VO2max

The monthly newsletter of RunCoachJason.com

Dr. Jason Karp, running & fitness coach, consultant, freelance writer

February, 2005

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In this issue:

Integrating Science with Application—Refueling for Optimal Recovery

Research on VO2max

Lactic Acid Myths

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Integrating Science with Application—Refueling for Optimal Recovery

It is well known that endurance performance is influenced by the amount of stored carbohydrate (glycogen) in skeletal muscles, and that intense endurance exercise decreases muscle glycogen stores.  Despite what you may read in the popular media about low-carbohydrate diets, exercise is a carbohydrate activity, so you need a high carbohydrate diet if you want to run.

 

Muscles are picky when it comes to the time for synthesizing and  storing glycogen.  The synthesis of new glycogen between training sessions occurs most rapidly if you consume carbohydrates  within 30 minutes to an hour after exercise.  Indeed, delaying carbohydrate ingestion for 2 hours after a workout has been shown to reduce the rate of glycogen resynthesis by half.  The most recent evidence suggests that ingestion of 1.2 to 1.5 grams of carbohydrate per kilogram of body weight per hour for a few hours following a workout is optimal for athletes.

 

Initially consume carbohydrates from fluids since the nutrients are absorbed more quickly than from solid foods.  For most commercial sports drinks, such as Gatorade, the above recommendation corresponds to 6 to 7.5 glasses every hour for a 70-kg (154-lb.) athlete.  Admittedly, this is a lot to drink.  For optimal recovery, “carbohydrate replacement” drinks are a better option than “fluid replacement” drinks like Gatorade.  Recent research conducted in our laboratory at Indiana University found that chocolate milk, which is high in carbohydrates, was just as or more effective than other commercial sports drinks for recovery.  Bottoms up with Hershey’s!

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Research on VO2max

One of the most prominent debates in exercise physiology concerns the limiting factors of VO2max, and whether those factors are of a central (oxygen delivery) or peripheral (oxygen use) nature.  Central factors include cardiac output and blood flow, while peripheral factors include mitochondrial and capillary volumes.  Although it is more intellectually appealing and accurate to regard this problem as an integration of many factors, there have, and continue to be, many attempts to pin it on a single most-limiting factor.  For example, research supporting central limitations include findings that VO2max of the quadriceps is greater when they are isolated during exercise compared to whole-body exercise, VO2max decreases with beta blockers due to a decrease in cardiac output, blood doping increases VO2max by increasing hemoglobin concentration, and the capacity for VO2max to increase is much less than that for mitochondrial and capillary volumes.  Research supporting peripheral limitations include findings that VO2max decreases as the partial pressure of oxygen in the muscle (the driving force for diffusion from the muscle capillaries to the mitochondria) decreases, and VO2max increases as a result of an increase in oxygen diffusing capacity when oxygen delivery is held constant.  While unfit people seem to be equally limited by peripheral and central factors (they lack both a high blood flow and abundant metabolic machinery), highly-trained distance runners seem to be more centrally limited.  After all, there is a structural limit to how big the left ventricle of your heart—and thus stroke volume and cardiac output—can get with training.  Since VO2max becomes more stable when one is highly-trained, peripheral adaptations to training, resulting in improvements in lactate threshold and economy, become more important. 

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Lactic Acid Myths

Does lactic acid cause fatigue?  Does it cause your muscles to burn?  Does it cause muscle soreness?  The answer to all of these questions is of course not.  Fatigue is thought to be caused by a number of things, depending on the type of activity, none of which have to do with lactic acid.  Lactic acid has nothing to do with the presence of muscle acidosis and the preconceived association with a burning sensation, which may simply be due to an increase in muscle temperature that accompanies intense exercise.  Muscle soreness is caused by microscopic tears in the muscle fibers.

 

Ever since my first 400-meter race on the track in sixth grade, I have been enamored with lactate.  Although it is a very useful molecule, it has been misunderstood for years by so many, especially regarding its relationship to fatigue.  In My Love Affair With Lactate, which will appear in the March issue of Track Coach magazine, I detail the reasons for this misunderstanding and defuses the many myths about lactate.

 

For a complete list of my publications, go to http://www.runcoachjason.com/publications.  

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©2005 Jason Karp.  All rights reserved.