The benefits of lactic acid accumulation in muscle cells has been recently debated. Scientists arguing that lactic acid is “the latest performance-enhancing drug” have drawn false conclusions by over interpretation of their data (Lindinger). In “Point:Counterpoint: Lactic acid accumulation is an advantage/disadvantage during muscle activity” a series of debates took place within the Journal of Applied Physiology in search of the truth behind the benefits of Lactic acid accumulation. Jens Bangsbo and Carsten Juel of Copenhagen Muscle Research Center and the University of Copenhagen argue that “, the negative consequences of lactic acid accumulation far exceed any positive effects” (Lindinger). Multiple studies on lactic acid production in humans have linked elevated lactate levels to higher pH in muscle cells. In one study, after completing an arm exercise, subjects were able to perform a subsequent leg exercise at about 75% compared to controls (Lindinger). In experiments with animal models, muscles incubated in lactic acid that underwent repeated exhaustive stimulation showed faster fatigue development (Lindinger). In an experiment with isolated dog muscle, lactate ion perfusion reduced muscle twitch force by 15% (Lindinger). Most experiments conclude that lactate acid effects are associated to the function of the muscle membrane and not the skinned muscle fibers. Other studies have linked lactic acid formulation with impaired performance of Ca²⁺ release channels (Lindinger).

Evidence also suggests lactic acid production plays a role in conveying fatigue related information to the brain (Ishii). In one study eleven healthy adults performed hand grip exercises at varying intensities for 120 seconds. The exercises caused significant fatigue while their brain activity increased at 30% and 50% maximal voluntary contraction (Ishii). Blood lactate and flow rates also increased during the study; most notably at these percentages. The authors through analysis were able to conclude that these two factors may convey load intensity to the brain during fatigue (Ishii).

Ishii, Hideaki, and Yusuke Nishida. “Effect of Lactate Accumulation during Exercise-induced Muscle Fatigue on the Sensorimotor Cortex.” Journal of physical therapy science vol. 25,12 (2014): 1637-42. doi:10.1589/jpts.25.163

Lindinger, Michael Ivan. “Lactic Acid Accumulation Is an Advantage/Disadvantage during Muscle Activity.” Journal of Applied Physiology, vol. 100, no. 6, 2006, pp. 2100–2102., doi:10.1152/japplphysiol.00213.2006.

For this week’s blog post I am discussing the idea that lactic acid accumulation during muscle activity is advantageous. Many people believe that lactic acid accumulation is the cause of muscle fatigue but this is not true and is supported by the information in the Point:Counterpoint article as well as a further reason study that I found.

The Point:Counterpoint article explains how there are a few main causes of muscle fatigue, none of them being accumulation of lactate. The authors describe muscle fatigue as a “disturbance to any of the steps in excitation-contraction (EC) coupling” (1410). Based on this definition, they then explain the types of muscle fatigue, which include a buildup of K+ in the T-system and metabolic fatigue.  A buildup of K+ in the T-system depolarizes the fiber, which then slows or prevents the Na+ channels from recovering, and ultimately results in failure of action potentials. On the other hand, metabolic fatigue refers to the effects of metabolites and decrease in substrates. They even add that the slightly lowered pH as a result of lactate ions and high intracellular H+ seems to slow the onset of fatigue.

A research article that further the supports the idea of lactate having a positive impact rather than a negative one, describes an experiment performed on mice. They investigated mouse skeletal muscle tissue under the conditions of control, injected lactate, injected cardio toxin, and injected lactate after injected cardio toxin. The injections were performed 5 days a week for 2 weeks. The results showed that in the lactate group and lactate after cardio toxin group, there was an increase in muscle weight, fiber cross-sectional area, and facilitation of the recovery process as a result of the damages caused by the cardio toxin. These findings suggest that lactate can potentially stimulate muscle hypertrophy and/or the generation of muscle tissue and therefore support the idea that lactate accumulation is positive. Applied to exercise in humans, maybe the lactate helps to regenerate our muscle cells that get damaged from exercise such as weight lifting.

