Being hungry is a lack of energy. But this is just a sign that we need to move around and start foraging. Most of us do not even feel hungry when we have breakfast, it is just something we feel we should do to keep us going. Often if we eat at this time, it can lead to a large amount of a hormone called insulin being released to deal with the glucose from the food we are eating. This may be followed by a corresponding blood sugar dip as glucose is packed away in the cells.
Bursts of energy
So what we can we do to get some energy? From the minute we move, our muscles do not need insulin to provide energy anymore. Theoretically we can bomb down the road as fast as possible for a hundred metres or run and hurl ourselves over the nearest fence, without even needing to breathe! This is a very quick reaction using an energy system known as our creatine-phosphate system, typically used by sprinters, weight lifters or high jumpers. Because it is not a very efficient system we can only keep it up for about eight to fifteen seconds.
After about ten seconds, we can go a lot further using carbohydrate. If we start to run at a high intensity, the point at which we are not able to speak any more, we use our anaerobic energy metabolism. This means we are creating energy without the need of oxygen which takes a while to get round the body. This mechanism is employed by non-endurance athletes to build up speed and strength. The more intensely muscles have to work, the more they have to use the anaerobic route. Constant contractions mean that oxygenated blood cannot get to the muscles.
Running at a lower intensity means that our aerobic carbohydrate metabolism kicks in and we need to use oxygen. This involves the mitochondria which are the power houses of our muscle cells and typically each one has a thousand of them. The length of time we can keep going at this pace all depends on the body’s stores of glycogen which is our glucose store. On average glycogen stocks can last for up to ninety minutes although with untrained people, these can dwindle faster. If we keep on going then we will start to burn fat.
Whilst from the time we set off all energy metabolisms are working together at once, but one will dominate. The body really has to feel the need to use fat and so the enzymes that produce the burning of fat are only active when there is no other choice. This is why marathon runners have to train to do the long runs, to teach the body to switch from a predominantly aerobic metabolism to a fat-burning one.
Good times and bad times
When exercise was the basis of survival and hunter gatherer populations would move long distances to hunt for food. They were able to do this because once muscles are active they do not need to rely on glucose coming in from the diet. At times they would have been able to top up their glycogen and rely on this. But at others, the coffers will have been verging on empty and this is perfectly normal. It sends a message to the mitochondria to tell them they need to be more energy efficient and increase in number. The more our cells register there are good times and bad, the more effective this system becomes and the better we are at regulating our energy production. We can help this by moving on empty and varying the type of exercise we do.