My boyfriend is a healthy 21 year old male and I'm a healthy 21 year old female. He and I just started going back to the gym for the first time in a few weeks and our first night was tonight. We did the rowing machines and lifted some for about an hour or so. A few hours later, he had deep purple stretch marks on both his shoulders. He's gotten them before from lifting, but usually they appear months later, not hours. Is this normal? I've never gotten them before. Let us know!