When you want to get fit, it is usually for one of three reasons:

  • to lose weight at the same time
  • to feel in better shape (ie. not be puffing up those stairs)
  • to prepare for a sporting event or be better at your favorite sport

Whichever happens to be the case, a better knowledge of how the body works will help to achieve the desired goal.

For a start, go find out about nutrition.

Energy production systems

Let's have a look at what happens if you decide to go out and run for half an hour - not just an quiet jog; set off quite fast.

  1. For the first 30 seconds, you won't feel any different.
  2. Then, your heart-rate will go up, along with your breathing.
  3. After about two minutes you'll probably realize that you set your sights too high and slow down a bit.
  4. After a while, you'll start to feel a bit hot and thirsty.
  5. You get home and do a short sprint just to show your SO how good you are.
  6. You cool off, have a drink and feel rather pleased with yourself - in fact, you feel great.
  7. Try running up the stairs - a bit tough !
  8. Try doing some push-ups - no trouble (no more than usual)!
  9. The following morning, you wake up to discover that your legs didn't like being used at such short notice.

All this can be explained by the way glucose gets to the muscles and how it is transformed once it gets there.

The cells have a supply of glucose which is gradually used up, they also get a regular inflow from the liver via the blood-stream. As the cellular glycogen gets depleted, the body provides more and more energy from fat. If the liver glycogen gets depleted, the brain will no longer get the glucose it needs from the blood and you may feel faint or even pass out. This is called hypoglycemia. It is not very likely to happen though, unless you're following some weird diet or have a glandular problem like diabetes.

To run (or for any other physical exercise), your muscle cells need energy; a cell traps energy gained through one of three metabolic processes by transforming ADP into ATP. The ATP then transforms back into ADP to release the energy. The three processes which transform ADP into ATP are the following:

glucose reacts with oxygen to form water and carbon dioxide and releases energy. It is called aerobic because it uses oxygen. Fat can also be used instead of glucose.
lactic anaerobic
glucose does not find any oxygen to react with and the cell still needs some energy; the glucose breaks down into lactic acid, releasing some energy, but not as much as with the aerobic process. The lactic acid then has to be cleaned out of your system, or you'll get muscular pains and even cramps.
alactic anaerobic
This process uses phosphocreatine (PCr): using certain enzymes, PCr can give a phosphate to transform ADP into ATP without the use of oxygen. PCr is created whenever the body can through one of the other two processes. This process is the most productive, but it is limited by the amount of creatine present in your cells.

Here is what happened during that run:

  1. Those first seconds were just enough time for the PCr to do its job; as you didn't need any extra oxygen, your breathing and heart rate stayed normal. This was the alactic anaerobic metabolism.
  2. No PCr left. You start to enter a mixture of both aerobic and lactic anaerobic metabolisms, you are probably going too fast for the muscles to get enough energy through the aerobic process (your blood can't circulate enough oxygen) so lactic acid from the other process builds up...
  3. ... so you slow down, because the lactic acid is beginning to make your legs feel heavy.
  4. These processes are not particularly energy efficient and most of the wasted energy goes off as heat; you loose a lot of liquid cooling you down.
  5. Once you had settled down into a nice steady pace, using the aerobic metabolism almost exclusively, your body even found time to build up your PCr again, so the final sprint was almost effortless.
  6. Particularly if you don't do this sort of thing often, all that running was probably a bit painful. The body produces its own painkillers: endomorphines. The reason you feel great now is that a) you're quite proud of yourself and b) your body has not yet realized that the pain is over and it can stop producing endomorphine. You're getting high on your own dope! For some people, this is the reason they continue working out: watch out, it's addictive.
  7. The body has not yet replenished the muscular glycogen in the legs...
  8. ...but it has almost not used that of the arms.
  9. This all comes from setting out too fast: in most cases, you should avoid using the lactic anaerobic metabolism like the plague. You should also do stretching before and especially after any training.

The cardiovascular system

You will have noted that the energy system you are using will depend on whether enough oxygen is getting through or not. There are two factors involved here: the first is that there is a maximum rate at which your heart can beat which will also limit the maximum volume of oxygen you can breathe per minute; the second is how much oxygen your heart can pump round. As there is a linear relationship between your oxygen intake and your heart rate and the second is dependent on the first, we often talk of the activity level in terms of oxygen intake, but use heartbeats as units (as they are more easily measurable).

