5 Reasons You’re Not Gaining Muscle Mass


One of the top benefits of resistance training, and certainly the reason that many people stay diligent in lifting weights, is to build muscle.

Unfortunately, even with the best intentions and what feels like a hard effort, plenty of people find that they are lifting weights but not gaining muscle mass or can’t build muscle easily despite following a strength training program.

In fact, one of the most common fitness questions that many people who are lifting weights ask is: “Why am I not gaining muscle mass after working out?”

In this article, we will discuss the process of building muscle and the reasons why you might be lifting weights but not gaining muscle.

More specifically, we will cover: 

  • Dietary Reasons You’re Not Gaining Muscle Mass
  • Why Am I Not Gaining Muscle? Possible Workout Routine Mistakes

Ready? Let’s dive in! 

A person lifting weights, but not gaining muscle.

Dietary Reasons You’re Not Gaining Muscle Mass 

Diet plays a significant role in how long it takes to build muscle and how successful your gains in muscle mass from lifting weights will be.

#1: You Aren’t Eating Enough Calories and/or Protein

If you are consistently burning more calories than you are consuming or create too much of a caloric deficit in the window of time after your strength training workouts (0-2 hours or so after your workout), you won’t be able to build much muscle. 

The composition of your diet also matters. Food quality and macronutrient intake can affect your ability to burn fat and gain lean body mass.

Although refueling with protein after working out is important no matter what type of exercise you perform, it is particularly important after strength training because resistance training workouts, by nature, cause structural damage to muscle fibers that then require new amino acids to repair.

These amino acids come from the protein you consume in your diet, so drinking a protein shake right after your workout can help ensure that your muscles have the ready supply of the amino acids they need to begin recovering and rebuilding new muscle tissue.

A person drinking a protein shake.

There are many functions of protein in the body, from forming enzymes to catalyze biochemical reactions to serving as structural components in molecules and facilitating muscle protein synthesis, or the process of muscle repair and growth.

The muscle-reparative function of protein is typically the primary reason that you need to consume protein after working out.

When you exercise—particularly heavy resistance training workouts—you cause microscopic damage to your muscle fibers, which in turn signals the body to deliver amino acids (the building blocks of protein) to the damaged muscle fibers for assembly into new reparative proteins.

The amino necessary to manufacture the new proteins should come from the proteins in foods you consume; otherwise, the muscle damage may not be repaired, meaning you won’t see benefits from your workouts. In fact, your recovery, strength, and lean body mass will be compromised. 

Moreover, if you’re not eating enough protein to meet your needs, healthy muscle tissue must be broken down to make the necessary proteins for all of the other essential roles of protein in the body.

Protein powders and shakes.

The Academy of Nutrition and Dietetics and the National Academy of Medicine recommend that for general health, the average adult should strive for a daily protein intake of 0.8 grams of protein per kilogram or 0.35 grams per pound of body weight.

However, the daily protein needs of athletes are even higher. The American College of Sports Medicine recommends that athletes consume at least 1.2–2.0 grams of protein per kilogram of body weight per day, and protein needs to be spread out throughout the day. 

Protein needs are even higher if you’re in a caloric deficit.

Evidence suggests that the most effective diet to follow when trying to build muscle in a caloric deficit (which is necessary during the cutting phase of bodybuilding) is to consume 2.3-3.1 g/kg of lean body mass per day of protein, 15-30% of your total calories from fat, and the remainder from carbohydrates. 

With that said, though it is possible to gain muscle in a caloric deficit, it is not ideal. One of the main reasons you might find you can’t build muscle is that you aren’t eating enough calories.

Muscle protein synthesis is an energy-requiring process, so you need to be taking in enough calories in addition to protein to rebuild and repair muscles after working out.

The caloric needs for muscle protein synthesis is the reason why most health and fitness experts say that you need to be in a slight caloric surplus (consuming 10-20% more calories per day than you’re burning) to effectively support significant hypertrophy or muscle growth.

A person eating yogurt.

#2: Your Post-Workout Fueling Does Not Contain Enough Protein, Calories, and Carbohydrates

You might not be gaining muscle mass from lifting weights if your post-workout fueling is inadequate. 

