Guest Post by Scott Bias
The Burn – Heavy Legs – Hitting The Wall.
We’ve all felt it!
During intense exercise you will experience burning and fatigue in your muscles, referred to as acidosis. Traditionally this has been explained as an increase in the body’s production of lactic acid. The cause of acidosis during intense exercise has been a major topic of discussion between fitness professionals and trainers for years. Many fitness specialists believe that lactic acid or lactate production is the cause of muscle fatigue during intense exercise.
Recently, Robergs and colleagues (2004) Completed an extensive review of the biochemistry of exercise-induced metabolic acidosis. This reexamination delivers a much more complete understanding of lactate production and acidosis. From this publication, brief highlights of the history of lactic acid understanding will be covered as well as a more contemporary scientific understanding of acidosis. Some practical training applications will be offered that can dramatically improve an athletes muscle stamina, strength endurance and VO2max (The volume of oxygen consumed at max effort).
A Brief History of Lactic Acid!
In 1789, Carl Whilhelm Sheele, a Swedish chemist, isolated an acid in sour milk samples. This milk origin led to it being named ‘lactic acid, which means relating to milk. By 1810 chemists had verified the presence of lactic acid in other organic tissues such as meat and blood. By 1833, the actual chemical formula for lactic acid had been determined. By 1869, scientists observed different isomers (atomic compounds with differing energy states) of lactic acid along with its formation in fermentation reactions. Fermentation is an enzyme-driven chemical change in an organic (contains carbon) compound whereby the substance is split into simpler compounds.
The prevailing understanding regarding lactic acidosis in humans can be attributed to some early researchers of skeletal muscle biochemistry during exercise. Two noted original researchers were Otto Meyerhoff and Archibald V. Hill, who in 1922 both received a Nobel price for their research into energy capabilities of carbohydrate metabolism in skeletal muscle.
It was Meyerhoff who suggested that lactic acid was a side reaction to glycolysis (break down of sugar) in the absence of oxygen. The research of Hill and Meyerhoff solidified the acceptance of lactic acid production and acidosis into the mind-set of academia although this was primarily based on incomplete observations of cell metabolism at the time. The Nobel prize quality of work of Meyerhoff and Hill was proof enough to the scientific world at that time, that lactate production and acidosis were cause-and-effect.
It’s important to point out that this revealing history of acidosis and lactate, exposes one important message. There really never was experimental research demonstrating a cause-effect relationship between lactate production and acidosis. Yet, the work of these early pioneers has been accepted as the final explanation of acidosis for more than 80 years.
Lactate is Still Thought to Cause Acidosis Today.
Many educators and researchers still believe that lactate production is the cause of acidosis. Most textbooks simply do not provide and explain the chemically balanced reactions occurring during metabolic acidosis. This incomplete description of acidosis in textbooks has led to the acceptance of lactate as cause, by most fitness professionals today.
What’s the Actual Cause of Acidosis?
During vigorous exercise, the ATP (Adenosine Triphosphate, a compound cells derive energy from) demands of muscle contraction are considerable. Every time an ATP molecule is split for energy, it is broken down into an ADP (Adenosine Diphosphate) molecule and inorganic phosphate molecule, with the release of one hydrogen ion (aka proton). It’s that increase in protons that defines and causes acidosis, quantified by a decrease in pH below 7.0.
When the ATP demands of exercise are being met by aerobic metabolism (aka mitochondrial respiration), the accumulated protons get used for important aspects of cell metabolism. However, during extremely intense exercise (above steady cardio), an accumulation of protons occurs in the muscle due to a much higher involvement of the phosphagen and glycolytic energy systems providing ATP for muscle contractions. Robergs et al. (2004) biochemically explain and illustrate (with chemical structure reactions) how the ATP supplied from the phosphagen and glycolygic energy systems is the source of the increased proton accumulation in the cell, and thus THE CAUSE of acidosis which you experience as muscle fatigue and burning. This stage is known today as Lactate Threshold but perhaps now that we know lactate is not the true culprit its time for a more accurate description.
What to do about Acidosis!
So now that we’ve redefined the cause of general muscle fatigue during exercise as excess hydrogen (protons) and not lactic acid, what can we do about it. There are specific training methods that result in better proton buffering capacity by building mitochondrial and capillary density. This means that your muscles can improve their ability to work longer and harder before eventually succumbing to fatigue from acidosis.
The key here seems to be training at the right intensity. Enough time must be accumulated at 80 to 90% of max heart rate, VO2Max (Volume of oxygen consumed) or applied muscle tension (lifting weights). One of the best methods for accomplishing this is HIIT high Intensity Interval Training. Intervals are basically an intense phase followed by a rest phase, repeated over and over. This can be applied to sprinting, weight training and pretty much any other sport specific activity.
By spending enough time in this IMPROVEMENT ZONE you are sending a message to your cells to adapt to high hydrogen (proton) levels and become more efficient at processing them during intense exercise.
Why do intervals?
If you go out and sprint at 90% of your max for as long as you can, you will get exhausted very quickly. Most likely within the first 200 meters your pace will slow down enough so that you are no longer in the improvement zone. On the other hand, if you stop at 100 meters and rest, then repeat the sprint 6 to 8 more times, every run will be of high enough intensity to be in the improvement zone. 8 x 100 meters = 800 meters of near max effort sprinting.
That’s a lot of time in the ZONE compared to one continuous effort that fades before the 200 meter mark. The more quality basketball training time you spend at 80 to 90% of max effort, the better your body adapts to high proton levels and the longer and harder you can perform at a high level.
Work Hard! Train Hard!