The Benefits of Skeletal Muscle on the Endocrine System
Skeletal Muscle plays an extremely important role in health and impacts the endocrine system in very important ways.
Recall that there are three types of muscle in our body:
Skeletal Muscle : this is the muscle we most commonly think of when speaking of muscle. This is the muscle attached to our bones, aka, skeletal system ergo, skeletal muscle. Humans can ‘control’ the movement of this type of muscle.
Smooth Muscle : the type of muscle found in the walls of blood vessels and esophagus, to name some examples. The movement of these muscles is not under our conscious control.
Cardiac Muscle : the muscle of our heart. The coordinated movement of this type of muscle is also not under our conscious control.
Improving or maintaining an adequate amount of skeletal muscle needs to be an important part of the health plan endocrinologists discuss with patients. Below are 3 important impacts skeletal muscle has on the endocrine system.
Insulin Resistance
This, in my opinion, is one of the coolest things about skeletal muscle and how it supports the endocrine system. When we exercise, the pancreas dramatically reduces insulin production. This is curious, since glucose is the preferred energy source of our body’s cells and in order for glucose to get into cells, insulin is needed to inform the cells of circulating glucose so that the cells can then allow glucose in and use it as energy. But if insulin levels go down, then this signaling to the cells to take in glucose for energy doesn’t happen, so how can muscles move during exercise?
WELL - skeletal muscle has this really amazing trick where they are directly able to pull glucose from the blood WITHOUT the need of insulin. This process is known as non-insulin glucose uptake. But the only way for this to happen is if we move our muscles through exercise. So during the exercise, not only are we able to keep our circulating blood glucose levels improved as the muscles directly pull the glucose from the blood and use it immediately as energy, but the pancreas gets a break and gets to rest. How amazing it this?! Repeatedly doing this is a phenomenal way to improve and restore insulin sensitivity.
Medical conditions that directly benefit from improved insulin sensitivity include: many types of diabetes (pre-diabetes, type 1 and 2, gestational), metabolic dysfunction associated liver disease (MASLD, formerly known as Non-alcoholic Fatty Liver Disease (NAFLD)), and PCOS (through restoring ovulation and restoration of regular menstrual cycles).
Click on this link to view my Instagram explanation of this phenomenon: View Post
2. Metabolism
When we refer to our ‘metabolism’, frequently people are referring to Total Energy Expenditure (TEE), or how much total energy our bodies use on a daily basis. TEE is made up of Resting Energy Expenditure (REE) aka Resting Metabolic Rate (RMR) + Non-Resting Energy Expenditure (NREE - which is exercise) + Thermogenic Effect of Food (TFE - which is how much energy the body uses to digest food).
So written in a formula format:
Daily TEE = REE/RMR + NREE + TEF
The higher one’s TEE, the more calories this individual is using per day. Each of the three components do not share equal weight in making of TEE, however.
Approximately 60% of one’s TEE is determined by RMR (I will be using the phrase RMR from here forward). The RMR is the amount of energy the body uses while resting for cellular processes, for digestion, for brain function, and another important determinant of RMR is maintenance of skeletal muscle. Skeletal muscle can make up to 20% of our RMR. Therefore, by increasing our skeletal muscle mass, we can increase how much skeletal muscle contributes to our RMR.
NREE refers to the amount of energy an individual uses for movement and activity, aka exercise and makes up 20-30% of daily TEE. Moving our bodies for the purpose of exercise, moving the big muscles of our legs, pushing or pulling against resistance, stretching and lengthening for balance, each help strengthen skeletal muscle and in turn increase the NREE contribution of our daily TEE. It is important to note that there are Non-Exercise Activities Thermogenesis (NEAT) that can contribute to NREE, such as fidgeting, knitting, gardening, etc. that are not planned exercise activities, but do contribute to NREE. Not surprisingly, skeletal muscles are also used for each NEAT.
3. Bone Density
Did you know that bone is a part of the endocrine system?! Bone health and metabolism is subject to complex hormonal signaling within the body. Loss of bone density significantly increases the risk of bone fractures. Improving skeletal muscle mass and strength can prevent bone fractures in a couple of ways. First, through training in diverse ways, skeletal muscle helps support posture and balance and this is important in preventing falls, with falls being the frequent culprit of broken bones. Second, by working on improving muscle mass and strength, the contraction and relaxation of the muscle causes engagement of the tendons of muscles, which are what connect muscles to bones. Where the tendon attaches to the bone forces the bone to undergo remodeling, which strengthens the bone. And so, even if there is a fall, with stronger bones, one may not be as susceptible to suffering a fracture.
This is why part of the treatment of osteoporosis, a medical condition defined by a significant decrease in bone mineral density, is weight bearing exercises, since it can help maintain and in some cases, help build bone mineral density.
So you see, skeletal muscle mass holds a very important role in the endocrine system and efforts put forth in building or maintaining an adequate amount of skeletal muscle impact several components of endocrine health.