Your body is designed to adapt to its environment. During exercise, major changes occur in the activity and function of muscle cells. This adaptation occurs in multiple types of muscle and is important in your body's preparation for a good workout.
Metabolic Changes
When you decide to pick up a dumbbell and start your first set of curls, an electrical signal is sent from your brain, down into your muscle. As muscle cells increase activity, they begin to release products of cell metabolism, such as carbon dioxide and waste materials. These chemicals are signals to the body that exercise has begun and are detected by sensory nerves surrounding the muscle. Ultimately, these nerves feedback to stimulate the sympathetic nervous system, which exerts widespread effects throughout the body. The sympathetic nervous system is a major player in the physiologic adaptations of muscles during exercise.
Vascular Smooth Muscle
The acute effects of sympathetic activation span multiple systems. This is because the activity of any given organ is dependent on how abundant its blood supply is. A special type of muscle cell, known as vascular smooth muscle, surrounds your blood vessels, and is capable of controlling blood flow by increasing or decreasing its contraction. When your sympathetics cut off blood flow to a region of the body, they do so by contracting vascular smooth muscle. This is the case throughout the digestive tract during exercise, for example.
The opposite is true in organs more essential to physical activity; as such, blood vessels will dilate in the heart and skeletal muscle during exercsie. The increased blood flow enables the cardiac and skeletal tissue to continue contracting for as long as possible. In this case, the sympathetics have automatically shifted the blood supply to organs that need it most in that moment. During exercise, the body is revved up and preparing itself for intense physical activity, and this is reflected in blood vessel diameter changes throughout the body.
Cardiac Muscle
The other major muscle type that undergoes adaptation during exercise is cardiac muscle. The effect of adrenaline, epinephrine and norepinephrine, which are all chemicals of the sympathetics, is to increase the heart rate and the strength of contraction. This dramatically improves cardiac output and primes the system for a fight or flight reaction.
Skeletal Muscle
Ultimately the sympathetic effects come full circle back to your skeletal muscle. The sympathetic state of the body involves a flood of adrenaline moving through the entire circulatory system. Blood vessels in your biceps are dilated to supplement the increased cell activity. A study from the Institute of Exercise and Sports Sciences in Denmark reports that there are increases in skeletal muscle uptake of glucose during exercise. This occurs because of multiple adaptations including increased glucose delivery, cellular transport, and intracellular rates of glucose breakdown.
The Big Picture
In short, the physiologic adaptations occurring in muscle of multiple types located throughout the body highlight the body's remarkable ability to adapt to new challenges and environments.
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