The optimal state for the human movement system is to be in balance or homeostasis. This so-called physiological balance, homeostasis, is the ability of an organism to keep the internal environment as constant as possible in an ever-changing external environment. This is a principle used in fitness and strength training science with the premise that the human body resists disturbances to this homeostasis. After all, the body wants to remain in balance continuously to perform various functions accurately. For example, if the body temperature threatens to rise, the body will resist to maintain the temperature around 37 degrees Celsius.
What is homeostasis
There are many causes that change the internal environment of the body. Examples include exercising, eating, being ill, and moving from a warm environment to a cold one. Many of these stimuli, also called inputs, cause the body to become imbalanced. Subsequently, regulatory systems such as the nervous and endocrine systems attempt to return the internal environment to balance. These regulatory systems regulate, among other things, pH (acidity), glucose level, oxygen level, and osmotic value.
Examples of regulatory mechanisms fall under 2 types of reactions:
- Negative feedback reactions
- Positive feedback reactions.
An example commonly used to explain a negative feedback loop well is through temperature regulation with a thermostat and air conditioning. When the air conditioning has been running for a while, the room temperature will have dropped significantly, and after a while, the air conditioning stops cooling. This air conditioning started because there was a high temperature inside, and now it causes a change because the temperature drops. It is this change that ultimately sends a “negative” signal. After all, the thermostat indicates at some point that it is no longer warm. Then the air conditioning turns off because it is no longer necessary to cool the room, and the desired temperature is reached. It is important to know that these processes are continuously ongoing. If the air conditioning is off and it is warm outside, the room temperature will rise again.
This is the case with many different processes in the body. The example of the air conditioning fits nicely with regulating our body temperature. Our body temperature is normally 37 degrees Celsius. This is regulated by two antagonistic mechanisms; shivering and sweating. Shivering occurs when the body temperature becomes too low, for example, in a cold environment. Sweating occurs when the body temperature rises. This can happen in a warm environment but also during exercise, for example. Your body temperature rises, and as a result, your body moves further away from homeostasis. Various systems are activated, causing the body to cool down.
Negative feedback
A negative feedback loop ensures that the body returns to homeostasis. A positive feedback loop stimulates further activity. Most processes in the body fall under negative feedback mechanisms.
An example of a negative feedback loop is eating a meal.
- When you eat, the glucose level in your blood rises.
- This high glucose level is detected by insulin-secreting cells of the pancreas.
- Insulin causes liver cells to take up and store glucose as glycogen.
- Insulin also causes other body cells to take up glucose.
- This results in a decrease in the amount of glucose in the blood, and insulin production stops (negative feedback). The blood glucose level is back in homeostasis.
Positive feedback
An example of a positive feedback loop is breastfeeding.
- A baby sucks on the nipple.
- This sends impulses to the hypothalamus.
- The hypothalamus signals to the posterior pituitary to release oxytocin.
- Oxytocin released into the blood stimulates milk secretion from the mammary gland.
- Milk is released, and the baby can continue to feed (positive feedback).
In positive feedback, lowering the temperature would actually make the air conditioning work harder and make it even colder.
Homeostasis and glucose
The first step in both processes is the stimulus. Eating a meal raises your blood sugar, which in turn causes an increase in insulin that lowers this sugar by converting it into fats, among other processes. If you skip that meal, there’s also no stimulus to throw your body off balance. If you unintentionally skip a few meals, causing the blood glucose level to drop, that’s a stimulus that sets your body to work by releasing glucagon. Glucagon causes a rise in blood glucose level back to balance. So, your body is actually continuously working to stay within various values in which it can function well.
An example of normal blood values falling within homeostasis:
Blood pH: 7.35-7.45
Bicarbonate: 24-28 mEq/l
Sodium: 135-145 mEq/l
Calcium: 4.5-5.5 mEq/l
Oxygen level: 17.2-22.0 ml/100ml
Urea: 12-35 mg/100ml
Amino acids: 3.3-5.1 mg/100ml
Proteins: 6.5-8.0 g/100ml
Blood lipids: 400-800 mg/100ml
Glucose: 75-110 mg/100ml
If certain values remain outside of this range for a long time and homeostasis is not maintained, then the body becomes ill. Nutrition is a very important factor in this, as the body needs certain nutrients to function properly. Under normal circumstances, the body is quite capable of staying within the correct variables of homeostasis.
Homeostasis and fitness
The beauty of the human body is its ability to adapt to desired needs. This process is also called General Adaptation Syndrome (GAS). This is the case, for example, during strength and cardio training. With training, you want to achieve becoming stronger, faster, or better conditioned. You achieve this by taking your body away from its original homeostasis, resulting in a certain stress for the body. After a period of, for example, cardio training, the body will adapt, for example, your resting heart rate will decrease, and during training, your heart rate will not rise as quickly. The body adapts in the way you train it, and this is also called the SAID principle (specific adaptation to imposed demands). The human body is therefore made to adapt to certain stress factors (training), and with good nutrition and enough rest, the body will emerge stronger or better conditioned.
