A Rigorous and Integrated On-Water Monitoring System for Performance and Technique Improvement in Rowing.

This paper presents a prototype, on-water rowing monitoring system and its testing results for a single scull boat. The proposed system aims at recording critical kinetic (athlete biomechanics and oar/seat movements) and kinematic (boat position, velocity, acceleration, and attitude) parameters for sport performance evaluation and rowing technique improvement. The data acquisition unit is organized in two parts: the first part aims at logging boat kinematics based on GNSS/INS filtering, while the second one facilitates kinetics data recording using a series of analog sensors (potentiometers, strain gauges) installed on the athlete's body and the boat seat and oars. Both parts are connected to a central unit featuring analog voltage digitizers and a micro-PC for device handling and data storing. In order to test the performance of the system a series of field trials were undertaken featuring different observation scenarios as well as intentionally induced errors in the rowing technique. Analysis revealed the high performance of the system in terms of sensor completeness and setup procedures as well as operational efficiency. Moreover, system performance evaluation exercised through studying raw data recordings and resultant parameters at stroke cycle and average (standardized) stroke cycle level confirmed the fruitfulness of the proposed approach and system and its potential for implementation on a broad scale. Finally, the data acquired from the proposed system were used to compute the adopted input parameters and performance indicators to characterize the system in terms of functionality and operational efficiency.

Does a 4-week training period with hand paddles affect front-crawl swimming performance?

This study investigated the effects of a 4-week training with hand paddles (HPD) on front-crawl swimming performance (SP), clean swimming speed (SPEED), stroke rate (SR), stroke length (SL) and tethered force (TF). Twenty swimmers (10 men and 10 women) were paired according to performance and gender, and were randomly assigned to control (CON, 22.4 ± 2.3 years) or HPD (21.8 ± 1.9 years) groups. During 4 weeks both groups performed the same training, except for a sprint training set (3 times/week, 10 × 10 strokes all-out, 1-min rest) completed with (HPD = 320 cm2) and without (CON) paddles. Afterwards, both groups performed the same training over a 2-week taper period. SP, SPEED, SR, SL and TF were assessed before (PRE) and after the 4-week period (POST), after the first (T1) and second taper weeks (T2). Swimmers rated their perceived exertion for the sprint training set (RPETS) and the training session for determining internal training load (ITL). SP, SPEED, SR, SL and TF did not change from PRE to POST, T1 and T2. ITL and RPETS were not different between groups. Training 4 weeks with HPD does not affect swimming performance, so the use of HPD remains unsupported in such period.

Physical activity in pre-school children: Trends over time and associations with body mass index and screen time.

Background: Pre-school years are important for adopting health behaviours; however, today's children seem to be overweight, present low physical activity (PA) levels and exceed screen time (ST) recommendations.Aim: To examine (a) time trends in PA in Greek pre-school children, (b) the associations among PA, body mass index (BMI) and ST and (c) potential PA differences between boys and girls.Subjects and methods: Data from five cross-sectional cohorts (2005 [n = 252]; 2008 [n = 212]; 2011 [n = 187]; 2014 [n = 194]; 2017 [n = 128]) were compared. PA was assessed using Omron HJ-720IT-E2 pedometers, whereas ST was reported by participants' parents. A 4-way ANOVA was applied on children's average week step counts.Results: A significant association (F = 828.90, p < 0.001, η2 = 0.638) between ST and PA was revealed, with children that had ST < 1 hour/day presenting the higher PA levels and being the only ones that met PA recommendations (11,500 steps/day). Statistically significant PA differences, though of no practical importance, were found among cohorts. There were no significant PA differences between boys and girls or among BMI categories. Nevertheless, obesity prevalence was found to exist at alarming levels (24.5% in 2008-41.4% in 2017), and a large percentage of children (23.6% in 2008-63.3% in 2017) presented excessive ST (> 2 hours/day).Conclusion: Effective interventions aiming at reducing ST and enhancing PA seem imperative if children's health is to be safeguarded.

Effect of an 11-Week In-Water Training Program With Increased Resistance on the Swimming Performance and the Basic Kinematic Characteristics of the Front Crawl Stroke.

Gourgoulis, V, Valkoumas, I, Boli, A, Aggeloussis, N, and Antoniou, P. Effect of an 11-week in-water training program with increased resistance on the swimming performance and the basic kinematic characteristics of the front crawl stroke. J Strength Cond Res 33(1): 95-103, 2019-The purpose of the study was to assess the effect of an 11-week in-water training program with increased resistance on the swimming performance and the basic kinematic characteristics of the front crawl stroke in young female swimmers. Twelve swimmers were matched in pairs according to their best performance in 50-m front crawl swimming and then were randomly assigned to an experimental or to a control group. Both groups followed exactly the same swimming training program. The only exception was that the experimental group performed a sprint training section with increased resistance pulling a water parachute, whereas the control group performed the same section without parachute. Before and after the intervention program, the best performance of both groups in 50-, 100-, and 200-m front crawl swimming were assessed. Moreover, the basic kinematic characteristics of the stroke were calculated during 50-m front crawl swimming with maximal intensity. Two-way repeated measures analyses of variance revealed significant improvement in the best performance in all swimming distances only in the experimental group (3.22-7.26%). As far as the basic kinematic characteristics of the stroke are concerned, significant modifications were found only in the mean swimming velocity in the experimental group (2.18%), whereas no significant changes were observed in the stroke length, the stroke rate, and the duration of the propulsive, and nonpropulsive phases in both groups. Thus, the findings of the current study revealed a positive effect of the in-water resistance training program in the swimming performance of young female swimmers of moderate performance level, without any negative influence in the basic kinematic characteristics of the stroke.

Intracyclic Velocity Variation of the Center of Mass and Hip in Breaststroke Swimming With Maximal Intensity.

Gourgoulis, V, Koulexidis, S, Gketzenis, P, and Tzouras, G. Intra-cyclic velocity variation of the center of mass and hip in breaststroke swimming with maximal intensity. J Strength Cond Res 32(3): 830-840, 2018-The aim of the study was to compare the center of mass (CM) and hip (HIP) intracyclic velocity variation in breaststroke swimming using 3-dimensional kinematic analysis. Nine male breaststrokes, of moderate performance level, swam 25-m breaststroke with maximal intensity, and their movements were recorded, both under and above the water surface, using 8 digital cameras. Their CM and HIP velocities and their intracyclic variations were estimated after manual digitization of 28 selected points on the body in a complete arm and leg breaststroke cycle. Paired sample t-tests or Wilcoxon tests, when the assumption of normality was broken, were used for statistical analyses. In both, CM and HIP velocity-time curves, the results revealed a similar pattern of 2 clear peaks associated with the leg and arm propulsive phases and 2 minimal velocities that corresponded to the arm and leg recovery phase and the lag time between the leg and arm propulsive phases, respectively. However, despite this similar general pattern, the HIP minimum resultant velocity was significantly lower, whereas its maximal value was significantly greater, than the corresponding CM values. Consequently, the HIP intracyclic swimming velocity fluctuation significantly overestimates the actual variation of the swimmer's velocity in breaststroke swimming.

The influence of the hand's acceleration and the relative contribution of drag and lift forces in front crawl swimming.

The aim of this study was to assess the effect of the hand's acceleration on the propulsive forces and the relative contribution of the drag and lift on their resultant force in the separate phases of the front crawl underwater arm stroke. Ten female swimmers swam one trial of all-out 25-m front crawl. The underwater motion of each swimmer's right hand was recorded using four camcorders and four periscope systems. Anatomical landmarks were digitised, and the propulsive forces generated by the swimmer's hand were estimated from the kinematic data in conjunction with hydrodynamic coefficients. When the hand's acceleration was taken into account, the magnitude of the propulsive forces was greater, with the exception of the mean drag force during the final part of the underwater arm stroke. The mean drag force was greater than the mean lift force in the middle part, while the mean lift force was greater than the mean drag force in the final part of the underwater arm stroke. Thus, swimmers should accelerate their hands from the beginning of their backward motion, press the water with large pitch angles during the middle part and sweep with small pitch angles during the final part of their underwater arm stroke.

Pedometer determined physical activity and obesity prevalence of Greek children aged 4-6 years.

