Mar 2014 08

Who needs carbs anyway?

By: Dave Wheeler

Whether it’s picking up a coffee mug, pounding along a race track, or pumping iron at the gym, all body movement is caused by muscle contraction which pull on tendons that then pull on joints.

Muscle contraction needs energy to make it happen. The source of energy that muscles use to contract is called ATP. Because ATP is so important in generating movement, the body has a number of different “fuel tanks” for it.


the carbohydrate fuel tank for atp


The built-in tank - creatine phosphate

Muscles have a tiny store of ATP within them. They also have a store of creatine phosphate which can be turned into ATP. Together, this store of readily-available ATP is called the phosphagen system.

Being stored within the muscle itself, this energy source is available to the muscle pretty much instantly, so when movement starts, this fuel tank is the first used.

On the downside, there’s only enough ATP to keep muscles working for about 10-15 seconds. After that, the tank runs dry, and once its gone, its gone.

In-muscle ATP can be replenished during recovery, but not during exercise itself, so another source of fuel is needed to keep muscles working for more than 10 seconds.


The carbohydrate fuel tank

The next fuel tank that’s used to create ATP is carbohydrate.

The carbohydrate fuel tank actually fuels two different engines: each engine supplies ATP to muscles:

  • The anaerobic system, and
  • The aerobic system


The anaerobic system

The anaerobic system converts carbs into ATP without using oxygen. It can provide enough ATP to fuel up to a 90 seconds of exercise.

The downside is that lactic acid is produced as a by-product. Lactic acid is what causes muscle-burn and DOMS (delayed onset muscle soreness).

When the supply of ATP from the anaerobic system runs dry, the switch is tripped over to the aerobic system (assuming that it’s turned on - see below).


The aerobic system

The aerobic engine produces 20 times more ATP than the anaerobic system, so its a really efficient way of fuelling muscle movement. But it’s also slower.

The aerobic system uses oxygen to “burn” the carbohydrate. ATP is a by-product of this burning process.


oxygen - the flame of carbohydrate metabolism for atp


Because it relies on oxygen-rich blood being pumped around the body to the muscles, it’s slower than the other fuel tanks. As a person continues to exercise, breathing rate increases and blood flows faster around the body. This takes more oxygen to the muscles allowing more carbs to be burned in the oxygen fire, and therefore more ATP to be generated.

This works well unless the level of intensity of the muscle workout is higher than can be fuelled by the level of oxygen being pumped around the body (for example, pumping iron hard at the gym with high weight low reps).  In this case, the anaerobic system kicks in again, with lactic acid build up as a result. This point is known as the lactic threshold, anaerobic threshold or, in technical circles, VO2 max.


Simple and complex carbohydrate?

Anything more than the first 10 seconds of muscle movement needs to get the muscle-fuel ATP from carbohydrate.

Carbs are therefore essential to all movement. The higher the intensity of movement (e.g. exercise) the more important it is to ensure that there[s sufficient carbohydrate in the body to be burned in the oxygen flame. There are, in fact, 2 types of carbohydrate.

Complex Carbohydrates, also known as starchy carbs, take longer to digest and therefore enter the bloodstream and finally the muscle. This means that there’s a kind of drip-feeding of ATP from the complex carbs that you eat, letting you exercise for longer.

For a balanced diet around half of what you eat should be complex carbohydrate, which include:

  • pasta
  • rice
  • potatoes
  • breakfast cereals
  • beans
  • lentils
  • white bread
  • vegetables
  • fruit

Oh, and that minimum of 5 fruit and veg a day is just that… a minimum. Believe it or not, the recommended amount veg & fruit is 5-9 portions per day.

Eating plenty of complex carbohydrate throughout the day will ensure that your body has enough energy to keep you going - and will stop you hitting the wall.

The 2nd type of carb is called simple carbohydrate, found in sugar, jam, cake, biscuits, sweets and soft drinks. Simple carbs provide a short-term boost of ATP to muscles as they’re quickly digested and enter the bloodstream fast. This can be good for boosting short-term energy (which you need after a run, for example), but the spike doesn’t last long.

In a later blog, I’ll write more about carbohydrate consumption & loading for those that do sport,  but for now the big message to take away is to make sure that you’re eating enough complex carbs.