Two friends at the age of 45 agree on a joint bike ride. They plan a 35-km route. Joyce goes to the fitness center three times a week, doing activities (yoga, weight training, spinning, weight training ) week after week. The second girl Sue, does not perform any regular physical activity.


It’s a beautiful Saturday afternoon and our girls hit the road. Both are two hours after breakfast and they have ideal weather conditions for starting their ride. The route takes place over a slightly undulating landscape, with no unpleasant climbs. The first minutes of riding are at an average speed of 20 kph  and do not cause them any problems. During this part of the journey, their working muscles are using glucose as  their primary source of energy.


After about 20-30 minutes of continuous cycling , there is a change in the fit, trained body of Joyce. Her body quickly realized that this was another training session . From long-term experience, her body expects that this ride will not be an easy bike ride, energy demands will increase and could continue for a long time. Since sugar reserves – “gas” (glycogen in the liver and muscle) are limited, her body is now becoming more like a “diesel” – using fat stores for energy and that saves the limited carbohydrate reserves. Joyce does not have to be afraid, her total body fat is 18% she can theoretically be able to go at least 1000 km. There is no problem to keep using fat for energy but there is with using the sugars. If her body depleted the sugar stores, then this would soon become the end of a pleasant ride. This is because for the perfect utilization of fats, we always need a certain amount of carbohydrates (glucose) in the body. Glucose is a kind of burning fire for perfect oxidation of fatty acids. This trained body knows well and subconsciously  how to treats sugars, it will also use lipids (fats = glycerol + fatty acids) stored in fat cells as a source of energy.


Sues non- trained body does not know what to expect and cheerfully consumes a large amount of carbohydrates during the first 10 km. Our girls have covered 20 km. Sues body finds out that the sugar reserves are badly exhausted. Since some cells in the body are dependent on glucose, the body must not let it fall too low. As Sue is untrained, that’s why she started using fats 30 mins later then Joyce.  Alarmingly for her body, her glucose stores are now very reduced. There is still some available and enough, for another 15 km, enough to feed the brain and burn fat. However, blood glucose control sensors indicate a noticeable decrease in blood glucose, which forces Sue to “lose gas” and slow down. Slowing down the speed will use less sugar and enable her to get safely to the finish.  Every uphill makes it more and more difficult for her. The average speed is down to 15 km. Joyce is getting bored with the slow ride, but she is a friend. Tired Sue has been suffering for a while, even though she has got enough fat on her body to burn. Sues body prematurely used her carbohydrate energy stores and now is paying the price. She has slowed reactions, blurred vision, weak legs and arms, experiencing a typical hypoglycemic crisis. But Sue wants to prove that she is not a doll, and there is only a “mere” 6 km remaining. But these last kilometers  are suffering for her. With the help of an energy gel, she manages to continue and get to the finish. How is Joyce feeling ? For a trained girl, this trip was an easy activity. She has got a fit body, used to regular overload and also utilities fats for energy. Sues carbohydrate stores last for 35 km. If she wanted to, she could do it again and go faster. Although both went the same distance, Joyce burned more fat than Sue.


What I want you to take from this story? Train, train, train. Gradually, you will be able to burn more fat, earlier and more perfectly in physical work. Not only when you exercise , but even at rest. How is it possible? You can find the answer in next blog. What happens in the body after physical activity.


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