There are several ways to measure or monitor strength. Your subjective sense is that there is some weakness on that side. This is a valid measurement. But more specific tests can be done to measure actual arm strength.
A handheld device called a dynamometer measures grip strength. This is a measure of forearm strength. A physical therapist can also test the strength of individual muscles. Some examiners use resistance to extension of the middle finger as a valid measurement.
Strength measurements are compared to the other side and to preinjury levels (if known). The results must be evaluated depending on whether it's your dominant arm that was affected.
Normal strength should be within 90 per cent of the opposite side. Equal strength from side to side may be a sign of weakness. The dominant arm is almost always stronger than the nondominant side.
You may need a specific strength-training program to restore full strength and function to the operative side. See a physical therapist for a strength evaluation and training program. It should take six to eight weeks to see the results you are looking for.