Analogies and metaphors are commonly used to simplify complex ideas. The human body is often compared to a machine, while the brain and nervous system are compared to a computer. While these comparisons can offer a rudimentary understanding of how certain body processes work, it’s important to understand that their value is limited and potentially harmful.

We, as humans, are not machines, we are biological organisms. This is a tremendously important distinction to make when we consider our physical health and performance. A machine is built from various materials and parts. When the initial building process is complete, the machine is the strongest it will ever be.  As the machine performs its task over time, it will continuously degrade and the individual parts will wear out. This is not the case with humans. There is no such thing as “wearing out” the human body, or any of its parts. 

The nature of a biological organism is that it adapts. From the moment of conception to the last moments of life, we adapt. If we consume more calories than we burn, we store fat. If we lift heavy objects, we build muscle. If we are exposed to UV light, we produce melanin. We are constantly adapting to our environment. While the human body’s ability to adapt will decrease over time, it does not disappear as long as there is life. 

Our musculoskeletal system is constantly adapting. Our body is constantly building up, and breaking down, the tissues that makeup our “parts”. Davis’ law states that soft tissue (muscle, ligaments, skin etc.) models along imposed demands. Put more simply, when muscles, ligaments, tendons and skin are exposed to stress, they will build tissue in response to that stress. For the purpose of this article. “stress” is a physical demand placed on the body. For example, if you spend a lot of time running and jumping, the tendons of your legs will get stronger and will be able to tolerate more stress than if you were sedentary. As opposed to a machine, which will inevitably weaken with time, the human body becomes stronger in response to various stresses. Conversely, if the body does not receive enough stress, we will become weaker as Davis’ law works both ways. 

Understanding Davis’ law can help guide our strategies for health and performance. If our bodies were machines, it would be in our interest to avoid stress unless absolutely necessary as stress equates to degradation. Since Davis’ law implies that our bodies have the potential to become stronger and more resilient in response to stress, it’s in our interest to expose ourselves to physical stress. This is why regular exercise is essential for health, performance and injury prevention. 

An important caveat is that the amount of stress must be appropriate. Too much stress and we risk injury, too little stress and we risk weakness and an impaired ability to tolerate stress. The amount of stress we are exposed to is dictated by the volume, intensity and frequency of the exposure. For example, when we estimate the amount of stress we expose our bodies to while running, we typically consider runs per week (frequency), speed (intensity) and duration (volume). If we understand our personal tolerance to specific forms of stress, and we are able to control the dosage (amount of stress), we can easily strategize to make our bodies strong and resilient. This is how we can thoughtfully manage injuries, improve performance and create durability. 

In addition to exposing ourselves to an appropriate dosage of stress, we must also support our ability to adapt by responding with an adequate dosage of rest. In order for our bodies to become stronger, we need to provide stress to initiate a hormonal and neurological response. Once the body is exposed to an adequate amount of stress, rest is needed to allow the body to create the appropriate adaptation. 

Balancing our exposure to stress with adequate rest is the basic solution to successfully improving our health and performance. A general understanding of Davis’ law allows us to better grasp the essentials of injury rehab, injury prevention and performance.