Why Strength Training Is Essential if You're on a GLP-1
If you spend any time with us, reading our posts or watching our videos, we are all about the benefits of strength training.
Whether it’s to simply be and feel stronger, live longer, look your best or perform better, it’s an important part of any fitness regimen.
And if you are in a calorie deficit, whether through diet or a GLP-1, it’s even more paramount.
In this post, we are going to get into some of the science, mechanisms and data around strength training, GLP-1s and other weight loss drugs and why the relationship between them is probably more crucial than many realize.
GLP-1s and What They Do
GLP-1 medications, and similar weight-loss drugs, have changed the way many people approach weight loss. For some, they can be an incredibly helpful medical tool. They are not cheating, nor are they something to judge. They are one option that may help people improve appetite control, health markers, and body weight.¹
Whether weight loss comes from a GLP-1 medication, another weight-loss medication, or a traditional nutrition approach, the physiology behind successful weight loss is remarkably similar: the body must spend more energy than it takes in. In other words, a calorie deficit must exist.
GLP-1 medications help people achieve and sustain that calorie deficit by mimicking the hormone glucagon-like peptide-1 (GLP-1), which is naturally released after eating. This hormone acts on the brain to increase feelings of fullness, reduce hunger, and slow gastric emptying.² As a result, many people naturally consume fewer calories without feeling as hungry, making a calorie deficit easier to maintain.
But here's the part that often gets overlooked.
When your body loses weight, it doesn't automatically lose only body fat.
During any significant weight loss—whether from medication, nutrition, surgery, or increased activity—the body typically loses a combination of fat mass and lean mass.³ Lean mass includes muscle, and muscle is far more important than simply how we look.
Muscle helps support movement, joint health, balance, bone strength, blood sugar regulation, mobility, and independence throughout life.⁴ It is one of the body's most valuable tissues for maintaining health as we age.
It also helps us achieve a fit look (some use terms like “toned” or “athletic”) many of us are working towards.
That is why strength training matters so much.
True strength training isn't simply exercising until you're tired or burning calories. It means challenging your muscles with enough resistance and effort that they must adapt.
Whether you're using dumbbells, barbells, kettlebells, resistance bands, machines, or sometimes your own bodyweight, the goal is the same: progressively ask your muscles to do something that is a bit more difficult over time.
Strength Training Changes the Equation
Your body is remarkably adaptable. Every day, it's constantly asking a simple biological question:
"What tissues do I need to keep?"
Muscle is valuable tissue. It requires energy, nutrients, and continual repair.
During a calorie deficit—whether achieved through a GLP-1 medication or by intentionally eating fewer calories—the body naturally looks for ways to conserve energy.
If muscles aren't being challenged, the body has less reason to maintain all of that tissue.
Strength training changes that conversation. Each workout places muscles under mechanical tension.
That tension activates signaling pathways within the muscle [most notably the mammalian target of rapamycin (mTOR)] which stimulates muscle protein synthesis, the process of repairing and rebuilding muscle tissue.⁵
At the same time, resistance training reinforces that these muscles are still essential for producing force, moving efficiently, maintaining balance, and performing the physical demands of everyday life.
In effect, your body receives two competing messages.
The calorie deficit says:
"Energy is limited."
Strength training says:
"These muscles are still essential."
When those two signals occur together, the body has a much stronger reason to preserve muscle while meeting more of its energy needs from stored fat.
Although fat and muscle are never used in an all-or-nothing fashion during weight loss, resistance training shifts that balance toward retaining more lean tissue.
Research consistently shows that resistance training substantially reduces the amount of lean mass lost during weight loss, especially when paired with adequate dietary protein.⁶
But preserving muscle isn't just about preserving muscle mass. It's about preserving function.
Muscle is the body's engine for producing force. Every time you stand up from a chair, swing a pickle ball paddle, jump. climb stairs or a hill, carry groceries, lift a child, catch yourself from a stumble, or simply get up off the floor, you're relying on your muscles to generate force.
Exercise scientists often refer to this as functional capacity—your ability to perform the physical demands of everyday life safely and independently.
As we age, maintaining that capacity becomes one of the strongest predictors of long-term health, independence, and quality of life.⁷
This becomes especially important after age 40.
Adults naturally lose muscle mass and strength as they age—a process known as sarcopenia.⁸
If someone is simultaneously losing weight through a GLP-1 medication or any calorie-restricted diet, preserving muscle becomes one of the most important health priorities.
Maintaining muscle helps protect mobility, improve metabolic health, gives you more energy throughout the day, support better blood sugar control, and helps keep you doing the things you love for decades to come.
Perhaps the better goal isn't simply weight loss—it's body recomposition.
Body recomposition means losing more fat while preserving as much muscle, strength, and physical function as possible.
Unfortunately, your bathroom scale can't tell the difference between losing 20 pounds of mostly body fat and losing 20 pounds that includes a significant amount of muscle.
Your long-term health, however, absolutely can.
Two people may lose the exact same amount of weight, yet one finishes healthier, stronger, and more capable because they protected their lean muscle throughout the process.
Current American College of Sports Medicine (ACSM) recommendations encourage adults to perform resistance training at least two days per week, training all major muscle groups while progressively increasing the challenge over time.⁹
The emphasis isn't simply on movement, it's on applying enough resistance to stimulate adaptation.
Recent ACSM guidance also emphasizes that muscles should be trained with sufficient effort, generally finishing sets close to muscular failure, and that progressive overload (not simply completing repetitions) is what drives long-term improvements in strength and muscle retention.
At Park Fitness, we view this in a practical, non-judgmental way.
If a GLP-1 medication helps someone improve their health, reduce disease risk, or finally achieve weight loss after years of struggling, that's something worth celebrating.
But our goal has never simply been helping people become lighter only.
Our goal is helping people become stronger.
Because strength protects the very muscle that allows you to move well, remain independent, maintain your ability to do the things you love, and continue living an active life for decades to come.
So whether your calorie deficit comes from a GLP-1 medication, another weight-loss medication, or simply improving your nutrition, strength training shouldn't be viewed as optional.
It is one of the most effective ways to ensure that the weight you lose is primarily fat and not the muscle you'll depend on for the rest of your life.
Weight loss changes the scale.
Strength training helps protect the body behind the number. Let’s get stronger!
References
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity.New England Journal of Medicine. 2021;384:989-1002.
- Drucker DJ. Mechanisms of Action and Therapeutic Application of Glucagon-Like Peptide-1. Cell Metabolism.2018;27(4):740-756.
- Rubino DM, Greenway FL, Khalid U, et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance. JAMA. 2021.
- Wolfe RR. The Underappreciated Role of Muscle in Health and Disease. American Journal of Clinical Nutrition.2006;84(3):475-482.
- Phillips SM. A Brief Review of Critical Processes in Exercise-Induced Muscular Hypertrophy. Sports Medicine.2014;44(Suppl 1).
- Weinheimer EM, Sands LP, Campbell WW. A Systematic Review of the Separate and Combined Effects of Energy Restriction and Exercise on Fat-Free Mass in Middle-Aged and Older Adults. Nutrition Reviews. 2010;68(7):375-388.
- Westcott WL. Resistance Training Is Medicine: Effects of Strength Training on Health. Current Sports Medicine Reports. 2012;11(4):209-216.
- Cruz-Jentoft AJ, Bahat G, Bauer J, et al. Sarcopenia: Revised European Consensus on Definition and Diagnosis.Age and Ageing. 2019;48(1):16-31.
- American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 11th Edition; and ACSM Position Stand: Progression Models in Resistance Training for Healthy Adults.