What's the most solid foundation in construction that would allow for the most flexibility?

I'd have to go with pressure treated lumber on that one, without a firm specification as to the problem. But the bigger question is what you are trying to do? There are a lot of different types of flexibility and things can be done properly to accommodate them all. For

What is the best type of cement to use for precast products?

Depends on the use and the aggregates available. In the west, I see a lot of Type II/IV used because of sulfates and oxides in the sand. Also, in precast, you're looking for a high early strength anyway, so it's not so much the type but sometimes the admix used.Controlling

How much strength can I gain in 5 days? I haven't worked out in a long time and I need to have decent strength within 5 days.

Here's what I would do. Do whatever exercise it is asap and do it pretty good, maybe 85% effort. Then do it again the next day at less. Then rest. You'll be sore by this time but you'll have a good 3–4 days recover so you can be ready to go on the 5th day. That's

How solid would a foundation made from CMUs be vs. a solid concrete foundation?

On paper, the conpressive strength of CMU blocks can be as strong as poured concrete, but I don't think they make good footings in the real world as explained below. You can use it for wall stems however.CMU is pre-manufactured in perfect size. When you dig a hole in the ground to put in the footing, the trench/pad

When setting up a home gym, will I be able to setup a squat rack on the floor of the inside of my house, or should it be only on concrete?

Our squat rack is on concrete but with padded flooring. If you are going to put it on a wood floor, wnsurentour joist offer good support and consider bracing. Aside from a lot of weight you don't want to drop large barbells on finish floor. Get additional plywood to distribute weight and protect.