So we have the maximum oxygen intake (maxVO2 - maximum volume of oxygen) which is usually calculated as being 220 - your_age (as I just said, we use heartbeats as units). This is a maximum about which you can do very little; if you go (much) above it, there is something very wrong with the way your body is working. Then there is the aerobic limit (limVO2), the maximum amount of oxygen you can pump round, which is usually situated around 60% of your maxVO2; after this, your heart can not keep up with the amount of O2 your body is requesting and many cells are forced to enter the anaerobic metabolism. This is the limit you will be working on, the 60% is only an approximation and will depend on many other factors.


What does this mean for getting fit? First and foremost, identify your needs; do you want to lose weight? feel fitter? train for a competitive event? Let's just assume you do fit nice and cosily into one of those categories.

To lose weight, you need to burn fat (along with all the eating properly stuff) but without using up so much energy that you have to eat even more to compensate; the trick is to work out at around 40% of your maxVO2, which is the zone in which the highest proportion energy is obtained from fat (around 50%), and to do it for long periods (minimum of 20 minutes). There is no such thing as a workout that takes only 10 minutes a day. How you actually get your exercise is pretty irrelevant, so long as you go for something that you enjoy and which does the whole body. Another cute myth most people will be relieved to get rid of is that working on a particular set of muscles does not get rid of the fat in that area of the body - so don't bother with stomach crunches and rowing machines if you want to get rid of that beer belly, it will just make your muscles hurt more without any extra effect. Swimming and cross-country skiing are the best as they exercise the whole body.

If you want to feel fitter, then alternating between fat burning and endurance is probably the best; in all cases, stay below your limVO2, so that you don't get too many aches and pains; around now is probably the best time to break it to you: don't do into lifting weights and "pumping iron" on health grounds: they do nothing for your fitness. Always make sure you get plenty of liquid during and after your workout, and that you let your body warm up gradually before going "all out".

By now you're probably thinking of getting a bit more competitive. You should probably ask your doctor about doing a fitness test which will determine your maxVO2 along with your limVO2 and many other things besides. You then need to decide what sort of metabolism you will be using in your chosen sport, as it will be essential in deciding what sort of training you are going to do; basically, there are five zones which each correspond to an approximate percentage of your maxVO2 (a fitness test will be able to pinpoint those zones more accurately):

  • recovery / fat burning (40%)
  • extensive endurance (50%)
  • intensive endurance (60%)
  • resistance (70%)
  • anaerobic training (80%)

Recovery basically cleanses your body of all toxins and allows for a more intensive training program, to be used without moderation. Extensive endurance trains your body to be more efficient in it's energy consumption, good for any long regular efforts (anything over 3 minutes actually), it should be done for about 40mn per session. Intensive endurance attempts to move the limVO2 up to be able to go faster for all endurance events; don't do this for too long (25-30 mn). It is the most difficult to get right as you have to try to keep your heart rate just below the limVO2. Resistance training is actually repeated incursions of about 1mn into the 70% zone and then waiting for the pulse to go down to 40-50% before starting again; it pretty much matches what footballers and most other team game players go through and is ideal for all competitions which last between 30 seconds and 3 minutes. This is a (metaphorical) killer if you don't already have a reasonable all-round fitness level; the aim of it is to get your body used to coping with lactic acid, so expect a fair bit of pain the first time. Anaerobic training is designed to push up the levels of phosphocreatine, it is pretty much the same as resistance training except you would only actually do one or two bursts of activity in a session, and these would last no longer than 20 seconds. It's basically speed training.

Remember that any athlete needs allround fitness as well, along with a good diet and technical and mental training.

After any training session, don't forget to do some stretching along with drinking plenty of water. You will also find that reducing alcohol, tobacco and any other recreational drugs improves the body's physical capacity no end. If you are just the casual type, motivation is likely to be a big problem; this is something you will have to come to terms with. If you had been thinking of making the big leap, you may want to okay it with your doctor; in particular if you: are pregnant, suffer from heart problems, are older (ie. it's been a long time since you last did any strenuous activity). If you're adding a diet on top of that, you really should see a doctor or nutritionist to make sure you don't go without important nutrients.

Good Luck!

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