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4 Parts of the Body That Really Like Exercise

May 30, 2017

We hear it all the time: exercise is beneficial to your overall health. Some you hear preached by your trainer(s), however some others you may not even think (or know) about and some serve a wide swath of major rolls in your body’s overall function. The benefits on the heart, muscles, nerves, and vascular structures are all commonly known. What about some lesser-known bodily beneficiaries of exercise? Let’s take a look at a few of them.

Bone Marrow

Multiple types of tissue comprise human bones. The type most intuitively associated with bones is known as osseous tissue, the hard, rigid cells that provide the sturdiness to our bones and allows them to act as the base framework to our bodies. The benefits of exercise on the structural role of bones are commonly discussed with regards to injury prevention, but something else happens inside our bones that also benefits from exercise, and it’s quite fascinating.

Within most bones lies our bone marrow, which serves quiet a different function than osseous tissue. There are two types of marrow tissue: red marrow and yellow marrow. Both types contain mesenchymal stem cells (MSCs), which are cells that can differentiate and become many different types of cells as they mature. MSCs are largely implicated to have roles in organ tissue regeneration and healing and are also found in our muscle cells. After endurance exercise, our bone marrow tissues (especially red marrow) increase the amount of MSCs they produce. As these new cells differentiate as a result of endurance training, they typically develop in one of three different manners, some become fused to our muscle cells (see previous link), they develope in hematopoetic cells which eventually become different types of blood cells, or they can become osteogenic cells and aid in the strengthening of osseous bone tissue.

One other thing that happens in bone marrow has to do with the yellow marrow. Yellow marrow is largely responsible for producing cartilage and other connective tissues. As we age throughout life, levels of red marrow decline, and levels of yellow marrow increase. This can present a problem for our bone structure because the reason yellow marrow appears to have a yellow color when observed under a microscope is that yellow marrow contains deposits of adipose tissue (aka fat tissue). This can affect the structural integrity of our bones, and with the accompanying decrease of red marrow. More yellow marrow also means the body cannot repair damages to other tissues as effectively. But with regular exercise, we see a decrease in these adipose deposits through an increase in osteogenic (osseous bone-producing) and myogenic (muscle-producing) chemical precursors and a deterring of adipogenic (fat-producing) precursors in the bone marrow. To summarize all this, more stem cells become available for use, and more of those cells become other more helpful types of cells instead of becoming fat cells.

Immune Tissue

Exercise’s role here is largely related to the regulation of inflammatory molecules in the body, and the cells that respond to these molecules. There are some benefits to shorter term infection fighting, however I want to focus on the inflammatory molecules, and the dealings with those that fall largely within the roles of macrophages

Macrophages are a type of immune cell. Pockets of macrophages, are interspersed at different locations throughout the body, and they also are found in the blood stream. Part of their function is to serve as the body’s hazmat disposal system. This includes disposing of harmful pathogens (i.e. bacteria) as well as residual waste from damaged or dead cells as well as waste from other organic processes that I’m not going to get in to. When these cells are activated, they, along with other cells in the body, release pro-inflammatory molecules that basically act as alarms, attracting other immune cells to the site where they are needed. In the case of infection, that is all well and good, but in the case of diseases such as metabolic syndrome and type II diabetes, this process goes into overdrive mode.

Muscles are highly responsive to blood glucose levels, and so are the macrophages around them. When pro-inflammatory macrophages are activated, they secrete a cell signal called interleukin 1 beta (IL-1 β). IL-1β stimulates glucose uptake into cells, and has been shown to increase glucose uptake in cells that are overexposed to IL-1 β to such a degree, that it causes serious damage to the affected cells. This damage puts the affected cells in an inflamed state, and the cell signals that are released as a consequence are picked up by macrophages that then become activated, setting off a vicious cycle of more inflammatory cell signals being released.

We are starting to learn more and more on exactly how these macrophages and muscles work in tandem, and there is evidence now that these overactive macrophages do play a role in the development of muscular insulin resistance if they are responding to gratuitous amounts of pro-inflammatory molecules including IL-1β. There is also evidence that high-saturated fat diets adversely influence in immune cell-mediated insulin suppression, like the kind exhibited by macrophages on muscle tissue. What’s more, diabetic individuals also tend to have elevated numbers of these macrophages when compared to healthy individuals; in short diabetic individuals have more macrophages that are more active. There are also cell-signaling pathways from fat tissues that can further amplify these other signaling pathways, and further contributing to impaired insulin tolerance in muscle cells. This has huge physiological implications because the largest consumers of glucose are in fact, muscle cells.

