Building Bigger Shoulders: What Science Says About Deltoid Growth

Your Shoulder’s Secret Architecture

Imagine your shoulder is like a baseball cap sitting on top of your upper arm bone. That rounded cap shape comes from your deltoid muscle (DEL-toyd), a thick, triangular muscle that wraps around your shoulder joint. It has three distinct sections, almost like three separate muscles working together:

• The anterior deltoid (the front)
• The lateral deltoid (the side, sometimes called the “middle delt”)
• The posterior deltoid (the back)

Of these three, the lateral deltoid gets the most attention from people who want wider-looking shoulders. It is the section that, when it grows, creates that broad, capped appearance.

But building this muscle is not as simple as just picking up weights and raising your arms. Recent research has looked at questions that gym-goers have debated for years: Are cables better than dumbbells for lateral raises? Does your elbow angle matter? And how much can the deltoid actually change in size?

Let us walk through what the science says.

What the Research Shows

Dumbbells vs. Cables: A Surprisingly Clear Answer

One of the most common debates in any gym is whether cable lateral raises or dumbbell lateral raises are better for growing the lateral deltoid. The logic behind cables goes like this: a cable machine can apply more tension when the muscle is in a stretched (lengthened) position, and some research on other muscles suggests that loading a muscle at longer lengths might help it grow faster.

A 2025 study published in Frontiers in Physiology put this question to the test directly. Researchers recruited 24 resistance-trained men and women (averaging about 7 years of lifting experience) and used a clever within-participant design. Each person trained one arm with dumbbells and the other arm with cables for 8 weeks, performing 10 weekly sets of lateral raises per arm taken to failure.

The researchers controlled for nearly everything: range of motion, lifting tempo, number of sets, rest periods, and proximity to failure. They measured muscle thickness at two sites on the lateral deltoid using ultrasound.

The results? Both exercises produced virtually identical muscle growth.

The statistical analysis provided what scientists call “moderate” to “extreme” evidence in favor of the null hypothesis, meaning the data strongly supported the conclusion that there was no meaningful difference between the two exercises. The researchers had hypothesized that cables would win, but the data told a different story.

This is worth emphasizing: these were experienced lifters, and both conditions still produced measurable growth of 3 to 5 percent in just 8 weeks. That is a meaningful change for people who have already been training for years.

Why Your Elbow Angle Matters During Lateral Raises

Here is something many gym-goers overlook. When you perform a lateral raise, the angle of your elbow changes how hard your deltoid has to work.

A 2023 study published in Sisli Etfal Hastanesi Tip Bulteni examined 53 bodybuilding athletes (44 men, 9 women) and measured surface electromyography (sEMG) (eh-lek-tro-my-AH-gruh-fee), which tracks the electrical activity in a muscle during movement. The researchers had participants perform lateral raises with their elbow at three different angles:

• 180 degrees (arm fully straight)
• 150 degrees (slightly bent)
• 120 degrees (noticeably bent)

In male participants, muscle activation decreased significantly as the elbow angle got smaller. In other words, a straight arm during lateral raises produced the highest deltoid activation. The difference between a straight arm (180°) and a bent arm (120°) was about 15% less activation in men.

Interestingly, in women, the differences were not statistically significant. The researchers speculated this might be related to differences in training style, though the small sample of women (only 9) makes it hard to draw firm conclusions.

An important caveat: higher muscle activation measured by sEMG does not automatically guarantee more muscle growth. sEMG tells us how much electrical signal the muscle is producing, but hypertrophy (hy-PER-truh-fee), which means muscle growth, depends on many other factors too. Still, activation is one piece of the puzzle, and this study suggests that keeping your arm straighter during lateral raises may give the lateral deltoid a slightly greater stimulus.

The Anatomy Behind It All

Understanding why these exercise details matter requires a quick look at deltoid anatomy. Think of your lateral deltoid like a fan attached to the outside of your shoulder. It connects from the acromion (ah-CROW-mee-on), the bony point at the top of your shoulder, down to a spot partway along your upper arm bone (the humerus).

When you raise your arm out to the side (a movement called shoulder abduction), the lateral deltoid is the primary mover. But here is the thing: the deltoid’s force production changes depending on where your arm is in space. Scientists call this the length-tension relationship. The lateral deltoid is estimated to reach the descending portion of this curve (where it starts losing force-producing ability) when your upper arm is roughly parallel to your torso.

This is why the cable vs. dumbbell question was interesting in the first place. Cables can keep tension on the muscle when the arm is down at your side (where the deltoid is longer), while dumbbells provide the most challenge near the top of the movement (where the deltoid is shorter). But as the 2025 study showed, this difference in resistance profile (rih-ZIS-tuhns PRO-file), meaning where in the movement the exercise is hardest, did not translate into different amounts of growth.

A Note on Cosmetic Deltoid Reduction

While most people reading this want to grow their deltoids, it is worth noting that some individuals seek the opposite. In parts of Asia, cosmetic procedures to reduce deltoid size have been studied.

