Define Lean Muscle

Lean muscle is a broad term that's used when you talk about body composition. Both aesthetically and for overall health reasons, it's a good thing to have a lot of lean muscle compared to fat. When you strength train to build muscle, you can either build lean muscle or "bulky" muscle.

Longer rests between sets encourage greater muscle growth. (Image: swissmediavision/E+/GettyImages)

What Is Muscle Tissue?

Muscle tissue is made up of cells that contract and lengthen to facilitate movement of different body parts. The cells are often called muscle fibers because they are long and slender. Muscle tissue is supplied with blood via a network of blood vessels running through it.

There are three types of muscle tissue in the body:

  1. Smooth muscle surrounds your organs and controls involuntary movements, such as blinking and breathing.
  2. Cardiac muscle specifically controls contractions of the heart muscle to pump blood throughout the body.
  3. Skeletal muscle attaches to the bones and is in charge of voluntary movements, such as walking.

All three types of muscle contribute to your total lean body mass. Skeletal muscle is the type that can be made larger and stronger with resistance training. The cardiac muscle can also be strengthened with regular exercise.

Lean Muscle vs. Lean Mass

Lean muscle mass is a misnomer. All muscle is lean, meaning that it does not contain fat. Lean muscle mass is sometimes confused with lean body mass, which is the combined weight of your muscle, bone, ligaments, tendons and internal organs. Lean body mass comprises a small amount of essential fat found in bone marrow and internal organs.

You may have also heard the term fat-free mass. This is your total body weight minus lean muscle mass. Most methods of measuring body composition measure fat vs. fat-free mass, according to Len Kravitz, Ph.D., and Vivian H. Heyward, Ph.D., of the University of New Mexico.

Building Lean Mass

You can improve your body composition and lower your fat mass by building lean mass. Resistance training breaks down the muscle fibers, after which the cells repair themselves, growing larger and stronger. Progressively challenging your muscles encourages even greater gains in mass and strength.

Lean vs. Bulky Muscles

There are several different variables in resistance training that you can manipulate depending on your goals. Some people want to build large, "bulky" muscles, while others desire what are often referred to as "lean" or "toned" muscles. Here, lean refers to less mass and a more compact appearance.

The first thing to note is that whether you develop lean or bulky muscles depends on a lot of factors beyond your control: genetics, gender, hormones and more. Some people with certain body types have difficulty gaining muscle mass. They can get strong, but their muscles are naturally smaller.

Women generally can't gain as much muscle mass as men without a special diet and supplements. Many of them are afraid to strength train because they don't want to "bulk up." What they don't realize is that, with a few exceptions, most women won't bulk up no matter how they train.

Training for Hypertrophy

Hypertrophy means muscle growth. Although research is still inconclusive, the long-standing theory is that you can manipulate certain factors, such as volume, intensity, weight and rest, to encourage greater hypertrophy.

Different experts recommend different hypertrophy strategies. The National Academy of Sports Medicine's recommendation for hypertrophy is to use low to intermediate repetitions and progressive overload, which simply means consistently adding weight and/or volume. This challenges the muscles to continually adapt to increasing stimuli.

As an example, NASM suggests performing a chest press for three to five sets of six to 12 repetitions at 75 percent of one rep max (1RM). Your 1RM is the most weight you can lift with proper form for a single repetition.

Research on Hypertrophy

There is a wealth of research on the most effective way to build muscle mass. While NASM says that low to medium rep ranges are best for building muscle, a 2015 study published in the Journal of Strength and Conditioning Research found that it doesn't matter how many reps you do. If you work to failure, you will gain muscle whether you use high reps (25 to 35) and low load or low reps (8 to 12) and high load. However, high load and low reps is still the best way to increase strength.

When you're working to failure, rest between sets is necessary for your muscles to recover the phosphocreatine stores they use to resynthesize adenosine triphosphate — the energy for muscular contractions. According to NASM, 1 to 2 minutes is ideal for hypertrophy. But research differs.

A study published in 2016 in the Journal of Strength and Conditioning Research determined that longer rests of 3 minutes were actually more effective for building muscle mass compared to shorter rests of 1 to 2 minutes.

Other Factors in Hypertrophy

In addition to volume, load, frequency and rest between sets, how you recover, what you eat, how you sleep, how much stress you have in your life and a variety of other factors affect how much muscle you can grow.

How much protein you eat plays a major role in building muscle. Protein contains amino acids — the building blocks of muscle. Your body breaks down protein to its constituent amino acids and then uses those to repair muscle damage and build new muscle.

The recommended dietary intake (RDI) for protein for the general population is 0.8 grams of protein per kilogram of body weight per day. For someone who weighs 175 pounds, that's 63 grams of protein. However, research shows that those looking to build muscle need quite a bit more. A report published in 2018 in the British Journal of Sports Medicine found that higher intakes of up to 1.6 grams of protein per kilogram (double the RDI) promote greater muscle growth.

Building "Lean" Muscles

If you don't like the look of larger muscles, don't give up strength training. Having more lean muscle mass helps you burn fat because muscle is more metabolically active than fat. Building muscle also strengthens and protects your bones from osteoporosis and arthritis. It may also improve blood sugar control, sleep and mental well-being.

To prevent bulky muscles, simply reverse some of the strategies for building large muscles. Perform fewer sets — one to three — and rest for less time between sets. You also might try alternate forms of resistance training, such as yoga, barre and Pilates, known for building leaner muscles.

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