Physiological question re: exercise

[Slapshot]

For the first 5-7 minutes of aerobic exercise, my legs burn (quads and calves). I usually do Stairmaster but it happens on the elliptical too. I drink plenty of water beforehand, and I stretch. Like clockwork, usually around the 7 minute mark, I stop for 30-60 seconds and then start again. Once I restart the pain is gone, and I complete my workout normally.

Sometimes the discomfort is significant enough that I almost stop. But, now that I know it's temporary, I plow through it (I can do anything for 7 minutes, I tell myself).

I suspect it's lactic acid buildup. Is this caused by lactic acid? If so, any suggestions on how to avoid/reduce it? If it's not lactic, any ideas?

Thanks very much...

[SunnySmile501]

Re: Physiological question re: exercise

This is what I found so far. I still need to google low carb and lactic acid, because lactic acid is a glucose/glycolysis thing. Maybe since you don't have much glucose?

Lactic Acid Build Up and Soreness in Muscles

by Stephen Roth, Ph.D.

As our bodies perform strenuous exercise, we begin to breathe faster as we attempt to shuttle more oxygen to our working muscles. The body prefers to generate most of its energy using aerobic methods, meaning with oxygen. Some circumstances, however, --such as evading the historical saber tooth tiger or lifting heavy weights--require energy production faster than our bodies can adequately deliver oxygen. In those cases, the working muscles generate energy anaerobically. This energy comes from glucose through a process called glycolysis, in which glucose is broken down or metabolized into a substance called pyruvate through a series of steps. When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown--and thus energy production--to continue. The working muscle cells can continue this type of anaerobic energy production at high rates for one to three minutes, during which time lactate can accumulate to high levels.
A side effect of high lactate levels is an increase in the acidity of the muscle cells, along with disruptions of other metabolites. The same metabolic pathways that permit the breakdown of glucose to energy perform poorly in this acidic environment. On the surface, it seems counterproductive that a working muscle would produce something that would slow its capacity for more work. In reality, this is a natural defense mechanism for the body; it prevents permanent damage during extreme exertion by slowing the key systems needed to maintain muscle contraction. Once the body slows down, oxygen becomes available and lactate reverts back to pyruvate, allowing continued aerobic metabolism and energy for the body’s recovery from the strenuous event.
Contrary to popular opinion, lactate or, as it is often called, lactic acid buildup is not responsible for the muscle soreness felt in the days following strenuous exercise. Rather, the production of lactate and other metabolites during extreme exertion results in the burning sensation often felt in active muscles, though which exact metabolites are involved remains unclear. This often painful sensation also gets us to stop overworking the body, thus forcing a recovery period in which the body clears the lactate and other metabolites.

Lactic Acid Build Up and Soreness in Muscles

[SunnySmile501]

Re: Physiological question re: exercise

Hmmmmm...you're a lawyer--I'll supply the "evidence"--you make the case.

ATP-CP Anaerobic Energy Pathway
The ATP-CP energy pathway (sometimes called the phosphate system) supplies about 10 seconds worth of energy and is used for short bursts of exercise such as a 100 meter sprint. This pathway doesn't require any oxygen to create ATP. It first uses up any ATP stored in the muscle (about 2-3 seconds worth) and then it uses creatine phosphate (CP) to resynthesize ATP until the CP runs out (another 6-8 seconds). After the ATP and CP are used the body will move on to either aerobic or anaerobic metabolism (glycolysis) to continue to create ATP to fuel exercise.
Anaerobic Metabolism - Glycolysis
The anaerobic energy pathway, or glycolysis, creates ATP exclusively from carbohydrates, with lactic acid being a by-product. Anaerobic glycolysis provides energy by the (partial) breakdown of glucose without the need for oxygen. Anaerobic metabolism produces energy for short, high-intensity bursts of activity lasting no more than several minutes before the lactic acid build-up reaches a threshold known as the lactate threshold and muscle pain, burning and fatigue make it difficult to maintain such intensity.

Berkeley -- In the lore of marathoners and extreme
athletes, lactic acid is poison, a waste product that
builds up in the muscles and leads to muscle fatigue,
reduced performance and pain.

Some 30 years of research at the University of California,
Berkeley, however, tells a different story: Lactic acid can be
your friend.

Coaches and athletes don't realize it, says exercise
physiologist George Brooks, UC Berkeley professor of
integrative biology, but endurance training teaches the body
to efficiently use lactic acid as a source of fuel on par with
the carbohydrates stored in muscle tissue and the sugar in
blood. Efficient use of lactic acid, or lactate, not only
prevents lactate build-up, but ekes out more energy from the
body's fuel.

<snip>

He and his UC Berkeley colleagues found that muscle cells use
carbohydrates anaerobically for energy, producing lactate as
a byproduct, but then burn the lactate with oxygen to create
far more energy. The first process, called the glycolytic
pathway, dominates during normal exertion, and the lactate
seeps out of the muscle cells into the blood to be used
elsewhere. During intense exercise, however, the second ramps
up to oxidatively remove the rapidly accumulating lactate and
create more energy.

