Matteo Cortesi

Motion analysis of front crawl swimming applying CAST technique by means of automatic tracking

Abstract Kinematic analysis of swimming is of interest to improve swimming performances. Although the video recordings of underwater swimmers are commonly used, the available methodologies are rarely precise enough to adequately estimate the three dimensional (3D) joint kinematics. This is mainly due to difficulties in obtaining the required kinematic parameters (anatomical landmarks, joint centres and reference frames) in the swimming environment. In this paper we propose a procedure to investigate the right upper limb’s 3D kinematics during front crawl swimming in terms of all elbow and shoulder degrees of freedom (three rotations of the shoulder, two of the elbow). The method is based upon the Calibrated Anatomical Systems Technique (CAST), a technique widely used in clinics, which allows estimation of anatomical landmarks of interest even when they are not directly visible. An automatic tracking technique was adopted. The intra-operator repeatability of the manual tracking was also assessed. The root mean squared difference of three anatomical landmarks, processed five times, is always lower than 8 mm. The mean of the root mean squared difference between trajectories obtained with the different methodologies was found to be lower than 20 mm. Results showed that complete 3D kinematics of at least twice as many frames than without CAST can be reconstructed faster and more precisely.

Planimetric frontal area in the four swimming strokes: implications for drag, energetics and speed.

The purpose of this study was to use the planimetric method to determine frontal area (Ap) throughout the stroke cycle in the four swimming strokes as well as during streamlined leg kicking. The minimum Ap values in all strokes are similar to those assessed during streamlined leg kicking (about 0.13m(2)). Active drag (Da=1/2ρ Cd Ap v(2)) was then calculated/estimated based on the average Ap values, as calculated for a full cycle in each condition. Da is the lowest in the streamlined leg kicking condition (Da=19.5v(2), e.g., similar to the values of passive drag reported in the literature), is similar in front crawl (Da=30.0v(2)), backstroke (Da=26.9v(2)) and butterfly (Da=28.5v(2)) and is the largest in the breaststroke (Da=37.5v(2)). Based on the C vs. v relationships reported in the literature for the four strokes it is then possible to estimate drag efficiency: for a speed of 1.5ms(-1), it ranges from 0.035-0.038 (breaststroke and backstroke, respectively) to 0.052-0.058 (butterfly and front crawl, respectively). This study is the first to establish Ap values throughout the swimming cycle for all swimming strokes and these findings have implications for active drag estimates, for the energetics of swimming and for swimming speed.

Effect of swim cap model on passive drag.

Abstract Gatta, G, Zamparo, P, and Cortesi, M. Effect of swim cap model on passive drag. J Strength Cond Res 27(10): 2904–2908, 2013—Hydrodynamics plays an important role in swimming because even small decreases in a swimmers drag can lead to performance improvements. During the gliding phases of a race, the head of a swimmer is an important point of impact with the fluid, and the swim cap, even if it covers only a small portion of the swimmers body, can have an influence on drag. The purpose of this study was to investigate the effects on passive drag (Dp) of wearing 3 different types of swim caps (LSC: a lycra cap; CSC: a silicone cap; HSC: a silicone helmet cap without seams). Sixteen swimmers were tested at 3 velocities (1.5, 1.7, 1.9 m·s−1), and the Dp measurements were repeated at each condition 5 times. A statistical analysis revealed significant differences in drag (p < 0.01) among caps: Dp is 5–6.5% lower for HSC than for CSC at all speeds and 6% lower in HSC than CSC at 1.9 m·s−1. No differences in Dp were observed between LSC and CSC at all speeds. Thus, the differences in Dp are based on the type of material (lycra vs. silicone) and on the presence/lack of seams: the HSC swim cap is the most rigid, the most adherent to the swimmers head, and does not allow the formation of wrinkles compared with the other 2 investigated swim caps. Therefore, the following conclusions can be made: (a) swimmers should take care when selecting their swim cap if they want to improve the fluid dynamics at the “leading edge” of their body and (b) because Dp is affected by the swim cap model, care should be taken when comparing data from different studies, especially at faster investigated speeds.

