If I can only do one thing to help my swimming what should it be?

Lat pull down is the singular best exercise for swimming as the strength of the lats are so very important for the stamina of the swimmer. The latissumus dorsi runs the length of your back up and down your sides. It is responsible for your strong stroke and forceful rotation propelling your stroke forward. A strong lat will not only increase swim speed and power, it will also enable you to swim longer at a faster speed without tiring so quickly. To perform the exercise, sit in front of the lat pull down machine at the gym and grab the bar with your knuckles pointing forward, away from you. Your arms should be slightly wider than shoulder width distance. Grab the bar with your arms extended and keep your back flat, not extended or arched. Contract your lower abdominal muscles to protect your low back and then flex your elbows and bring the bar down to your chest. It is okay to lean back just slightly, but if you are muscling through the exercise by shifting the weight of your trunk back to move the bar down, then you have too much weight on the stack and you should lighten the load. Keep your elbows flexed to your sides and hold the weight at your chest for one to two seconds before returning the bar overhead with a slow and controlled movement. Repeat the lat pull down twelve times, rest for thirty seconds and then repeat another twelve reps. You can progress to three sets of eight reps. Keep the weight challenging, but do not compromise form.