Why Won’t My Legs Grow?

You’ve been training hard for several months, but your thighs don’t seem to be getting any bigger. You must be doing something wrong, you think to yourself, but you’re not quite sure what that something is.

Today, I want to show you 10 reasons why your leg muscles aren’t growing as quickly as you’d like. 

1. Insufficient Training Volume

When it comes to building bigger legs, your training volume is a critical factor affecting how quickly those leg muscles are built.

By training volume, I’m talking about the total number of work sets (not warm-up sets) you do for each muscle group, both in a single training session and over the course of a week.

Research shows that a dose-response relationship exists between the number of sets you do for a muscle and the speed at which that muscle grows [1].

In other words, the higher your training volume – up to a point at least – the faster your quadriceps. hamstrings, glutes and calves will grow. 

If your overall training volume is too low, the stimulus for growth will be relatively weak, and you’ll find that gaining muscle happens a lot more slowly than it otherwise would do.

If you’re a newbie to resistance training, aim for somewhere between 10-12 sets per muscle group per week.

Once you’ve moved past the beginner stage of training, chances are you’ll need a higher volume of training to keep making progress. In this case, 13-18 sets per muscle group per week is closer to the mark.

In terms of training frequency, you want at least two leg days a week.

Training legs once a week can certainly work in the sense that it will lead to muscle being built. 

But in general, I think most people will see better results with a routine that involves training legs at least twice every seven days.

2. Not Eating Enough Calories

When it comes to adding muscle mass to your legs, your training routine is only half the story. You also need to pay attention to the nutrition side of the equation.

Building muscle takes energy, and a diet designed to maximize your rate of muscle gain requires eating more calories than your body needs to maintain its weight.

That means being in a calorie surplus, rather than the deficit required for weight loss. 

It is possible to build muscle in a caloric deficit. But in most cases, gaining muscle in a caloric deficit tends to happen a lot more slowly than it does in a calorie surplus.

That is, without enough calories, thighs and calves will grow a lot more slowly than they otherwise would do.

How many extra calories do you need?

In most cases, somewhere between 300-500 calories a day above your maintenance requirements should be enough to get the job done.

Where should those additional calories come from?

If you prefer a lower carb intake, aim to get around 30% of your total daily calories from carbohydrates, with the rest coming from protein and fat. If you feel better with higher carbs, go for a diet providing around 50% carbohydrate.

3. You’re Not Training Hard Enough

Many times in the gym, I’ll see personal trainers having a full on conversation with a client, all while said client is right in the middle of an actual set. 

They’re not offering encouragement or providing helpful pointers about proper form. Rather, it’s just general chit chat about what they did at the weekend, when they’re getting the bathroom done, and where they’re planning to go on holiday.

If you’re able to have a conversation with your trainer (or anyone else for that matter) during a set, or your mind is doing anything other than focusing 100% on the exercise you’re doing, you’re almost certainly leaving gains on the table.

Stimulating hypertrophy does require that you reach a certain threshold of effort when you’re in the gym. 

You certainly don’t need to push yourself to failure – that point where you’re physically unable to complete another rep. But you do need to get reasonably close. 

Training harder doesn’t necessarily mean lifting heavier weights. In fact, gaining muscle doesn’t require that you lift very heavy weights in the gym. Your leg muscles can be made to grow with a variety of rep ranges and loads, ranging from light to medium to heavy.

4. Your Leg Workout Involves Short Rest Periods

Some say that a leg workout geared towards bigger legs should involve short inter-set rest periods. And by short, I’m talking somewhere in the region of 30-60 seconds.

In fact, most research shows that workout routines incorporating longer rest intervals actually deliver better results in terms of both lower body strength and size [2, 3]. 

And by long, I’m talking about giving yourself 2-3 minutes of rest between each set.

Why do longer rest intervals work better?

With short inter-set rest periods, particularly with exercises like heavy squats, leg presses or lunges, residual fatigue from the previous set will bleed into the next one. This has the effect of reducing the number of repetitions you’re able to do.

As a result, the strength of the muscle-building stimulus generated by a given leg workout is weakened, which in turn puts the brakes on muscle growth.

5. Inadequate Protein Intake

Protein is one of the most important nutrients for building muscle, mainly because your muscles need it to repair and recover after training. 

Without enough protein in your diet, your quadriceps, hamstrings, calves and glutes aren’t going to grow as quickly as they otherwise would.

To calculate the amount of protein you need, aim for at least 0.7 grams of protein per pound of body weight per day. If you prefer metric, multiply your bodyweight in kilograms by 1.6.

That will do the job for most people.

While you can go higher, there is a ceiling on the amount that your body can use to synthesize new muscle tissue. And most research suggests that ceiling is somewhere in the region of 0.7 grams per pound, or 1.6 grams per kilogram, of bodyweight per day.

What about supplements?

As long as you’re getting enough high-quality protein from your diet, it is possible to build muscle without the need for protein supplements.

However, eating enough protein on a regular basis isn’t always easy to do, which is where supplements can help.

Let’s say that your daily diet provides around 100 grams of protein. However, you’ve calculated that your daily protein intake should be closer to 150 grams per day, and you’re finding it very difficult to get that extra 50 grams from your diet.

In this case, a protein supplement can help you bridge that gap, and will make a difference to the speed at which muscle is gained.

