In Fair Isle sweater when you reach the underarm point of the sweater, the gussets and back sweater stitches were placed on a stitch holder and the front of the sweater was worked back and forth up to the shoulder. Next, the back stitches were worked to the shoulder. In Fair Isle sweaters the shoulder seams were attached together in one of a number of ways. The support stitches were then put back on a needle and stitches were selected up around the remainder of the opening.
These live stitches were worked down to the cuff to form the sleeve. Joining the sleeves from the armhole down was an important part of the design of the sweater for several reasons. The stitches being picked up and then knit down and so that the sweater was being worked in one piece.