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The Relation between the forces affecting a swimmer's body and torque. 10.6084/m9.figshare.2059974. https://doi.org/10.1371/journal.pone.0177368.g003
Source publication
This study aims to investigate the effect of changes in buoyancy when a swimmer respires in a horizontal posture. We attempted to evaluate the levelness of swimmers’ streamline posture by simultaneously measuring the lung capacity and buoyancy under water. The buoyancy was measured based on the changes in the vertical loads of the upper and lower l...
Citations
... In this position, the center of buoyancy (CoB) rests toward the cranial (i.e., head) end of the prone body, whereas the center of gravity (CoG) rests on the caudal (i.e., pelvic or lower) side (Hay, 1993). Therefore, when a person remains still in the water, underwater torque acts downward against the center of gravity, which causes the lower extremities of the body to drag (Watanabe et al., 2017). When in a streamlined posture, even if there is no difference in height or weight, beginning swimmers frequently encounter difficulties in maintaining a horizontal position because their centers of buoyancy and gravity are much further apart vertically than those of expert swimmers (Watanabe et al., 2014). ...
The study aimed to experimentally verify the efficacy of wearing flotation aids to add buoyancy from the pelvis to the side of the thigh on the swimming performance of beginning swimmers who were capable of swimming around 25 meters at a time. The study recruited seven male university students who were members of the Physical Education Department and who lacked experience in specialized swimming instruction. The study found statistical difference in prone flotation between the use of flotation aids (7.27±1.92 sec) and without flotation aids (3.50±0.72 sec). During swimming for distance in a 5 min. swim test, we found statistical differences between the use of flotation aids (185.0±29.6 m) and without flotation aids (172.6±24.4 m). Moreover, no overall differences in stroke length and stroke rate were observed between flotation and no flotation use conditions.
... In the aquatic environment, the human body is exposed to two vertical forces with opposite direction, namely gravity and buoyancy. When a human holds a horizontal static position in the water, the centre of mass (CM) is located about 2 cm more caudally (towards the legs) than the centre of buoyancy (CB) (Watanabe et al., 2017), thereby producing a rotational torque (buoyant torque) that causes the lower-limbs to sink (Gagnon & Montpetit, 1981;Kjendlie et al., 2004;Payton & Reid, 2014). ...
The purpose of the present study was to investigate differences between front crawl and backstroke swimming in hydrodynamic (produced by swimmers) and buoyant torque around the transverse axis. Ten swimmers performed 50 m front crawl and backstroke at four selected velocities (same velocities for both techniques). All trials were recorded by four underwater and two above-water cameras to collect data for three-dimensional whole-body motion during one stroke cycle (defined as a period between two consecutive wrist entries to the water). The inverse dynamics approach was applied to obtain buoyant and hydrodynamic torque around the transverse axis. The differences between front crawl and backstroke techniques across four levels of velocity were assessed with a two-way repeated-measures ANOVA. There was a main effect of technique on the mean buoyant and hydrodynamic torque, with 30–40 % larger leg-raising buoyant torque and leg sinking hydrodynamic torque in front crawl than in backstroke (p ≤ 0.001). The time-series data revealed that the hydrodynamic leg-sinking torque had its peaks during the first half of the underwater upper-limb motion in front crawl, but that was not observed in backstroke, implying that the strategy of counterbalancing the buoyant torque is different between the techniques.
... By measuring the reaction force at one or both supporting point(s), the whole-body CoM p can be obtained according to the principle of moments, i.e. rotational equilibrium ( Figure 1). This method is still often used to directly quantify CoM p of the whole-body at present [31,77]. However, despite the accuracy, a large limitation is that only a static CoM p can be acquired and it is not possible to apply the obtained information for dynamic conditions. ...