6. Too Much Cardio

Too much cardio, running in particular, does have the potential to put the brakes on muscle growth if you’re not careful. 

It does so by interfering with the quality of your workouts, slowing recovery, as well as interfering with some of the molecular signaling pathways that drive muscle hypertrophy.

How much cardio is too much? 

That’s going to vary from person to person, and there are no strict rules that say exactly how much cardio you can do without interfering with growth in the thighs and calves.

As a general guide, I’d suggest limiting the amount of moderate-intensity cardio you do to a couple of hours a week. 

Don’t do any intense cardio immediately prior to training legs. You’re better off doing it once the heavy lifting is out of the way, or better still on a completely different day. 

Finally, be very careful with high-intensity interval training (HIIT), which does have the potential to put the brakes on muscle hypertrophy if you do too much of it.

If you want to do HIIT while you focus on building muscle, limit it to 1 or 2 short sessions a week.

7. Limited Number of Leg Exercises

Compound exercises like the squat and deadlift work a large number of muscle groups simultaneously, making them a very efficient way to increase lower body strength and size.

However, to ensure complete development of all the lower body muscles – glutes, hamstrings, quadriceps and calves – your leg day should include both compound and isolation exercises. 

That is, your thighs and calves will grow more quickly if you include a variety of exercises, including squats, leg extensions, leg curls, leg presses, Romanian deadlifts, calf raises, and so on.

Here’s why:

Take the quadriceps, which is made up of four different muscles – vastus medialis, vastus lateralis, vastus intermedius and rectus femoris.

Squats alone don’t do a great job of targeting rectus femoris, the muscle running down the front of your thigh.

In fact, when researchers used MRI scans to assess muscle growth after ten weeks of squat training, they found three of the four muscles that make up the quads grew by roughly five percent  [4]. But rectus femoris didn’t grow at all.

For complete quad development, you’ll need to combine squats with an isolation exercise like the leg extension, which hits rectus femoris to a greater extent than the squat [5].

It’s a similar story with the hamstrings, which is the collective term for three muscles found on the back of your thigh:

• Biceps femoris (long head and short head)
• Semitendinosus
• Semimembranosus

The majority of muscles making up the hamstring muscle group are biarticular, which means they cross two joints, the hip and the knee.

This gives the hamstrings two main roles:

• Knee flexion
• Hip extension

If you want your hamstrings to grow, it’s a good idea to incorporate exercises that involve both hip extension (such as the Romanian deadlift or 45-degree hip extension) and knee flexion (such as the seated leg curl or lying leg curl) in your resistance training program [6].

8. You’ve Got Below Average Genetics

One of main reasons your thighs and calves aren’t growing as quickly as you’d like is the fact you’ve got below average genetics.

Not everybody puts on muscle at the same rate, even if they do the same training and eat the same food.

That’s because there are genetic factors outside your control that affect how long it takes to build muscle, as well as the maximum amount of muscle you can expect to gain.

Some people gain muscle quickly when they start weight training, while for others the gains come much more slowly, even if they lift and eat the same.

In one study, researchers found that a 10-week lower body training program led to an average increase in muscle size of 8 percent [7].

However, some subjects saw their quads grow by a disappointing 1 percent, while others saw gains of 15 percent. 

That’s a big difference. Although everyone did the exact same leg exercises, there were large differences in quadriceps growth from person to person.

9. Relying Too Much on Squats

While the barbell squat is often hailed as the king of exercises, not everyone is going to benefit from it to the same extent.

For example, having long legs and a short torso will typically mean that your hips and lower back take on a proportionally greater share of the workload during the squat compared to someone with shorter legs.

If you do have long legs and a short torso, squat variations such as the front squat allow for your torso to remain in a more upright position, meaning that more of the work will be done by your thighs.

The hack squat, dumbbell hack squat, leg press, deficit lunge and walking lunge are also viable alternatives.

10. You’re Not Training Through A Full Range Of Motion

Most research shows that training your muscles through a full range of motion generally leads to greater gains in muscle size than partial reps.

Why is that?

When you train a muscle through a full range of motion, you subject it to a high level of tension at long lengths.

By that, I mean you’re challenging your muscles when they’re in a stretched position.

Various studies have been done to establish the importance of training at long muscle lengths when it comes to hypertrophy.

In one trial, a team of Japanese scientists compared seated and lying leg curls to see which one stimulated more growth in the hamstrings [8].

Seated leg curls differ from lying leg curls in that they cause some of the hamstring muscles (specifically the ones that cross the hip) to be put in a stretched position.

After 12 weeks of training, the seated leg curls stimulated significantly more muscle growth in the hamstring muscles that cross the hip, which were the ones trained at long muscle lengths.

A similar study, this time using the leg extension, also shows a faster rate of growth when a muscle is trained at longer muscle lengths [9]. 

Partial reps performed in the bottom third of the movement, which challenge the muscles at long lengths, stimulated more growth than partial reps done in the top third of the movement.

None of this means you need to use a full range of motion on every exercise. 

Research shows that squats, for example, stimulate just as much growth in the quads whether they’re done to parallel, slightly above parallel, or slightly below parallel.

In other words, squatting arse-to-ankles isn’t necessary to make your quads grow. But it’s a good idea to include other exercises in your routine that allow you to train the muscles in your hips and thighs through a larger range of motion, such as walking lunges or split squats.