What if strength or endurance is not a big factor, and your primary goal is just to lower your body fat percentage? Is it okay to do cardio either before or after? Also, my other main question was regarding stretching. Is it okay to stretch the muscle being emphasized in between sets or is it better to do it afterwards?
Your first question regarding body fat and cardio can be answered with a "yes." If you are not concerned with dropping some muscle tissue or power related performance issues, then before and after is the way to go.
Almunzaini et al investigated calorie expenditure and aerobic work. They took two groups, one completed 30 minutes of aerobic work and the second group split the training load into two 15 minute sessions that were six hours apart. Both groups work at the same relative intensity (70 percent Vo2 max.). Their research found that by splitting the training session, the metabolic expenditure was greater due to an elevated post exercise metabolism also known as elevated post exercise oxygen consumption (EPOC).
EPOC is usually associated with heavy work loads and the body trying to pay back all the substrates that get used up like glycogen, phosphate, myoglobin-oxygen and the processing of lactic acid back into usable glucose and proteins. This elevated processing costs energy, which means calories, which means fat expenditure (intra cellular lipids). So to answer your question before and after will help you lean out. Do not forget the dietary portion of the equation and keep hydrated.
The stretching portion of your inquiry is interesting. There is two ways to answer this question. First, if you want to recover between efforts, then circulation needs to be promoted. If a muscle has been stimulated over 30 percent of its maximum capacity, it starts to inhibit blood flow. The higher the intensity, the less blood flow. After a lift, the muscle remains somewhat tight from the effort and probably inhibits passive blood flow. If a person was to "loosen" up between lifts either by stretching or "shaking" out the fatigue the repeated exercises efforts may remain higher from a more sufficient recovery and lead to higher training intensities. You can see some athletes trying to stay loose before and after events like the swimmers, track and field people, the combative athletes and, of course, the gymnasts. Stretching while the muscle is flushed with blood may improve flexibility without as much pain, like when you're cold.
The second side: Some people believe that by stretching between exercises or sets you may loose the mechanical advantage the "stiffer" muscle provides when flushed with blood. I can not remember where I read this info and have not been able to locate it, but I know it exists. If I run across it, I will post an addendum to this Q&A for you. Hope this information helps you out.
- Almunzaini,K.et al. Effects of split exercise session on excessive post exercise oxygen consumption and resting metabolic rate. Canadian Journal of Applied Physiology. vol.23, n5, pp433-443, 1998
- McGrail,J. et al. Dependence of lactate removal on muscle metabolism in man. European Journal of Applied Physiology vol.39, pp.89-97. 1978
- Rasmussen,B. and R.Wolfe. Regulation of fatty acid oxidation in skeletal muscles. Annual Review of Nutrition vol.19, pp.463-484. 1999