In the fitness world, the words “fuel tank” or “gas tank” get thrown around a lot.
Basically, this “tank” refers to carbohydrates (glycogen) that are stored in your skeletal muscles.
Our muscles primarily use a mixture of carbohydrates and fat to fuel exercise.
Just like the petrol tank in your car, you use more fuel when you step on the accelerator and less when you take a slow, scenic drive on cruise control mode.
Likewise, in exercise at a lower intensity, fat becomes the primary fuel used, but as you increase intensity, your muscles dig into the glycogen reserves to power through the workout.
As you exercise, your body breaks down glycogen into glucose for energy.
When your glycogen stores are running low, your body has less fuel and you will begin to feel tired.
However, unlike vehicles, most research suggests that this human fuel tank can never be totally empty after a workout, no matter how hardcore the activities are.
You’ll always have a bit of fuel left.
Rate of depletion
Our bodies have two types of skeletal muscle fibres: slow-twitch (type I) and fast-twitch (type II).
Slow-twitch muscle fibres support long-distance endurance activities like marathon-running, while fast-twitch muscle fibres support quick, powerful movements such as sprinting or weightlifting.
In a recent study published in the journal Acta Physiologica, researchers looked at the utilisation of muscle glycogen during heavy resistance exercise in elite power and Olympic weightlifters.
The male weightlifters were asked to perform resistance exercises consisting of squats, deadlifts and rear foot elevated split squats.
Muscle biopsies (of the vastus lateralis, which is the muscle on the lateral side of the thigh) were obtained before and after the exercise session.
Post-exercise, the muscle glycogen decreased by 38%.
So if they started with a full tank, they still had 62% of fuel left.
But the researchers also observed that fast-twitch muscle fibres depleted faster (55% decrease) than slow-twitch muscles.
What does this mean?
If you’re lifting heavy weights with the intention of building bulk or are running a marathon, you need to have a fuller tank before commencing your workout.
For the ordinary person who’s working with light weights and doing isolation movements or taking a brisk walk, you can “operate” without a full tank – a banana is enough.
That’s right, you don’t need to load up on other carbohydrates.
One banana will do
A lot of people make the mistake (or give the excuse) that they’re loading up “fuel” in preparation for a hard workout.
They consume all sorts of kuih-muih thinking they will burn them off in an aerobic class.
And they wonder why the weighing scale never budges or decreases despite working out.
The American College of Sports Medicine, American Dietetic Association and Dietitians of Canada recommend consuming 30g to 60g of carbohydrates from glucose, or glucose and fructose, for each hour of endurance exercise.
A medium-sized banana has about 25-30g of carbohydrates.
Each gramme of carbohydrate and protein yields four calories per gramme, while each gramme of fat yields nine calories.
A 30g banana contains 120 calories.
Bananas make a great pre-workout and post-workout snack as they are easily digestible and versatile.
They can be incorporated into smoothies, as well as fruit salads or oats, making it easy to add them into your routine.
They’re also a good source of antioxidants and potassium – a mineral that may help prevent muscle cramps.
This is why you’ll often see professional athletes loading up on bananas before they compete.
Other good choices to fuel up before a workout include eggs, yoghurt, sweet potatoes, yam, cottage cheese, a slice of toast and peanut butter, fresh fruits, or a fruit/yoghurt smoothie.
Smoothies are easy to digest, so you won’t feel sluggish during your workout.
But stay away from store-bought ones as most of them are high in added sugar.
Make your own version with some protein/calcium-rich yoghurt or soy milk, and banana.
Dilute it with ice and water, and this will also help you stay hydrated.
Liquid always absorbs faster than solids, but still, have them at least 30-45 minutes before your workout to lessen the burden on your digestive system.
Healthy foods may be good for weight loss and muscle-building, but may not necessarily be suitable as a pre-workout meal and can leave you feeling weak.
I would also stay away from energy/protein bars, nuts and trail mixes, as these are high in fat and digest slower, so your body cannot use them as fuel immediately.
Running on empty?
Many people have asked me if it’s okay to work out on an empty stomach in the morning.
Well, there is nothing wrong with it if you’re embarking on a light workout as you may actually end up burning more fat.
But if you’re doing a high intensity activity, you can get light-headed or lethargic from the drop in blood sugar levels.
Having said that, every individual is different and it really depends on your goal.
If you want to lose weight, go ahead, but if your intention is to strengthen muscles, then put a little bit into the “tank”.
My brother runs 15km on an empty stomach without any problem, while I need to add “fuel” before any activity.
More importantly, your body should feel comfortable and have the energy to complete the workout.
Keep hydrated though.
Ideally, you should “refuel” with a snack within 45 minutes after your workout.
Depending on the intensity of your activity, the “tank” might need more time to be refilled post-workout.
Focus on getting some healthy carbohydrates and proteins into your body.
This gives your muscles the ability to replenish the glycogen they just lost through training.
It also helps your tired muscles rebuild and repair with the available proteins and amino acids.
Again, you can peel a banana and pop it into your mouth, or have that banana and yoghurt smoothie.
Doing so can reduce inflammation and replenish muscle glycogen stores, ultimately promoting quicker recovery.
Before the Covid-19 pandemic and when the economy was thriving, many gyms would place a complimentary basket of bananas at the front counter for members to fuel up.
When times got challenging, they would charge for the fruit.
Eventually, they stopped offering it as the peels would be found scattered in studio corners and locker rooms.
Low-fat chocolate milk is also highly recommended as a recovery drink, as it has the ideal carbohydrate-to-protein ratio for optimum post-workout recovery.
Personally, I doubt anything can beat the taste of chilled Milo (the one from the truck) after any workout!
You can also have a slice of toast with some scrambled eggs, as the bread’s carbohydrates put back the energy you burned during exercise, while its fibre keeps your blood sugar levels stable, and the eggs provide the protein.
Another favourite of mine from my varsity days is a peanut butter jelly banana sandwich – spread some peanut butter and jelly/jam on the toast, cut the banana into thin slices and cover with another slice of toast.
When I was first introduced to this sandwich, I’d have it everyday for breakfast and after a workout!
Rest for 24 hours to recover and you’ll be all set to go again.
Revathi Murugappan is a certified fitness trainer who tries to battle gravity and continues to dance to express herself artistically and nourish her soul. For more information, email firstname.lastname@example.org. The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.