Activewear looks like a category and behaves like a technical discipline. The tolerances are tighter and the failure modes are different.
Fabric selection is performance driven
Stretch and recovery, moisture handling, opacity under tension and abrasion resistance all matter. A fabric that performs well at rest can fail when stretched, which is exactly when the customer notices.
Seam construction
Flatlock and coverstitch seams reduce bulk and chafing. Seams also need to stretch with the fabric, which means stitch selection has to accommodate movement rather than resist it.
Fit tolerances are tighter
Compression and close fitting garments have far less tolerance for grading error than loose casual wear. Fit sampling should include the extremes of the size range and evaluation in motion.
Opacity under stretch
Testing opacity on a flat swatch is not sufficient. Fabric must be evaluated stretched to the degree it will experience in wear, which is a common and avoidable production failure.
Decoration needs care
Prints and applications must stretch with the garment. Standard screen printing can crack on high stretch fabric, so decoration method should be selected with the fabric in mind.