Paddles
Hand paddles go over your hands (seriously!) and are designed as a swimming tool to build your upper-body muscles.
How do they do that? Well, you'll go faster in the water with paddles, but the reason you go faster is that your arms are taking on more resistance with the paddles' surface area than your hands would on their own.
Paddles can also force corrections to your technique by the way they pull through the water.
More: 10 Ways to Fight Boredom While Lap Swimming
Fins
While paddles add resistance to your arms, fins add resistance to your legs. While you go noticeably faster with a pair of fins on, your legs are still doing the work to get you moving down the pool.
Fins also promote ankle flexibility, which will help your kicking in the long run.
Kickboard
Kickboards are used mostly to isolate the legs and work on your kicking. Even advanced swimmers are frequently seen using a kickboard during their warmup to get the legs loose and ready for the workout.
More advanced kickboards sometimes have slots for gripping, which multiplies the amount of training you can do to include single-arm workouts and other kicking workouts.
More: 6 Strength Training Moves for Swimmers
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