On the contrary, more recent studies agree that the short head of the biceps has a tendon that inserts on the radius more distally and having a larger surface area than the long head segment (Athwal et al. 2007) indicating that it may be the primary elbow flexor (Jarrett et al. 2012).
In an overhand, also called a pronated grip, your biceps (the muscles on the front of your elbows and your primary elbow flexors) are in a mechanically disadvantageous position.