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The Reliability of an Instrumented Start Block Analysis System

Elaine Tor, David L. Pease, and Kevin A. Ball

The swimming start is highly influential to overall competition performance. Therefore, it is paramount to develop reliable methods to perform accurate biomechanical analysis of start performance for training and research. The Wetplate Analysis System is a custom-made force plate system developed by the Australian Institute of Sport—Aquatic Testing, Training and Research Unit (AIS ATTRU). This sophisticated system combines both force data and 2D digitization to measure a number of kinetic and kinematic parameter values in an attempt to evaluate start performance. Fourteen elite swimmers performed two maximal effort dives (performance was defined as time from start signal to 15 m) over two separate testing sessions. Intraclass correlation coefficients (ICC) were used to determine each parameter’s reliability. The kinetic parameters all had ICC greater than 0.9 except the time of peak vertical force (0.742). This may have been due to variations in movement initiation after the starting signal between trials. The kinematic and time parameters also had ICC greater than 0.9 apart from for the time of maximum depth (0.719). This parameter was lower due to the swimmers varying their depth between trials. Based on the high ICC scores for all parameters, the Wetplate Analysis System is suitable for biomechanical analysis of swimming starts.

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How Does Drag Affect the Underwater Phase of a Swimming Start?

Elaine Tor, David L. Pease, and Kevin A. Ball

During the underwater phase of the swimming start drag forces are constantly acting to slow the swimmer down. The current study aimed to quantify total drag force as well as the specific contribution of wave drag during the underwater phase of the swimming start. Swimmers were towed at three different depths (surface, 0.5 m, 1.0 m) and four speeds (1.6, 1.9, 2.0, 2.5 m·s–1), totaling 12 conditions. Wave drag and total drag were measured for each trial. Mixed modeling and plots were then used to determine the relationships between each towing condition and the amount of drag acting on the swimmer. The results of this study show large decreases in total drag as depth increases, regardless of speed (–19.7% at 0.5 m and –23.8% at 1.0 m). This is largely due to the significant reduction in wave drag as the swimmers traveled at greater depth. It is recommended that swimmers travel at least 0.5 m below the surface to avoid excessive drag forces. Swimmers should also perform efficient breakouts when transitioning into free swimming to reduce the duration spent just below the surface where drag values are reported at their highest.

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Wave Characteristics of Olympic Breaststroke Swimmers

Ross H. Sanders, Jane M. Cappaert, and David L. Pease

The purpose of this study was to investigate the wave characteristics of breaststroke swimming. Particular emphasis was accorded the question of whether modern breast-stroke is "flylike" (referring to the butterfly stroke) and whether "waves" travel along the body during the breaststroke cycle. Selected body landmarks and the center of mass (CM) of 8 Olympic breaststroke swimmers were quantified. Fourier analysis was conducted to determine the amplitude, frequency composition, and phase characteristics of the vertical undulations of the vertex of the head, shoulders, hips, knees, and ankles. The differences in phase between these landmarks for the first (HI) and second (H2) Fourier frequencies were investigated to establish whether body waves traveled in a caudal direction. While the motion of the upper body was somewhat flylike, the velocity of the HI wave from the hips to ankles was variable among subjects and, for all subjects, was too slow to be propulsive. Contrary to what one would expect, the range of vertical motion of the CM was inversely related to the range of hip vertical motion. The two highest placing subjects, based on preliminary heat times (SI and S4), were distinguished by a large range of hip vertical motion and a small range of CM vertical motion.

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Three-Dimensional Analysis of the Men‘s 100-m Freestyle during the 1992 Olympic Games

Jane M. Cappaert, David L. Pease, and John P. Troup

Twelve male 100-m freestyle swimmers were videotaped during the 1992 Olympic Games. Four cameras, two above water and two below, recorded the same stroke cycle of the swimmer at approximately the 40- to 45-m mark. The whole body and the recovering arms were digitized from the videotapes to recreate a complete stroke cycle. Body position variables and hand reaction forces (Schleihauf, 1979) were calculated. Swimmers were divided into elite and subelite groups based on their swimming velocity and were compared for differences in biomechanical variables. Elites used slightly lower hand forces while maintaining a higher propelling efficiency. Subelites had opposite rotations about the longitudinal axis of the body rather than symmetrical body roll. The elite swimmers were different from subelites in that their pulling patterns were more efficient and their body position was more streamlined. These variables assisted them in achieving faster swimming velocities without requiring higher propulsive forces.

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Monitoring the Effect of Race-Analysis Parameters on Performance in Elite Swimmers

Elaine Tor, David L. Pease, Kevin A. Ball, and Will G. Hopkins

Time trials are commonly used in the lead-up to competition. A method that evaluates the relationship between time trial and competition performance in swimming would be useful for developing performance-enhancement strategies.


To use linear mixed modeling to identify key parameters that can be used to relate time-trial and competition performance.


Ten swimmers participated in the study. Each swimmer was analyzed during 3 time trials and 1 competition. Race video footage was analyzed to determine several key parameters. Pooling of strokes and distances was achieved by modeling changes in parameters between time trials and competition within each subject as linear predictors of percent change in performance using mixed modeling of log-transformed race times.


When parameters were evaluated as the effect of 2 SD on performance time, there were very large effects of start time (2.6%, 90% confidence interval 1.8–3.3%) and average velocity (–2.3%, –2.8% to –1.8%). There was also a small effect for stroke rate (–0.6%, –1.3% to 0.2%). Further analysis revealed an improvement in performance time of 2.4% between time trials and competition, of which 1.8% (large; 1.4–2.1%) was due to a change in average velocity and 0.9% (moderate; 0.6–1.1%) was due to a change in start time; changes in remaining parameters had trivial effects on performance.


This study illustrates effective analytical strategies for identifying key parameters that can be the focus of training to improve performance in small squads of elite swimmers and other athletes.

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Pitching Effects of Buoyancy During Four Competitive Swimming Strokes

Raymond C.Z. Cohen, Paul W. Cleary, Simon M. Harrison, Bruce R. Mason, and David L. Pease

The purpose of this study was to determine the pitching effects of buoyancy during all competitive swimming strokes—freestyle, backstroke, butterfly, and breaststroke. Laser body scans of national-level athletes and synchronized multiangle swimming footage were used in a novel markerless motion capture process to produce three-dimensional biomechanical models of the swimming athletes. The deforming surface meshes were then used to calculate swimmer center-of-mass (CoM) positions, center-of-buoyancy (CoB) positions, pitch buoyancy torques, and sagittal plane moments of inertia (MoI) throughout each stroke cycle. In all cases the mean buoyancy torque tended to raise the legs and lower the head; however, during part of the butterfly stroke the instantaneous buoyancy torque had the opposite effect. The swimming strokes that use opposing arm and leg strokes (freestyle and backstroke) had smaller variations in CoM positions, CoB positions, and buoyancy torques. Strokes with synchronized left-right arm and leg movement (butterfly and breaststroke) had larger variations in buoyancy torques, which impacts the swimmer’s ability to maintain a horizontal body pitch for these strokes. The methodology outlined in this paper enables the rotational effects of buoyancy to be better understood by swimmers, allowing better control of streamlined horizontal body positioning during swimming to improve performance.