Biomechanics and Medicine in Swimming XI

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Norwegian Peoples Aid (2007). Annual drowning statistics for Norway Quan L., Cummings P., (2003). Characteristics of drowning by different age groups. Inj Prevention, 9(2), 163-166 Stallman, R.K. (1998). A comparison of functional buoyancy among African and European children and youth. Proceedings of Nairobi Congress in 1996; The African Assoc. of Health, Physical Education, Dance and Recreation. Safe Traffic (2008). Traffic statistics for Norway chaPter6.medicineandwatersafety Movement Economy in Breaststroke Swimming: A Survival Perspective stallman r.K., Major J., hemmer s., haavaag G. The Norwegian School of Sport Science When adopting a head up position in breaststroke the center of gravity is displaced backward, farther from the center of buoyancy. This causes a tendency for the legs to sink, increasing the angle of the body with the horizontal plane and concurrently, resistance. Increased resistance theoretically reduces survival possibilities. The purpose of this study was to quantify the difference in energy expenditure for breaststroke with the head held constantly above the surface and for breaststroke performed with normal breathing. Classic Douglas bag respirometry was used. During submaximal swimming, the volume of oxygen uptake was significantly higher when swimming with the face constantly above the surface than with normal breathing. Both pulse rate and blood lactate levels were also significantly higher when swimming ”head up”. Key words: breaststroke, movement economy, survival IntroductIon The goals of swimming instruction are numerous but the preservation of life should be common to all programs. Historically, attempts have been made to justify one swimming technique above others, both as the first to be learned and as the most important one. It is well known that North America has a long tradition of teaching crawl early if not first, and that Europeans generally favor breaststroke. It has been argued that breaststroke is the easiest stroke to swim with the head up for those who prefer not to place the face in the water. While this may in some ways be true, it is irrelevant and in many ways contradicts the goals of water safety. Swimming educators have long focused on the necessity of breath holding/breath control, buoyancy control, orientation, balance and rotation in the teaching of swimming. The 19th century produced the concept of ”watermanship” often described as the all around aquatic movement development needed for survival (Sinclair & Henry, 1893, Thomas,1904). These same authors also used the expressions ”fancy swimming” and ”scientific swimming” referring to the ability to move in the water in harmony with the powers of nature rather than trying to overcome them. Lanoe (1963) and Whiting, (1971) define a swimmer as one who can cope with an unexpected submersion. Modern aquatic professionals emphasize a thorough aquatic experience relating the characteristics of the water to our bodies (Skullberg, 1985, Wilke, 2007,), and a movement reperatoir which permits almost any movement in any direction at any time. This reminds us of the unlimited demands and solutions of the synchronized swimmer or water polo player. Cureton (1943) and the USA Navy (1944) emphasized that an unlimited number of dangers requires an unlimited number of solutions. Recently the expression watermanship has been modernized to ”aquatic competence” (Langendorfer & Bruya , 1995). To advocate swimming breaststroke with the head up or to choose breaststroke as the easiest way to swim with the head up for those who do not like the water, is to negate virtually all of the goals of aquatic professionals with regard to water safety – drowning prevention. It is beyond discussion that such persons are more poorly equipped to cope with an involuntary submersion (Stallman, et al, 2008). While this is common sense, there remains a tendency to argue for breaststroke first for the very reasons cited above. Before going on, the point must be made that this discussion is not about choosing between front crawl and breaststroke. Both are poorly suited as a first swimming technique. And neither is it a matter of choosing from among the four competitive techniques when so many others are available. However, in the context of this study, the purpose 379
BiomechanicsandmedicineinswimmingXi was i) to emphasize the importance of effective breathing and breath control (in any stroke), and ii) to quantify the burden of added resistance when swimming breaststroke with the head continually above the surface, considered in a survival context. Lastly the point must be made that survival is often a matter of efficiency of movement (or good technique). It has nothing to do with swimming fast, although efficient movement is also faster. At any given velocity, the more efficient the movements, the less energy they will require. The less energy required per unit time or distance, the longer one will be able to continue in any necessary pursuit of survival whether it be to swim or to remain in the same place. This is a point sadly overlooked by many swimming instructors, who often express the idea that good technique is only important for the competitive swimmer. Most aquatic experts (e.g. Cureton, 1943, The USA Navy, 1944, Lanoe, 1963, Wilke, 2007, Stallman, 2008 ) consider breathing in an optimal way, the most important aspect of efficient technique. Methods While quantifying energy expenditure under the two conditions named above was the primary goal of the study, it was recognized that several factors might influence it. Factors considered possible confounders were: skill level, buoyancy, endurance, drag characteristics and motivation. From 40 volunteers, 20 were selected (12male, 8 female) to give a broad, representative sample with relation to buoyancy and ankle drag. This would reduce any bias because of these two factors. The subjects were university physical education students, average age 26.1 (range 19.5-35.0). Buoyancy was determined by hydrostatic weighing as described by Katch et al. (1967). As function was of greatest interest, weight at both full inspiration and full expiration was recorded uncorrected for trapped air spaces and residual volume. Body density as determined by Brozek et al. (1963) was calculated but not included in the study. The term functional buoyancy (Stallman, 1971) is used for the uncorrected values. Ankle drag was measured as described by Cureton (1943). The subject adopted a stretched prone position, arms forward and together, with full inspiration. A Salter spring scale registered the weight of the ankles resting on a horizontal rod just below the surface, heels under water. Skill level was defined by a composite of two values: the number of strokes required to swim 25m (as few as possible) and the fastest time possible for 25m. Twenty five meters was chosen to minimize the influence of endurance and to maximize the influence of technical skill. All trials were repeated 3 times and the best performance was used in the analysis. Energy cost was measured by classical Douglas Bag respirometry while swimming in a flume. The sub-maximal velocity of 0.5 m·s -1 was used for all subjects. If this velocity resulted in unusually high levels of plasma lactate, the subject was eliminated. Given that these were physical education students, few were eliminated for this reason. The subjects swam approximately 10 min. unhindered to reach a steady state. They then immediately entered the flume where they swam for approximately 3 min. with gas collection during the last min. This same operation was repeated twice for each subject. Half of the group was randomly selected to swim first with the head up while the other half swam first with normal breathing. A blood sample to determine plasma lactate levels (La) was taken after each trial. Lastly, the ability to swim for a longer period of time (simulating a survival situation) was measured by swimming to exhaustion. It was hypothesized that when swimming with the head up, the swimming time to exhaustion would be shorter. Each subject swam to exhaustion on two different occasions. Again, half randomly with head up first and half with normal breathing first. The subject swam easily first for 5 min. Then five min. at 0.5 m·s -1 . If the subject was able to continue, the velocity was increased by 10% and they swam for an additional two min. If after these two min. the subject was still swimming, the velocity was again increased by 10%. They swam in military trousers and shirts. 380 results When swimming with the face constantly above the surface, the oxygen uptake (VO 2 ) expressed in ml/meter was significantly higher than with normal breathing (p=
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Biomechanics and Medicine in Swimmi
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Bibliographic information: Biomecha
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Figure 1. General biomechanical par
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average VO2 measured during resting
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Fourteen highly trained male swimme
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Figure 2. Repeatability of the LTin
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-ARM * 5 Biomechanicsandmedic
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• Without restriction; • Blinde
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