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Balance of biomechanical and physiological contributions to swimming performance.
No full textSwimming is a unique activity carried out in a unique environment. Performance depends on interplay between biomechanical and bioenergetic aspects, thus if we can understand their interaction, as a function of velocity, we can understand the biophysics of swimming.
The relationship between stroke frequency and velocity and their impact on drag and efficiency are critical. The biomechanical aspects dictate the velocity-dependent metabolic demands of swimming, thus the maximal performance is determined by the balance of metabolic power among aerobic and anaerobic pathways. Training is a determinant of swimming performance, and applying bioenergetic principles could improve performance
AEROBIC TRAINING AND CARDIOVASCULAR RESPONSES AT REST AND DURING EXERCISE IN OLDER MEN AND WOMEN
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The influence of drag on human locomotion in water
No full textPropulsion in water requires a propulsive force to overcome drag. Male subjects were measured for cycle frequency, energy cost and drag (D) as a function of velocity (V), up to maximal V, for fin and front crawl swimming, kayaking and rowing. The locomotion with the largest propulsive arms and longest hulls traveled the greatest distance per cycle (d/c) and reached higher maximal V. D while locomotoring increased as a function of V, with lower levels for kayaking and rowing at lower Vs. For Vs below 1 m/s, pressure D dominated, while friction D dominated up to 3 m/s, after which wave D dominated total D. Sport training reduced the D, increased d/c, and thus lowered C and increased maximal V. Maximal powers and responses to training were similar in all types of locomotion. To minimize C or maximize V, D has to be minimized by tailoring D type (friction, pressure or wave) to the form of locomotion and velocity. Copyright © 2005 Undersea and Hyperbaric Medical Society, Inc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
IV. Oxygen transport system before and after exposure to chronic hypoxia
Full text linkMaximal VO2 on the treadmill (VO2max) and on the bicycle ergometer (VO2peak), maximal cardiac output (Qmax), by a CO2 rebreathing method, maximal heart rate (HRmax), blood hemoglobin concentration (Hb), and hematocrit (Hct) were measured on six subjects before (B) and 3 weeks after (A) prolonged exposure to chronic hypoxia. It was observed that after high-altitude exposure VO2max, VO2peak, and Qmax were lower (P < 005) than before [A: 4.13 ± 0.67; 3.28 ± 0.41 and 16.89 ± 2.49 (1/min ± SD); B: 4.39 ± 0.39; 3.53 ± 0.34 and 21.81 ± 1.27, respectively}, whereas Hb and Hct were larger (A: 162 ± 8 g/l and 0.46 ± 0.02; B: 142 ± 7 and 0.41 ± 0.02) and HRmax was unchanged (178 ± 7 vs 175 ± 9 bts/min). Thus, we calculated stroke volume of the heart and the Hb flow at VO2 peak were lower in A than in B (95 ± 15 vs 124 ± 7 ml and 2,723 ± 307 vs 3,129 ± 196 g/min) (P < 0.05, respectively), whereas the arteriovenous O2 difference was greater in A than in B (195 ± 16 vs 162 ± 19 ml O2/l; P < 0.05). At any given submaximal work load, VO2 and HR were the same in B and in A, whereas Q was lower in A by ~ 2-3 l/min. However, because of the increased Hb, leading to a higher arterial O2 content, at any work load the O2 flow remained unchanged
How fins affect the economy and efficiency of human swimming
No full textThe aim of the present study was to quantify the improvements in the economy and efficiency of surface swimming brought about by the use of fins over a range of speeds (v) that could be sustained aerobically. At comparable speeds, the energy cost (C) when swimming with fins was about 40 % lower than when swimming without them; when compared at the same metabolic power, the decrease in C allowed an increase in v of about 0.2 ms-1. Fins only slightly decrease the amplitude of the kick (by about 10 %) but cause a large reduction (about 40 %) in the kick frequency. The decrease in kick frequency leads to a parallel decrease of the internal work rate (int, about 75 % at comparable speeds) and of the power wasted to impart kinetic energy to the water (k, about 40 %). These two components of total power expenditure were calculated from video analysis (int) and from measurements of Froude efficiency (k). Froude efficiency (F) was calculated by computing the speed of the bending waves moving along the body in a caudal direction (as proposed for the undulating movements of slender fish); F was found to be 0.70 when swimming with fins and 0.61 when swimming without them. No difference in the power to overcome frictional forces (d) was observed between the two conditions at comparable speeds. Mechanical efficiency [tot/(Cv), where tot=k+int+d] was found to be about 10 % larger when swimming with fins, i.e. 0.13±0.02 with and 0.11±0.02 without fins (average for all subjects at comparable speeds)
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