Your body position is key during the swim if you want to be fast and efficient in the water.
"The main problem for triathletes - in fact, most nonspecialist swimmers - is that the hips and legs sink," says Lumley.
"People often overemphasise a long, smooth stroke, which looks impressive but means there is a dead point in the stroke where there's no forward propulsion. Improving your kick will help that."
Try leg and core exercises (crunches, jack-knifes, raises) that require you to lie prone on a Swiss ball, which mimics your swimming position.
Improving your stroke is easier when you can recognise flaws. "Tie a band around your ankles and swim without kicking," says Lumley. "This makes you more aware of what your legs and hips are doing."
Try to avoid lateral movement, and keep your entire body as streamlined as possible.If you're from a running background, you are likely to have stiff ankles.
"An effective stroke requires flexible ankles," says Lumley. "Train with fins, as these will help increase flexibility over time."
Don't get stuck in a crowd, especially if you are still perfecting your stroke. "Stay out wide but also think about how the course is laid out," says pro triathlete Tom Sturdy, who also has a master's in biomechanics.
"I once decided to stay left during the swim, only for the whole field around me to turn left into me at the buoy, so I learned to stay on the outside of the pack. You also need a position that makes sighting easy, so use the shore if you can't see ahead."
Taking care of your trisuit is vital, too. "I only wear mine for racing, unless it's new and I want to try it out," says Sturdy. "Don't wear it in a pool because the chlorine will affect it; hand wash only, even if the label says it's machine washable, and don't hang it out in direct sunlight."