Beast or broken?

The last 8 months I've really dedicated myself to nutrition and training. Anytime I've found a weakness I've trained that weakness until I became good at it. A couple weeks ago I was doing 40 meter dashes. I was fast, but I ended up being sore for almost a week. I realized I found a weakness. This morning I attempted more 40 meter sprints. On the 2nd sprint i pulled an abductor muscle. I've made great progress the last year. But I'm also a lot more breakable now that I'm in my 40's. I figure if I continue to push myself as hard as I have been I'll be a beast, or very broken.