The role of Myoglobin

[Guest guest]

Perhaps this paragraph from Wilmore and Costill on myoglobin will help us

understand the role of myoglobin and the importance of aerobic training in many

high intensity sports.

Ralph Giarnella MD

Southington Ct USA

*******************************

Myoglobin:

When oxygen enters the muscle fiber it binds to myoglobyin. This iron

containing compound shuttles the oxygen molecules from the cell membrane to the

mitochondria.

The ST (slow twitch, TypeI) fibers contain large quantities of myoglobin, which

gives these fibers their red appearance.

The FT (fast twitch,Typei II) fibers, on the other hand, are highly glycolytic,

so they require (and have) little myoglobin, giving them the a whiter

appearance.

More important, their (Type II fibers) limited myoglobin supply limits thier

oxygen capacity, resulting in poor aerobic endurance for these fibers.

**(these three sentences are very important since it helps us understand the

importance of not ignoring the Type I fibers in our training RG)**

Myoglobin stores oxygen an releases it to the mitochondria when oxygen becomes

limited during muscle action. This oxygen reserve is used during the transition

from rest to exercise, providing oxygen to the mitochondria during the lag

betwen the begin of exercise and the increased cardiovascular delivery of

oxygen.

Aerobic training has been shown to increase muscle myoglobin content by 75%-80%.

This adaptation would be expected only if it enhances a muscle's cpacity for

oxidative metabolism.

**(The importance of high intensity aerobic training RG)**

Physiology of Sport an Exercise, Chapter 6, Metabolic Adaptations to Training,

Wilmore and Costill 3rd edition.

>

> Subject: Re: The aerobic mechanism in the 400 metres

> To: Supertraining

> Date: Tuesday, September 30, 2008, 8:39 PM

> I somewhat misstated the Weyand/Bundle's conclusions

> which were as follows:

>

> " Under both normoxic (20.93% O2) and hypoxic (13.00%

> O2) conditions, four fit adult men completed 15 all-out

> sprints lasting from 15 to 180 s as well as progressive,

> discontinuous treadmill tests to determine maximal oxygen

> uptake and the metabolic cost of steady-state running.

> Maximal aerobic power was lower by 30% (1.00 ± 0.15 vs.

> 0.77 ± 0.12 ml O2 · kg-1 · s-1) and sprinting rates of

> oxygen uptake by 12-25% under hypoxic vs. normoxic

> conditions while the metabolic cost of submaximal running

> was the same. Despite reductions in the aerobic energy

> available for sprinting under hypoxic conditions, our

> subjects were able to run just as fast for sprints of up to

> 60 s… "

>

> Maximum aerobic power was reduced by 30%, but the actual O2

> made available to the runners was reduced from 20.93% down

> to 13% which is closer to a 38% reduction in available O2.

>

> The following is a partial description of the test

> procedure:

>

> “For the hypoxic sessions, dry gas was drawn from a

> pressurized cylinder through a large-bore polyethylene

> tubing

> into a 300-liter meteorological buffer balloon. Inspired

> air

> was drawn from the buffer balloon through a corrugated tube

> via a one-way respiratory valve, which subsequently

> directed

> expired air into a series of 120-liter meteorological

> balloons.â€

>

> In essence, they were breathing stale air that had been

> further scrubbed of oxygen.  I believe an exhaled breath

> contains about 15% O2, not 13%, but it has been a long time

> since my last CPR class.

>

> “For the normoxic sprints, a buffer balloon was not used;

> ambient air was

> inspired directly through the one-way valve. "

>

> Jon Haddan

> Irvine, CA

> ===================================

>