The brachialis runs from the lower, front part of the upper arm, across the elbow to the middle of the forearm. It provides most of the strength for elbow flexion. When you do a biceps curl, you are primarily exercising your brachialis. However, when your forearm is fixed, the brachialis rotates the upper arm toward the forearm, as in an overhand pull-up.
It is often said that the biceps are for show and the brachialis is for go.
Pain from brachialis trigger points refers mainly to the base of the thumb. Use of your thumb may aggravate it. You may also experience pain in the crook of your elbow. Pain referred into the shoulder does not impair shoulder movement.
Brachialis trigger points are typically activated from stress overload of elbow flexion. This can include activities as diverse as using a power tool, carrying groceries, ironing, playing a musical instrument, or typing when too close to the keyboard. Activities such as rowing, pull-ups or backhand tennis strokes can activate brachialis.
In “tennis elbow”, brachialis trigger points can develop after a supinator activation, along with trigger points in the biceps.
Corrective actions include trigger point pressure release, stretching, and avoiding activities that overload the muscle, such as elbow flexion, turning your hands down when lifting, and sleeping with the arms flexed.