FUELLING EXERCISE
This will take you 6-7 minutes to read
Fuelling exercise:
In order to fuel exercise, we need to understand some basic energy mechanisms, such as adenosine triphosphate (ATP), Phosphocreatine, anaerobic (without oxygen)/ aerobic (with oxygen) glycolysis (the breakdown of glucose by enzymes, releasing energy) and lipolysis (the breakdown of fats and other lipids to release fatty acids which fuel exercise).
What causes fatigue?
Potentially down to a lack of ATP (energy currency of the body necessary for muscle contraction).
There’s multiple ways to increase ATP:
1. Increase Phosphocreatine which increases ATP in a RAPID manner, but the total store of phosphocreatine is relatively small by comparison to other fuel sources (this is where creatine monohydrate supplementation can help, by increasing Phosphocreatine stores).
2. Anaerobic glycolysis – an anaerobic break down of carbohydrates – which is a pretty rapid provision of ATP but total store is relatively small.
3. Oxidation of carbohydrates – breaking down of carbohydrates in the presence of oxygen. This is a MUCH bigger store compared to the previous points, but provides ATP at a much slower rate than the previous two.
4. Finally, your BIGGEST STORE of potential ATP is through the oxidation of fat but has the SLOWEST provision of ATP.
Please reference “Image A” found at the bottom of this news letter, as you can see, a large supply of ATP is used by the ATP store that is already stored in the body, followed by phosphocreatine which has a rapid production of ATP which also drops rapidly, useful for more explosive lifts. As exercise duration progresses, the role of aerobic glycolysis becomes more important and as it progresses further so does lipolysis. One thing that does NOT OCCUR which I always hear social media “fitfluencers” say is that these occur one at a time. These energy systems work together. You can also clearly see the sheer rate of ATP production thanks to carbohydrates, which are king for high intensity exercise.
Won’t eating carbs cause an increase in blood sugar?
Yes, but unless you are diabetic this does not matter. Spikes in your blood sugar levels are NORMAL. Only when you have consistently high blood sugar, due to insulin resistance, usually due to being seriously overweight or a diabetic is this a problem. When you eat your blood sugar will rise, but blood sugar will go down due to insulin which transports glucose into your cells for energy or stored as glycogen for later use.
During exercise, calcium is released as well during every muscle contraction (calcium is like the gunpowder for your muscle contraction). This is important because during exercise adrenaline is released which down regulates insulin (how scary… I say sarcastically). Luckily, calcium can also act a mediator/ transporter of glucose into cells (yay).
Carbohydrates are king of performance:
As you can see on “Image A”, when exercise intensity increases, needing a higher production of ATP, glycolysis is especially important for the highest rates of energy ATP production. During exercise with limited carbohydrate availability, blood glucose levels decrease to about 50% of maximum in exercise when begun in a glycogen depleted state compared to a glycogen fuelled state. (1)For an increased duration of exercise intensity, carbohydrates are the required fuel.
How mechanisms are maintained with ingestion of carbohydrate during exercise?
1. Maintaining blood glucose concentration.
2. Maintaining carbohydrate oxidation.
3. Sparing endogenous glycogen.
4. Synthesising glycogen during low intensity periods.
What type of exercise can carbohydrates be beneficial?
1. High intensity (80% VO2 max for 1 hour)
2. Moderate intensity (60-70% VO2 max >2 hours)
3. Intermitted exercise (football, hockey, rugby)
There are limitations to carbohydrate oxidation:
We all would love to have all the energy in the world, but unfortunately there are limitations. In theory, we would assume, the more carbohydrates we consume the more elevated our blood glucose concentration, the more glucose we can transport into our muscle, therefore a greater degree of carbohydrate oxidation… We all might think, “This sounds AMAZING, let’s go train at a hell of an intensity for a long period of time thanks to carbs”, but NO.
No matter the source of single carbohydrate, we cannot get above 1.2g per minute of oxidised carbohydrate. This suggests, no matter how much single carbohydrates we ingest, we can only use around 1.2g per minute of carbohydrate for ATP production.
There are a number of potential carbohydrate ingestion limitations:
- Gastric emptying
- Intestinal absorption
- Regulation by liver
- Entry into peripheral circulation
- Uptake into muscle
- Oxidation in muscle
What carbohydrate source should I have for exercise?
Carbohydrate oxidation rates increase once you start using multiple sources. The highest oxidation rates can be found with a mixture of glucose and fructose, which is about 1.75g/ minute.
(2)
“Image B” found at the bottom of this news letter is a well recognised graph by A. Jeukendrop for the total, type and timing of carbohydrates around exercise.
How many carbohydrates should I have to maximise muscle strength and hypertrophy?
Strength: The literature tends to lean towards 5 to 8g /kg per day.
Hypertrophy: The literature tends to lean towards 3 to 8g / kg per day.
(3) (4)
When to eat before exercise and what to not eat?
I recommend to clients to avoid eating within the hour before a heavy exercise session. Digestion requires blood supply. When you begin to exercise, where does your blood flow head towards? Your muscle. This could potentially cause stomach cramps, bloating, flatulence and so on. To maximise results, I try ask for clients to have consumed at least 20% of their total daily intake of carbohydrates before their session or the amount of carbohydrates proposed in the graph by Jeukendrop at least an hour before training (labelled “Image B” at the bottom of this news letter).
Please try avoiding high fibre carbohydrates just before exercise, as fibre takes longer to digest so this could cause a more severe reaction ie. Increased gastrointestinal issues.
However, saying this, everyone is different. If you never have gastrointestinal issues then LUCKY YOU but if you do this might be worth considering.
In terms of examples of foods to eat depending on the duration of exercise, I will need to do another news letter which looks at the glycemic index and glycemic load with food examples. I’ve got to keep you all intrigued, so there will be a part 2 to this news letter :)
Other exercise and office performance:
Depending on the amount of fat vs carbohydrates you consume can cause all sorts of adaptations to aid in the adaptation of exercise for both mind and body. Nutrition can help with performance in the office too. If you ever need guidance for increasing performance at work, I can help there. These news letters are mainly for those who want to exercise at the gym but these principles can be applied to ANY performance protocol. More specific periodised nutrition (yes, you can periodise nutrition like you do an exercise plan) will be required to aid with your specific goals.
Thank you for your time,
Rich
Please review this blog and tag me on your social media. I will appreciate it a lot. :)
How I can help you?
Personal Training and Online Coaching for all levels of fitness with accurate calorie targets and nutritional advice which will be realistic around your goals, evidence based and health prioritised.
Performance Nutrition for working professionals that incorporates nutrition around your life style, aiding in better sleep, reduced stress, increased concentration and, of course, increased performance.
Performance Nutrition for the athlete who is trying to increase their performance physically, cognitively, prepare for competition, fuel for competition or simply to make weight.
I use evidenced based practice. There are no guesses.
References:
Wagenmakers AJM, et al. Carbohydrate supplementation, glycogen depletion, and amino acid metabolism. AM J Physiol 1991; 260;E883.
Jeukendrup(2008), EJSS, 8(2), 77-86
ThomasDT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics,Dietitians of Canada, and the American College of Sports Medicine: nutritionand athletic performance. J Acad Nutr Diet. Mar2016;116(3):501-28. doi:10.1016/;.jand.2015.12.006
KerksickCM, Wilborn CD, Roberts MD, et al. ISSN exercise & sports nutrition reviewupdate: research & recommendations. J Int Soc Sports Nutr. Aug2018;15(1):38. doi:10.1186/ s12970-018-0242-у