Cellular Adaptation

Cellular adaptation refers to changes made by a cell in response to environmental changes that are big enough to demand change. This is a process where the cells of your body change in various ways to meet the demand placed on it. The five major types of cellular adaptation are:

  • Atrophy (decrease in cell size)

  • Hypertrophy (increase in cell size)

  • Hyperplasia (increase in the number of cells)

  • Dysplasia (abnormal changes in cell shape, size, or organisation

  • Metaplasia (cell type is replaced by another cell type)

Hypertrophy and Atrophy

When you progressively overload a muscle cell (so long as the load isn’t too great and too soon) the muscle cell will respond by making itself larger and stronger (hypertrophy). If the load is too great for the cell to handle, then it will rupture and die (injury).

Inversely, if you decrease the load on a muscle cell (if you are bed ridden for example), the muscle cell will respond by making itself smaller and weaker (atrophy). The body is very efficient with its energy. If you don’t continuously maintain a level of function, you’ll lose it. This principle applies to all cells, including nerve cells.

Neurological adaptation:

Movement requires communication through neurological pathways which are formed of nerve cells. These also undergo adaptation as those pathways are used more and more. When you learn a new skill, a network of neurons become connected. At first this is a very weak connection, but as you repeat it, it will become stronger over time.

Just like training your muscle cells, the neurological pathways and connections that make up that skill will grow and will be reinforced through repetition and demand (as long as the demand is appropriately progressive). A layer of fat called ‘myelin’ is eventually wrapped around these connections to make it even faster. When the connection is faster, it becomes more efficient, requiring less effort - this is the beginning of a new habit being formed.

In a well balanced exercise program, it isn’t just load that is increased to create adaptation. The complexity of your movements (skills) is also a variable that you should take into consideration, especially if the client is starting with a low base of coordination. Progressively overload that complexity so that skill is acquired efficiently.

Your strategies for training or retraining motor behaviour should be at the appropriate level of stress for cells as well as the appropriate level of complexity for the individual.

Progressive Overload:

Progressive overload is a simple principle of exercise training that involves gradually increasing the cumulative stress placed on the musculoskeletal and nervous system. The aim of this is to optimally stimulate the development of muscle, stronger and denser bones, ligaments, tendons, cartilage, blood flow, neural connections, and ultimately increase strength, endurance, and overall performance.

To optimise results and minimise injury, four main variables are controlled so that training stimuli and its impact on the physiological systems of the body can be managed.

  • Volume is the total number of repetitions multiplied by the resistance (weight) used to perform each repetition.

  • Intensity is the percent value of maximal functional capacity, or expressed as percent repetition maximum.

  • Frequency is how often a person engages in training activities. Strongly related to training consistency.

  • Interval duration is the time in between sets of same exercise or between different exercises.

In general, you would gradually increase one to two of these variables at a time. An excess of training stimuli can lead to overtraining - a decline in training performance and increased risk of illness, injury, or desire to exercise. To manage this, it is helpful to periodise the variety of training stimuli over the course of a long term program (see ONI Movement Training Model).

Specific Adaptations to Imposed Demands (SAID):

The SAID principle (specific adaptations to imposed demands) states that the type of exercise stimulus placed on the body will determine the expected physiological outcome. Changes to the structures and systems of the human body do not occur without a preceding outcome. The body is very adaptable and adjusts to (mostly) any physical stimulus that it is exposed to regularly. Each physiological system - neural, endocrine, metabolic, fascial, muscular, and skeletal - will respond and adapt to the specific physical demands applied through a progressively more challenging exercise program.

According to the SAID principle, an individual who performs only muscle-isolation exercises can expect to strengthen the specific muscles used during exercise but may not achieve the intermuscular coordination necessary to improve skills such as coordination and dynamic balance. This is why it is so important to not only train independent joint function (isolation), but also the compound movement that those joints make up (integration).