How are Strouhal number, drag, and efficiency adjusted in high level underwater monofin-swimming?

• Published in: Human movement science 2007-06, Vol.26 (3), p.426-442
• Main Authors: Nicolas, Guillaume, Bideau, Benoit, Colobert, Briac, Berton, Eric
• Format: Article
• Language: English
• Subjects: Acceleration; Active drag; Biological and medical sciences; Biomechanical Phenomena; Biomechanics; Energy Metabolism - physiology; Fin-swimming; Froude efficiency; Fundamental and applied biological sciences. Psychology; Humans; Joints - physiology; Muscle, Skeletal - physiology; Physical Exertion - physiology; Postural Balance - physiology; Signal Processing, Computer-Assisted; Stress, Mechanical; Strouhal number; Swimming - physiology; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports
• ISSN: 0167-9457; 1872-7646
• DOI: 10.1016/j.humov.2007.03.002

Strouhal number (St) corresponds to a wake parameter based on the tail kinematics of swimming animals according to St=A·f/U, where f is the stroke frequency, A is the fin-beat peak-to-peak amplitude, and U is the forward speed. St number is a trade-off between amplitude and frequency that generates a forward velocity. This parameter may therefore be affected by swimming technique, which can be evaluated through active drag (AD) and Froude efficiency (ηF). The aim of our study was therefore to (1) investigate the range of AD and ηF values for high level monofin-swimmers, (2) explore the range of St numbers, and (3) examine to what extent this latter non-dimensional parameter may affect AD and ηF. To this end, experiments have been conducted on 12 international level monofin-swimmers. St number, ηF (calculated according to the elongated-body theory), and AD (computed with velocity perturbation method) were calculated at the same time for an underwater fin-swimming trial, at maximal speed. Lowest values of St numbers (St=0.34) corresponded to fin-swimmers with highest velocities (R=−.77, p