Should you relaxation your arms within the preacher curl bench, you minimise the involvement of other muscle teams, such as the deltoids or upper back. This enables for a far more targeted and rigorous contraction from the biceps. A barbell curl can be a pull-variety isolation exercising that actually works totally on your biceps https://www.theorthopaedicandpainpractice.com/understanding-burning-pain-in-the-upper-right-arm-causes-symptoms-and-treatment-options/