Do some people actually have buoyant legs?

Excellent vid, thanks for sharing. In that vid I'd say the results are more a product of good balance, and good streamlining... and good buoyancy (notice how the guy lets air out as he pushes off). The body follows the head. Head and hip position are fundamentally important to swimming technique (as is so clearly illustrated in this vid). The "good" swimmer has her head down, and the spine is straight as an arrow between the head and the hips. (Yoga is great for learning good spinal/body alignment.) There may be some genetics involved here. Basically: muscle sinks and fat floats, and females tend to carry a bit of extra padding around the hips (not that there's anything wrong with that). But both the swimmers in the example look pretty athletic, so I doubt body fat content comes into play here much. If you learn to increase your lung capacity you can increase your buoyancy. Then all you have to do is get the balancing act down. Good body alignment is useful as well. I have excellent lung capacity, developed primarily through swimming and Yogic breathing exercises. I'm not super lean (I do have a fair amount of muscle mass), but I'm not carrying a lot of extra padding either, and I tend to pop up to the surface like a cork when I come off the wall on anything but my back (because I'm letting air out then). Additionally... This vid is an excellent example of how pelvic rotation affects body alignment. Her pelvis is rotated forward (butt tucked in), his pelvis is rotated way back (butt sticking out). This is really easy to do while standing up. Try it and pay attention to you posture as you change from one extreme to the other. Try changing you pelvic rotation as you swim and notice how it affects your balance, speed and streamlining as you move through the water. To get an idea of what is correct body alignment, get your back (and head) against a wall and slide down till your thighs are parallel to the floor, knees together, directly above the ankles (like you’re sitting in a chair), feet parallel, arms relaxed at your sides. Don’t forget to breathe. Lengthen the spine as you do this (try imagining a cord attached to the top of your head, pulling you up). As with all exercises, you want to learn to relax into it. This posture is something I learned in Yoga class for strengthening the quadriceps and teaching good spinal alignment. See how long you can hold it. Try measuring by counting the breaths, using steady, rhythmic (Yogic) breathing. (Any good Yoga teacher will constantly emphasize the breath throughout the class.) Probably the most bulletproof test for gauging body balance and alignment is this simple standing posture/exercise/pose (or in Yogic terms: asana). Stand up and notice where your weight is. Is it more on your heals?... Or is it more on the balls of your feet? You want to stand with the feet together (under the hips, or “shoulder width apart”) and parallel (try it with the outsides of the feet parallel as well). Now lift yourself up onto the balls of your feet and see how long you can keep your balance. Remember to keep good alignment (as in the above “chair” asana). Your whole body should be straight and aligned (though you will be leaning forward some in order to maintain balance). Focus on the breath, and on activating the muscles you need, and relaxing the muscles you don’t need (especially the arms) to keep the asana in place. Again, relax into it and gauge the duration by counting (the breaths, if you last that long). As you start to loose your balance relax back down to a standing position, but always keep the weight more on the balls of your feet. Repeat this exercise as many times as you wish. You can simply shift between the up and down position (as a strength building exercise), but always try and hold the up position occasionally to gauge your progress. This is an excellent exercise for strengthening the ankles and legs, as well as teaching good posture. As you go about your day, get in the habit of noticing where your weight is as you are standing. If you are like most people it will be on the heals. Ever hear the old expression “Don’t sit on your heals”? There's a lot more to it than you first might think. If you want to practice these exercises routinely be sure to visit a good Yoga teacher. I may have missed something. I have made a number of posts related to breathing, balance, flotation, etc., but this one has some useful links (especially for Yogic breathing): Flotation is Fundamental – Good Breathing is the Key (As usual, it is always a good idea to get the tutelage of a good Yoga instructor.) You might find the rest of the above linked thread useful as well. And there are other similar threads throughout this forum many of which I've posted to. you can find them by searching on key words (with the forum search function), or you can "find all posts by bud" from my profile and locate them that way.