@robertbernkastel Hello! We did some research and consensus seems to show that it comes down to lactic acid buildup — that is, if you’re lifting at 80–90% of maximum strength, lactic acid will build up faster in slow twitch fibers compared to fast twitch fibers, and if you’re lifting lighter weights, lactic acid will build up more in your fast twitch fibers after exhaustion. This just means that you still have room to engage your fast twitch fibers after your heavy lifting. Just remember that it’s gotta be 30–50% of your new maximum strength (since you’ve already been exercising). Hope that helps!