Exercise Variety and Hypertrophy: What the Science Says

Bodybuilders have claimed for years that different exercises affect different parts of a muscle. You’ll hear that one exercise, for example, develops the “peak” of the biceps, while another exercise gives it “width” or “thickness.”

Some coaches, on the other hand, say that all you need to grow is a handful of basic exercises.

Constantly striving to add weight in compound lifts like the squat, bench press, barbell row and deadlift is the best and most effective way to make your muscles grow.

So, who’s right?

Are you better off with one of the 5×5 workouts, where the focus is on adding weight to a small number of compound lifts?

Or should your training sessions include a bit more variety, where you use different exercises for the same muscles?

Let’s find out.

Muscle Meets Magnet

Back in the 1990’s, a Swedish scientist by the name of Per Tesch took a group of experienced bodybuilders and got them to perform a variety of different exercises.

Then, he used magnetic resonance imaging (MRI) to “look inside” their bodies to see which muscles were used to do the exercises. 

Publishing his findings in a book called Muscle Meets Magnet, Tesch found that a change in grip width, hand position or even just the direction in which the feet were pointing, led to a change in the region of the muscle that was worked most during an exercise. 

For example, the wide grip barbell curl worked the short head of the biceps to a greater extent than the long head. The incline curl, on the other hand, distributed the work evenly across both the long and short head of the biceps.

As well as MRI, researchers have used a technology known as electromyography (EMG for short) to chart electrical activity in a muscle during various exercises. 

EMG can be carried out in two ways. 

• The first involves placing electrodes on the surface of the skin directly above the muscles that you want to analyze. 
• The second uses fine wire or needle electrodes inserted into the muscle belly itself.

EMG lets researchers see how different exercises, as well as variations in angles and grips, affect regional muscle activity. 

In one study, US scientists used EMG to examine the effects of different bench angles on muscle activity in the chest and shoulders [1]. 

They found that changing the angle of the bench led to a shift in muscle activation, with both the upper chest and anterior deltoid more active during the incline compared to the flat bench press.

This is something that’s shown up in research on other muscle groups. 

The lying leg curl, for example, increases muscle activation in certain parts of the hamstrings – the lower lateral and lower medial hamstrings in particular – compared to the stiff-legged deadlift [2].

“The differences in activation of the lower hamstrings was stark,” says study author Brad Schoenfeld.

“The leg curl showed greater lower lateral hamstrings activity of approximately 170% and lower medial hamstrings activity of approximately 65% compared to the stiff-legged deadlift.”

While the squat leads to high levels of muscle activation in vastus lateralis and vastus medialis (two of the four muscles that make up your quads), the leg extension has been shown to preferentially recruit rectus femoris, which is the muscle running down the front of your thigh [5].

Exercise Variety and Regional Hypertrophy

These studies tell us that exercise selection, as well as variations in angles and grips, have an impact on regional muscle activation.

But how much of a difference does it make to muscle growth? 

In other words, does a short-term difference in regional muscle activity translate to a long-term gain in muscle mass in that particular region? 

Several studies have attempted to answer this very question. And the answer is a qualified yes.

Japanese researchers found that the part of the triceps that were highly active during dumbbell skull crushers were the parts that grew the most when the exercise was performed three times a week for 12 weeks [3]. 

The same group of researchers also report that muscle activity in the triceps during the dumbbell bench press matched up with muscle growth in that exact same area after 12 weeks of training [4]. 

The leg extension, performed three times a week for three months, leads to faster growth in rectus femoris compared to the other three muscles that make up the quads [5].

What’s more, a training program that involves several exercises for the quads – the leg press, squat and lunge – led to muscle growth in all heads of the quadriceps, while a squat-only program did not [6].

Training programs involving a greater number of exercises have also been shown to stimulate growth in more regions of a muscle than programs that involve doing the same exercises.

Brazilian researchers, for example, looked at muscle growth in two groups of men who did a full-body workout three times a week for nine weeks [7].

Both groups did the same number of sets and reps, but with one key difference.

The first group did the same exercises in every workout, while group two used different exercises for the same muscles.

Here’s what the training routines looked like in both groups.

Fixed Routine

• Bench Press
• Front Lat Pulldown
• Leg Press
• Leg Curl
• Biceps Curl
• Triceps Extension

Varied Routine

Workout 1

• Bench Press
• Front Lat Pulldown
• Leg Press
• Leg Curl
• Biceps Curl
• Triceps Extension

Workout 2

• Incline Bench Press
• Rear Lat Pulldown
• Half Squat
• Seated Leg Curl
• Preacher Curl
• Seated Cable Triceps Extension

Workout 3

• Decline Bench Press
• Narrow Grip Lat Pulldown
• Hack Squat
• Single-Leg Seated Leg Curl
• Incline Dumbbell Curl
• Triceps Kickback

Ultrasound scans were used to assess muscle thickness in the quadriceps, biceps and triceps.

To assess growth across the whole of the muscle, rather than just one location, ultrasound scans were taken at both the proximal (the part of the muscle closest to the center body) and distal ends (the part of the muscle furthest away from the center of the body), as well as in the middle.

So, what happened? Who gained the most muscle?

The varied exercise routine led to a significant increase in muscle thickness across all 12 sites measured.

However, the same results weren’t seen in the group following the non-varied routine, which didn’t stimulate significant growth in all regions of the muscle.

In some locations, such as the proximal region of the biceps and the proximal and middle region of the lateral thigh, the varied exercise group saw roughly twice the increase in muscle thickness compared to the group that did the same exercises throughout the 9-week program.

There are, however, a few caveats.

For one, EMG is useful for comparing biomechanically similar movements, such as lat pulldowns and chin-ups, or flat and incline bench presses. 

But with movements that are very different, you can’t always rely on EMG to tell you which exercise is going to stimulate a faster rate of muscle growth.

In one trial, researchers tested the hip thrust and squat to see which one would make the glutes grow more quickly [8].

Previous EMG data indicated that the hip thrust did a better job of activating the glutes [9]. But it was actually the squat that led to more muscle being built.

What’s more, the extent to which the shape of a particular muscle can be altered is not unlimited.  

You and I can do concentration curls until the end of time. But we still won’t get a biceps peak like Robby Robinson.

In most cases, guys with a large biceps peak have a relatively short muscle belly and longer tendons. And the length of your tendons and muscle bellies can’t be altered through training. 

It’s much the same story when it comes to calves. 

Guys with high calves can do endless sets of calf raises with their feet pointing out at different angles. But the long Achilles tendon and short muscle belly will limit their ability to make their calves bigger. 

People with good calf development usually have short Achilles tendons and longer muscle bellies, where the potential for growth is that much greater.

Final Thoughts

You can’t completely isolate one area of a muscle relative to another. And the potential shape and size of each muscle is determined ultimately by the genetic blueprint you were handed at birth. 

But you can make the most of that potential by using different exercises, as well as variations in grip width and angles, to emphasize different sections of a muscle.

That is, training a muscle with several exercises is more effective than training that same muscle with a single exercise. 

By using several exercises rather than just one, you target different regions of a muscle, leading to more complete development of a muscle group.