, it also ruins every training or competition. For those of you who are not involved in endurance sports: Bonking is the term used to describe the drop in performance during an intensive running session, caused by complete depletion of the glycogen reserves in the muscle. In strength training, this can perhaps be compared best to the feeling of going to failure, except that muscle failure in strength training is due to neuromuscular exhaustion and therefore primarily due to redistribution of ions in nerve and muscle cells. Let’s find out how to make the most of your training through adequate energy supply.
Energy sources for muscle work
Depending on their workload, muscles rely on different energy sources. Initially, the muscle uses phosphate-rich compounds, more precisely ATP (or adenosine triphosphate), the universal energy source in the body. However, ATP is broken down easily and therefore not kept in large quantities - it is not meant for energy storage. ATP is thus only used for a few seconds of work, before the muscle switches to another phosphate-rich energy source, creatine phosphate (KP). But its reserves in the muscle only last for about a minute. Energy must then be obtained from the body's energy stores. This is primarily the glycogen stored in the muscle. Glycogen is the storage form of glucose in the body. These reserves are usually enough for about an hour of muscle work. The muscle therefore increasingly utilizes fat stores as energy source as the duration of exercise increases.
To optimize use of energy from glucose, muscles need sufficient oxygen for so called aerobic glucose metabolism. During high-intensity training, in which the muscles are insufficiently supplied with oxygen, glucose can only be used in anaerobic metabolism. This provides less energy and is therefore less efficient. In addition, the anaerobic breakdown of glucose produces lactate. Over time, lactate leads to acidification of the tissue. The body compensates by breaking down lactate as quickly as possible. In addition, lactate also serves as an energy source for muscles; the heart muscle even prefers lactate to glucose, if it’s available in sufficient quantities.
This is different when the body's own fats are used as energy source in muscles: overall, the breakdown of fats requires more oxygen than the breakdown of glucose and there is no alternative metabolic pathway for when muscles are insufficiently supplied with oxygen. In consequence, high-intensity activity can only be sustained by the muscle, as long as it is adequately supplied with glucose. Once the glycogen reserves are depleted and no additional glucose is supplied, the intensity of muscle work must be reduced.
Energy requirements of different training sessions
The need for energy sources for a training session depends on the intensity and duration. The following table provides an overview:
Trainings session | Intensity | Duration | Oxygen supply | Trainings goals | Pimary energy source |
Endurance sports | |||||
Sprint | 95-100% HFmax | max. 10 sec | anaerobic |
|
|
Interval | 90-95% HFmax | max. 2 min | anaerobic |
|
|
Threshold training | 80-90% HFmax | max. 30-60 min | Threshold |
|
|
Endurance run | 70-80% HFmax | 3-90 min | aerobic |
|
|
Long run | 60-80% HFmax | Hours to days | aerobic |
|
|
Strength training | |||||
Maximum strength training | 85-100% 1RM | max. 5 sec | anaerobic |
|
|
Speed power training | 30-70% 1RM | max. 5 sec | anaerobic |
|
|
Plyometric training | 30-70% 1RM | max. 3 sec | anaerobic |
|
|
Hypertrophy training | 65-85% 1RM | 15-40 sec | anaerobic |
|
|
Eccentric training | 100–120% 1RM | 3-10 sec | anaerobic |
|
|
Strength endurance | 40-60% 1RM | Seconds to minutes | aerobic |
|
|
Functional Training | 40-80% 1RM | mostly 30-60 sec | aerobic |
|
|
Isometric training © Nutrinavi | 30-100% 1RM | Seconds to minutes | aerobic |
|
|
1RM = One repetition maximum
Energy supply for optimizing workout performance
So what does this mean for your training?
Regardless of the sport, you need to provide your muscles with the energy reserve they need in order to perform at your best.
For primarily glycogen-dependent training sessions
Make sure your glycogen stores are sufficiently filled before training!
If you want to run high-intensity intervals, you shouldn't start with empty glycogen stores, otherwise the planned intervals will turn into a battle in the gray zone.
Before an intense session, eat a small amount of carbohydrate-containing food, ideally foods with quickly metabolized, i.e. free, sugars.
Just try which foods you tolerate best. Regardless of whether it's a banana, porridge or the milk roll for you, try to time the meal so that the maximum increase in blood sugar falls in the same period as the increased glycogen requirement. How long exactly it will take your blood sugar to peak depends on what you eat. For high glycemic foods, you can assume that blood sugar level will be high after about 20-30 minutes and then quickly drop again.
Only plan high-intensity sessions after regeneration of energy reserves from previous trainings is completed.
You’ll likely achieve better training performance, if you space out high-intensity, glycogen-dependent interval sessions or plan a break after a long fat-storing endurance session which used up all your muscle glycogenand.
In case your glycogn-based training is anaerobic and lactate-producing, your performance will be significantly limited by acidification. You can maintain your performance for longer and regain it more quickly if you support lactate breakdown. This may lead to two conclusions:
If you want to be fit as quickly as possible for the next repetition after a lactate-producing exercise, stay active to increase lactate breakdown in the time in between.
Walking between two intervals is better than standing still and easy running is better than walking.
If you specifically want to improve your muscle's lactate metabolism capacity, you should slow down cardiac lactate breakdown and do the opposite.
Rumors have it that some professionals even squat after a lactate interval to keep a high lactate concentration in the muscle for as long as possible and delay its distribution in the system.
For primarily fat-emphasized endurance units
Consume sufficient energy from carbohydrates during exercise to slow down the depletion of your glycogen stores.
Even if intensity makes your training a primarily fat reserve based session, a small part of your glycogen reserves will always be metabolized until they are depleted.
Training sessions which are intended to train the fat metabolism can become more effective, if you go in with depleted glycogen storage, as this forces the muscle cells to utilize fat for energy supply right from the start.
This “train low” approach is less suitable for female athletes and should only be used with caution. This is because glucose has an important signaling effect in maintaining an ovulatory menstrual cycle. (More on this elsewhere.)
For training sessions primarily based on phosphate-rich compounds (ATP and KP):
(Here nutrition plays a minor role)
Make sure you have sufficient carbohydrate intake and full glycogen stores.
The body most effectively obtains ATP, which has to be synthesized later in the course of a set, from glycogen.
If you want to use supplements to improve performance, you can add creatine.
Creatine supplements increase creatine phosphate stores and thereby improve ATP resynthesis during short, intense exercise. (There is a lot of evidence for creatine boosting the performance during strength training, but no evidence - or just inconclusive data - that creatine boosts training performance in endurance sports, not even for ATP and KP based training sessions!)
Literature:
Kreider, R.B., Kalman, D.S., Antonio, J. et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. J Int Soc Sports Nutr 14, 18 (2017). https://doi.org/10.1186/s12970-017-0173-z
C. Raschka, S. Ruf: Sport und Ernährung - Wissenschaftlich basierte Empfehlungen, Tipps und Ernährunsgpläne für die Praxis, 4. Auflage, 2018, Thieme, Stuttgart.
W. Friedrich: Optimales Sportwissen - Grundlagen der Sporttheorie und Sportpraxis, 2. Auflage, 2007, Spitta GmbH, Balingen.
