You’ve been training consistently – but some muscles seem to respond right away, while others barely change. Your quads are showing definition, but your biceps? Not so much. It makes you wonder: do some muscle groups just grow faster than others?
The short answer is yes. Due to a combination of biological and lifestyle factors, certain muscle groups do adapt faster than others, says certified strength and conditioning specialist Jake Harcoff, CSCS, head coach and owner of AIM Athletic.
The biggest influences on strength and/or size increase are muscle fibre composition – the ratio of different fibre types within a given muscle – genetics, and usage in day-to-day life, Harcoff says. Though muscles’ relative starting sizes, hormones, training history, and your current workout routine all play a role, too.
Below, experts delve deeper into exactly what influences muscle growth. Plus, they offer advice on what you can do if one muscle group seems to be lagging behind the rest.
Meet the experts: Alena Luciani, MS, CSCS, is a strength and conditioning specialist and the founder of Training2xl. Melody Schoenfeld, CSCS, is a certified strength and conditioning specialist and the 2019 NSCA Personal Trainer of the Year, and founder of Flawless Fitness in Pasadena, California. Jake Harcoff, CSCS, is a certified strength and conditioning specialist and the head coach and owner of AIM Athletic. Mark Kovacs, PhD, FACSM, CSCS, is a certified strength and conditioning specialist and human performance scientist. Milica McDowell, MS, DPT, is a doctor of physical therapy and the author of the upcoming book WALK.
The factors that influence muscle growth
From training to sleep and genetics, muscle growth depends on far more than just lifting heavier.
Muscle fibres
Much like your fave mock-neck sweater is made up of different types of threads, your muscle tissue is made up of different types of fibres. And that makeup can influence how they respond to training.
The two main types are slow-twitch (known as type I) and fast-twitch (type II). Fast-twitch muscle fibres are built to produce force quickly and on demand, which gives them great potential for muscle hypertrophy (the term for increasing muscle size), says Harcoff. As such, ‘muscles with a higher percentage of fast-twitch fibres, like the chest, shoulders, and arms, tend to grow more quickly,’ he says.
Slow-twitch muscle fibres, on the flip side, are better suited for endurance, says Harcoff. Because they’re designed for efficiency rather than size, they generally don’t grow as dramatically, says Harcoff. With that, muscles with a higher proportion of slow-twitch fibres – such as the calves, lower back, and muscles along the spine – often take longer to show visible growth, he says.
Muscle size
‘Some muscle groups are simply bigger at baseline than others,’ says Milica McDowell, MS, DPT, author of the upcoming book WALK. And bigger muscles have more total fibers available to grow, which can lead to faster noticeable changes in size.
The glutes and quads, for example, are among the largest muscles in the body. So, it can appear that those areas are making progress faster compared to smaller muscle groups, such as the biceps or triceps.
Body fat
To be clear: having body fat around muscles doesn’t stunt a muscle’s ability to change. ‘Adjacent fat has nothing to do with muscle growth rate, speed, or capacity,’ says McDowell. What overall fat mass can do, however, is cloud how defined those muscles look.
‘If you are trying to build muscle in an area where you carry more fat, it will be more difficult to see the results,’ she says. (This is why it’s so difficult to see abdominal definition in most individuals unless they have a very low body fat percentage. Still, you’re building muscle, even if you’re not seeing muscle definition, she notes.
Training reminder: You can’t spot-reduce body fat, says Luciani. If fat distribution is obscuring your progress, focus on the fundamentals—nutrition, sleep, hydration, and stress management—holistically rather than overtraining one area.
Genetics
The goods in your DNA impact your muscle gains – and in more ways than one. For one thing, ‘the number of fast- and slow-twitch fibers you have is genetically based,’ says Melody Schoenfeld, CSCS, 2019 NSCA Personal Trainer of the Year and founder of Flawless Fitness in Pasadena, California. In fact, scientists have identified dozens of genes that significantly change the amount of various muscle fibres you have, and where.
Genetics also influence your metabolism, hormone levels, and where your body tends to store fat – all of which can shape how (and how quickly) muscle definition becomes visible.
Important to remember, though: influenced doesn’t mean predetermined. With the right training stimulus, nutrition, and recovery, you can build strength and muscle across your entire body – even if some areas take a little longer to catch up.
Hormones
‘Your hormone levels don’t impact where you build muscle,’ says McDowell, ‘but they do impact how, and how much, muscle you can build.’
Building muscle requires support from hormones like testosterone and growth hormone, and even estrogen. So, if your hormone levels are imbalanced – meaning, your endocrine system is pumping out too many hormones, and suboptimal levels of others – muscle growth can slow down, she says.
Research has shown that hormonal conditions like diabetes, hypothyroidism, and menopause-related hormonal shifts can all reduce muscle-building capacity.
Life stage
Similarly, your current life stage can influence how quickly you build muscle – and how visible that growth is.
‘Estrogen has protective effects on muscle mass and influences fat distribution,’ says human performance scientist Mark Kovacs, PhD, FACSM, CSCS. ‘During menopause, declining estrogen levels can lead to reductions in muscle mass, particularly in the lower body, and an increase in central fat storage,’ he says. Taken together, these shifts impact how quickly muscle is gained and how visible it is.
Schoefeld adds that menopause-related changes can also impact the habits and physiological processes that support muscle growth. ‘The disruptions in sleep [common during menopause] can affect both workout performance and recovery, making it harder to train effectively,’ she says – thus impacting the rate of muscle growth throughout the body.
Muscle memory
Turns out, some of what feels like “stubborn” muscle growth may have less to do with biology and more to do with your training history.