Ohno, Y.; Ando, K.; Ito, T.; Suda, Y.; Matsui, Y.; Oyama, A.; Kaneko, H.; Yokoyama, S.; Egawa, T.; Goto, K. Lactate Stimulates a Potential for Hypertrophy and Regeneration of Mouse Skeletal Muscle. Nutrients 2019, 11, 869. https://www.mdpi.com/2072-6643/11/4/869.

It was not until recently that lactic acid was viewed upon as a potential source of energy, and, in fact, is not the reason for muscle fatigue. There are several different types of muscle fatigue, the varying differences are dependent on the type of physical activity as well as the muscle fiber type. The first type of fatigue is due to a buildup of K+ in the transverse-tubular system and in the adjacent muscle fibers. This buildup depolarizes the fiber and hinders Na+ channels from recovering. This type of fatigue can be significant since the concentration of K+ during intense activities can reach high levels. Another type of muscle fatigue is known as “metabolic fatigue.” This type of fatigue emerges due to the indirect or direct effects of metabolite buildup and decrease in substrates within muscle fibers. In fast twitch muscle fibers, cellular ATP drops to extremely low levels and can cause a reduction in the release of Ca2+. This fatigue can also occur due to the direct or indirect effects of glycogen depletion. Decreasing the pH of muscle fibers from 7.1 to less than 6.7 does not expedite or cause onset fatigue, instead, it slows its onset. In fact, decreasing intracellular pH to 6.7 negates the inhibitory effects of an increase in extracellular potassium concentration.

According to a paper in the American Journal of Physiology, UC Berkeley researchers concluded from their lab results that muscle cells use carbohydrates anaerobically for energy, which produces lactase as a byproduct, and then uses the lactate alongside oxygen to generate more energy. The first method is called the “glycolytic pathway”, and is the main pathway during normal exercise. During this method, lactate trickles out of the muscle cells to be used elsewhere. However, during intense workouts, the rapidly accumulating lactate is oxidatively removed to create more energy.

https://www.sciencedaily.com/releases/2006/04/060420235214.htm

Lactate accumulation has been thought to cause muscle fatigue and adverse affects during exercise but there is enough evidence to dispute this point. According to the Point:Counterpoint article, lactic acid accumulation is not the cause of muscle fatigue, it is due to the issues in the excitation-contraction coupling. Increase in K+ causes fatigue by depolarizing the fibers and interfering with the Na+ channels.  As metabolites increase such as ADP and Mg2+ and ATP and glucose decrease, muscles fatigue as well. EC coupling is also not affected by the pH changes that come along with lactate accumulation, in fact the lower pH actually releases more Ca2+. McArdle’s disease also stands as an example of how lactate is unrelated to muscle fatigue because these patients are unable to produce lactic acid, yet they fatigue much faster. This provides evidence that the muscle fatigue is indeed caused by other factors and metabolites, not lactic acid. Fast twitch glycolytic fibers also express a specific monocarboxylate transporter that produces a high amount of lactic acid, whereas they could have a different isoform that does not produce as much acid. It must be beneficial for these muscles to have this increased lactate production.

Not only is lactic acid not responsible for muscle fatigue, it also has separate benefits that make lactic acid accumulation beneficial. An article I read titled, “Effect of Lactate Accumulation during Exercise-induced Muscle Fatigue on the Sensorimotor Cortex” used eleven healthy men and a handgrip muscle fatigue exercise to record rates of lactate accumulation and consequent brain activity flow. They found that as the muscles began to fatigue lactate did accumulate in the muscles, but there was also a strong positive correlation with signals to the sensorimotor cortex. Brain activity and signaling could be affected by lactate levels, meaning that without the build up of lactate the sensorimotor pathways could be altered. Lactic acid definitely increases with increased exercise, but there is not enough evidence to say that lactic acid causes muscle fatigue and it is actually likely correlated with pathways that are beneficial for the muscles.