Passive Drag Reduction Using Full-Body Swimsuits: The Role of Body Position

Abstract Cortesi, M, Fantozzi, S, Di Michele, R, Zamparo, P, and Gatta, G. Passive drag reduction using full-body swimsuits: the role of body position. J Strength Cond Res 28(11): 3169–3176, 2014—This study aimed to analyze whether using full-body swimsuits affects the swimmers body alignment and to what extent changes in the body position are responsible of the passive drag (Dp) reduction experienced by the swimmers when using these swimsuits. Fourteen swimmers performed 20-m towing trials using a full-body synthetic rubber swimsuit, a full-body textile swimsuit, a traditional brief swimsuit, and a traditional brief swimsuit with a pull buoy. In all trials, the speed-specific drag (k = Dp per v2), the trunk incline (TI), and the lower limbs incline (LI) were determined. In comparison with both conditions in which a full-body swimsuit was not used, k was significantly lower when using the rubber swimsuit (−8.4 and −12.2% vs. the brief swimsuit with and without pull bouy, respectively), and the textile swimsuit (−6.9 and −10.8% vs. the brief swimsuit with and without pull bouy, respectively). No differences in TI were observed among conditions, whereas LI was significantly higher when using the rubber swimsuit or the brief swimsuit with pull buoy than when using the traditional brief swimsuit. A linear mixed model showed that k can be reduced by increasing LI (that is lifting the lower limbs), by decreasing TI (that is keeping the trunk more horizontal), and by using either the rubber or textile full-body swimsuit rather than the traditional brief swimsuit. In conclusion, full-body swimsuits involve a reduction of a swimmers passive drag caused by intrinsic properties related to the “material composition” of the swimsuits and also influenced by changes in the swimmers body position.

The relationship between power generated by thrust and power to overcome drag in elite short distance swimmers

At constant average speed (v), a balance between thrust force (Ft) and drag force (Fd) should occur: Ft−Fd = 0; hence the power generated by thrust forces (Pt = Ft·v) should be equal to the power needed to overcome drag forces at that speed (Pd = Fd·v); the aim of this study was to measure Pt (tethered swims), to estimate Pd in active conditions (at sprint speed) and to compare these values. 10 front crawl male elite swimmers (expertise: 93.1 ± 2.4% of 50 m world record) participated to the study; their sprint speed was measured during a 30 m maximal trial. Ft was assessed during a 15 s tethered effort; passive towing measurement were performed to determine speed specific drag in passive conditions (kP = passive drag force/v2); drag force in active conditions (Fd = kA·v2) was calculated assuming that kA = 1.5·kP. Average sprint speed was 2.20 ± 0.07 m·s-1; kA, at this speed, was 37.2 ± 2.7 N·s2·m-2. No significant differences (paired t-test: p > 0.8) were observed between Pt (399 ± 56 W) and Pd (400 ± 57 W) and a strong correlation (R = 0.95, p < 0.001) was observed between these two parameters. The Bland-Altman plot indicated a good agreement and a small, acceptable, error (bias: -0.89 W, limits of agreement: -25.5 and 23.7 W). Power thrust experiments can thus be suggested as a valid tool for estimating a swimmer’s power propulsion.

Effect of Swim Cap Surface Roughness on Passive Drag

Abstract Gatta, G, Cortesi, M, and Zamparo, P. Effect of swim cap surface roughness on passive drag. J Strength Cond Res 29(11): 3253–3259, 2015—In the last decade, great attention has been given to the improvements in swimming performance that can be obtained by wearing “technical swimsuits”; the technological evolution of these materials only marginally involved swim caps production, even if several studies have pointed out the important role of the head (as main impact point with the fluid) on hydrodynamics. The aim of this study was to compare the effects on passive drag (Dp) of 3 swim cap models: a smooth silicon helmet cap (usually used during swimming competitions), a silicon helmet cap with “dimples,” and a silicon helmet cap with “wrinkles.” Experiments were performed on 10 swimmers who were towed underwater (at a depth of 60 cm) at 3 speeds (1.5, 1.7, and 1.9 m·s−1) and in 2 body positions: LA (arms above the swimmers head) and SA (arms alongside the body). The Dp values obtained in each trial were divided by the square of the corresponding speed to obtain the speed-specific drag (the k coefficient = Dp/v2). No differences in k were observed among swim caps in the LA position. No differences in k were observed between the smooth and dimpled helmets also in the SA position; however, the wrinkled swim cap helmet showed a significant larger k (4.4%) in comparison with the model with dimples, when the swimmers kept their arms alongside the body (in the SA position). These data suggest that wearing a wrinkled swim cap helmet can be detrimental to performance at least in this specific position.