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In the previous article we saw how long (at least 40 minutes), how often (5 times a week) and which kind (running, walking quickly) of aerobic activities we need to perform to lose weight in the best way possible. We still have to talk about “how” and “when”. As for the “how”, things are a bit more complicated, since we have to introduce the concept of intensity. Intensity is basically the amount of labour performed in the unity of time. Obviously, if we are talking about running, intensity is combined with velocity. If I want to increase intensity, I will have to increase velocity. If I run at 8 km (labour) per hour (time), intensity is higher than if I ran at 6 km per hour. Of course, it also depends on the subject’s specific characteristics: training level, age, sex, weight. An out of shape 50-year-old overweight woman will certainly struggle more, that is, she will certainly produce more intense labour, running at 8 km per hour than Baldini (Olympic Marathon champion). Hence the need of a useful conventional parameter to measure the intensity level. In aerobic activities this parameter is the heart frequency. The heart frequency (HF) increases in linear progress with the increase of labour intensity, until reaching a maximum level beyond which it does not increase despite the increase in labour intensity. Such value is called Maximum heart frequency. Maximum frequency can be generally and easily calculated – approximately – applying the following formula: maxHF=220-age..
There are also other more complex and more precise formulas, but I think this one is reliable. According to this formula, a 40-year-old person has a maxHF of 180 beats. During aerobic activities, the body can use fats or sugars for energy purpose. The use of either fats or sugars depends on various factors; training, since the more someone is aerobically trained, the easier it is for them to use fats for energy purposes; duration, since it takes about 30-40 minutes to be able to use fats for energy purposes; and, even more important, training intensity. The lower the intensity of your training, the more you use fats for energy purposes; the higher the intensity, the more you use sugars. Physiology studies report that the ideal intensity to burn fats should be at around 50% of maximum beats. So, in the case of a 40-year-old person, 90 beats per minute. However, if with an increase in intensity – that is in beats – we get an increase in the percentage of used sugars, it is also true that the total amount of calorie consumption increases, too, thus compensating the decrease of fats used for energy purposes. For example, if we are performing a physical activity and we burn 200 calories using 100% of fats, then we have burned 200 calories of fats. If, instead, we perform a more intense physical activity burning 500 calories and we only use 50% of fats as fuel, then we will have burnt 250 calories of fats, that is, 50 calories more. The further energy shortage now at sugars’ expense will then partially be balanced later, thanks to the formation of ATP by the aerobic energetic metabolism at fats’ expense. Moreover, higher-intensity aerobic exercise influences the metabolism and the hormonal levels, favouring higher fat burning at rest even in the following hours. High-intensity aerobic exercises reduce the insulin levels and increase the glucagon level, thus improving vasodilatation and favouring an higher oxygen supply. This means higher fat oxidation. If you think about it, it is quite easy to understand, and it makes sense: you have more chances of losing weight by riding a bike or by sweating rather than by comfortably chatting with a friend or by reading the newspaper without even crumpling it. When training in your aerobic activity, the intensity range to follow in order to reach these positive effects is between 60 and 80% of your maximum beats. So, in the case of a 40-year-old person, the range is between 110 and 145 beats. I thought I could talk about the “when”, too, but I was wrong. So, we will discuss about it in the next article, and maybe there will be a surprise for somebody.