When resistance-trained men perform bicep curls with their shoulders pulled back, the lower part of the biceps muscle becomes stiffer in most individuals, which may reflect localized mechanical...
Mechanism
Synthesis from 1 study
When you do a bicep curl with your arm stretched back, your bicep gets stretched extra far while it’s also trying to control the weight going down. This pulls too hard on the part of the muscle near your elbow, tearing tiny pieces inside it. That’s why that part becomes looser and less stiff...
Most probable mechanism
When someone does a bicep curl with their arm stretched back behind them, the bicep muscle gets pulled extra tight. When they lower the weight slowly, the muscle is forced to stretch while still trying to contract, which tears tiny parts inside the muscle fibers near the elbow end. This damage makes that part of the muscle less stiff, which is what the measurements show.
Shoulder extension elongates the biceps brachii, increasing passive tension in its elastic components including titin and connective tissue.
High-load eccentric elbow flexion under this elongated state imposes excessive mechanical strain on sarcomeres, particularly in the distal region of the long head.
Mechanical strain disrupts sarcomeric Z-disks and cytoskeletal proteins, reducing tissue integrity and leading to decreased shear modulus.
Evidence from Studies
Supporting (1)
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Biceps brachii regional shear modulus following elbow flexion exercises at different muscle lengths.
Contradicting (0)
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