It’s a simple fact: Guys want big arms. Just walk into any commercial gym and you’ll see a line of people standing in front of mirrors working on their biceps and triceps.

Yet so many guys struggle to grow their arms, regardless of how much time they spend. And although you might respond with more arms work, it’ll be in vain. The truth is, you can train your arms as much as you want, but if you keep making a few critical mistakes you’ll never get great results.

Escape the black hole of ineffective arms training by learning the eight reasons why your arms still aren’t growing, and what exactly you can do to fix it.

1. Not Eating Enough

The biggest problem isn’t that you don’t have big biceps; it’s that you aren’t big at all. If you’re 6′ and 160lbs, you’ll never have big arms. You’re too skinny. If you want big arms or a big chest, you need to get big all-over.

Eat more to get bigger arms.

Follow this rule: take your height in centimeters (sorry, America) and subtract by 100. Your result is your minimum target weight in kilograms. For example, if you’re 6′ (183cm), you should weigh at least 183lbs (83kg). If not, get there first.

2. You’re Training Your Arms Every Day

No body part grows by beating it every day—you need to rest to let your arms recover. In the hours after a workout, your muscles lose strength and power as they heal; after 36-48 hours, the muscle actually gets stronger, which is a process called “supercompensation”.

You must give yourself rest. Also, you arms are tiny compared to other muscle groups like your legs or back, can’t handle as much stimulus, and may take longer to super-compensate.

3. You’re Not Training Your Legs

Researchers from Norway found that performing legs exercises before arms exercises led to bigger and stronger arms than arms exercises alone over 11 weeks. The study showed that immediately after you train your legs, you’ll have more testosterone and growth hormone in your blood—by training your arms afterward, you’d get superior results.

Make sure to blast your legs with heavy exercises like squats, deadlifts, and lunges to elevate your anabolic hormone concentration. Although training your legs leads to acute increases, it also leads to higher levels long-term.

4. You’re Not Using Complex Movements

Although isolation exercises are the backbone of arms workouts, you’ll never build huge arms without strong surrounding muscles, too.

Instead, add complex exercises to target not only your arms, but also your forearms, shoulders, back, and chest. To build your triceps, add weighted dips, close-grip bench presses, and barbell overhead presses. To build your biceps, include chinups and reverse-grip barbell rows.

5. You Neglect Your Triceps

Too many guys work their biceps only.

Remember that your triceps give your upper arms their size. (The triceps actually occupies two-thirds of your upper arm.) And to build truly huge arms, you need to hammer your triceps just as much as your biceps.

6. You’re Not Varying the Volume

Take a scientific approach to build massive arms. With any muscle group, there are fast- and slow-twitch muscle fibers, each adapting to a different level of volume and intensity. Spend 3-4 weeks developing a specific fiber, and then cycle to another one.

Do you always do 3 sets of 8 reps of biceps curls? Add massive volume with band-resisted curls, and do as many as you can until failure (40 or more reps) for a few weeks. Do you always do dropsets? Try going extra heavy and repping out only 5 reps for 4 or 5 sets.

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7. You’re Not Varying the Stimulus

Most people train their biceps and triceps with dumbbells, EZ bars, barbells, and cables only. And although those are great, you can unleash a different stimulus on your arms by using other tools in your training.

For example, use a thick-handle dumbbells or barbells to boost your neural drive and activate more musculature. If thick-handle weights aren’t available, use fat grips or wrap a small towel around the handles.

Also, use bands to explode past sticking points. During the biceps curl, for example, you engage the biceps more toward the top-half of the movement than the bottom-half. By using a band, you can better match the strength curve of the biceps curl because the resistance will be easiest at the bottom (when the muscle is fully stretched) and get harder as you rise.

8. You’re Not Strengthening Your Grip

The stronger the grip, the stronger the person—a vise-like grip lets you handle heavier weights and build more muscle. It’ll also sculpt thicker forearms and send more neural drive through your arms.

Strengthen your grip with a variety of weighted carries, heavy pulls, and specialty handles like fat grips or thick-bars.