Two topics that are getting a lot of discussion time recently are glycemic index and lactic acid. But what do they mean for cyclists and fueling for a ride?
I’ve posted and digested some information below for you to read on the subjects. Some references I found had way too much math in them for me to understand, so I simply dismissed them as inaccurate…
See what I mean:
Plasma glucose (A), serum insulin (B), and serum free fatty acid (FFA;C) concentrations (marked by brackets) for the 2-h period postprandial and during 2 h of steady-state exercise.
Now, back to English:
The glycemic index (GI) reflects how quickly an ingested carbohydrate will trigger a rise in the circulating blood glucose level, the higher the GI, the faster the blood sugar response. The GI of any carbohydrate ranks that food relative to pure glucose — and runs from 0 to 100 (with 100 being equal to pure glucose). All else being equal (a liquid versus solid supplement, a low fat versus fat containing food), the glycemic index will identify the energy supplement which will provide the quickest blood sugar boost, again, the higher the GI, the faster the energy boost.
A number other factors influence how quickly the carbohydrates in food raise blood sugar levels, including:
- Fiber content. Fiber helps shield the carbohydrates in food from immediate digestion, so the sugars in fiber-rich foods tend to be absorbed into the bloodstream more slowly.
- Ripeness. A ripe fruit or vegetable has a higher sugar content than one that is still green and, therefore, has a higher glycemic index.
- Type of starch. The type of starch granules in a food influences how fast the carbohydrates are digested and absorbed into the bloodstream. The starch in potatoes, for example, is digested and absorbed into the bloodstream relatively quickly.
- Fat content and acid content. The higher a food’s fat content or acid content, the slower its carbohydrates are converted to sugar and absorbed into the bloodstream.
- Physical form. Finely ground flour has a higher glycemic index than more coarsely ground flour.
Bottom line is: Some athletes and coaches have speculated that altering the GI of the training diet or pre race meal might influence their performance with a low GI pre race meal conferring an advantage (less insulin surge and blood sugars remaining elevated over a longer period of time post meal). However, controlled studies have failed to demonstrate any advantages of a low compared to a high GI pre-race meal.
And, of course, there is a little bit of a debate on lactic acid too. And to keep from misinterpreting or misprepresenting something out of sheer ignorance, I’ve copied two articles about the topic instead of my usual “Readers Digest” compilation.
Lactic Acid Is Not Muscles’ Foe, It’s Fuel
By GINA KOLATA; May 16, 2006 New York Times
Everyone who has even thought about exercising has heard the warnings about lactic acid. It builds up in your muscles. It is what makes your muscles burn. Its buildup is what makes your muscles tire and give out.
Coaches and personal trainers tell athletes and exercisers that they have to learn to work out at just below their “lactic threshold,” that point of diminishing returns when lactic acid starts to accumulate. Some athletes even have blood tests to find their personal lactic thresholds.
But that, it turns out, is all wrong. Lactic acid is actually a fuel, not a caustic waste product. Muscles make it deliberately, producing it from glucose, and they burn it to obtain energy. The reason trained athletes can perform so hard and so long is because their intense training causes their muscles to adapt so they more readily and efficiently absorb lactic acid.
The notion that lactic acid was bad took hold more than a century ago, said George A. Brooks, a professor in the department of integrative biology at the University of California, Berkeley. It stuck because it seemed to make so much sense.
“It’s one of the classic mistakes in the history of science,” Dr. Brooks said.
Its origins lie in a study by a Nobel laureate, Otto Meyerhof, who in the early years of the 20th century cut a frog in half and put its bottom half in a jar. The frog’s muscles had no circulation — no source of oxygen or energy.
Dr. Myerhoff gave the frog’s leg electric shocks to make the muscles contract, but after a few twitches, the muscles stopped moving. Then, when Dr. Myerhoff examined the muscles, he discovered that they were bathed in lactic acid.
A theory was born. Lack of oxygen to muscles leads to lactic acid, leads to fatigue.
Athletes were told that they should spend most of their effort exercising aerobically, using glucose as a fuel. If they tried to spend too much time exercising harder, in the anaerobic zone, they were told, they would pay a price, that lactic acid would accumulate in the muscles, forcing them to stop.
Few scientists questioned this view, Dr. Brooks said. But, he said, he became interested in it in the 1960’s, when he was running track at Queens College and his coach told him that his performance was limited by a buildup of lactic acid.
When he graduated and began working on a Ph.D. in exercise physiology, he decided to study the lactic acid hypothesis for his dissertation.
“I gave rats radioactive lactic acid, and I found that they burned it faster than anything else I could give them,” Dr. Brooks said.
It looked as if lactic acid was there for a reason. It was a source of energy.
Dr. Brooks said he published the finding in the late 70’s. Other researchers challenged him at meetings and in print.
