Our basic daily energy needs are dictated by our Basal Metabolic Rate - this is your energy use in a rested state to support normal body functioning.
When we add exercise into our day our energy requirements increase. If we don't add sufficient calories, our bodies start burning our energy stores, namely fat. Now for those wanting to lose fat, this probably sounds pretty terrific. But what happens when we don't have sufficient energy stores, or fat stores, or we are burning energy faster than our body can convert fat into available energy.
The common athletic term is bonking but in more moderate forms of exercise we probably start feeling light headed, unco-ordinated, and weak. All of these symptoms are signals that you are demanding more than your body can provide. Your blood sugars have dropped to a level below normal.
To maintain sufficient energy throughout the day to complete your scheduled tasks you need to understand your energy requirements and ensure you meet these in the right way at the right time.
And the right way is NOT reaching for the nearest snack bar every time you start feeling yourself sliding. The right way is about planning in advance to give not only energy but nutrition.
This is particularly important when you are planning strenuous exercise. Most strenuous exercise aims to build muscle. Whether that is heart muscle doing cardio workouts or overall body muscle with weight training. If during and immediately following muscle building exercise your body cannot access sufficient nutrients from muscles, it starts eating away at the existing muscle tissue, effectively reversing your goal to build up and maintain muscle.
Now it's worth getting a little scientific here to understand why you need to manage your energy stores during exercise. So let's look at our body's energy system
When we need energy, our body breaks up a substance called adenosine triphosphate [ATP]. ATP is a high-energy molecule consisting of three phosphates attached by energy bonds to adenosine. Energy is released by breaking off a phosphate from ATP to form adenosine diphosphate [ADP]. This is a continual cycle of energy production with ADP converted back into ATP.
Now obviously for this to work, we need ATP in the body in the first place. ATP is created in the body by three systems, working simultaneously. The contribution from each system depends on the type of exercise we are doing, its intensity and duration.
ATP-CP system [6 second burst] - ATP-CP is our short burst energy system; something your body will tap into during a six second sprint. This system doesn't require oxygen. This is an anaerobic energy support system. CP [creatine phosphate] is a high-energy molecule where the phosphate can be broken off very quickly, releasing energy. It is used to convert ADP back to ATP. Since our muscled don't have large stores of CP, supply is used up very quickly. To increase creatine levels in the muscle, many athletes use creatine supplements.
Anaerobic system [90 second burst] - the high power anaerobic system breaks down glucose for energy, providing two molecules of ATP. Unfortunately this process also produces lactic acid. If lactic acid builds up in the muscles faster than our body can clear it, we get muscle fatigue - that 'hit the wall moment' that all athletes know about.
Aerobic system [Endurance] - our aerobic system supports the slow breakdown of glucose for energy, using oxygen. It provides 38 molecules of ATP; nearly 20 times more than the anaerobic system. It's the aerobic system that also uses fat to produce ATP energy. This is why endurance training can make the muscles use fat more efficiently.
So now that we understand the three energy production systems, lets look at how we can meet those short term demands using energy fuel. The three main energy fuels for exercise are carbohydrates, fat and protein. These nutrients are broken down in the body to provide energy, measured as kilocalories [kcal] per gram [g]. As a rough guide of how much energy is released from each type of nutrient:
carbohydrate provides 3.75kcal/g
protein provides 4kcal/g
fat provides 9kcal/g
Now don't go thinking that fat is the best energy food just because it releases twice as much energy a carbohydrates. The best energy food for exercise, especially intense workouts, is glucose. Glucose is formed in the body from the breakdown of carbohydrates [sugars and starches]. This glucose is stored as glycogen in the muscles and liver. Unfortunately, just like your home storage constraints, the body can also only store a limited amount of glycogen. An average size adult weighing 70kg [11 stone] stores around 450g, or 1,700 kcal, of glycogen.
If your exercise program is going to use more than 1700 during and immediately following exercise, then your body will run out of supplies are start looking elsewhere. The amount of each fuel [carbohydrate, fat and protein] your body uses during exercise depends on your dietary intake, fitness level, type of exercise, length of workout, training intensity, and frequency of training sessions. For instance, anaerobic exercise uses only glucose, whereas aerobic exercise uses all three fuels. As intensity increases, the demand for protein outstrips the demand for glucose and fat. That's why low-intensity exercise, such as walking is so great for burning a greater proportion of fat.
During moderate and high-intensity exercise, supply for energy starts with glucose, but with time, your body will gradually use more fat and less glucose in an attempt to conserve the limited glucose stores. The fitter you are, the more efficiently your muscles use fat and the longer you can work out. That's why the fitter you are, the more often you can train without draining the body, and the more calories you use. Listen to your body. If you start feeling sluggish, co-ordination and balance start to go a bit wonky, or you feel light headed - YOU ARE IN FATIGUE MODE. Your body has run out of glycogen. [NB: dehydration can also cause these symptoms].
So now you understand the energy system of the body and the additional demands you make on it during exercise, here are a few guidelines to getting the best from your workout, and protecting your body at the same time.
Stay well hydrated before, during and after your workout. Not only does it help your body function better, it avoids confusion as to what is causing any fatigue.
Be proactive with energy supply management. Don't wait until you feel fatigue before you boost your energy stores. Remember it takes time for energy to be released from the food we eat.
Eat more carbohydrates in advance of longer harder training sessions - this is why marathon runners bulk up on pasta for 2-3 days prior to a big race.
Provide your body with additional protein in the 45 minutes following a strenuous workout; then again, with some carbohydrates - about 2-3 hours following.
For serious athletic training programs learn more about the use of safe and effective bodybuilding supplements such as creatine monohydrate, L-carnitine, L-glutamine and protein powder.
And to be safe, always consult your medical advisor before undertaking any exercise program or taking supplements.
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