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Ключевые слова: Водное поло, дыхательная и сердечно-сосудистая системы, двигательные функции, индивидуальные и командные действия. Keywords: Waterpolo, respiratory and cardiovascular systems, motor function, individual and team actions.
UDK:531:533:577.3:611.7:79
K.J. van Zwieten a, K.P. Schmidt a,I.A. Zubovaa,
O.E. Piskunb, S.A. Varzinb
BIOMECHANICAL ANALYSES OF ROAD CYCLING
a University of Hasselt, Diepenbeek, Belgium, b Peter-the-Great St. Petersburg Polytechnic University, St. Petersburg, Russiakoosiaap.vanzwieien@uhasseli.be
Introduction, theoretical approach. A biomechanical analysis of cyclingcan be realized theoretically witha closed kinematic chain [1], consisting of elements of the rider, and elements of the bicycle on either side (Figure 1). These elements are: 1) Frame, 2) Crank, 3) Pedal & Foot, 4) Lower leg, 5) Upper leg, 6) Pelvis. On the frame's saddle, the pelvisis supposed to moverotation-wise only [2]. Themobility of the chain is then calculated by applying Grubler's equation for planar linkages [3], resulting in a total of 3 degrees of freedom (DOF). In motion, this closed kinematic chain isthus controlled and stabilized by 3 sets of antagonistic muscle groups, namely extensors and flexors of hip, knee, and ankle respectively.
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Figure 1. Bicycle and rider represented as a closed kinematic chain (after [2]). Practical approach. A practical and more realistic biomechanical analysishowever, reveals various other important features of road cycling, starting from the following. "For a racing bike traveling fast, about 80 percent of the work the cyclist does will go in overcoming air resistance" [4]. Therefore road cyclists do prefer to usea so-called
aerodynamic position (Figure 2). Their "aero position" inevitably implies an anterior tilt of 15°-20° of their pelvis (Figure 2, red line) [5].
Figure 2.Anterior pelvic tilt (red line) in aerodynamic position (after [5]). Material and methods. Based on [6], an anterior pelvic tilt of 20° was simulated by means of osteology of the pelvis, starting from its neutral position. The results of it, amore posterior position of the tuber ischiadicum, and a more anterior position of spinailiaca anterior inferior, were taken into account. Resulting changes of lengths of those muscles that have their anatomical origins on these bony landmarkswere then observed, using the pictures of [6]. These muscles are:the hamstrings and one part of the quadricepsfemoris, namely rectusfemoris muscle. This muscle and the hamstrings are most active during a pedal stroke [7].
Observational results. In the optimal aerodynamic position, 20° anterior pelvic tilt results in 7,5 % increase of the lengths of hamstrings biceps femoris (long head) and semimembranosus, and6 % decrease of the length of quadriceps muscle partrectusfe-moris.
Results and Conclusion.The observed increases and decreases of lengths of these muscles in aero position may lead to respectively hamstrings passive insufficiency, andrectusfemoris muscle active insufficiency, as these muscles are now likely to shift away from their plateau region of optimal force (= 100 %) [8]. Discussion.Such imminent muscle insufficiencies are reflected in "thigh injuries" "quadriceps and hamstring strains", as described in cyclists [9]. Using a "gravity seat" possibly neutralizes some anterior pelvic tilt [10]. To restore optimal muscle force however, Electro Vibro Stimulation (EVS) is strongly recommended [11].
Acknowledgements. The authors thank PeterGijsel, Nikolaas Van Riet, Ellen van den Goor,Tim De Jonghe, Riekje van Osnabrugge, Jan Krol, Jana De Brandt,and Bart Bil-lietfor their stimulating interest during the preparation of this paper.
References
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