Hold the band at both ends with arms straight out in front of you at shoulder height, palms down. Pull it apart by driving your hands out to the sides and squeezing your shoulder blades together, keeping your elbows straight rather than bending them into a row. The band's pull grows the further apart your hands travel, so the last few centimetres before your arms are fully open are where your rear shoulders and upper back do the most work. Return to the start slowly instead of letting the band snap your hands back together — that return is where a lot of the tension gets wasted.