### Abstract

It is unknown how demands on torso muscles from internal and external torque produced by swimming motions and fluid forces in front crawl differ between swimming speeds. A better understanding can be developed by examining the torque acting between the upper and lower torso. However, due to the inability to measure external torque in a fluid environment, internal torque cannot be determined directly. We developed a model to estimate torque between the upper and lower torso about the longitudinal axis to compare demands on torso muscles between different front crawl swimming speeds. Since flutter kicking is the only movement in front crawl that follows a six-beat pattern, the frequency component of whole body torque that matches a six-beat rhythm (i.e. the third Fourier harmonic (Sanders and Psycharakis, 2009; Yanai, 2003) is likely generated almost entirely from external torque acting on the lower limbs. Our model therefore estimated the external torque on the lower limbs by 1) calculating whole body angular momentum about the longitudinal axis, 2) obtaining net external torque as the first derivative of whole body angular momentum, and 3) estimating the torque acting on the lower limbs as the third harmonic of net external torque. Torque between the upper and lower torso was then predicted with a standard Newtonian inverse dynamic approach by estimating torque acting between each segment in a sequence commencing at the lower limbs and progressing towards the head. Whole body and segmental angular momentum data of fourteen elite male Scottish front crawl specialists swimming at sprint and 400m speeds were provided by the third and fourth authors. Using these data as input, the model indicated that peak torques between the upper and lower torso were 1.9 (SD 0.68) times greater at sprint speed (102.8 SD 25.5 N∙m) than at 400m speed (56.6 SD 15.0 N∙m).This suggests that as speed increases swimmers must increase torso muscle torque about the longitudinal axis. Coaches can use these findings to prescribe appropriate loads when designing event-specific strength training.

Original language | English |
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Title of host publication | BMS |

Publication status | Published - 2018 |

### Keywords

- Swimming kinematics
- Kinetics
- Modelling
- Joint Torque

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## Cite this

Andersen , J., McCabe, C., & Sanders, R. H. (2018). A model to test for differences in torso muscle torque between front crawl swimming speeds from three-dimensional digitised video. In

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