This week I am writing on the side of lactate build up is advantageous during exercise.

The author argued for that lactic acid accumulation inside muscle fibers is not responsible for muscle fatigue. In fact, the reason that muscle fatigue occurs is due to the disturbance of any of the steps in excitation-contraction (EC) coupling in muscles. There are several types of muscle fatigue, and each one is caused by different attributes of exercise. One major type of fatigue is caused by the buildup of potassium ions in the transverse-tubular or T tubular systems. The other type of fatigue occurs by direct or indirect effects of the accumulation of metabolites, as we discussed in class earlier this week. And finally, the reduction of calcium ions released from the sarcoplasmic reticulum (SR) can indirectly cause muscle fatigue.

Lactate ions in the cytoplasm of muscle cells, even at high concentrations, do not impair EC coupling. Along with this, high concentrations of hydrogen ions, a by-product of the breakdown of lactate, has few, if any, harmful effects on EC coupling. This is because normal controlled calcium release is little, if at all, inhibited by low pH, which would incur with high concentrations of hydrogen ions in the body. In fact, in a single intact muscle fiber, decreasing pH from 7.1 to less than 6.7 does not cause or accelerate the onset of fatigue, but actually slows its onset! An increase in intracellular acidity can increase cytoplasmic calcium and consequent activation of contractile apparatus, because SR calcium pumps bind and requester calcium even more so at acidic pHs. This would actually reverse the  reduction of calcium ions, which as I mentioned above, is one of the causes of muscle fatigue.

Another cause I mentioned, is the accumulation of metabolites during exercise. I found an article on google scholar (did not find one I liked on pubmed,) that researched biomarkers of peripheral muscle fatigue during exercise. The article kept mentioning how their was an increase in lactic acid accumulation in increased exercise intensity and how that proved muscle fatigue, however gave no evidence to support that. Meanwhile, they were mentioning other metabolites that we spoke of earlier this week, such as ammonia, hypoxanthine and xanthine, that have been proven to disrupt EC coupling.

Lactate is helping us out people! We <3 lactate.

Source: https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/1471-2474-13-218

This week I am writing about why lactate accumulation is advantageous to the body.  Using the article given by Coach Kirkton, I found some reasoning why it helps out the body. The body can experience multiple kinds of muscle fatigues, the first is caused by a build up of K+, which depolarizes the fiber and prevents Na+ channels from recovering. Another type is called “metabolic fatigue” due to the indirect/direct accumulation of metabolites and a decrease in substrates within the fibers. It can also occur from glycogen depletion.  The accumulation of lactate causes a change in pH within the muscle fibers, which actually slows the onset of fatigue. The pH changes from 7.1 to less than 6.7 which causes the solution to be acidic. This acidity increases the Ca concentration and help activate the contraction. The pH also counteracts the inhibitory affects of the raised [K+]. In short, the lactate accumulation helps prevent or slow down the failure of the action potential of the muscle fibers.

I also found another article, titled “Lactate: valuable for physical performance and maintenance of brain function during exercise”.  Not only can lactate slow the high [K+] but also noxious metabolites such as Inorganic phosphates. They also facilitate the removal of muscular proton and acts together with catecholamines to work in reducing fatigue. Lactate also regenerates NAD+ which is used within glycolysis to produce energy. Lactate is also important for cognitive function, it ensures that inhibitory signals within the CNS are detected, so it protects neurons from damage by acidosis.

For a long time lactate has been seen as a waste product but it actually an alternative energy source that the body can use to recover and continue to work. It not only does it help the body during exercise but also when the body is at rest. This is why lactate accumulation is helpful and advantageous for the human body.

