RENEE MONTAGNE, HOST:
Good morning. I'm Renee Montagne. In a "Mad Men" world, a man was judged by his handshake. Now - looks like a man's firm grip is going the way of the rotary phone. And smartphones are to blame. A new study in The Journal of Hand Therapy finds that millennials' constant texting, snapping, scrolling and gaming are causing the muscles in their hands to weaken, especially the guys. One possible upside - smartphone addiction has given millennials stronger thumbs. It's MORNING EDITION. Transcript provided by NPR, Copyright NPR.