Enlarged veins in forearm. No big deal or something serious? (Photo)

The pictures that you show are normal forearm veins and nothing to worry about.  With weight lifting and straining, these veins will increase in size as they engorge with blood.  This is normal. The same thing occurs when you put your arms down below your heart and when you raise the arms above your heart, the veins empty and shrink in size.

The pictures show normal veins on your arms. Usually more prominent in individuals that do more exercise like you. They DO NOT  need treatment.

No need to worry about these veins - they are more prominent in weight lifters. The important thing you said is that they decompress when you raise your arms which makes it unlikely that you have clots in your deep veins. Don't worry about these veins - no treatment necessary.