A MODELLING METHOD FOR DISCRETE LOW SAMPLMG FREQUENCY TEMPORAL SERIES ON THE EVALUATION OF INTRACYCLIC SWIMMING SPEED FLUCTUATIONS

Profiles of intra-cycle swimming speed fluctuations has been widely used as a high informative parameter on swirn~ningb iomechanics. Methods described in Iiterature can be divitled on: (i) frec swimming and (ii) linked swimming approaches. Linked swimming methods allow high sampling frequencies. NevertheIess, they present the disadvantage of mechanical links between the swimmer and the registration device. In the other hand, free swirmni~lgm ethods (eg. film ar~ti video methods) (nay allow CG stirdres, but tliey are very tirne consuming and low interactive if we consider high sampling frequencies. Interactivity with training, llowever. call be improved. if we can use a modelling method that can respect the phenomena cyclical characteristics. and requiring low sampling frequencies than, for instance, Fourier time series. 111 this paper, a method of discrete intra-cycle velocity fl~~ctuatioan alysis with reduced sampling frequencies is described. The method was used over velocity/time series obtained from intermittent light-trace photographic evaluation, and consists in a transformed polynomial repression to the estili~ationo f the first and last dependent temis of the regression equation (equal initial and final velocities and instantaneous accelerations). Three consecuti\re breaststroke cycles, sampled with a 5Hz frequency, were superimposed in accordance with a cycle period (T). estimated from the time interval between two consecutive absolute minimllnls. Optimised estimates of X r l l degree , polynomial coefficients were performed using Marqua1.t (1963) algorithm (Srutpul>hic.s 5.1. ) in successive trial and error regressions. with different T values, until rL maximum vi~lutw: as achieved. 011ceT was calculated. bl and bl = bg were also calculateti according to specially dcl-ived ecluations: 1-1 b, = -1x(I -l)biTl-l l . ~ and ' 1=2 i=l I The culves were derived and integrated (PC-hl~lrl~3l.h1 .3 in order to assess instantaneous and mean values of \,elocity and ac.celeration in ;~nd betoeen minir~~uamn d ~nasimlims ucct'ssivr velocity peak poiiits. Mean Ihorizcntal resultant impulses per phase were also estimated. Subjects Lvere 13 P o r t ~ ~ g ~ ~ e s top-level breast~trokersR. esults pointed o ~th~att: (i) mean minim~~vmel ocit!, associated with the recovery of the legs (V I ) \\.;IS .10 (k.035) 1n.s-1: (ii) mean maximal velocity associated with the Ies Lick (V2) \\,as 1.43 (f.039) tii.s-r: ( i i i ) I I I C ~ I1I1 linin1u:li i~ltc~.illedii~vttt' l~cit); ~sso~i;~t\veidtl l the tr,~nsitionp li;~se between leg and arm strokes (V3) \\(as 1 .O7 (k.0271 m.s- 1: [iii) mean pe;~h velocity associated with thc arm stroke (V 1) was 1.26 (k.O.78) ~ns-1:(i v) mean acceleration and ~.esultanitm pulse between V I ;~ndV 2 ~vere3 .03 (rt.i!-I) m.s-2 and 61.40 (k3.726) Ns: (v) betueen V2 and V i were - 1 .OX n1.s-2 and -2 1 . 1 ; (f3.478) Ns: (vi) betwern V3 ;~nci V-l \\.ere .h9 (k.0X-l) n1.s-2 ;~nrl 11.32 j f 1.853) Ns ;~nd( \!ill het\\/een V1 and V I \vrlt. -1.24 (+.02h) 111s-2a nd 5 I . I3 (f.962) Ns

