How Wobbly Weights Change Shoulder and Core Muscle Work
Activity of Shoulder Stabilizers and Prime Movers During an Unstable Overhead Press.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists wanted to see how using shaky weights affects shoulder and core muscles when lifting overhead. They tested three types of bars: one steady, one shaky straight bar, and one very wobbly Earthquake bar.
Surprising Findings
The Earthquake bar increased biceps brachii activation during an overhead press—a muscle not typically thought to be heavily involved in this movement.
Most people assume overhead pressing mainly works shoulders and triceps, but this shows the biceps may play a larger stabilizing role when instability is introduced.
Practical Takeaways
Use an Earthquake bar (or similar unstable bar) during overhead pressing to increase muscle activation and core engagement at lighter loads.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists wanted to see how using shaky weights affects shoulder and core muscles when lifting overhead. They tested three types of bars: one steady, one shaky straight bar, and one very wobbly Earthquake bar.
Surprising Findings
The Earthquake bar increased biceps brachii activation during an overhead press—a muscle not typically thought to be heavily involved in this movement.
Most people assume overhead pressing mainly works shoulders and triceps, but this shows the biceps may play a larger stabilizing role when instability is introduced.
Practical Takeaways
Use an Earthquake bar (or similar unstable bar) during overhead pressing to increase muscle activation and core engagement at lighter loads.
Publication
Journal
Journal of Strength and Conditioning Research
Year
2018
Authors
Martin Williams, Dustin S Hendricks, Michael J Dannen, Andrea M Arnold, Michael A. Lawrence
Related Content
Claims (4)
When men lift weights overhead with a shaky Earthquake bar, they wobble more than when using a regular or slightly shaky bar — their balance gets a tougher workout.
When guys lift weights overhead using a shaky bar with weights swinging off it, their core and shoulder muscles have to work harder than when using a regular, steady bar.
When guys lift weights overhead with a shaky bar, their back muscles work harder—but not all wobbly bars have the same effect. One type makes certain muscles fire more, while another type ramps up even more muscles, showing that not all unstable bars are the same.
If your shoulders move well and your core is strong, doing overhead pressing—whether in front or behind your head—is safe for your shoulders and spine.