I pretty much only dive with frog kicks now. The advantages are numerous!
1. Way more efficient. The stroke has a built in resting phase where you coast without any motion for a second or two. Where as in traditional flutter kicking you are constantly kicking thus working harder and going through air much faster over the course of an entire dive. One of the biggest misconceptions in diving is that speed matters. It doesn't, slow and steady means longer bottom times and more time doing what you went there to do in the first place.
"Work smarter, not harder " ~ Mr. Scrooge McDuck
2. Saves reefs! When flutter kicking your fins can extend below your body over 12-16 inches. Divers tend to like to get down close to the reef to see the little critters and don't realize that although they are a foot over the reef, their fin tips are not and are dragging and beating up coral. Even if your tips aren't touching the reef, the force of the downstroke of a flutter kick alone can break off a piece of fragile coral. Unfortunately, I've seen it happen. With your knees bent you can get real low and close to the reef and not have to worry about damaging the reef because your tips are up and out of the way. Your propulsion force is sent directly behind you instead of downward protecting the reef.
3. Best for proper trim. Having your knees bent shifts your center of gravity up your body. Many divers, even experienced divers tend to dive in a heads up position. In other words not perfectly flat and horizontal like you see in the videos above. Since your body is not as long with your knees bent, it shifts your center of gravity up your body and thus lowers your head position and making it easier to get into, and stay in a flat horizontal position throughout the dive. Staying flat and horizontal means you cut through the water much easier and are able to glide saving energy and air!
4. And yeah as many have noted before, it keeps other divers behind you from cursing you because you just went through an area and silted up everything and made everyone behind you swim through pea soup! In recreational open water diving it's annoying. In technical confined environments, it can get you or your buddy killed. Stuck in a wreck or cave 150 feet underwater with zero vis is not a fun place to be.
The videos above show different variations on the frog kick for different purposes.
The first video is a pretty standard frog kick as I know it. The diver has a larger wider sweeping motion with his legs. This gives you the most power and forward thrust. The guy featured through most of that first vid was going through his kick cycles a little fast actually and really wasn't holding onto the resting portion of the kick long enough. After the power portion, the diver should let himself glide for a second or two. before beginning the next kick cycle. At the end of that 1st vid a second dive shows up and his timing is much better and you can see how the frog kick gives you a nice long resting glide (continued at beginning of 3rd vid).
The second vid and the beginning of the 3rd vid show what I know to be the modified Frog kick. The main difference is the the knees and legs do not come apart in the same large arcing sweeping motion as the first video. In these videos the legs and knees stay about shoulder width, or slightly wider on the loading stroke, apart and the knees stay closer to a 45 to 90 degree angle and don't come down as much. This gives good power on the stroke but confines the propulsion to directly behind you and keeps you more streamlined.
The third video shows the difference between a modified frog and a confined frog. Around the 1:15 mark the diver switches into the confined space version and here the knees and legs do not come apart more than shoulder width and almost all the motion is in the rolling of the ankles and feet. Great for squeezing in tight spaces and not kicking the surroundings.
Btw. I know that different divers and even teaching organizations have different names for the same kicks, lol!
Hope this helps everyone and thanks Kamala for bringing this topic up, if more divers used these techniques we'd have healthier reefs, unsilted wreck dives, and longer bottom times, all good things for divers!!!

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Edited by jesterdiver, 09 March 2014 - 11:58 AM.