Suzana Matheus Pereira

Biomechanical Analysis of Backstroke Swimming Starts

The relationships between the start time and kinematic, kinetic and electromyographic data were examined in order to establish the common features of an effective backstroke swimming start. Complementarily, different starting positions were analysed to identify the parameters that account for the fastest backstroke start time under different constraints. 6 high-level swimmers performed 4×15 m maximal trials of each start variants with different feet position: parallel and entirely submerged (BSFI) and above water surface (BSFE), being monitored with synchronized dual-media image, underwater platform plus handgrip with a load cell, and eletromyographic signal of RECTUS FEMORIS and GASTROCNEMIUS MEDIALIS. Mean and SD values of start time for BSFI and BSFE were 2.03 ± 0.19 and 2.14 ± 0.36 s, respectively. In both starts, high associations (r > =0.75, p < 0.001) were observed between start time and centre of mass resultant average velocity at glide phase and horizontal impulse at take-off for BSFI, and centre of mass horizontal position at the start signal for BSFE. It was concluded that the greater impulse during the take-off and its transformation into a fast underwater movement are determinant to decrease the start time at BSFI. Regarding BSFE, a greater centre of mass pool-wall approximation might imply a flatter take-off angle, compromising underwater velocity and starting performance.

Analysis of the lateral push-off in the freestyle flip turn

Abstract The aim of this study was to examine the contact phase during the lateral push-off in the turn of front crawl swimming to determine which biomechanical variables (maximum normalized peak force, contact time, impulse, angle of knee flexion, and total turn time within 15 m) contribute to the performance of this turn technique. Thirty-four swimmers of state, national, and international competitive standard participated in the study. For data collection, the following equipment was used: an underwater force platform, a 30-Hz VHS video camera, and a MiniDv digital camera within an underwater box. Data are expressed as descriptive statistics. Inferential analyses were performed using Pearsons correlation and multiple linear regressions. All variables studied had a significant relationship with turn performance. We conclude that a turn executed with a knee flexion angle of between 100° and 120° provides optimum peak forces to generate impulses that allow the swimmer to lose less time in the turn without the need for an excessive force application and with less energy lost.

Backstroke start kinematic and kinetic changes due to different feet positioning

Abstract The backstroke swimming start international rules changed in 2005. This study compared two backstroke start variants, both with feet parallel to each other but in complete immersion and emersion. Six elite swimmers performed two sets of 4 maximal 15 m bouts, each set using one of the variants. The starts were videotaped in the sagittal plane with two cameras, providing bi-dimensional dual-media kinematic evaluation, and an underwater force plate and a handgrip instrumented with a load cell collected kinetic data. Backstroke start with feet immerged displayed greater centre-of-mass horizontal starting position, centre-of-mass horizontal velocity at hands-off and take-off angle. Backstroke start with feet emerged showed greater wall contact time, centre-of-mass horizontal and downward vertical velocity at take-off, lower limbs horizontal impulse, and centre-of-mass downward vertical velocity during flight phase. Backstroke start with feet immerged and emerged displayed similar centre-of-mass horizontal water reach, back arc angle and 5 m starting time. Irrespective of the swimmer’s feet positioning, coaches should emphasise each variant’s mechanical advantages during the wall contact phases. Furthermore, the maintenance of those advantages throughout the flight should be stressed for better backstroke start performance.

Kinematic, kinetic and EMG analysis of four front crawl flip turn techniques

Abstract This study aimed to analyse the kinematic, kinetic and electromyographic characteristics of four front crawl flip turn technique variants. The variants distinguished from each other by differences in body position (i.e. dorsal, lateral, ventral) during rolling, wall support, pushing and gliding phases. Seventeen highly trained swimmers (17.9 ± 3.2 years old) participated in interventional sessions and performed three trials of each variant, being monitored with a 3-D video system, a force platform and an electromyography (EMG) system. Studied variables: rolling time and distance, wall support time, push-off time, peak force and horizontal impulse at wall support and push-off, centre of mass horizontal velocity at the end of the push-off, gliding time, centre of mass depth, distance, average and final velocity during gliding, total turn time and electrical activity of Gastrocnemius Medialis, Tibialis Anterior, Biceps Femoris and Vastus Lateralis muscles. Depending on the variant, total turn time ranged from 2.37 ± 0.32 to 2.43 ± 0.33 s, push-off force from 1.86 ± 0.33 to 1.92 ± 0.26 BW and centre of mass velocity during gliding from 1.78 ± 0.21 to 1.94 ± 0.22 m · s−1. The variants were not distinguishable in terms of kinematical, kinetic and EMG parameters during the rolling, wall support, pushing and gliding phases.

Kinematic and Electromiographic Analysis of the Water Polo Crawl While Leading the Ball: A Pilot Study

Our aim was to conduct a kinematic and electromyographic characterization of the water polo front crawl while leading the ball technique. A high level male water polo player performed an experimental protocol of 3x15m at front crawl while leading the ball (with rest intervals of 2min between repetitions). Each repetition was performed in accelera- tion. One complete stroke cycle was analyzed for each repetition of 15m using surface electromyography to analyse the biceps femoris, gastrocnemius medialis, tricips brachii, biceps brachii, deltoideus posterior and rectus femoris muscles. The protocol was also recorded by 2 surface and 4 underwater cameras in order to assess centre of mass (CM) velocity during the cycle and its fluctuations. EMG signal was digital filtered (35-500Hz), full-wave rectified, calculated the linear envelope, normalized to the maximal isometric voluntary contraction and integrated (iEMG). The fluctuations of CM velocity were assessed though the coefficient of variation of the instantaneous velocity. Results showed that tricips brachii and gastrocnemius medialis were the most active muscles in the beginning of the cycle and that gastrocnemius medialis, deltoideus posterior and tricips brachii displayed the highest values (and biceps brachii the lower values) of maximum electric activity and iEMG. It was observed an increase in the velocity of the CM at the beginning of the cycle, decreasing slightly afterwards, implying a reduced coefficient of variation (16.8). It should be evidenced the different involvement of the studied muscles in the cycle of front crawl while leading the ball and the consequent differences in the CM velocity.

Kinematic and Electromiographic Analysis of the Water Polo Crawl While Leading the Ball: A Pilot Study~!2009-07-05~!2009-11-09~!2010-04-20~!

Our aim was to conduct a kinematic and electromyographic characterization of the water polo front crawl while leading the ball technique. A high level male water polo player performed an experimental protocol of 3x15m at front crawl while leading the ball (with rest intervals of 2min between repetitions). Each repetition was performed in acceleration. One complete stroke cycle was analyzed for each repetition of 15m using surface electromyography to analyse the bíceps femoris, gastrocnemius medialis, tricips brachii, bíceps brachii, deltoideus posterior and rectus femoris muscles. The protocol was also recorded by 2 surface and 4 underwater cameras in order to assess centre of mass (CM) velocity during the cycle and its fluctuations. EMG signal was digital filtered (35-500Hz), full-wave rectified, calculated the linear envelope, normalized to the maximal isometric voluntary contraction and integrated (iEMG). The fluctuations of CM velocity were assessed though the coefficient of variation of the instantaneous velocity. Results showed that tricips brachii and gastrocnemius medialis were the most active muscles in the beginning of the cycle and that gastrocnemius medialis, deltoideus posterior and tricips brachii displayed the highest values (and bíceps brachii the lower values) of maximum electric activity and iEMG. It was observed an increase in the velocity of the CM at the beginning of the cycle, decreasing slightly afterwards, implying a reduced coefficient of variation (16.8). It should be evidenced the different involvement of the studied muscles in the cycle of front crawl while leading the ball and the consequent differences in the

Hand force symmetry during breaststroke swimming

Hand force symmetry during breaststroke swimming The aim of this study was to analyze the hand force symmetry during the breaststroke and its relationship with swimmers’ performance. Seventeen breaststroke and/or medley specialists participated (12 men and 5 women, 19.5 ± 5.2 years and average performance of 73.4 ± 7% of the 50 m breaststroke world record). Each swimmer performed three repetitions of 25 m breaststroke swimming at maximal speed. Pressure sensors from Aquanex acquisition system were placed in both swimmers’ hands and Mean Force (Fmean) and Maximal Force (Fmax) were measured. The symmetry index proposed by Sanders was calculated and the time of a 50-m breaststroke trial at maximum speed (T50m) was used as a performance indicator. The variables were compared between hands using tests for dependent samples, and the relationship between variables were investigated using Spearman correlation test. The Fmean applied was 47.9 ± 16.7 N and 47.9 ± 14.5 N for right and left hands, respectively. The Fmean corresponded to 120.7 ± 43.6 N e 112.8 ± 35.7 N for right and left hand, respectively. No signifi cant differences were observed for none of the variables between right and left hands. Analyzing the subjects individually, it was possible to observe asymmetries levels up to 30.6% for Fmean and 35.9% for Fmax, however the relationship between symmetry indexes and the 50 m breaststroke performance was not statistically signifi cant.