Health Reporter/Editor
Let’s get one thing straight: Muscle is muscle. Despite what many fitness influencers may have you believe, there’s no such thing as 'lean muscle' or 'bulk muscle.' It’s all made from the same stuff. And no matter how many times you come across workout routines online with claims to 'lean' or 'bulk up' your muscles, know that it's all the same thing — strength training.
Now, while you can’t influence the shape your muscles take on as they form, you do have some say in how they look on you, K. Aleisha Fetters, author and certified strength and conditioning specialist, tells TODAY.com. That, she explains, comes down to a number of choices you make both in the gym and outside of it. If you’re looking to achieve a specific physique, whether for a leaner or bulkier appearance, what it takes goes beyond your workout routine. Is There a Difference Between 'Lean' and 'Bulk' Muscle? There are three types of muscle in the human body, according to Cleveland Clinic: smooth muscle, on the inside of organs; cardiac muscle, only inside the heart; and skeletal muscle, the muscles you use and strengthen with exercise. Skeletal muscle is all made from the same tissue and fibers, whether you train in a Pilates class or the weight room, says Fetters. The misconception that muscle can be lean or bulky lies in its appearance. “When people , they’re usually describing a look — muscle that appears more defined because there is less body fat covering it,” Cedric X. Bryant, Ph.D., chief executive officer at the American Council on Exercise, tells TODAY.com. As for 'bulk' muscle, that “typically refers to having more overall muscle size, often paired with higher calorie intake to support growth. The muscle itself is the same — what changes is how much muscle you have and how it appears on your frame,' Bryant adds. The differences in how muscle looks on various bodies, says Bryant, are driven by total muscle mass, training intensity, nutrition, individual body structure, and overall body fat. More body fat will make you appear bulkier and less body fat, leaner. There are pros and cons to both 'lean' and 'bulk' physiques. 'A leaner physique may support agility, endurance, athletic movement, muscle definition and relative strength,” says Bryant. “A more muscular physique may support greater absolute strength and power, higher resting metabolism, and long-term muscle preservation with aging.” Both, he emphasizes, “can be healthy and functional.” Are There Any Differences Between Skeletal Muscles? Yes, but it has nothing to do with how lean or bulky they are. Instead, it’s all about how muscle fibers work and which ones are optimized during exercise. “Your muscles are made of thousands of small fibers woven together,” according to the Cleveland Clinic. To function, these fibers stretch and press together, it adds. Skeletal muscle fibers don't all serve the same purpose, however. They can be classified into two groups: type 1, or slow-twitch fibers, and type 2, also known as fast-twitch fibers. All muscles have both, but some rely on more of one kind than the other. Type 1 fibers are “really beneficial for someone who wants to sustain a lower intensity effort for a long duration,” says Fetters. Think: long-distance runners and cyclers. These type 1, or slow-twitch, fibers are the ones you use for most daily activities since they can work for long periods without quickly getting fatigued. They rely on blood and oxygen to function and use up energy at a slower pace than fast-twitch fibers, per the Cleveland Clinic. Type 2, or fast-twitch, fibers are tailored to high-intensity movement, which calls for speed and power, such as sprinting, jumping and high-intensity interval training, says Fetters. These fibers need carbs for fuel. While all skeletal muscle is made from the same tissue and we all rely on both types of muscle fibers for movement, 'type 2 muscle fibers can grow in sizes that give that bulky look,” says Fetters, whereas slenderer athletes tend to rely more on type 1 fibers. Is a Lean or Bulk Muscle Physique Better for Health? Since there’s no real difference between lean and bulk muscle, says Bryant, 'no single physique guarantees better health.' 'What matters most is maintaining muscle and strength, staying physically active, supporting metabolic and cardiovascular health and following a sustainable routine,' he adds. Those with lean physiques tend to consume fewer calories, whether they’re in a caloric deficit, a small surplus or at maintenance, says Fetters. Those who appear bulkier are often eating in a caloric surplus so that they can properly energize their bodies for muscle gain. Those additional calories will also lead to more body fat overall. Bottom line: Appearing lean or bulky is “influenced by muscle mass, body fat, genetics and lifestyle,” says Bryant. “The best approach is the one that fits an individual’s goals, body and life — while prioritizing strength, movement and long-term consistency,' rather than appearance.
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