Cher, there are several different avenues to accomodate the stretchiness in knits. Many machines come with a special stitch for that purpose. Or you can use a slight zigzg stitch.

On the polar fleece, since the areas I was sewing didn't have to really stretch much, I just used a larger stitch and stretched the fabric with my hands fore and aft as it went through the feed dogs.

There have been cycling specific patterns posted here before that you could probably find with a search. The pattern I used, actually came with several pieces, but I only used 2, the front and back. It's a pattern for a bolero or shrug to be worn over real clothes. You could make it sewing 5 simple seams, but I did 8 as I did a seam finish on all but the underarm seams.