“I had huge fights, I had terrible trouble getting my grants funded, I had my papers rejected,” Dr. Brooks recalled. But he soldiered on, conducting more elaborate studies with rats and, years later, moving on to humans. Every time, with every study, his results were consistent with his radical idea.
Eventually, other researchers confirmed the work. And gradually, the thinking among exercise physiologists began to change.
“The evidence has continued to mount,” said L. Bruce Gladden, a professor of health and human performance at Auburn University. “It became clear that it is not so simple as to say, Lactic acid is a bad thing and it causes fatigue.”
As for the idea that lactic acid causes muscle soreness, Dr. Gladden said, that never made sense.
“Lactic acid will be gone from your muscles within an hour of exercise,” he said. “You get sore one to three days later. The time frame is not consistent, and the mechanisms have not been found.”
The understanding now is that muscle cells convert glucose or glycogen to lactic acid. The lactic acid is taken up and used as a fuel by mitochondria, the energy factories in muscle cells.
Mitochondria even have a special transporter protein to move the substance into them, Dr. Brooks found. Intense training makes a difference, he said, because it can make double the mitochondrial mass.
It is clear that the old lactic acid theory cannot explain what is happening to muscles, Dr. Brooks and others said.
Yet, Dr. Brooks said, even though coaches often believed in the myth of the lactic acid threshold, they ended up training athletes in the best way possible to increase their mitochondria. “Coaches have understood things the scientists didn’t,” he said.
Through trial and error, coaches learned that athletic performance improved when athletes worked on endurance, running longer and longer distances, for example.
That, it turns out, increased the mass of their muscle mitochondria, letting them burn more lactic acid and allowing the muscles to work harder and longer.
Just before a race, coaches often tell athletes to train very hard in brief spurts.
That extra stress increases the mitochondria mass even more, Dr. Brooks said, and is the reason for improved performance.
And the scientists?
They took much longer to figure it out.
“They said, ‘You’re anaerobic, you need more oxygen,’ ” Dr. Brooks said. “The scientists were stuck in 1920.”
Every Cyclist’s Enemy: Exploring Lactic Acid
By Edmund R. Burke, Ph.D.
We have all experienced the severe leg pain that comes at the end of a hard jam, a fast climb, or an all-out sprint. This pain is caused by a nemesis of the hard-working cyclist: lactic acid build-up in the muscles.
Just What Is Lactic Acid?
Lactic acid is the end product of anaerobic metabolism, which occurs when there is insufficient oxygen to produce the energy (ATP) required by exercise.
Glycogen stored in the muscle cells is the sole fuel used for anaerobic work. It breaks down to glucose, then pyruvate, and finally to lactic acid when there is not enough oxygen present to the muscle cells.
When that’s as far as the process can go because of a lack of oxygen, the result is muscular pain. On the other hand, a sufficient supply of oxygen will allow some lactic acid to be burned and some to be converted back to glycogen. This is the relatively pain-free process of aerobic metabolism.
So, a major factor in lactic acid buildup is the exercise intensity. At about 75 to 85 percent of a cyclist’s aerobic capacity, lactic acid production begins increasing in direct proportion to work. When a very high or maximum level of work is reached, lactic acid production becomes constant.
Why it Hurts
At high lactic acid levels, muscular contraction is inhibited. This happens because proteins in muscle cells can function only within a certain range of acidity. Excess lactic acid simply shuts down cellular reactions. The result is acute muscle fatigue. Either the exercise must be stopped or its intensity greatly reduced.
During exercise and for a time afterward, lactic acid escapes from muscles into the blood. Amounts as high as 20 times the resting level have been found after extreme anaerobic work. The exact fate of this excess is not entirely understood.
We do know that the liver is involved with its removal of some lactic acid from the blood. The liver transforms lactic acid into glucose, which is either stored as glycogen or sent out as blood sugar. Through another complicated process, lactic acid is used for fuel by certain heart and muscle cells.
Always keep pedaling after a hard effort. Lactic acid is more rapidly removed from the muscles and resynthesized by light exercise than by rest.
Can Training Make Your Muscles Produce Less Lactic Acid and Tolerate it Better?
It appears so. When your aerobic capacity is increased with training, you produce less lactic acid than you do when untrained. The reason: your aerobic system can better handle lactic acid’s precursor, pyruvate.
You are also better able to burn fat for fuel, a process that does not directly produce lactic acid. During maximum efforts, you will also be able to withstand higher lactic acid levels in the muscle, before they begin to fatigue.
Dr. Edmund R. Burke was among the pioneers in applying scientific principles to endurance sports training, especially cycling. As an exercise physiologist, he was responsible for several advances in sports drink formulation and almost single-handedly developed the subcategory of performance recovery drinks. A former director of the Center for Science, Medicine and Technology at the U.S. Cycling Federation in Colorado Springs, he worked with the U.S. Olympic cycling team during the 1980 and ’84 Games. Dr. Burke is the author of 17 books on fitness, training and physiology, including the best-selling Optimal Muscle Recovery.