The communication about the swimmers' internal perception of flow and the movement control is hampered because of missing mutual information about effect of interaction of actions of limbs and invisible motion of displaced (clear) water. Interaction as part of the connectivity of a two-bodies energy sphere. According to Schack {2004) the sensory picture of a voluntary action is a template to organise motor commands and guide motor control. lt is widely known that elite swimmers have an excellent perception of water motion using somatosensory, proprioceptive or vestibular and visual cues. Swimming as a self-induced activity in aquatic space means displacing water mass at low energy costs while yielding high swimming speeds in reaction and this is what elite swimmers strive to reach using a right feel for water. Takagi & Wilson (1999) emphasised that without pressure no propulsion exists and a pressure differential method is potentially a useful means in stroke analysis of cyclic 3D hand action. Pressure-time recordings are 'essential complementary information' (Loetz et al. 1988) helping to detect wrong hand positions when unusual pressure graphs occur {Van Manen et al. 1975). Klauck & Ungerechts {1997) pointed out that the interaction goes with pressure changes and momentum-induced effects of displaced water mass while drag-even if it is repeated often-does not explain the interaction effects sufficiently. Hence, kinematics of limbs' actions is not necessarily a direct indicator of flow effects. Ungerechts & Klauck {2014) highlighted that interaction is a means to transfer metabolic energy via limb's action to a unit volume of water which changes the energydensity, known as 'pressure' which in liquids or currents differs from the term pressure solid body mechanics (although in both cases the physical unit is [Pa]). Hermann et al. {2012) pointed out the importance of change of pressure, as an 'intermediate level' (Fig. 1) in connection with momentuminduced locomotion in aquatic space, a level which lacks attention in most swimming literature.
© Copyright 2014 XIIth International Symposium for Biomechanics and Medicine in Swimming. Published by Australian Institute of Sport. All rights reserved.