Clearing up some misconceptions about the cause of muscle soreness.
By Ken Kashubara, CSCS, USATF-1
The advent of information technology has caused a revolution in education. Tonight, today’s students can read studies published this morning. Never before has the newest information been so available. High school students in AP classes, and collegiate student-athletes, know more than ever before.
Coaches need the athletes’ trust and respect in order for coaches to help athletes reach their full potential. Students are going to class and learning that lactic acid is not the cause of muscular soreness. Lactic acid is not even the cause of the “burn.” Students read the proof and study the facts for their tests. Then when they go to practice, and hear a coach talk about recovery runs “to flush lactic acid,” the students may lose some respect for that coach. They may question the coach, thinking, “well if they think this, and it’s wrong, what else are they wrong about?”
We coaches mostly refer to what we were taught. We were taught the best information available at the time. Even now, when completing an internet search, hundreds of articles on workouts, soreness and recovery provide faulty lactic acid information.
The purpose of this article is to help coaches relay recent scientific information to today’s athletes in a way that they understand.
Why we were taught that lactic acid was the cause
The onset of lactic acid as the culprit of soreness begins with the Krebs Cycle (aka Citric Acid Cycle), continues with the Cori Cycle (aka Lactic Acid Cycle), and ends with the Lactate Threshold. All three of these biological processes are real and valid scientific facts.
The Krebs Cycle is a series of chemical reactions that generates energy for all aerobic organisms (1). The intensity of energy demands determines the substrates for energy. Lower intensity processes use fats as a substrate. When movement increases in difficulty, glucose is used as a faster energy source. Phospho-creatine is used as a substrate when the energy demand is immediate. No matter the energy demand, all substrates must convert into ATP (Adenine Triphosphate) to produce energy.
The Cori Cycle becomes significant in sport as energy demands increase. The human body needs constant energy fuels of ATP during exercise. When an exercise is aerobic (with oxygen), glucose is broken down into pyruvate, and feeds into the Krebs Cycle. When the exercise demands require anaerobic energy (without oxygen), glucose becomes pyruvate, and pyruvate is converted into lactate (2). Lactate is then taken by the bloodstream to the liver. In the liver, lactate is built back into pyruvate, which is built further into glucose.
CORI CYCLE CHART
The Lactate Threshold occurs when blood lactate begins to increase exponentially during anaerobic respiration. Early studies determined that blood lactate levels are elevated during high intensity exercise (3). Lactate is produced faster than the bloodstream can clear it from the muscles during high intensity exercise.
Given this information, early deduction was that since blood lactate (aka lactic acid) was elevated during high intensity exercise, it was the cause of the muscular burn. Furthermore, since high intensity exercise often results in muscular soreness, then lactic acid must be the cause.
This was the best conclusion available at the time. Unfortunately, it is not true.
What is the cause of the burn?
The breakdown of ATP for energy creates the release of hydrogen ions in the bloodstream. This process accelerates with higher intensity exercise, such as sprints and the kick at the end of mid- and long distance races. These hydrogen ions (H+ ion) are protons, and the cause of the “burn.” They impair performance by inhibiting anaerobic ATP production, which hinders the muscle contractile process, and increases acidity of the blood, eventually leading to muscular failure.
Humans may vomit after an extreme bout of exercise. This occurs because the accumulation of H+ ions decrease the pH level of the blood, making it acidic. The already-acidic stomach acids reach an untenable level, and the body vomits in order to reduce the acidity of the body.
Athletes adapt to improve their fitness levels by increasing buffering ability of these hydrogen ions (4). Buffers resist pH change. The first line cellular buffers are proteins; secondary blood buffers include hemoglobin. Perhaps the best adaptation to prevent pH changes is ventilation. Increased oxygen intake, better cellular respiration, increased mitochondria counts, a higher anaerobic threshold, and increased VO2 max all contribute to resisting pH changes during exercise.
Humans can get sore without passing the anaerobic threshold
Take a highly-trained track & field athlete. Make him/her participate in a sixty-minute elite-level gymnastics stretching class. During the class, most of the body positions are static and passive. The athlete is instructed to relax and let gravity do the work. The athlete’s heart rate will not significantly increase. He won’t burn a significant amount of calories when compared to a track practice. He will not get near the lactate threshold. However, the next day, the high level track athlete will be sore. In fact, he will barely be able to get out of bed. How is that possible if he doesn’t cross the lactate threshold?
Delayed Onset of Muscular Soreness (DOMS) is defined as the occurrence of pain arising 24-48 hours after a bout of unaccustomed muscular activity (5). Soreness stems from minor musculoskeletal tears. The pain arises from inflammation, which is the first phase of tissue healing. The muscle repairs itself by increasing collagen production, and then remodels itself with proper collagen fiber alignment and increases tissue strength (6).
The key phrase of the above paragraph is “unaccustomed muscular activity.” Individuals adapt to the imposed demands of their training programs. Take any high level athlete, and place him into a training program with entirely different performance demands, and the athlete will become sore. The principle of overload also applies here. The muscles can get sore from the principle of overload, because the body is not accustomed to the increased volume of work.
Coaches must also keep in mind that soreness can not be completely eliminated from training. Athletes do not have to get sore every workout in order to improve. However, if enough muscle damage occurs, soreness will occur, no matter what precautions are made or supplements taken. Coaches know how to limit the intensity of muscular soreness. Workouts should include a general warmup, specific warmup, introduce exercises simple to complex, easy to hard, and include a cooldown in all workouts.
