At risk of exposing my ignorance can someone explain the difference between frog kick and flutter kick? These are terms I am not familiar with and suspect are seldom used in the UK.
Both the collateral ligaments (and the anterior cruciates) stabilise the knee and prevent lateral (sideways) movement but allow free flexion and extension at the knee (fore and aft).
Thus the risk in contact sports. A blow to the outside of the knee will cause it to buckle (the lower leg effectively moving outwards laterally from the neutral position causing a "knock knee" effect). this stretches the medial collateral ligament (MCL).
Of course the same occurs if the foot is pulled outwards from the neutral position against a hip held fixed by the massive thigh muscles, or alternatively if these same thigh muscles are used to pull the starightened leg laterally inwards to to the neutral position against resistance at the foot. As I understand it, this is what occurs during the power stroke of what I understand by a frog kick. If I am right, this explains why a frog kick will put additional strain of the MCL, causing considerable pain if this is already damaged and indeed may cause damage itself. In addition fins are designed to work most efficiently with an up and down motion so I suspect such a frog kick will cause a rotational strain at the knee.
I gather a flutter kick is the simple up and down movement of the legs/feet in the same rotational axis as the knee, thus producing no lateral or rotational strain at the knee joint. I was taught the most efficient flutter kick is to kick from the hips with the legs straight (using the powerful thigh muscles) rather than at the knees (largely using the quadriceps alone). In any case these kicks cause very little lateral strain on the knees. Hence this could explain why epconti finds a flutter kick does not aggravate his knee injury and why and voldolaz developed problems with his by using a frog kick.
There is a third possible use of fins, of course, and that is simply to hold the legs rigidly togther and swim like a dolphin, moving the fins up and down together. I have done this occassionally as it can produce a burst of rapid speed but it is very tiring.
When holding station and doing a "helicopter" manoeuvre or changing direction underwater a certain amount of lateral strain at the knees is inevitable. However, I would suggest that, whatever finning technigue is used, any lateral or rotational strain at the knee should be avoided whenever possible.
We are not frogs and our legs are designed for walking and running, not for finning!
:froggy:
