When sewing activewear, elastic used to finish arm, neck and leg openings and provide stability to bindings and edges. There a number of different styles of elastic that can be used when sewing active wear (and a few styles that are not recommended to be used when sewing activewear). Sew elastic to activewear using either a zigzag stitch on your sewing machine or an overlocker or serger stitch. A 3-thread overlocker stitch is generally easier to use when sewing in elastic than a 4-thread overlocker stitch. Swimwear elastic is my favourite elastic for sewing activewear, especially leotards and swimsuits. Swimwear elastic is a vulcanised flat rubber ribbon elastic. It generally comes in a variety of widths and if you live in Australia it can be purchased at an ultra cheap price from www.glitteranddance.com.au
If you cannot find swimwear elastic another style of elastic should work fine. However, you may need to adjust the length of elastic required, as different styles of elastic have differing amounts of stretch. Some options for alternative elastic include: Braided swimwear elastic looks similar to standard braided elastic but is made from fibres that allow it to last longer when used in garments that will be regularly subjected to chlorine. It is your second best choice for swimwear.
Regular braided elastic can be used in activewear garments, however, you may need to adjust the amount of elastic used to get the right fit.
Lastin is not recommended for use in activewear garments as, in my experience, it is too thin to stabilise the seam and tends to stretch out when you stitch through it.
Fold over elastic (FOE) can be used as an alternative means of finishing edges and comes in a range of widths and both printed and plain designs. It can also be used to form straps for leotards and crop tops.
Decorative elastic comes in various widths and sizes. It can used where the elastic will be visible after it has been applied, as a decorative trim, or as an alternative way of forming straps in some garments.
Wide braided elastic, such as 5cm (2 inch) wide braided elastic, can be used to form chest bands and waistbands for garments and provides a nice stable waistband for garments such as tutu skirts.
If you prefer not to use elastic, many openings, such as armholes and neck openings can be finished with folded stretch fabric. This can provide a softer, more comfortable finish for some garments.
Trouble shooting adding elastic to activewear:
If the edge is too gathered or is uncomfortably tight for the wearer, I would recommend lengthening the amount of elastic used.
If the edge is rolling outwards or the finished edge is stretched out, this is a sign you need to shorten the amount of elastic used.