Monofins For Freedivers: Part II
Posted By Aharon & MT Solomons on 25 April 2005
And what has all this got to do with Freediving?
Rhythm and amplitude of movement?
One of the first questions the freediver wants solved is, ‘which is the most efficient style?’ This in effect means the most efficient both from the point of view of oxygen consumption and movement through the water. There is a lot to be learned from the studies on biomechanics and changes in buoyancy at depth in dolphins, see Randolph Skrovan, T.M. Williams, P.S. Berry, P.W. Moore and R.W. Davis “The Diving Physiology of Bottlenose Dolphins (Tursiops Truncatus).
Dolphins, for example, and the human breath-hold diver, share the same problems of trying to maximize the use of a limited oxygen supply with energy loss through movement during breath-hold dives. A study of the tactics of the dolphin’s movement in handling this particular issue is very revealing. In the initial phases of descents and ascents in dives to 100m, there is a period lasting several seconds of large amplitude strokes (representing 20% - 50% of body length) during the maximum effort phases of descent and ascent in overcoming the problems of buoyancy on the surface and at depth, drag after the turn around. This was followed by a phase of ‘normal’ stroke rate and amplitude, which would correspond to a normal horizontal swimming gait and this in turn was followed by a ‘burst and glide’ pattern of strokes down to the period of negative deceleration, i.e. the point at which if the dolphin were to stop stroking there would be no deceleration. Also as the dolphin changed pacing intermittently from an active swim to the glide the amplitude of its stroke also changed to a smaller stroke (less than 20% of body length). The final phase of the descent is the ‘glide’.
In the paper mentioned above, they very interestingly succeeded in quantifying the energy-saving factor of these particular tactics. ‘By incorporating a prolonged glide period the bottlenose dolphin realized a theoretical up to 21% energetic saving in the cost of a 100m dive in comparison with dives based on neutral buoyancy models. Thus modifying locomotor patterns to account for physical changes with depth appears to be one mechanism that enables diving mammals with limited O2 stores to extend the duration of a dive.’ and extend its diving depth range.
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