BACKGROUND: Pre-school age is important for developing healthy attitudes towards physical activity (PA). However, research on pre-schoolers' pedometer-determined PA is limited. AIM: To describe pre-schoolers' ambulatory activity; investigate step count differences in respect to Body Mass Index (BMI) categories and examine the prevalence of obesity. SUBJECTS AND METHODS: Pre-school aged children (n = 250; 5.5 ± 0.4 years) from Komotini (Greece) wore Omron HJ-720IT-E2 pedometers for 10 consecutive days. Height and weight were measured and BMI was calculated. RESULTS: Three-way repeated measures ANOVAs revealed that children performed more steps on weekdays than during weekends (p < 0.001) and during leisure time than school (p < 0.001). Significant differences appeared between normal and obese children's counts on weekdays (p < 0.001), weekend days (p < 0.05), during school (p < 0.001), after school (p < 0.005) and in weekly steps (p < 0.005). No gender differences were detected. Moreover, according to a sample t-test analysis, children's daily steps were significantly different from the 10,000 steps/day guideline, while obesity prevalence was 15.6%. CONCLUSION: School-based ambulatory activity is lower than after school ambulatory activity, independent of BMI-category and gender, although obese children demonstrated fewer steps. Taking into account the high rate of both the obesity prevalence and children not meeting the 10,000 steps/day guideline, the need for preventive policies becomes obvious.

The post-activation potentiation effect on squat jump performance: age and sex effect.

This study examined the post-activation potentiation (PAP) effects on squat jump (SJ) performance and on peak rate of force development (RFDpeak) in preadolescent (10-12 y), adolescents (14-15 y) and adults (20-25 y) males and females. All participants performed a SJ with and without prior conditioning stimulus (PAP and control protocol, respectively), consisting of 3 × 3-second maximal isometric squats. Jump height and RFDpeak of the vertical ground reaction force during SJ were assessed before, and at 20 seconds and at 4 minutes following the conditioning stimulus. The results revealed a different pattern of age-effect on SJ performance within males and females. The RFDpeak significantly increased as a factor of age in both males and females (P < .05). Increase in SJ performance after conditioning stimulus occurred only in men (P < .05), with no effects in teen-males, boys, and female groups. There was a significant PAP effect on RFDpeak in both adult groups (P < .05) and teen-males, with no effects in children. In conclusion, the PAP effects on SJ performance and RFDpeak are age- and sex-dependent; that is PAP appears as a viable method for acutely enhancing SJ performance in men but not in pediatric population.

The effect of leg kick on sprint front crawl swimming.

The aim of this study was to examine the influence of leg kick on the pattern, the orientation and the propulsive forces produced by the hand, the efficiency of the arm stroke, the trunk inclination, the inter-arm coordination and the intra-cyclic horizontal velocity variation of the hip in sprint front crawl swimming. Nine female swimmers swam two maximal trials of 25 m front crawl, with and without leg kick. Four camcorders were used to record the underwater movements. Using the legs, the mean swimming velocity increased significantly. On the contrary, the velocity and the orientation of the hand, the magnitude and the direction of the propulsive forces, as well as the Froude efficiency of the arm stroke were not modified. The hip intra-cyclic horizontal velocity variation was also not changed, while the index of coordination decreased significantly. A significant decrease (13%) was also observed in the inclination of the trunk. Thus, the positive effect of leg kick on the swimming speed, besides the obvious direct generation of propulsive forces from the legs, could probably be attributed to the reduction of the body's inclination, while the generation of the propulsive forces and the efficiency of the arm stroke seem not to be significantly affected.

Sprint resisted swimming training effect on the swimmer's hand orientation angles.

The current study aimed to determine the effect of an 11-week sprint resisted swimming training programme on the swimming performance and the orientation angles of the hand. Fourteen young female swimmers were divided into two equivalent groups and were trained with specific sprint training sets. The experimental group performed these sets using a swimming parachute. For the evaluation of the intervention, before and at the end of the 11 weeks period both groups performed 50 m front crawl with maximal intensity and their underwater motion was recorded using four cameras. Their underwater movements were manually digitised using the Ariel Performance Analysis System and the statistical treatment of the data revealed a significant increase of the mean swimming velocity (3.76 ± 0.04 %) and stroke rate (3.09 ± 0.08 %) only in the experimental group. Moreover, a significant reduction of the total stroke duration (-4.26 ± 0.09 %) and the relative duration of the non-propulsive phases (-12.70 ± 0.23 %) was also observed only in the experimental group. The resultant velocity of the hand, and the pitch and sweepback angles of the hand remained unaffected in both groups during the pull and push phases. However, a significant decrease of the pitch angle (-47.44 ± 3.37 %) during the entry & catch phase was observed only in the experimental group. The increased performance and the higher mean swimming velocity after the current sprint resisted training programme was mainly due to the temporal modifications of the stroke, along with the pitch angle reduction during the entry & catch phase.