A 2023 pilot study in Annals of Dermatology tested botulinum toxin type A (BOT-yoo-lin-um TOK-sin), commonly known as Botox, on 12 Korean women with deltoid hypertrophy. The participants received either 16 or 32 units of the toxin. Both doses reduced upper arm circumference over 12 weeks. However, patient satisfaction was mixed. The researchers noted that factors like skin quality, fat distribution, and overall arm shape affected how people felt about their results, even when the muscle itself measurably shrank.

A related 2023 paper in Surgical and Radiologic Anatomy discussed botulinum toxin applications for body contouring more broadly, including the use of 3D CT scanning to measure muscle volume changes. While the case described focused on calf muscles rather than deltoids, it highlights the growing clinical interest in using precise imaging to track muscle size changes.

These cosmetic studies are relevant to our topic because they confirm something important: the deltoid responds measurably to interventions that change its stimulation. When you add stimulus through resistance training, it grows. When you block the nerve signals with botulinum toxin, it shrinks. The muscle is responsive.

Who Benefits Most

The research reviewed here applies to different groups in different ways.

People Who Will Benefit Most from These Findings

Who Should Be Careful

• People with shoulder pain or impingement: Lateral raises to 90 degrees of abduction can aggravate shoulder issues. The 2025 study noted that some participants experienced pain and had to adjust their movement plane. If you have shoulder problems, consult a physical therapist before performing lateral raises.
• People considering cosmetic procedures: The botulinum toxin research is preliminary (very small sample sizes), and results were mixed in terms of satisfaction. These procedures should only be discussed with a qualified medical professional.
• Women interpreting the EMG study: The finding that elbow angle did not significantly affect muscle activation in women was based on only 9 participants. That is too few to draw confident conclusions.

How to Train Your Lateral Deltoid

Based on the research, here is a straightforward approach to lateral deltoid training.

Exercise Selection

Pick whichever lateral raise variation you prefer. The 2025 study showed no meaningful difference between dumbbells and cables when range of motion and effort were matched. The best exercise is the one you will do consistently with good form.

Volume and Frequency

The participants in the 2025 study performed 10 weekly sets of lateral raises (5 sets per session, twice per week) and saw 3 to 5 percent growth in 8 weeks. This is a reasonable starting point for most lifters.

Form Tips Based on the Research

1. Keep your arm relatively straight. The EMG study suggests that a fully extended elbow (180°) produces the highest medial deltoid activation, at least in men. A slight bend is fine for joint comfort, but avoid excessive elbow flexion.

2. Raise to about 90 degrees of shoulder abduction. Both studies used 90 degrees (arm parallel to the floor) as the top of the movement. Going higher shifts the work more toward the trapezius.

3. Control the tempo. The 2025 study standardized the lifting and lowering phases to about 1 second each. Avoid swinging or using momentum.

4. Use lifting straps if grip is a limiting factor. All participants in the cable vs. dumbbell study used lifting straps to ensure grip strength was not the reason a set ended.

5. Eat enough protein. Participants were encouraged to consume at least 1.6 grams of protein per kilogram of body weight daily (about 0.73 grams per pound). Most were in a calorie surplus during the study, which supports muscle growth.

A Sample Weekly Plan

Day 1 (e.g., Monday)

• Lateral raises (dumbbell or cable): 5 sets of 12-16 reps to failure
• Other shoulder/upper body work as desired

Day 2 (e.g., Thursday)

• Lateral raises (dumbbell or cable): 5 sets of 12-16 reps to failure
• Other shoulder/upper body work as desired

This gives you 10 direct sets per week, matching the study protocol that produced measurable growth in experienced lifters.

The Bottom Line

What We Know

• Dumbbells and cables produce equal lateral deltoid growth when range of motion, effort, and volume are matched. This is supported by strong statistical evidence from a well-designed study.
• A straighter elbow during lateral raises produces higher medial deltoid activation in men, though the practical impact on long-term hypertrophy is not yet confirmed.
• The lateral deltoid can grow 3 to 5 percent in 8 weeks even in experienced lifters doing 10 weekly sets to failure.
• Both exercises work on both the upper and lower portions of the lateral deltoid similarly. No regional differences were found.

What We Don’t Know

• Whether cables might outperform dumbbells over longer training periods (more than 8 weeks) or in beginners.
• Whether allowing a greater range of motion with cables (going below the standard starting point) would change the results.
• Whether the elbow angle findings from the EMG study translate to real differences in muscle growth over time.
• Why women in the EMG study did not show the same angle-dependent activation pattern as men.
• The optimal total weekly volume for lateral deltoid growth across different training levels.

The Practical Message

Stop worrying about whether cables or dumbbells are “better” for lateral raises. The evidence says they are effectively the same for building your lateral deltoid. Instead, focus on what actually drives muscle growth: training close to failure, getting enough weekly volume, keeping your arm relatively straight, using a full range of motion, and eating adequate protein. Consistency with these fundamentals matters far more than your equipment choice.

Quick Reference: Key Studies

Last updated: July 2025

This article synthesizes findings from peer-reviewed research. It is for educational purposes only and does not constitute medical advice. Consult a healthcare provider before starting any new regimen.