Stress and Homeostasis

By: Barbell Logic Team

Stress and Homeostasis: How changes to your environment cause a  physical response that we can use to get stronger

So, you’ve decided to move. You’re leaving your beachfront California property for the high desert of Santa Fe, New Mexico. Altitudinally, you will be moving from sea level to 7,000 ft. above sea level. You arrive in the city, visit the Georgia O’Keeffe Museum, say “hi” to George R.R. Martin hanging out at the plaza, then you decide to unload your moving van. As you do, you notice that despite your recent dive into strength training, you are getting more easily winded. Your heart rate jumps up with the first box that you unload, and it doesn’t come down until you are done. Loading the van back in California had been easy, but now you feel completely out of shape.

You can, and should, blame the altitude. You may not have realized it, but the trip upward from zero to 7,000 feet is similar to the training you are doing in the gym. When you lift weights, the goal is to cause significant stress to your body. You can observe this stress in regulatory changes in blood pressure, heart rate, and energy production in your body, which is then followed by change—you get a little bit stronger for your efforts. The change in altitude also represents significant stress to your body, especially when you tried to move those boxes. Starting at about 7,000 feet of elevation, your blood-oxygen level decreases markedly. In the very short term, your body has to deal with decreased oxygen supply, hence your elevated heart rate and shortness of breath while moving. But changes follow any significant stress to the body when it is given time to recover, and just like you adapt to lifting weights, your body will adapt to your new elevation.

Significant stress is any phenomena that disrupt the optimal functioning of your body. The stress event can take place over a very long period of time. It can be environmental. Or it can occur instantaneously.

The hallmark of stress is that it takes some aspect of your normal function and changes it. When you moved from sea level to 7,000 feet you changed your body’s ability to maintain blood-oxygen levels. Fortunately, our bodies are really good at restoring the balance and will adapt to higher elevation environments so that you do not suffer from a prolonged oxygen imbalance.

Stress that disrupts the body’s regulatory systems can be harmful. Chronic stresses that give your body no opportunity to adapt and restore balance can significantly shorten your life span. Smoking or health issues like obesity, for example, continuously alter regulatory cardiovascular functions preventing the body from functioning, causing long-term problems if the stress is not removed or mitigated. Sudden and irrevocable stress can occur through catastrophic injury; a sudden loss of fluids and blood pressure and the building blocks to make energy lead to death.

Your body works hard to maintain a state of equilibrium called homeostasis. In the example of moving from sea-level to high-altitude living, the change in barometric pressure and the decrease in the number of oxygen molecules contained in each breath means that your body experiences a lower blood-oxygen saturation. Our bodies need a constant supply of oxygen for energy production. At the extreme—say you decide to climb Mt. Everest—you might experience hypobaric hypoxia. The loss of sufficient oxygen for energy production results is a loss of function and possibly death. But a lot of things will happen first: your body will shift down your energy usage and cause you to feel fatigued, your heart rate will go up to speed the delivery of less-oxygen rich blood, your breathing rate will increase to take in more oxygen, your lips and fingernails may turn blue as your body pulls blood away from non-essential-to-live extremities. All these reactions are your regulatory systems’ attempts to restore homeostasis.

The neat part about homeostasis is that your body will change its structure and function in response to a disruption. If you are in Santa Fe rather than the slopes of Everest, the 7,000 foot altitude means that you experience a significant decrease in blood-oxygen saturation. But your body will begin to engage both short-term and long-term adaptations to deal with the change. At first, your breathing will deepen, your heart rate will increase or more quickly increase in exertion, and you may feel the need to urinate more often as your body tries to maintain blood pH levels. After a few days, however, you will have undergone physiological changes that allow you to stay at a higher altitude. Your body will make systematic adjustments to oxygen transport and muscle energy metabolism, developing glycogen-sparing processes. As a result, “systemic oxygen transport requirements during exercise at altitude can be satisfied with a lower cardiac output, and thus reduced cardiac work, than on arrival.” (Medical Aspects: https://web.archive.org/web/20120916195023/http://www.usariem.army.mil/Pages/download/harshenvironmentsvol2.pdf). These changes are why you will see Olympic-level endurance athletes bounding around the mountains of Santa Fe; they are acclimating to the altitude hoping to bring these changes with them when they return to and race at lower elevations.

Minor disruptions to homeostasis occur every day without your changing locale or being injured. This cycle of disrupting homeostasis and restoring it is how our bodies learn, grow, and adapt to our environments. It is by this constant, dynamic balancing act that humans have survived and thrived in intemperate climates, at extreme altitudes, and harsh environments. There are some constants: We need water, we need our blood to stay in our bodies, we need the building blocks to produce ATP for energy, and we need to maintain a narrowly-defined core temperature. Disruption to any of these constants are going to cause problems, but when the disruption is minor and the body recovers, the net result may be that we are better able to handle whatever event caused the disruption in the first place.

Knowing this about our bodies gives us a powerful tool. If we intentionally disrupt homeostasis and then give our bodies the time and resources to restore its proper functioning, we can dictate certain changes. This is the process of training. You load a barbell with iron plates and move it vertically through space because it is hard work. Hard enough that it raises your blood pressure and heart rate, burns ATP, and causes stress to your musculoskeletal system. Muscles are effector cells that signal change to the body. When the stress of training is high enough to disrupt homeostasis, it causes an alarm response that kicks your body’s regulatory systems into high gear to restore the balance.

When a significant stressor signals the need for changes, your body does not assume that the stress was a one-time event. It prepares for repeat events. Your body reacts to restore homeostasis and signals changes to the necessary functioning and structures of the body that will help you survive repeated bouts of that stress. Your body adjusts to this new state that you introduced when you did your last training session. It adjusts its systems for producing energy and producing force, and it changes its structure, growing tissue to accomplish the work and resist the strain of training.

The key to returning to homeostasis is facilitating these changes. The body needs time and resources to recover from training. Now that we’ve defined stress in terms of homeostasis, we can also look at recovery needs in the same framework. We will continue by answering the questions of how food, water, and sleep aid our return to homeostasis and discussing recovery and homeostasis in future articles.