Lactate is good, and it’s not lactic acid
Lactate production does not cause acidosis, in fact it is the opposite. Lactate production during intense exercise prevents pyruvate accumulation and supplies the NAD(+) needed for phase 2 of glycolysis (7). Lactate delays muscle fatigue and helps exercise performance remain high.
Another reason for the myth of lactic acid creating acidosis in the body may stem from the misconception that lactic acid and lactate are the same compound. They are not. Lactic acid is an acid, and can release a hydrogen ion once pH conditions drop below 7.0 (8). However, the human body does NOT produce lactic acid. Lactate (not an acid), is a product of a side reaction in glycolysis.
Lactate may be in the muscles during the cooldown. However, within a few hours of the completion of a workout, the lactate is completely removed from the muscles. It is not present in the muscles the next day when the recovery workout takes place.
Why do recovery runs actually work?
Recovery runs work. Sore track athletes feel better after completing them, much like the old-school bodybuilding “flushing” workouts. (On a side note, track & field is not the only sport that still refers to recovery workouts as “flushing lactic acid.” The common mistake is nearly an epidemic across western sports coaching vocabulary, and the fountainhead of this article.)
Understanding recovery is the key to understanding why recovery runs work. Recovery can be defined as the body’s ability to repeat or exceed performance after an effort. This includes the normalization of physiological functions (blood pressure and heart rate), restoration of energy storage (glucose and glycogen), and replenishment of cellular enzymes (such as phosphofructokinase.) Recovery is also characterized by continued removal of metabolic end-products (9). Muscle recovery happens during and after workouts.
Recovery is important in all workouts, and is planned in micro- and macrocycles. How long rest is enough between sets to repeat performance? How long between workouts to increase performance? These questions are especially important in track & field. In sports such as basketball or American football, athletes need to be able to jump and accelerate when they are not fully recovered from an effort. Track coaches have the advantage of planning regular rest intervals during practice.
Recovery workouts help the body because of oxygen, warmup effect, training effect, and growth hormones. A recovery workout increases the heart rate, and in turn, increases oxygen intake. The blood brings the oxygen to the muscle, and the oxygen promotes healing. Recovery runs also warm the muscles, which relieves the pain of stiffness.
Light workouts still give the body a training effect. The workouts promote muscle modeling, and increases production of growth hormones. These compounds, combined with oxygen, decrease inflammation and rebuild the impacted muscles, removing soreness and improving function.
The purpose of this article was to translate recovery workout terminology to words that today’s athlete understands and respects. Today’s society is very sensitive to vocabulary. As the Tao Te Ching states, “Perfect words leave no doubts.”
Coaches can no longer use the words “lactic acid” when describing the cause of muscle burning or soreness. Lactic acid is not present in the human body. Hydrogen ions cause the burn. Lactate actually promotes glycolysis. The body gets sore from muscle damage and the ensuing inflammation. Lactate is not present in the muscles by the time the next day’s recovery run takes place.
Coaches can no longer use the phrase “to flush lactic acid” to explain why athletes are completing the running. Say, “this exercise will help promote muscular healing by increasing oxygen and growth hormones in the inflamed muscles,” or simply, “this recovery run will make you feel better.”
Today’s student wants to know why he is doing what he’s doing, and is taught to ask questions. Coaches need to be prepared with the proper answers.
1. Jay J. Weitzman PD (1987). Krebs citric acid cycle: half a century and still turning. London: Biochemical Society, p 25
2. Smith, A.D., Datta, S.P., Smith, G. Howard, Campbell, P.N., Bentley, R., (Eds.) et al.(1997) Oxford Dictionary of Biochemistry and Molecular Biology. New York: Oxford University Press.
3. Moran, Paul; Prichard, Jonathan G; Ansley, Les; Howatson, Glyn. The influence of blood lactate sample site on exercise prescription. Journal of Strength and Conditioning Research, February 2012—Volume 26—Issue 2—p 563-567
4. Owen Anderson, PH.D. Buffers, the hydrogen slayer, Runner’s World, February 27, 2017
5. Zimmerman, K; Leidl, K; Kasha, C, et al. Central projection of pain arising from delayed onset of muscular soreness (DOMS) in human subjects. PLoS One, 2012; 7(10):e47230. DOI: 10.1371/journal.pone.0047230
6. Thomas R. Baechle, Roger W. Earle, editors. Essentials of Strength Training and Conditioning. Third Edition. National Strength and Conditioning Association.
7. Robergs, R.A., Ghaisyand, F., & Parker, D. 2004. Biochemistry of exercise-induced metabolic acidosis. American Journal of Physiology—Regulatory, Integrative and Comparative Physiology, 287, R502-16
8. Len Kravitz, PhD. IDEA Health and Fitness Association. Lactate—not guilty as charged. June 01, 2005.
9. Jonathan N. Mike, MS and Len Kravitz, PhD. Recovery in training: the essential ingredient. IDEA Health and Fitness Association. February 02, 2009.
Ken Kashubara is a Certified Strength and Conditioning Specialist and a USTF Level 1 Certified coach. He has been certified as a personal trainer by the National Academy of Sports Medicine and American Council on Exercise, and holds many other sport and fitness related certifications. He has trained national-qualifying competitors in track and field, tennis, rhythmic gymnastics and figure skating. Ken has published over 255 health and fitness articles, and his writing has been featured in three books. He runs a USATF approved club, Sport Heaven, out of his gym in Bloomfield Hills, Michigan.