Feels like i have twinging veins when i work out(lifting) and do certain exercises/motions? not sure if muscles or veins only in my left arm

Not veins: You usually cannot feel your veins unless they are clogged or inflamed. If this happens only when you work out, it is likely from the tendons or muscles. I suggest that you don't push yourself to this point since it may be a warning sign that you are approaching or exceeding your limits.

Either.....: Both are intimately related anatomically and repeated contraction of the muscle groups can directly affect vein movement during exercise. Depending on other symptoms associated with/following weight lifting would help ascertain if further investigation and/or treatment were necessary. Thank you..... Good question. T. Long M.D.