It seems like it should be pretty simple: if you work out, you gain muscle mass. However, it is possible to lose muscle mass even when you’re hitting the gym regularly. In most cases, this muscle loss is related to something you’re doing outside of your workouts, so it’s helpful to be mindful of all the things you’re doing.

Wondering why you’re losing muscle mass even though you work out? We can help you figure it out.

Understanding Muscle Loss: The Basics

Sometimes, despite regular workouts, you stop one day and realize: I got stronger, but my muscle mass went down. Several factors can influence muscle loss, and some of them might surprise you. You might also be surprised to learn how quickly you lose muscle.

Why am I losing muscle mass even though I work out?

If you’re losing muscle mass after workouts, there’s a reason beyond your workouts. The following factors could be causing muscle loss:

• You’re doing too much cardio and not enough strength training.
• You’re taking too many NSAIDs (like ibuprofen), which can interfere with muscle development.
• You’re dehydrated, which prevents your muscle repair and growth.
• You’re not eating enough protein to build and repair your muscle tissue.
• You’re not getting the omega-3 fatty acids your body needs to use the protein you eat more effectively.
• You’re not getting the calories your body needs.
• You’re over the age of 30 and beginning to experience age-related muscle loss.

Why do I lose muscle mass so fast?

You might begin to notice some loss of strength and muscle after as little as one to two weeks of disuse. Within three to four weeks, muscle mass and strength typically decline, and after eight to 12 weeks, substantial loss can occur.

If you’re losing muscle mass faster than expected, it’s likely due to one or more of the following:

• Inactivity
• An injury
• Illness or disease
• Age
• A restrictive diet or losing weight too quickly

Inadequate Nutrition: Are You Fueling Your Muscles Properly?

Your muscles need fuel to grow and function properly. Without adequate nutrition and calories, your body will begin breaking down protein—including muscle tissue—to meet energy needs. This leads to muscle loss.

The most important nutrient for muscle preservation is protein. If you’re losing muscle instead of fat, you may not be consuming enough protein. Research also shows that adequate protein intake can help preserve muscle during calorie restriction. Ideally, incorporate protein sources rich in omega-3 fatty acids, which improve insulin sensitivity and help your body use protein more effectively.

However, protein alone isn’t enough. A balanced diet with healthy fats, carbohydrates, and a variety of vegetables for muscle growth is essential for supporting your heart, brain, bones, and muscles. If you’re eating well but still losing muscle, you may simply need to increase your caloric intake to fuel both your workouts and muscle recovery.

Overtraining and Under-Recovery: The Hidden Culprits

Overtraining places excessive stress on your body, while under-recovery prevents your body from healing and rebuilding muscle tissue.

Overtraining

Overtraining occurs when you work out too often or too intensely without adequate rest. This overwhelms your body and increases your risk of injury and muscle loss. Signs of overtraining include:

• Feeling overly tired or run down
• Persistent, unusual soreness
• Inability to perform at previous levels
• Loss of muscle mass
• Poor sleep or disrupted sleep cycles
• Increased irritability or mood swings
• Weakened immunity
• Loss of appetite or digestive issues

Overtraining can also cause elevated cortisol levels, which reduce blood flow to muscles, increase lactic acid buildup, decrease strength, and impair recovery. It may also weaken your immune system.

Under-Recovery

When you’re focused on building muscle naturally, rest is just as important as training. Exercise creates microscopic tears in muscle fibers, and muscle growth occurs when those fibers heal. That healing happens during rest—not while you’re exercising.

Without proper rest and sleep, your muscles cannot recover or grow. Rest days also help regulate hormones like cortisol, further supporting muscle preservation.

Age and Genetic Factors: How They Influence Muscle Mass

Age-related muscle loss (sarcopenia) is a natural process. Most people lose about 0.5–1% of muscle mass per year after age 35. But that doesn’t mean muscle loss is inevitable or cannot be slowed.

Research shows that consistent physical activity—especially resistance training—can slow muscle decline and improve mobility. Strength training two to three times per week helps older adults maintain or even increase muscle mass. A nutrient-rich diet with quality protein, healthy fats, and plenty of produce is also crucial.

Genetics also influence your ability to gain or lose muscle. Certain genetic variations impact muscle structure, hormone responses, and recovery. As research evolves, personalized training and nutrition strategies may help counteract genetically driven muscle loss.

Rebuilding and Preserving Muscle Mass: What You Can Do Now

If you’re realizing, “I got stronger but my muscle mass went down,” you now have a clearer understanding of why that might have happened. Fortunately, muscle memory is real—your body “remembers” previous muscle growth, allowing you to rebuild faster once you resume proper training and nutrition.

To rebuild or preserve muscle mass, focus on giving your body what it needs to repair and grow:

• Eat a balanced diet rich in protein, omega-3s, and fruits and vegetables
• Stay properly hydrated
• Schedule regular rest days for recovery
• Get adequate sleep
• Include strength training along with cardio
• Avoid excessive NSAID use
• Increase training intensity gradually to avoid overtraining

For expert support, the coaches at Jack City Fitness can help you rebuild muscle mass safely and effectively. Whether you prefer classes, personal training, or independent workouts, we’ll customize a plan to help you reach your goals.

If you’re ready to get started, schedule your free consultation. We look forward to helping you build strong, functional muscle that supports your long-term health and fitness.