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Why Are My Arms So Skinny? 6 Main Reasons 

7 min read
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David J. Sautter post Reviewer David J. Sautter post Reviewer
Verified by David J. Sautter
NASM Personal Trainer, NASM Fitness Nutrition Specialist, ACE Sports Conditioning Specialist, NASM Performance Enhancement Specialist

Table of Contents

We see this question a lot — why are my arms so skinny? Well, there are several main reasons you might struggle to pack on muscle. 

If your fitness goal is to achieve bulging biceps, three-dimensional shoulders, or toned triceps (or all three), here are six reasons you might fall short when building muscle and sculpting definition. 

We’re not all genetically gifted with the arms of Jennifer Aniston or Chris Hemsworth, but there are simple tweaks you can make to improve muscle definition and build size. 

I Have Really Skinny Arms. Is It Normal?

Firstly, yes. We’re not built the same — and that’s a good thing! There’s nothing wrong with having skinny arms, but you’ll need to dial into your nutrition and workout plans to see what could be improved. 

From a genetics stance, there are also various body types, including:


  • Appearance: Slender, thin, long limbs, little muscle and fat.
  • Metabolism: Typically fast.
  • Muscle Gain: Difficult to gain muscle and fat.
  • Characteristic Features: Narrow shoulders and hips, thin bones, limited muscle definition.


  • Appearance: Naturally muscular and athletic.
  • Metabolism: Balanced.
  • Muscle Gain: Easier to gain muscle and maintain a lean physique.
  • Characteristic Features: Broad shoulders, narrow waist, thicker bones, well-defined muscles.


  • Appearance: Rounder or softer physique, higher body fat.
  • Metabolism: Slower.
  • Muscle Gain: Gains muscle easily but also prone to gaining fat.
  • Characteristic Features: Wider hips and shoulders, thicker bones, carries more fat, especially in the abdominal and thigh regions.

It’s worth understanding your body type first, and if you’re worried about your weight or continuing to lose weight, visit your doctor before making any adjustments to your training plan or nutritional intake.

So, Why Are Your Arms So Skinny? 6 Core Reasons

Here are six main reasons you might have really skinny arms, whether you exercise or not.

1. Your training plan isn’t right for you

Developing lean muscle mass and building bigger arms is harder than you might think. And it doesn’t happen overnight or without a plan.

If you want to build muscle, your training plan must be consistent (several times a week) and include the principles of resistance training, especially progressive overload. 

Training for muscle gain is called hypertrophy. That means adjusting variables like sets, reps, workout frequency, and weight ranges to challenge your muscles. Only when your muscles meet significant resistance can they adapt and grow. 

As a starting point, make sure you’re lifting enough weight while maintaining good form, and aim to reach 3-4 sets of 8-12 reps per exercise, 2-4 times per week for muscle gain. 

You may also like: How to Build Muscle

2. You’re focusing on the wrong exercises

Isolation exercises have a time and place for fixing skinny arms — they’re brilliant for fatiguing smaller muscle groups like the biceps and triceps quickly. But save your tricep extensions, bicep curls, or other isolation moves until the end of your workout as a “burnout” tool.

Beginners will see much better results using compound exercises — multi-joint, multi-muscle exercises like the bench press, push-up, or pull-up — which are much better at targeting your big and powerful muscle groups while recruiting your biceps and triceps. 

3. You’re doing too much

Yep, there’s such a thing as overworking thin arms and muscles. Overtraining could lead to burnout and fatigue, so remember your rest days. Did you know that sleep and recovery are when your muscles actually grow?

During exercise, your muscles undergo microscopic tearing or damage from the stress. If you’ve ever experienced muscle soreness after a workout — this is called DOMS (delayed onset muscle soreness), and research suggests it’s a result of the damage. [1]

When you rest, these fibers can recover, adapt and grow.

For muscle-building workouts, it’s usually best to give your muscles about 48-72 hours of rest before working the same muscle group again.

4. You are not eating enough

Peering at scrawny arms? You may not consume enough calories or quality macronutrients (protein, fat, and carbs) to support muscle growth. You could use a calorie counter or a similar fitness tracker to help determine a rough guide. 

These methods will ask questions about your training habits and metrics (think age or weight), but remember, it’s trial and error and shouldn’t be followed to the number!

To build muscle mass, you’ll need to consume a small surplus to fuel your training efforts. The guidelines for men are 2,500kcal and 2,000kcal daily for women (around a 10-15% increase), but these aren’t personal.

Your genetics (metabolism, body shape, body fat distribution, age, sex), sleep quality, stress levels, and everyday activity levels will all role-play how many calories you need. Again, a calculator can help give you an idea but the gold standard is chatting with a nutritionist or dietician.

5. Your nutrition needs adjustment

When training to put on size, your food quality matters. Protein fuels recovery and muscle tissue growth, so to get rid of your skinny arms, aim for around 1.6-2.4 grams per kilogram of your body weight. Learning how much protein your body can absorb per meal is also might be useful. 

We recommend whole foods and natural protein sources (we know the cheeseburger sounds more interesting), but protein powders and tasty supplements can help top you up! 

The Mayo Clinic recommends around 10-35% of your daily intake be protein. [2] Not a meat eater? Try the vegetarian diet to build muscle

6. Lifestyle

You could be doing everything right to combat scrawny arms and build muscle, but your lifestyle could sadly dampen your efforts.

Sleep quality has a regulatory effect on your body — the immune system, metabolism, and mood, for example. Get eight hours a night, focusing on a consistent bedtime routine. 

Stress levels are also important! Try to manage your stress with practices that lift your mood — some of our top stress-busting ideas include taking a walk in nature, reading a book, following a guided meditation, or using breathing techniques. 

Other factors include reducing alcohol consumption and moving more regularly throughout the day. It’s the little habits that add up!

Bottom Line

  • Thin arms could be a lack of consistency, challenge or overload in the gym, the wrong exercise selection, too few calories or poor nutritional choices, or genetics and body shape.
  • To reduce your chances of developing too-skinny arms, focus on consistent resistance training several times a week, hitting the correct reps and set ranges, opting for compound exercises, and saving isolation exercises for the end of your workouts.
  • Remember to rest and refuel with protein after workouts, and give your body at least 24 hours between efforts.
  • Aim for a small surplus of calories daily and 1.6-2.4g of protein per kilo of body weight, including whole foods and complex carbs.
  • Look at your lifestyle factors to ensure you get enough sleep and reduce stress levels.
Disclaimer This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!

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