Fortunately, exercise has a moderating effect on all of the above. Both aerobic, and resistance exercise have shown to have anti-inflammatory effects that translate to the restraining of these overactive immune cells. Exercise has also been implicated as a mechanism to actually reduce the number of these immune cells in individuals who may have elevated numbers, effectively returning these immune cells to normal numbers, and an appropriate level of responsiveness.

Brain Neurons

The brain is the body’s universal command and control center. So what if we could make it stronger, and more efficient? Fortunately, exercise can do that, thanks to a chemical called BDNF. BDNF (brain-derived neurotrophic factor) is one of many factors involved in neurological upkeep. BDNF is routinely found in low levels in those diagnosed with neurodegenerative diseases such as dementia, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease etc., and scientists are currently exploring its potential links to mood disorders. BDNF also decreases as we age. This is problematic, because many neural populations in our brain need BDNF to survive; without it, they degrade and die off, commonly leading to a wide range of neurological problems including the diseases previously listed.

The way BDNF works is through promoting neural plasticity. In training muscles, we often use the phrase: use it or lose it; if you don’t use your muscles, over time, you will literally start to lose muscles. Neural plasticity is the brain’s equivalent of this principle. Neural connections, called synapses, will strengthen and weaken over time depending on their level of activity; the lower the level of activity, the weaker the synapse will become, until eventually the brain will phase that particular synapse out.

We see BDNF increase significantly with regular exercise over a period as short as four weeks, and this increase has been linked to improved recall, learning, and memory. These aspects are under the control of the region of the brain known as the hippocampus. Not surprisingly, the size of the hippocampus will increase with exercise, this is largely attributed to higher levels of BDNF. The hippocampus also is the body’s major emotion center, and thus exercise has also been implicated as effective treatment for mood disorders such as depression and anxiety; both are conditions in which we also see lower levels of BDNF across the board. Such an increase would seem to benefit these individuals as well. The truly amazing thing here is that this, compared to the more chronic nature of the other issues I’ve mentioned up to this point, is that we can in fact see a substantial difference in such a short period of time. While other adaptations may require more long-term exercise adherence to see large effectual changes, this one requires a much shorter timeframe to take root.

Kidneys

The kidneys are your twin filter warehouses for your blood. 120-150 quarts of blood pass through them every day. The kidneys remove some of chemical wastes from cellular processes, but are largely responsible for regulating the fluid and ion balance of your blood. The kidneys also produce hormones that produce and monitor red blood cells, and help regulate bone composition.

Research has mainly focused on two areas, the first being exercise’s effects on patients with chronic kidney disease. There are some studies however, that have established a correlation between exercise and kidney function in adults currently without diagnosed chronic kidney disease. Thus it is important to use exercise to maintain levels of kidney function. So how exactly does exercise help the kidneys?

A major hormonal factor controlled by the kidneys that is of particular interest to exercisers is erythropoietin. This hormone secreted by the kidneys, stimulates the red marrow in bones to produce more oxygen-carrying red blood cells. What we see with exercise is a transient increase in what are called reticulocytes. Reticulocytes are immature red blood cells released by red bone marrow. A higher number of these cells indicate that the bone marrow is active and that the body is attempting to increase its capacity to deliver oxygen to working tissues. This occurs with both endurance, and resistance training. This effect seems to be modulated by hypoxic (low-oxygen) conditions in the kidneys themselves. Researchers think this is due to the decrease in blood flow to the kidneys during strenuous exercise, though much about the mechanisms surrounding this are unknown when exercising at lower altitudes. Exercise at high altitude however, we know plenty about.

When one ascends to altitude, the change in air pressure further contributes to hypoxic conditions in the kidneys, and the body as a whole. This triggers a greater response from the kidneys in an attempt to get more oxygen carrying capacity into the vasculature, and the level of erythropoietin will remain elevated as long as an individual remains at elevation. In this case, we know that a major contributing factor to increased kidney activity is the aforementioned hypoxic conditions of the outside environment, but down closer to sea level where conditions are “normoxic” (adequate oxygen conditions at lower elevations), the mechanisms are again not as well understood. Some have attempted to simulate altitude at sea level to improve training adaptations for athletes, outcomes in cardiac rehab patients, and even as a weight loss stimulator, but such efforts have seen mixed results depending on the kind of training performed by the subjects.

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