When measuring muscle activity with electrodes during bicep curls, the results can be affected by how the muscle stretches and where the electrode sits — so the numbers aren’t always a perfect measure of effort.
Scientific Claim
Surface electromyography (EMG) measurements during dynamic biceps curls are influenced by muscle length changes and electrode positioning, which may confound interpretation of activation levels in fusiform muscles like the biceps brachii.
Original Statement
“EMG data can be influenced by multiple factors (i.e., subcutaneous tissue, spatial filter transfer function, innervation zone (IZ), electrode placement, etc.)... During the concentric contraction of the biceps, the IZ shifts upwards, moving underneath the electrode, thus impacting amplitude values.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
The authors’ own discussion provides direct evidence for this mechanistic limitation, and the claim accurately reflects their stated concerns.
Evidence from Studies
Supporting (1)
When people did bicep curls with their arms in different positions, their muscle signals (EMG) got stronger—even though they lifted the same weight—showing that arm position affects the signal, not just how hard the muscle is working.