Muscle performance following an acute bout of plyometric training combined with low or high intensity weight exercise.

To determine the time course of performance responses after an acute bout of plyometric exercise combined with high and low intensity weight training, a 3-group (including a control group), repeated-measures design was employed. Changes in performance were monitored through jumping ability by measuring countermovement and squat jumping, and strength performance assessment through isometric and isokinetic testing of knee extensors (at two different velocities). Participants in both experimental groups performed a plyometric protocol consisting of 50 jumps over 50 cm hurdles and 50 drop jumps from a 50 cm plyometric box. Additionally, each group performed two basic weight exercises consisting of leg presses and leg extensions at 90-95% of maximum muscle strength for the high intensity group and 60% of maximum muscle strength for the low intensity group. The results of the study suggest that an acute bout of intense plyometric exercise combined with weight exercise induces time-dependent changes in performance, which are also dependent on the nature of exercise protocol and testing procedures. In conclusion, acute plyometric exercise with weight exercise may induce a substantial decline in jumping performance for as long as 72 hours but not in other forms of muscle strength.

Acute effect of front crawl sprint resisted swimming on the propulsive forces of the hand.

The purpose of the current study was to investigate the acute effect of sprint resisted front crawl swimming on the propulsive forces of the hand. Eight female swimmers swam 25 m with maximal intensity, with and without added resistance. A bowl with a capacity of 2.2, 4 and 6 L was used as low, moderate and high added resistance, respectively. The underwater motion of the swimmer's right hand was recorded using 4 cameras (60 Hz) and the digitization was undertaken using the Ariel Performance Analysis System. Repeated-measures ANOVA revealed that the velocity of the hand, the pitch and the sweepback angles of the hand, as well as the magnitude and the relative contribution of the drag and lift forces were not significantly modified and thus the magnitude of the resultant force did not change. Moreover, the magnitude of the effective force, as well as the angle formed between the resultant force and the axis of the swimming propulsion were not significantly affected. Thus, it could be concluded that resistance added as in this study did not alter the pattern of the propulsive hand forces associated with front crawl sprinting.

The influence of an 11-week resisted swim training program on the inter-arm coordination in front crawl swimmers.

The purpose was to assess the effect of an 11-week resisted swim training program using a water parachute on the inter-arm coordination in front crawl swimming. Fourteen female swimmers were divided into a control and an experimental group, and followed the same training program, except for the use of a water parachute by the experimental group in specific sprint sets. Before and after the intervention, the underwater motion of the swimmers was recorded using four camcorders and the digitisation process was undertaken manually. The two-way repeated measures analyses of variance revealed a significant increase of the swimming velocity, due to a significant increased stroke rate, because of the significant reduction of the total stroke duration, only in the experimental group. Moreover, their absolute and relative duration of the propulsive pull and push phases increased significantly, while the absolute and relative duration of their non-propulsive entry & catch and recovery phases decreased significantly. These modifications caused a significant increase in the index of coordination. Thus, this 11-week sprint resisted intervention program seems to improve the propulsion continuity and could be considered as an effective form of training, increasing the stroke rate and consequently the swimming velocity.

A Comparative Analysis of Symmetry Indices for Spatiotemporal Gait Features in Early Parkinson's Disease.

This study compared the five most commonly used equations for calculating gait symmetry in discrete variables among Parkinson's disease patients. Twelve patients (five women and seven men) performed ten consecutive gait trials on a 10 m walkway. Gait data were collected using eight optoelectronic cameras (100 fr/s). The analysis focused on various spatiotemporal parameters, including cadence, step time, stride time, single support, double support, walking speed, step length, stride length, step width, and foot angle. Five symmetry indices were calculated for each trial rather than averaging the ten recorded trials. The variability in and reliability of each symmetry equation were assessed using the coefficient of variation (CV) and intraclass correlation coefficient (ICC), respectively. Additionally, Bland-Altman plots were produced to visualize the agreement between each pair of methods for each spatiotemporal parameter. The results revealed that the symmetry ratio method exhibited lower variability and higher reliability compared with the other four indices across all spatiotemporal gait parameters. However, it was found that the reliability of a single trial was generally poor, regardless of the symmetry calculation formula used. Therefore, we recommend basing measurements of gait asymmetry in Parkinson's disease on multiple trials.