Source: https://academic.oup.com/biohorizons/article/doi/10.1093/biohorizons/hzu001/242608#26872984

1. I am not very athletic, so I don’t really have an athletic accomplishment to share. When I was younger, however, I was slightly more fond of outside activities. Even though I was a city kid, I would spend my summers in a suburban area, where it was more necessary to get entertainment outdoors. I enjoyed swimming, to the point that I could go everyday and never get bored. I also had an uncle who greatly enjoyed the outdoors, and who often took me out to experience nature. I would go hiking occasionally with my cousins during this time, or ride bikes. Although they aren’t exactly accomplishments, they are fond childhood memories relating to athletics.
2. Exercise physiology would give more insight into the human body. Someone who isn’t very active will have a very different body type compared to a trained athlete. A runner will have a different body type compared to a football player. With exercise physiology, you learn what these differences are, how they developed,and why they can develop. Biology is about understanding the differences in living organisms, so I think this course will teach me about biological differences  in a field that I’m currently unfamiliar with.
3. I previously took endocrinology, which could be helpful in understanding how some hormones are involved in exercise. I also took molecular genetics, which can also help to explain certain pathways and molecules that are common in physiology. It can also help to understand why some things are hereditary.

Hi class,

As some of you know, I am on the Crew Team here at Union and was a very active member until I separated my shoulder last term. Crew has pushed the boundaries of my cardiovascular and endurance performance. This past fall, the team and I competed at a few regattas before wrapping up for winter break. I wanted to come back from winter break as a more powerful rower, so I honestly just worked out like crazy – lifting weights and doing cardio. I came back and set a new personal record on the erg (rowing machine) every time I sat on one. What helped me perform better was that I pushed back the display screen so I couldn’t see how I was doing throughout the pieces. Instead of working for a number, I was listening to my body and pulling however hard my body could. I really couldn’t believe how well I was performing and it seemed the harder I worked, the harder I wanted to work! This also proved to me that your mind plays a huge role in restricting or enhancing your performance. When I stopped my mind from convincing me that I was tired, I realized that I could row harder, longer.  

I think that the mechanisms that govern performance during exercise (on a cellular or organismal level) may be reflections or even exaggerations of what takes place on a normal basis. When you put the body under stress to metabolize faster, it might help us highlight what takes place on a day to day basis. Here are a few other thoughts: (1) we already talked about negative feedback loops like the pH of the blood and respiration rates, so I am guessing that feedback loops in general play an important role in exercise physiology. I have noticed in my other classes that feedback loops pop up a lot in biology, so maybe studying them in exercise physiology will help us understand how they work in other biological systems. (2) Also, maybe studying comparative exercise physiology can help us characterize phylogenetic trees which would help biologists understand evolution further! And, (3) on Wednesday 4/3 we talked about sensors, integrators and effectors. Studying how these biological components work and communicate with each other may help us understand what occurs on a biochemical level. Or maybe it is the other way around, understanding what takes place biochemically can help us understand exercise physiology to a greater extent.

It seems that in all of biology, structure is inevitably related to function. To understand physiology we must first understand anatomy of the systems we will study. This is where pre-existing knowledge of biology, biochemistry, and neuroscience can come into play. I’m excited to take physiology to the next level – studying it when the body is put to stress (i.e. exercise). How much of our exercise physiology can be explained by what our ancestors physically needed to do to survive? Chasing down big game might explain our great long-distance endurance running ability. In this way, I can see history playing an important role in exercise physiology. I believe just having had discussions in previous upper-level science classes will help make our discussions in this class great – practice makes perfect. I can even see the material in BIO 112 – anatomy and physiology of the respiratory and cardiovascular systems – helping to contribute to our discussions in this class. Maybe also knowing the pKa’s of molecules such as carbonic acid – learned in organic chemistry and biochemistry – will help me contribute to discussions. Similarly, interactions of molecules must play a role in exercise physiology! I’m sure that learning back to front about proteins in BCH 382 and lipids and carbohydrates in BCH 380 will help in exercise physiology! These are the fuels that our muscles can use to power acute or prolonged exercise. Can’t wait to learn more!

