Elsevier

Journal of Biomechanics

Volume 54, 21 March 2017, Pages 123-128
Journal of Biomechanics

Short communication
Developing a methodology for estimating the drag in front-crawl swimming at various velocities

https://doi.org/10.1016/j.jbiomech.2017.01.037Get rights and content

Abstract

We aimed to develop a new method for evaluating the drag in front-crawl swimming at various velocities and at full stroke. In this study, we introduce the basic principle and apparatus for the new method, which estimates the drag in swimming using measured values of residual thrust (MRT). Furthermore, we applied the MRT to evaluate the active drag (Da) and compared it with the passive drag (Dp) measured for the same swimmers. Da was estimated in five-stages for velocities ranging from 1.0 to 1.4 m s−1; Dp was measured at flow velocities ranging from 0.9 to 1.5 m s−1 at intervals of 0.1 m s−1. The variability in the values of Da at MRT was also investigated for two swimmers. According to the results, Da (Da = 32.3 v3.3, N = 30, R2 = 0.90) was larger than Dp (Dp = 23.5 v2.0, N = 42, R2 = 0.89) and the variability in Da for the two swimmers was 6.5% and 3.0%. MRT can be used to evaluate Da at various velocities and is special in that it can be applied to various swimming styles. Therefore, the evaluation of drag in swimming using MRT is expected to play a role in establishing the fundamental data for swimming.

Introduction

Drag has a major influence on swimming performance because swimming is performed in water, which has a greater density than air. Therefore, the evaluation of drag is one of the most important issues in swimming research. However, it is extremely difficult to evaluate the actual drag during swimming (active drag) because the swimmer is continuously moving. To accurately measure the active drag, it is necessary to measure the entire pressure and friction distribution of the swimmer without disturbing their natural swimming movement. Hence, only a few methods have been developed to evaluate the active drag, each with several restrictions. In the measurement of active drag (MAD) approach (Hollander et al., 1986, Toussaint et al., 1988, Toussaint et al., 2004, Van der Vaart et al., 1987), only the front-crawl swimming stroke can be assessed owing to the apparatus structure. Furthermore, the method is limited to the use of arms only. This means that swimmers cannot use lower limb actions to maintain streamlined alignments, which they would use during normal swimming.

The velocity perturbation method (Kolmogorov and Duplishcheva, 1992, Toussaint et al., 2004) and the assisted towing method (Formosa et al., 2012) require that the swimmers swim with maximal effort. Hence, this method is not suitable for evaluating the active drag at various velocities, i.e., sub-maximal effort. The “energetic approach” proposed by Di Prampero et al. (1974) includes the motion of legs but extrapolates the data for active drag by adding (or subtracting) external loads to (or from) a swimmer and measuring the associated energy expenditure. Therefore, the development of a new methodology for estimating the drag in swimming, which can enable upper and lower limb motion (full stroke) at various velocities during front-crawl swimming, would provide swimmers and coaches with beneficial information on improving their swimming performances.

Accordingly, the purpose of this research is to develop a new methodology for evaluating the drag in front-crawl swimming at various velocities and at full stroke. We will introduce the basic principle and apparatus of the new method. We will also apply it to determine the active drag and compared it with the passive drag measured for the same swimmers.

Section snippets

Basic principle of a new method for estimating the drag in swimming using measured values of residual thrust (MRT)

Swimming velocity depends on the interaction between two forces: one is generated to propel the swimmer forward (propulsion), whereas the other acts in the direction that prevents propulsion (drag). For instance, when the drag is larger than the propulsion, the swimmer decelerates. In a water flume that can be used to freely adjust the flow velocity (U), the relations between the swimming velocity, propulsion (P), and drag (D) can be formulated from the characteristics of hydrodynamic forces,

Results

The active drag (Da), velocity at Tre = 0 (UTre0), coefficient of drag (kD), and stroke rate (SR) for each swimmer over five stages are shown in Table 3. In addition, Da and Dp for each swimmer is shown in Fig. 4. Moreover, the D vs. v relations in passive and active conditions were calculated for each subject and are also shown in Fig. 4. When pooling together data from all subjects, the relations can be expressed as Da = 32.3 v3.3, N = 30, R2 = 0.90, and Dp = 23.5 v2.0, N = 42, R2 = 0.89. We would report,

Discussion

The variability in Da evaluated using MRT indicated differences for both swimmers (Swimmer A: 6.5%, Swimmer B: 3.0%). As for the cause, we believe that in reality, the variability in SR influenced the variability in Da. Thus, it can be considered that Da as estimated using MRT was also impacted by the difference in SR, which was influenced by various factors such as the swimmers’ conditions and fatigue level. From a previous study on undulatory underwater swimming which reported on the

Future prospects

In this study, we evaluated active drag at various velocities for front-crawl swimming with lower limb motion. However, the new methodology (measured values of residual thrust; MRT) is special in that it is applicable to various swimming styles. Therefore, the evaluation of the active drag (Da) using MRT would allow us to compare Da for different swimming styles and motions (techniques) as well as to evaluate swimming efficiency by estimating physiological indices, e.g., oxygen uptake. Hence,

Conflicts of interest

None.

Acknowledgments

This study was supported by a Grant-in-Aid for Scientific Research [15K12641] from the Japan Society for the Promotion of Science – Japan.

References (13)

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