Analysis of upper limb propulsion in young swimmers in front-crawl through Statistical Parametric Mapping.

This study aimed to: (i) verify the within-subject effect of the dominant and non-dominant upper limb propulsion during consecutive arm-pulls through discrete (average) and continuous analysis (SPM), and; (ii) compare young swimmers' propulsion between both upper limbs through discrete (average) and continuous analysis (Statistical Parametric Mapping - SPM). The sample consisted of 17 young male swimmers (age = 16.02 ± 0.61-years) who regularly participate in national and international level competitions. A set of kinematic and propulsion variables were measured during a 25-m maximal trial in front-crawl. Statistical analysis of propulsion was performed using discrete variables and through SPM. Swimming velocity showed a significant decrease over time. A significant interaction between the "time" (consecutive arm-pulls) and "side" (dominant vs. non-dominant) effects was observed in both statistical analyzes. Only the dominant upper limb demonstrated a significant "time" effect with a significant difference (p < 0.05) between the first and third arm-pulls. SPM indicated that the "time" effect was observed between the âˆ¼ 34% and âˆ¼ 42% of the arm-pull. The differences between the first and third arm-pull were verified between the âˆ¼ 32% and âˆ¼ 43% of the arm-pull. A non-significant "side" effect was verified in both analyzes. Therefore, SPM analysis provided more sensitive and accurate outputs than discrete analysis. This will allow coaches to design specific training drills focused on specific moments of the arm-pull.

Swimming coaches' professional development and training practices: an international survey.

This study investigated swim coaches' perceptions of professional development issues and current training practices according to their coaching experience, education level, and gender. An online survey (January-April 2022) was completed by 123 swim coaches (96 male/27 female) of competitive swimmers based in 41 countries. The survey consisted of 36 questions divided into six sections: (1) background information, (2) developing swim coaching through learning, (3) self-evaluation, (4) interpersonal-intrapersonal interactions, (5) life skills, and (6) analyzing swimming performance. Pearson chi-square assessed the relationship between the frequency of responses and professional background and gender. The survey results indicated that swim coaches' educational level is potentially one of the most influential parameters affecting the coaches' perceptions about their own professional development. The data presented may be used for the future design of coach education programmes as they advance current knowledge on understanding psycho-social issues related to professional development and training perceptions involved in the competitive swimming environment.

Gait analysis comparison between manual marking, 2D pose estimation algorithms, and 3D marker-based system.

Introduction: Recent advances in Artificial Intelligence (AI) and Computer Vision (CV) have led to automated pose estimation algorithms using simple 2D videos. This has created the potential to perform kinematic measurements without the need for specialized, and often expensive, equipment. Even though there's a growing body of literature on the development and validation of such algorithms for practical use, they haven't been adopted by health professionals. As a result, manual video annotation tools remain pretty common. Part of the reason is that the pose estimation modules can be erratic, producing errors that are difficult to rectify. Because of that, health professionals prefer the use of tried and true methods despite the time and cost savings pose estimation can offer. Methods: In this work, the gait cycle of a sample of the elderly population on a split-belt treadmill is examined. The Openpose (OP) and Mediapipe (MP) AI pose estimation algorithms are compared to joint kinematics from a marker-based 3D motion capture system (Vicon), as well as from a video annotation tool designed for biomechanics (Kinovea). Bland-Altman (B-A) graphs and Statistical Parametric Mapping (SPM) are used to identify regions of statistically significant difference. Results: Results showed that pose estimation can achieve motion tracking comparable to marker-based systems but struggle to identify joints that exhibit small, but crucial motion. Discussion: Joints such as the ankle, can suffer from misidentification of their anatomical landmarks. Manual tools don't have that problem, but the user will introduce a static offset across the measurements. It is proposed that an AI-powered video annotation tool that allows the user to correct errors would bring the benefits of pose estimation to professionals at a low cost.

The relationship between motor proficiency and pedometer-determined physical activity in young children.