Most sports dietitians suggest that the ideal post-workout nutrition is a 3:1 or 4:1 ratio of carbohydrates to protein, with at least 20-30 grams of protein in your post-workout snack eaten within 30 minutes after exercise. 

If you aim for a minimum of 20 grams of protein with a 3:1 ratio of carbohydrates to protein, this means you need to eat 60 grams of carbs for a total of 320 calories (protein and carbohydrates each provide 4 kcal/gram). 

Keep in mind that this is the minimum, so if you are looking to maximize your muscle gains, you should bulk up this post-workout snack.

Again, the protein yields the amino acids necessary to manufacture new proteins to repair, rebuild, and strengthen muscle fibers; carbohydrates help replenish depleted muscle and liver glycogen stores, and calories support the muscle protein synthesis process. 

Yogurt and fruit.

Why Am I Not Gaining Muscle? Possible Workout Routine Mistakes

Increasing muscle mass is largely dependent on your exercise routine. Hypertrophy, or muscle growth, requires high-volume resistance training.

In order for muscles to grow, they need a stimulus, so the process of muscle hypertrophy involves first breaking down the muscles in your workouts because this is the stimulus that triggers the reparative process that ultimately builds muscle mass in step two.

Hypertrophy training—heavy resistance training workouts—causes microscopic damage to the muscle fibers because you exceed the capacity of the muscles (progressive overload).

Although purposeful, you have overworked your muscles, so there is some amount of structural damage, in the way of small tears, to the muscle fibers.

This damage, in turn, stimulates the reparative process of myofibrillar protein synthesis (MPS), often simply referred to as muscle protein synthesis.

During muscle protein synthesis, amino acids, which are the building blocks of proteins, are shuttled to the muscles, where they can be assembled into new proteins.

The new proteins are then inserted along areas of the damage and microtears on the existing muscle fibers, reinforcing the weakened spots, and thickening the existing muscle fibers, which ultimately enlarges the muscle.

A person lifting weights.

#1: You Aren’t Doing Enough Training Volume

The key to building muscle in body recomp efforts is to cause enough muscle breakdown through your hypertrophy training workouts that you maximize the stimulus that triggers muscle protein synthesis without inducing too much damage that you’ve injured tissue beyond the level of typical recovery and repair via healthy muscle protein synthesis.

Hypertrophy training to build muscle size is mainly achieved by way of increasing training volume over time (sets x reps), usually using loads that are 65-85% of your 1 RM. Typically, you perform 6–12 repetitions per set, and at least 3 sets per exercise, with 30-60 seconds of rest in between sets. 

#2: You Are Lifting Too Light

One of the most common mistakes that people make when they are lifting weights with the goal of building muscle is that they are not using enough resistance. Hypertrophy training requires that the load be at least 65% of your one-repetition maximum (1RM), but closer to 85% is ideal.

If you can do 12 or more reps with the weight using good form, it is time to increase the weight.

The exercises you perform matter as well. Focus on compound exercises like squats, deadlifts, lunges, step-ups, bench press, rows, pull-ups, lat pull-downs, etc.

People running on treadmills.

#3: You Are Doing Too Much Cardio

If you are doing too much cardio in addition to hypertrophy training, you might be compromising your muscle gains.

Cardio exercises, such as running, cycling, rowing, swimming, elliptical trainer, stair climbing, jumping rope, rebounding, and rollerblading, can inhibit muscle gains by burning too many calories and generating a greater caloric deficit, which puts your body in a catabolic (breakdown) state rather than an anabolic (muscle-building state).

Other factors can also affect your ability to build muscle mass, such as your sleep, stress, hormones, alcohol intake, training level, age, and genetics. 

It can be helpful to work with a dietitian, personal trainer, and/or doctor to dial in the best muscle-gaining program for your individual needs.

For information on how to get started on a healthy diet that can help with your muscle gain goals, you can check out our Ultimate 7 Day Meal Plan For Muscle Gain.

A trainer with a client at the gym.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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