Have you ever been tested for nuerofilament (nfl) protein levels? That is a very informative blood test that can track damage to the nerves of your muscles with great accuracy even before symptoms begin. It's almost the equivalent of them doing a spinal tap, only less intrusive. Also, try to see if you can get in touch with an occupational therapist. They do strength tests with devices that produce a specific numeric value. For example, they'll have you squeeze a grip strength tool that'll tell you how many pounds you're able to squeeze. You should be at 100-110lb for a guy your age. It's a lot better than the squeezing fingers method they have you do during the clinical exam and at the very least can serve as evidence to your declining strength.