The new academic year is upon us, which means it is time to leave the summer behind and go back to school or work, and slip into our pre-vacation routines. For some, this might take the form of waking up earlier, eating healthier or perhaps, getting into the habit of exercising on a more consistent basis. If there is anyone out there struggling to find the motivation to continue (or begin) a workout plan, here are several benefits of exercise from a molecular perspective.
A quick disclaimer beforehand: it would be impossible to explain in detail all of the benefits that exercise has on both mind and body. In fact, new research keeps coming out assessing new aspects of how being active helps us function. But remember, doing too much exercise can also be harmful as it may interfere with other processes that need to occur to stay healthy.
Definition of exercise
Throughout this article, I will refer to exercise as any physical activity sustained during a long enough period of time to improve one of these characteristics: endurance, strength, balance or flexibility.
Something that I will mention frequently is the use of energy in the form of ATP. If you are not familiar with this energy currency of the body, I recommend you read this article first, which explains what it is and how it is produced in our cells.
The World Health Organization (WHO) recommends doing at least 150-300 minutes of aerobic exercise and 75-100 minutes of higher intensity exercise each week for adults.
Benefits of anaerobic exercise
During endurance training, such as weightlifting, jumping rope, sprinting, biking or High Intensity Interval Training (HIIT), our cells are forced to supply energy quickly to the muscles. This means that there is not enough time to undergo aerobic metabolism (under oxygen-rich conditions). Therefore, our cells must undergo anaerobic metabolism (without oxygen). Surprisingly, the energy produced in aerobic metabolism is 32-36 ATP per molecule of glucose consumed, whereas in anaerobic metabolism this number descends to 2 ATP, but the latter is able to break down the nutrients much faster. Another downside of anaerobic metabolism is the accumulation of lactic acid, one of the substances that causes muscle fatigue. Fortunately, lactic acid can eventually be converted into pyruvate in the liver (through a process called the Cori cycle), which can then be oxidised further aerobically to yield more molecules of ATP.
You may be asking yourself, is the only benefit of aerobic exercise to rapidly burn nutrients? No! Research has shown that this kind of training activates a transcription factor known as hypoxia-inducible transcription factor 1 (HIF-1), which boosts the production of enzymes needed to break down glucose and of transporters to get this sugar into the cells. Essentially, it is a positive feedback loop, whereby the more those cells are working, the more energy they need, and the more glucose they will try to acquire and utilise (until the muscles accumulate too much lactic acid). Furthermore, HIF-1 can signal production of vascular endothelial growth factor (VEGF), which stimulates the production of blood vessels, allowing more oxygen to get to that tissue for future exercise.
Common anaerobic exercise routines include weightlifting, jumping rope, sprinting, biking or High Intensity Interval Training (HIIT).
Benefits of aerobic exercise
Aerobic exercise does utilise oxygen and thus can be performed during longer periods than anaerobic exercise. Running, walking, dancing or swimming constitute these kinds of activities.
Anxiety and depression
Although there needs to be more consistent research that takes into account factors such as training regimes, genetics, gender and hormonal status, a working hypothesis of scientists is that aerobic exercise improves mood. The release of certain hormones and neurotransmitters which trigger the body into a state of physical stress would help counteract the effects of anxiety and depression, proving as a good therapy for these conditions.
Anandamide is one such chemical that is released after exercising. As is a recurring theme in biochemistry, this compound does not have a direct action on the nervous system, but it causes an increase in the amount of brain-derived neurotrophic factor (BDNF). This protein helps enhance neurogenesis by promoting the growth of neutrons and supporting existing ones. Therefore, the three-fold increase in BDNF after exercise is linked to an overall better mood.
Our sensitivity to insulin is also maintained through exercise, so that we can control the levels of blood sugar more efficiently. This is the reason why having an active lifestyle prevent so many conditions such as Type II diabetes, obesity and cardiovascular diseases.
The β-cells of the pancreas secrete insulin in healthy individuals after meals due to the presence of high levels of glucose. Consequently, insulin binds to receptors on the cells, which in turn trigger glucose transporters (GLUT4) to be mobilised to the membrane. In essence, this hormone increases the uptake of glucose in muscles and liver, where they can then be stored into glycogen for later use. The more sensitive we are to insulin, the better we can utilise sugars.
A common disease known as insulin resistance impedes the patient’s cells from reacting to the hormone. Along with failure to produce insulin, this is one of the causes of type II diabetes. Through exercise, some of the processes that would lead to insulin resistance are reversed, promoting normal levels of sensitivity towards it.
One of the findings of exercise that I find most interesting is its effect on protein phosphorylation. It turns out that exercise causes the phosphorylation of around 600 proteins on more than 1000 different sites. The result is that these proteins become activated (by the addition of a phosphate group), which in this particular context means that they increase their ability to metabolise fuels more efficiently. Not only does exercise benefit you in the short run, but it builds mechanisms to improve your health on a longer time scale as well!
Additionally, regular exercise lowers blood pressure, while increasing HDL («good cholesterol») levels. This stands for High Density Lipoprotein, which is a type of cholesterol that we need for cell membranes and other structures.
In this article, we have seen two different kinds of exercise: anaerobic and aerobic. Each one encapsulates several activities and have specific benefits tied to them. A combination of these can lead to stronger muscles, better oxygen intake and distribution, improved mood, increased phosphorylation levels, reduced blood pressure… Indeed the benefits are numerous.
Remember, the next time you have a few minutes to kill, consider taking out your bike or going for a quick run instead of sitting. Your body will thank you!
- Stryer, L. et al. (2019) Biochemistry. 9th edn. New York, NY: Macmillan International Higher Education
- Cleveland Clinic. 2019. Aerobic Exercise Health: What Is It, Benefits & Examples. [online] Available at: https://my.clevelandclinic.org/health/articles/7050-aerobic-exercise [Accessed 25 September 2021].
- Heijnen, S., Hommel, B., Kibele, A. and Colzato, L., 2016. Neuromodulation of Aerobic Exercise—A Review. [online] NCBI. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4703784/ [Accessed 26 September 2021].
- Cover image: https://myheart.net/articles/exercise-with-heart-disease-is-it-safe-and-should-i-be-doing-it/
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