In biomechanics, human motion is described as rigid body dynamics due to the complex nature of the human body. During movements, the human body presents many types of deformation, such as stretching, bending, bulging and jiggling, which make precise assessments of physical interactions occurring in the human body extremely difficult. Therefore, for analytical convenience, the human body is often modelled as an inter-linked system of rigid bodies representing body segments. Under the modelled condition, the deformation of each body segment can be neglected, thereby the estimation of kinematic and kinetic phenomena in the human body is much simpler than the reality. Body segment parameters are fundamental inputs for the modelling process and are made up of the segment’s mass, density, centre of mass location and its moment of inertia. There has been a large number of studies quantifying body segment parameters, and the parameters vary one to another depending on the sex, age, ethnic group, and lifestyle of the samples as well as the method used in each study. Thus, it is of great importance for researchers to understand the background of each set of body segment parameters to select a modelling method that best suits their purpose and samples. In this chapter, different methodologies to assess body segment parameters are reviewed with historical and practical perspectives to provide information on the advantages and disadvantages of each set of parameters. Furthermore, to provide examples of the impact of selecting different methods on body segment parameter calculation, we compared several widely used models and discussed their accuracy as a technical report.
... No significant differences in characteristics with regard to height, the length between the tip of the longest finger and the soles of the feet, and BMI were observed between participants in the high performance group and those in the low performance group ( Table 4). The center of gravity was measured using the reaction board method 10,23 , and ground reaction force data were acquired using 90 × 60 cm force plates (Anima Corporation, Chofu, Tokyo, Japan) 24 . The participants were placed on the balance board in the supine position, and measurements were performed in both the streamlined body position and resting position. ...
Swimming is an extremely popular sport around the world. The streamlined body position is a crucial and foundational position for swimmers. Since the density of lungs is low, the center of buoyancy is always on the cranial side and the center of gravity is always on the caudal side. It has been reported that the greater the distance between the centers of buoyancy and gravity, the swimmer’s legs will sink more. This is disadvantageous to swimming performance. However, the way to reduce the distance between the centers of buoyancy and gravity is yet to be elucidated. Here we show that swimmers with high gliding performance exhibit different abdominal cavity shapes in the streamlined body position, which causes cranial movement of the abdominal organs. This movement can reduce the distance between the centers of buoyancy and gravity, prevent the legs from sinking, and have a positive effect on gliding performance.
... Swimming is a sport that can be learned by all ages, from babies, children to adults [1]. Naturally humans are able to master swimming skills, because humans have buoyancy [2]. Likewise, the nature of water is able to lift the weight of our body [3], there should be no one who cannot master the swimming movement. ...
Background
When in water, the Centers of Buoyancy (CoB) and Mass (CoM) of the human body are positioned cranially and caudally, respectively. With increasing distance between these centers, the sinking torque of the lower limbs increases, with a subsequent decrease in swimming performance due to increased drag.
Objective
To clarify the effect of additional buoyancy swimsuits on swimming performance.
Methods
The subjects were eight competitive male swimmers of mean ±SD age 21±2 years. Swimming performance was compared between Conventional (CS) and Additional Buoyancy Swimsuits (ABS). CoM and CoB were identified on land and in water, respectively, with the swimmers maintaining a horizontal posture. CoM was measured by the reaction board method. CoB was calculated as the force exerted in the vertical direction accompanied by changes in inspiratory volume. Swimming velocity and Blood Lactate (BL) concentration value during 200 m front crawl in trials at four different speeds (curve test) were recorded as swimming performance.
Results
No significant difference in inspiratory volume was observed between CS and ABS (small effect size, d =0.28). The distance between CoM and CoB was significantly shorter for CS than ABS ( p < 0.001; large effect size, d =1.08). Both swimming velocity at BL of 4 mmol·L ⁻¹ and maximal effort were significantly faster for ABS ( p < 0.042; 0.008), with large effect size ( d =0.91; 0.98). However, there was no significant difference in maximal BL between CS and ABS (small effect size, d =0.37).
Conclusion
ABS improves swimming performance by streamlining the horizontal posture.
