New Light On Muscle Efficiency: It Is Not The Power-plant

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New Light On Muscle Efficiency: It Is Not The Power-plant

http://www.medicalnewstoday.com/medicalnews.php?newsid=40147

A recent study from Scandinavia shows that the well-known differences

between individuals in the efficiency of converting energy stored in

food to work done by muscles are related to muscle fibre type

composition and to the content of specific molecules in muscle.

When muscles contract they use energy that is derived from food. It

is a two-step process. The first step occurs in mitochondria, where

the energy from molecules like glucose or fats is locked away in ATP

(adenosine triphosphate). This ATP travels from the mitochondria to

sites in the muscle where energy is needed, and the energy is

released and used. At both of these stages there is the possibility

for energy to be lost, causing a reduction in efficiency. The

proportion of food energy that ends up making the muscles move is a

measure of the efficiency of the system, and this is known to vary

considerably between people.

The main theory is that this variation comes from differences in the

efficiency with which mitochondria convert food energy to ATP. But

results published in this fortnight's edition of The Journal of

Physiology indicate that any differences in the efficiency of

individual mitochondria cannot explain the differences in overall

efficiency between people. Consequently these differences must lie in

the way the ATP is used within the muscle.

The research was carried out on healthy human volunteers by a team of

scientists working at the University of Southern Denmark, Odense, and

the Karolinska Institute/GIH, in Stockholm, Sweden. It combined

exercise testing of individuals, with laboratory analysis of muscle

samples.

The results showed that work efficiency was correlated with muscle

fibre type composition and with the amount of UCP3 protein - muscles

with high proportions of this protein had lower efficiencies than

those with low proportions.

" It's too early to say whether UCP3 causes this difference, or

whether it is a marker of some other process, but further research

might someday lead to training strategies that will help us improve

efficiency, or identify subjects who have the potential to become

more efficient over time, " says lead author Mogensen.

" The work is an excellent example of integrative physiology,

addressing questions both at the sub-cellular and whole body levels

that have implications for basic muscle energetics as well as

athletic performance, " says Professor Coyle, of the University

of Texas at Austin, in an accompanying editorial.