Training helps people get rid of the lactic acid before it
can build to the point where it causes muscle fatigue, and
at the cellular level, Brooks said, training means growing
the mitochondria in muscle cells. The mitochondria - often
called the powerhouse of the cell - is where lactate is
burned for energy.

"The world's best athletes stay competitive by interval
training," Brooks said, referring to repeated short, but
intense, bouts of exercise. "The intense exercise generates
big lactate loads, and the body adapts by building up
mitochondria to clear lactic acid quickly. If you use it up,
it doesn't accumulate."

To move, muscles need energy in the form of ATP, adenosine
triphosphate. Most people think glucose, a sugar, supplies
this energy, but during intense exercise, it's too little and
too slow as an energy source, forcing muscles to rely on
glycogen, a carbohydrate stored inside muscle cells. For both
fuels, the basic chemical reactions producing ATP and
generating lactate comprise the glycolytic pathway, often
called anaerobic metabolism because no oxygen is needed. This
pathway was thought to be separate from the oxygen-based
oxidative pathway, sometimes called aerobic metabolism, used
to burn lactate and other fuels in the body's tissues.
Lactic Acid Can Be Your Friend -Iinterval Training : ASDLC : Active Low-Carber Forums

[SunnySmile501]

Re: Physiological question re: exercise

More stuff

This study underscores at least two points. First, a reduction in carb intake appears to increase the use of fat during aerobic exercise. Second, drastically lowering carb intake for short periods will not adversely affect aerobic exercise. But what, about anaerobic exercise?

Other studies show that depleted muscle glycogen will not hamper anaerobic exercise as much as you'd expect, providing that a source of circulating blood glucose is available. Usually this glucose comes from liver glycogen stores, but a very-low-carb diet will deplete liver glycagen in 12 hours - what happens then? If no carbs are available, the body will convert branched-chain amino acids stared in muscle into glucose in a process occurring in the liver called glucaneogenesis.

But this will only happen if you're consuming a low-protein diet, an uncommon regimen in bodybuilding circles. In most instances, the body will convert excess food protein - up to 57% of protein calories - into glucose. The biggest problem with low-carb diets is that if you consume fewer than 50 grams of carbs a day, your body will convert active thyroid hormone (13) into an inert form called reverse 13. The body uses this device for protection against self-cannibalization. of tissue, such as muscle. Ketones also prevent muscle breakdown during low-carb diets.

Aerobic Exercise and Low Carbohydrate Diets

[Slapshot]

Re: Physiological question re: exercise

Hmm...none of that evidence adds up to lactic acid since I feel it right away. However, this might explain some of the sensation I feel: "If no carbs are available, the body will convert branched-chain amino acids stored in muscle into glucose in a process occurring in the liver called glucaneogenesis."

Thanks for the research. My research prior to posting found similar results. What I can't figure out is why the pain goes away at the same time. Perhaps an endorphin response...

[liv]

Re: Physiological question re: exercise

Do you work out every day?
I really suggest a rest once in a while - your muscles need to time to recuperate.

Also make sure you warm up - not necessarily stretching but light work till your body is nice and warm. Also stretch after your workout. See if that helps

It may sound like you are experiencing some delayed onset muscle soreness.

[Slapshot]

Re: Physiological question re: exercise

Thanks Liv - I work out no more than 5 times a week, alternating 30 and 45 minute sessions on the Stairmaster. The Stairmaster has a warm-up mode which I use, as well.

How would stretching afterwards help?

[kibskix]

Re: Physiological question re: exercise

i think its just a natural thing that happens when working out on some level with everyone. I played soccer for 10 years in my younger days, an I remember that there was a certain point in my 3 mile long runs in practice that in the beginning there was a point that was very uncomfortable but once you push through it, you get into a zone where its not as hard. and that was when i was a kid and eating all kinds of things, not low carb. i wouldnt worry about it.

[sadie147]

Re: Physiological question re: exercise

i think its just a natural thing that happens when working out on some level with everyone. I played soccer for 10 years in my younger days, an I remember that there was a certain point in my 3 mile long runs in practice that in the beginning there was a point that was very uncomfortable but once you push through it, you get into a zone where its not as hard. and that was when i was a kid and eating all kinds of things, not low carb. i wouldnt worry about it.

I agree with this. I run and do stationary bike, and my muscles also burn in the beginning..i thought this was just a natural process during exercise: hence the term 'feel the burn'.

[Kathi22]

Re: Physiological question re: exercise

I think it is the warm up pains. For me, it all burns at first then as I keep going it gets easier. I walk a lot for exercise and the beginning still gets me a little winded and burns my calf muscles then about 5 minutes in I am fine.