Both Biceps Load tests I and II rely on an increase in tension in the long head of biceps to identify a superior labral anterior and posterior (SLAP) lesion. This study aimed to evaluate the anatomical basis of Biceps Load tests I and II by measuring activity in the long head of biceps in the two clinical tests. Activity in the long head of biceps was measured in 12 healthy young participants using surface electromyography. Activity was only minimally increased in both Biceps Load I and II compared with the resting position. In the absence of convincing support for the anatomical basis of the test, investigations of diagnostic accuracy need to be replicated in order for the reported high accuracy of Biceps Load I and II tests to be supported with confidence.