Cultural messaging has long discouraged women from prioritising upper-body strength, which can quietly shape how your body responds to training later on. ‘That misconception that lifting weights with the upper body will make women look bulky historically led many to focus more on lower-body training – or avoid upper-body work altogether,’ says Harcoff.
As a result, the lower body often has a longer training history, while the upper body is essentially playing catch-up. ‘That difference in training age and exposure can make it feel like the lower body responds much faster,’ he says, ‘when in reality, the upper body just hasn’t had the same opportunity to adapt over time.’
Muscle memory also plays a role. ‘The more consistently you’ve trained a muscle in the past, the more efficiently it can rebuild and grow,’ explains Harcoff. The catch? ‘Many women simply haven’t had the same long-term exposure to upper-body strength training that builds that foundation,’ he says. Which means those muscles may take longer to respond – not because they can’t grow, but because they’re newer to the process.
How your training habits can create “lagging” muscles
Don’t hate the messenger: ‘If you notice a muscle group is responding more slowly than others, it may be human error,’ says McDowell.
In fact, as long as the list of biological influences may be, the following training habits are often the biggest factor in slow muscle growth.
1. Your workout splits are out of whack
Commonly, the issue is your workout splits or schedule. ‘Many people spend more time training the muscle groups they enjoy training, even without noticing it,’ says Luciani. Even small differences, like cutting your arm workouts short or always adding in a lower-body exercise when you have extra time, can add up.
2. You’re not progressively overloading all of your muscles
Across all muscle groups, the most efficient way to put on muscle is to progressively overload them – which means you gradually increase load, volume, or intensity over time, says Kovacs. Many people unintentionally apply this approach to some muscles but not others, he says.
For instance, ‘if your glutes are progressing but your arms are not, it may be that you’re applying the principle to your lower-body exercises for efficiency, while not graduating your upper-body in the same way,’ he says.
Sometimes, this comes down to confidence. People may feel more comfortable pushing heavier loads with their lower body – or know how to safely fail lower-body movements – while playing it safe with upper-body movements. Other times, it’s an equipment issue: the weights available, especially dumbbells, may not increase in small enough increments to allow for gradual progression.
3. Your form flubs are adding up over time
‘Improper form when doing certain moves or exercise selection could all be at play, too,’ says McDowell. If you’re cranking out back squats with hopes of growing your peach, consistently shifting your weight into your toes, your quads will take on more of the load than your glutes, explains Luciani.
Over time, that can lead to faster growth in the anterior chain (front of the body) than the posterior chain (back of the body), she says.
4. You’re cutting the range of motion
Failing to take a movement through its full range of motion can also hold you back, adds Luciani. ‘If, for example, you avoid breaking parallel every time you squat, you’re missing out on part of the muscle’s full stretch and contraction,’ she says. Similarly, if you end overhead presses with arms only partially extended, you’re robbing your shoulders of the muscle growth of those extra few inches.
That reduced stimulus limits how much the muscle is challenged, she says, which ultimately slows hypertrophy.
What to do if a muscle group is falling behind
Whether one muscle group is falling behind or you want to maximise your time at the gym more generally, doing these things will ensure maximum effectiveness and efficiency:
1. Refine your technique
Because your form and range of motion affect how much bang you get from each rep, Kovacs suggests meeting with a fitness professional for a movement check. ‘This will help ensure you’re utilising proper form and hitting the full range of motion necessary to maximise muscle activation and growth,’ he says.
2. Check your intensity
‘Are you actually challenging the muscle enough to stimulate growth?’ asks Luciani. Muscles need a strong enough stimulus to adapt – and that only happens when you’re consistently pushing yourself.
If you haven’t increased your weights in months, are coasting through sets, or stopping well short of technical failure, that muscle may not be getting the signal it needs to grow, she says.
Most programs written by a professional will follow the progressive overload principle, which keeps you working hard by design, says Kovacs. But if you’re doing your own thing or following a workout routine without prescribed weights, Luciani suggests aiming for a rate of perceived exertion (RPE) of 7 to 9. This allows you to achieve optimal muscle breakdown and, therefore, growth following recovery without significant risk of injury or burnout.
3. Use targeted accessory work
If your compound movements (like squats, deadlifts, and presses) aren’t doing the trick, accessory work might. ‘Isolation exercises can help bring up weaker areas,’ says Kovacs. These movements allow you to zero in on specific muscles that may not be getting enough stimulus during bigger, full-body lifts, he says.
For the upper body, this might include bicep curls and tricep extensions, while for the lower body, it might mean split squats or leg extensions. Here, ‘utilising moderate-to-heavy loads in the 6 12 rep range will be highly effective,’ he says.
4. Hone in your lifestyle habits
Sure, what you do in the gym is important, but for muscle growth, you can’t overlook the importance of a good diet and a sound sleep schedule.
‘Eating enough calories and protein to support muscle growth is also important,’ says Schoenfeld. ‘Building muscle is a lot more challenging if you’re eating in a significant deficit, or if your protein intake is inadequate.’ That’s roughly 0.7 to 1.0 grams of protein per pound of goal body weight, which is optimal for gains for most people.
Additionally, ‘sleep is when your muscles do most of their building and repair work,’ she says. So if you’re skimping on sleep – perhaps, getting less than the recommended seven to nine hours per night – you may not see the kind of response in your muscles as you might like, she says.
Gabrielle Kassel (she/her) is a sex and wellness journalist who writes at the intersection of queerness, sexual health, and pleasure. In addition to Women’s Health, her work has appeared in publications such as Shape, Cosmopolitan, Well+Good, Health, Self, Men’s Health, Greatist, and more! In her free time, Gabrielle can be found coaching CrossFit, reviewing pleasure products, hiking with her border collie, or recording episodes of the podcast she co-hosts called