Hormones play an active role in almost every function your body undertakes and they’re always in flux. As you might expect, hormones are affected by exercise and are a factor in how much muscle you build and strength you gain when you resistance train.
What exactly IS a hormone? Hormones are chemicals released by certain tissues. These chemical messengers enter the bloodstream where they affect the activity of other cells, cells that are often distant from the tissue that released the hormone. You’re likely already familiar with hormones like growth hormone and testosterone and the role they play in muscle development and strength gains, but they’re not the only ones. Here are five hormones that can impact the results you get from a strength- training workout.
Insulin is one of the best known and most important hormones your body produces. Secreted by the pancreas, it opens the door of cells to allow glucose and amino acids to enter. Once inside, cells can convert these fuel sources to energy in the form of ATP or store it for later. You want your pancreas to make ENOUGH insulin but not TOO much.
Excessive insulin production is associated with insulin resistance, a problem that often leads to type 2 diabetes and other health problems like heart disease. Insulin also tells fat cells to not release fat, so it’s a fat storage hormone in a sense.
Strength training increases insulin sensitivity, making cells more efficient at taking up glucose. Plus, developing more muscle mass improves insulin sensitivity as well. A study published in the journal Diabetes Care showed participants with type 2 diabetes who weight trained twice weekly experienced improvements in insulin sensitivity irrespective of whether they lost weight or not.
Growth hormone is involved in muscle building and is also a promoter of fat loss. In addition, preliminary research shows growth hormone is involved in aging too. Growth hormone levels decline with age and partially explains why we lose strength and muscle size. A small gland in your brain, called the pituitary gland, releases growth hormone with the greatest amounts released during the deepest stages of sleep. That’s why adequate sleep is so important. Growth hormone also rises in response to exercise, especially high-intensity exercise.
One way growth hormone boosts muscle growth is by increasing the amount of another hormone-like molecule called IGF-1 produced by the liver. It’s IGF-1 that acts directly on muscle to boost muscle growth. Growth hormone also stimulates the growth of bone and cartilage.
We think of testosterone as being a “male” hormone. While it’s true that testosterone is responsible for the masculine characteristics men have, like their broad shoulders and deep voice, women produce smaller amounts of this muscle-building hormone. Testosterone has another “perk” as well – it, in conjunction with growth hormone, promotes fat loss.
Men experience an increase in testosterone release in response to resistance exercise, especially high-intensity resistance training. It’s likely that women experience some increase as well, particularly with heavy lifting. On the other hand, long periods of endurance exercise can put the brakes on testosterone release and thereby thwart muscle and strength gains.
You release cortisol in response to stress and that includes the stress of exercise. Cortisol release is higher when you train for long periods of time in a glycogen-depleted state. In fact, long-distance runners who don’t consume enough carbs or calories can experience significant elevations in cortisol. That’s not a good thing since cortisol is a catabolic hormone that breaks down muscle tissue and suppresses your immune system. The intention is good – cortisol is trying to deliver amino acids, from the breakdown of protein, to your liver where the liver can use it to make glucose to fuel long periods of exercise, but longer term it works against you.
Strength training itself doesn’t usually lead to big spikes in cortisol or a more sustained release of this catabolic hormone unless you over-train. The best way to control cortisol is to consume enough carbs, keep cardio sessions short and intense, and give your body enough rest and recovery time between weight training and aerobic exercise sessions.
Glucagon is a hormone with an action opposite to insulin. Whereas your pancreas releases insulin when you’re well fed, you release glucagon when you have eaten for a few hours. It’s glucagon’s job to make sure your cells have access to glucose. Not only does glucagon convert glycogen stores in your muscles and liver to glucose, it breaks down fat stores so you can use them as an auxiliary fuel source. Breakdown of fat stores sounds like a positive, but glucagon can also stimulate the protein of muscle protein so your liver can use it to make glucose. Strength training is important for maintaining a healthy balance between insulin and glucagon,
The Bottom Line
When you lift weights, there are lots going on behind the scenes from a hormonal standpoint and these changes can impact the results you get – whether you build muscle or gain or lose fat. Growth hormone, testosterone, and insulin all help you build muscle strength and mass while glucagon and cortisol, being catabolic in nature, have the opposite effect – these hormones can interfere with your ability to build lean body mass.
You can reduce the impact cortisol and glucagon have by consuming enough calories and carbs, by not training in a fasted state, and by not overtraining or doing excessive cardio, especially in a carb-depleted state. Lifting heavier and getting enough sleep will help maximize release of growth hormone and testosterone. Now you know a little more about what’s happening from a hormonal perspective when you resistance train and how to train to get the most benefits. Take advantage of it.
Diabetes Care March 2005 vol. 28 no. 3 662-667.
Harvard Health Publications. “Growth hormone, athletic performance, and aging”
Essentials of Strength Training and Conditioning. Baechle and Earle. Second edition. 2000.
On Fitness. November/December 2015. “Hormonal Impact of Strength Training”
Diabetes Metab. 1996 Oct;22(5):299-304.
Taylor, J. M., Thompson, H. S., Clarkson, P. M., Miles, M. P., and De Souza, M. J. (2000). Growth hormone response to an acute bout of resistance exercise in weight-trained and non-weight-trained women. Journal of Strength and Conditioning Research, 14(2), pp 220-227.