Weighted Seated Bicep Curl (on stability ball) exercise animation (Male)

Weighted Seated Bicep Curl (on stability ball)

Target muscle
Brachialis
Synergist muscles
Biceps Brachii, Brachioradialis
Equipment
Medicine Ball
Body part
Upper Arms
Type
Strength

The weighted seated bicep curl on a stability ball is a strength exercise that primarily targets the brachialis, with the biceps brachii and brachioradialis working as synergists to flex the elbow. You curl a medicine ball with both hands while seated on a stability ball, so your core and hip stabilizers work throughout every rep. It suits lifters who want to build arm thickness while adding a balance challenge to a standard curl.

How to do the Weighted Seated Bicep Curl (on stability ball)

  1. 1Sit on top of a stability ball with your feet flat on the floor, roughly hip-width apart, and your knees bent at about 90 degrees.
  2. 2Brace your core and sit tall so your spine is neutral — avoid rounding your lower back or leaning back excessively.
  3. 3Hold a medicine ball in both hands at hip level, palms facing up and cupped under the ball, with your arms hanging straight down.
  4. 4Pin your upper arms against the sides of your torso and keep them there for the entire set.
  5. 5Exhale and curl the ball upward in a smooth arc until your forearms are nearly vertical and you feel a strong contraction in your upper arm.
  6. 6Pause briefly at the top without letting your elbows drift forward or your shoulders shrug.
  7. 7Inhale and lower the ball under control back to the fully extended starting position, resisting gravity on the way down.
  8. 8Repeat for the target number of reps, then set the ball down before standing up off the stability ball.

Form tips

  • Keep your upper arms stationary throughout the movement — any forward swing at the elbow shifts load away from the brachialis and brachioradialis.
  • Squeeze the medicine ball firmly between your hands to increase muscle recruitment in the forearm and upper arm.
  • Control the lowering phase to at least a two-count; the eccentric portion does significant work on the brachialis.
  • If you feel unsteady on the stability ball, widen your feet slightly to increase your base of support before adding more weight.
  • Choose a ball you can curl through a full range of motion — partial reps limit brachialis development.

Common mistakes

  • Swinging the torso back to help the weight up, which reduces brachialis tension and risks lower-back strain.
  • Letting the elbows drift forward at the top, which turns the movement into a front-delt raise and unloads the target muscles.
  • Using a ball so heavy it destabilizes your seat, which forces compensations in posture before the muscles are adequately fatigued.
  • Dropping the ball quickly on the descent, which wastes the eccentric phase and limits brachialis hypertrophy.
  • Sitting too far back on the stability ball so the hips drop below the knees, which creates an unstable base and encourages lumbar rounding.

Frequently asked questions

What is the brachialis and why target it specifically?

The brachialis is a muscle that sits beneath the biceps brachii and is the primary elbow flexor regardless of forearm rotation. Developing it pushes the biceps outward and adds visible thickness to the upper arm, contributing to overall arm size more than biceps work alone.

Why do this curl on a stability ball instead of a regular bench?

Sitting on a stability ball requires constant engagement from your core and hip stabilizers to maintain balance, adding a secondary training stimulus that a stable bench does not provide. The instability is modest enough that it does not significantly reduce the load you can use on the curl itself.

How should I hold the medicine ball for this curl?

Cup the ball from underneath with both palms facing up — this supinated hold maximizes brachialis and biceps brachii recruitment. Gripping the sides of the ball with palms facing each other makes it a neutral, hammer-style hold that shifts more emphasis onto the brachioradialis.

How heavy should the medicine ball be for this exercise?

Use a ball light enough to complete all reps through a full range of motion without swinging your torso or losing your balance. Start lighter than you would curl on a bench and move up only after you can hold a stable, upright position for the whole set.

Can beginners do this exercise?

It is better suited to intermediate lifters who already have basic core stability and are comfortable sitting on a stability ball under load. Beginners should first develop balance on the ball with body-weight drills before adding curls.

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