UNLABELLED: The aim of this study was to examine the relationship between motor proficiency and pedometer-determined physical activity in 5-6 year-old children. Participants (n = 232) were randomly recruited and assessed from 30 kindergartens in Northern Greece. Two trained researchers administered the measurements for the assessment of children's motor proficiency by using the BOTMP-SF. Physical activity was assessed by OMRON pedometers. Significant relationships between BOTMP-SF standard score and steps (S), aerobic walking time (AWT) and aerobic steps (AS), (p < .05) were found. When motor proficiency was divided into quartiles to assess the distribution of the relationship between motor proficiency and pedometer-derived variables, significant associations were found for AWT, S and AS (p < .001). Young children with high levels of motor proficiency were more active in contrast to their peers with lower motor proficiency. The findings add to the growing body of literature that considers motor skills/abilities as important elements of physical activity participation. ( ABBREVIATIONS: S-steps per day; AS-aerobic steps per day; AWT-aerobic walking time (minutes·day(-1)); BOTMP-SF-Bruininks-Oseretsky Test of Motor Proficiency-Short Form (standard score)).

Physiological responses and stroke-parameter changes during interval swimming in different age-group female swimmers.

The purpose of the study was to examine the physiological responses, the stroke-parameter changes, and the ability to sustain a velocity corresponding to critical velocity (CV) during interval swimming on female swimmers of different age groups. Eight children (C; age: 10.4 ± 0.6 years), 11 young (Y; age: 13.1 ± 0.4 years), and 7 adults (A; age: 19.9 ± 4.6 years) swam all-out efforts of 50, 100, 200, 400 m for CV and critical stroke rate (CSR) calculation. Subsequently, the swimmers performed an interval training set of 5 × 300-m (C) and 5 × 400-m repetitions (Y and A) at a velocity corresponding to CV. The CV was higher in the Y and A compared with the C group (C: 0.962 ± 0.05, Y: 1.168 ± 0.09, A: 1.217 ± 0.05 m·s(-1), p < 0.05). The velocity of 5 × 300 and 5 × 400 m was not different compared with CV (C: 100 ± 2%, Y: 98 ± 3%, A: 98 ± 3% of CV, p > 0.05). The blood lactate concentration was similar between groups and was maintained steady within each group (C: 4.5 ± 1.4, Y: 4.9 ± 1.4, A: 3.9 ± 1.3 mmol·L(-1), p > 0.05). Heart rate was higher in the C and Y compared with the A group during the last 100 m of each repetition (p < 0.05). Stroke rate remained unchanged during the repetitions and was similar between groups and no different to the CSR (p > 0.05). Stroke length of the fifth repetition was 4.5 ± 4.0% shorter compared with the second repetition in the Y and 5.3 ± 2.0% shorter compared with the first repetition in the A group (p < 0.05). During the 28- to 31-minute duration intermittent swimming, children and young and adult female swimmers were able to sustain CV with a steady and similar blood lactate concentration. Decreased stroke length may indicate an earlier fatigue in young and adult swimmers.

Comparison of the arm-stroke kinematics between maximal and sub-maximal breaststroke swimming using discrete data and time series analysis.

The aim of the current study was to compare the arm-stroke kinematics during maximal and sub-maximal breaststroke swimming using both discrete and continuous data analysis. Nine male breaststrokers swam 2 × 25 m with maximal and sub-maximal intensity and their full body 3-D kinematics were obtained using eight video cameras. The arm-stroke was divided into five phases: recovery, glide, out-sweep, in & down-sweep and in & up-sweep. The statistical treatment of selected discrete variables was conducted using t-test, while the analysis of their equivalent time series, when applicable, was conducted using Statistical Parametric Mapping. Sub-maximal trial, compared to maximal, presented lower swimming velocity, greater stroke length and less stroke rate. Moreover, the absolute and relative duration of the glide phase was longer, while the relative duration of all the other phases was shorter. The resultant hand velocity during the arm recovery was slower, as well as the hand velocity time series in the transverse and longitudinal axis which were slower from âˆ¼ 45 % to âˆ¼ 60 % and from âˆ¼ 5 % to âˆ¼ 15 % of the stroke cycle, respectively. Both discrete and continuous data analysis revealed that the main discriminating factor between the two conditions concerns to the adjustment of the glide and the recovery phase and consequently the continuation of the propulsive movements.