Question

What is the drawback relative to using exercise bands and how can I determine the force v. strain (pounds) when I stretch the device?

Answer

There isn't a drawback to using exercise bands for strength training. Exercise resistance bands are a good option to bulky expensive machines and have advantages over home gyms that lock you into a linear plane of motion. Home gyms have their place in strength training, but never rely solely on machines that don't recruit stabilizer muscles in compound movements or you'll end up injuring yourself.

I'm not sure what you mean by, "Force vs. Strain" but I'll assume that you wondering at what point the exercise bands provide their rated resistance. To help answer this question I consulted with Blake Kassel, the inventor and President of Bodylastics Exercise Bands (read my Bodylastics review here).

On the Bodylastics Exercise bands that I recommend and own, each of the colored bands (Black, Blue, Red, Green and Yellow) have a the weight (labeled in pounds of resistance) printed right on the clip as pictured below…

My Bodylastics Resistance Bands Clips w/ Weight Markings

Mr. Kassel from Bodylastics informed me that the true weight of the bands is measured at the mid point of the stretch. That means you're getting a little less weight in the beginning of an exercise with the bands unstretched, and a little bit more resistance at the end of an exercise when the bands are fully stretched.

I wouldn't worry too much about when you're getting the maximum resistance, the important thing is that you use them! With the Bodylastics, it's easy to put a combination of bands that will give you a killer workout for complete newbies all the way to hardcore bodybuilders - more on Bodylastics here