See you all in class tomorrow,

Tommy

1. My favorite athletic accomplishment is when I was ranked as #1 across the country for d3 shots blocked per game. Playing basketball in college was always a goal I had growing up. Not only getting to be on a collegiate team, but actually being a contributor on the team was really exciting. I’ve always been one of the taller kids on the court. That in combinations with my long arms help me be good at blocking shots. It was never a goal to be really good at blocking shots, it was always kind of an added bonus when you did.I honestly didn’t even know that shots blocked per game was a stat tracked that prominently. Making it to the top of the NCAA rankings was pretty cool and something I never thought would happen. .
2. Exercise physiology can serve as a paradigm for understanding biology in many ways. Learning about exercise physiology and different biological systems of the body gives you a broader understanding of biology. Learning about how energy is produced or how different muscles work/are used or how breathing plays works all boils down to biological concepts. Understanding the make up of a muscle with the different tissues and fibers is a small scale picture for learning biology. When you put all the muscle cells together it can create a muscle fiber and as you add more information together it leads to learning about how muscles contract or fatigue and ultimately, you can relate that to exercise. Relating it to exercise can be linking the muscle movements to how different muscles are activated for different exercises.
3. Some previous upper level courses I’ve had that can contribute to exercise physiology are Topics in Physiology and Orthopedic Biomechanics. Topics in Physiology is kind of self explanatory as to how it relates. It was the foundation and introduction to physiology learning about how some of the biological body systems work. Learning about the make up of muscles and how they work can be applied to exercise physiology when we learn about skeletal muscles. In Orthopedic Biomechanics we learned all about the different muscles in the body. We talked about different joints in the body and the muscles, tendons and ligaments that are in that area. We also talked about different injuries that can occur to those areas. This information can help contribute to exercise physiology discussions when learning again about muscles, but also when talking about exercise as a whole since you can do different exercises to activate different muscles. I also think it helped with the first weeks lab when we were in Alumni trying to figure out what muscles we had to location our machines on the scavenger hunt.

1. My favorite athletic accomplishment is probably going to sound like an odd one, as it is quite bittersweet. Starting in freshman year, I was on my high school’s lacrosse team. Lacrosse was not big in my town and our team was still in the developmental phases, as were many of the surrounding schools. During the third game of my sophomore year, we were playing our rival team. I went for a ground ball and was hip-checked by a girl who had originally played on her school’s men’s team (since there was no women’s team at that point). I felt my hip pop out when I hit the ground, but I was angry at this point, so I kept playing. I played the rest of the season, making sure to always ice my hip before and after playing. The trainer told me it was bursitis so he didn’t bench me. Flash forward to senior year of college, and I can no longer run without limping for the next two days. Turns out it wasn’t bursitis – I had torn my labrum and in the process of favoring my right leg, I destroyed my left hip. So while the story does not have a happy ending, the entire process taught me how much my body can endure if I refuse to quit, but also the consequences of ignoring my limitations.
2. Biology has never been my strongest subject, but I am interested in seeing how the cellular processes work together during seemingly simple everyday activities such as going for a run. I have always taken the biological processes for granted while focusing on the bigger picture, but I believe understanding the inner workings of the body will give me a greater appreciation for these simple everyday activities. I got a glimpse of this in Animal Physiology last term, but I want to dive deeper into understanding the differences between slow twitch and fast twitch muscle fibers and how these differences contribute to the overall functionality of the muscles to produce cohesive movements. I now recognize that it is crucial to look at all aspects of the system individually to understand how we live our day to day lives.
3. The previous upper-level courses that I’ve taken that would contribute the most would be Orthopedic Biomechanics, Mechanobiology, and Animal Physiology. Orthopedic Biomechanics would be helpful, as we learned about all the bones of the body and how they all experience loading in different ways from the various forces applied during both activity and when you are stationary. Mechanobiology (as much as we’ve done this term) seems to continue on this topic, focusing on how different types of bones respond to forces. Animal Physiology focused on how the various systems within the body respond to different conditions. By combining what I have learned in these various classes and what we will learn in this class, I hope to have a complete understanding of how the major systems within the human body work together to maintain homeostasis.