The kinematic profile of ventral swimming start: sex diversity

It has been suggested that sex distinctions in physiology may affect the swimming performance of each sex differently. Yet, sex-based performance dependency has not been taken into consideration by most of the researchers evaluating swimming start. Therefore, the purpose of this research was to determine the effect of sex heterogeneity on the spatiotemporal characteristics of swimming start by investigating the determinants of its performance. A total of fifty-two international-level swimmers (thirty females and twenty-two males) performed three repetitions of the kick-start up to the 15-m mark. During trials, data were collected using video cameras and instrumented starting block. To search for evidence of differences between the two groups, the one-way ANOVA was conducted. Pearson’s correlation coefficients were calculated between measurements widely used to describe overall starting performance and selected kinematical variables of swimming start. A sex effect was exposed for temporal variables describing all swimming start phases (p ≤ 0.015). Male swimmers, by spending less time during the push-off from the starting block (p = 0.002; ηp2 = 0.18), reaching higher take-off velocity (p < 0.001; ηp2 = 0.29), traveling longer distances during flight (p < 0.001; ηp2 = 0.40), and swimming faster in the water phase (p < 0.001; ηp2 = 0.40), took starting advantage over their female counterparts. Consequently, performance measures such as 5-m, 10-m, and 15-m start times indicated that male participants were faster than females (p < 0.001; ηp2 ≥ 0.40). Only in the group of male swimmers a significant correlation between variables describing overall starting performance (5-m, 10-m, and 15-m times), and variables commonly highlighted as starting performance determining factors (block phase duration, take-off horizontal velocity, and flight distance) was found. The current study shows that the spatiotemporal variables of swimming start, the relation between them as well as overall starting performance, vary by sex. Consequently, the requirement of sex factor and its heterogeneity effect should be included not only in detailed characteristics of separate variables but also in all approaches undertaken. Those findings seem to play a crucial role mainly in swimming start evaluations in post-pubertal age groups of swimmers

IN VIVO STIFFNESS EVALUATION OF HUMAN TENDONS

The behaviour of tendons was largely studied in vitro conditions, both in human and animal tissues (Abrahams, 1967; Benedict et a/., 1968; Woo et al. 1981), but information available in the literature about human tendons in vivo is scarce. Meanwhile, an advance in real-time ultrasonography enables the non-invasive determination of the displacement of the fascicles during muscle contraction, which made possible the study of deformation of the aponeurosis and the tendon (Fukashiro et al. 1995). Such techniques were used in the past for the study of vertical jumps. For instance, Kubo et al. (1999) showed that tendons have a parabolic like force-length relationship at low stress, and an almost linear relation at higher loads. To our knowledge, however, it was never used for the analysis of long jumpers

NEUROMUSCULAR ACTIVATION DURING ROTATION AND PUSH-OFF PHASES OF BACKSTROKE TO BREASTSTROKE TURNING TECHNIQUES IN AGE-GROUP SWIMMERS

The aim of this study was to assess and compare, through electromyography, the neuromuscular activation during the rotation and push-off phases of four backstroke to breaststroke swimming turns. Eight male swimmers volunteered in this study, comparing the open turn, the back flip turn and the crossover turn. The crossover turn was the one that most activated the studied muscle. Erector spinae (ES) and rectus abdominis (RA), as well as latissimus dorsi (LD) were the main activated muscles during rotation phase. Gastrocnemius medialis (GM) and Tibialis anterior (TA) were mainly activated muscles during the explosive action of the push-off phase. These results provided better understanding about neuromuscular contributions during rotation and push-off of turning performance

BIOMECHANICAL ANALYSIS OF ELEMENTARY BALLET JUMPS: INTEGRATION OF FORCE PLATE DATA AND EMG RECORDS

The purpose of this research was to analyze the electromyographic (EMG) activity, ground reaction force and muscular behavior (concentric,isometric or eccentric) of the lower limb during elementary ballet jumps: "saute" in first position; "saute" in fifth position; "saute en cou de pie". Three trials of each jump were performed by a experienced female Ballet dancer. Results pointed out the existence of a pre-activation effect before landing in almost all cases. They also showed the negative correlation of EMG on the agonistantagonist pair tibialis anterior and medial gastrocnemius and a positive correlation of the EMG activity of adductors and rectus femoris, between medial gastrocnemius and soleus, and between rectus femoris and the vertical ground reaction force. However, most of the parameters measured show great sensitivity to the technical execution making it impossible to generalize these findings

Standing Posture in Motor and Cognitive Dual-Tasks during Smartphone Use: Linear and Nonlinear Analysis of Postural Control

Analysis of the center of pressure (CoP) during cognitive or motor dual-tasking is widely used to characterize postural control. Most studies use traditional measures of CoP to quantify postural control, but given its complexity, nonlinear analysis of CoP is of growing interest in the area. This study aims to analyze CoP behavior in healthy young adults during standing posture performance while simultaneously performing motor or cognitive tasks on a smartphone, using linear and nonlinear analysis of CoP. Thirty-six healthy participants (23.08 ± 3.92 years) were found eligible for this study. They performed a single task (ST), cognitive dual-task (cog-DT), and motor dual-task (mot-DT). The total excursion of CoP, displacement of CoP in the anterior-posterior and medial-lateral directions, mean total velocity of CoP, and mean anterior-posterior and medial-lateral velocities of CoP were measured with a force plate. Approximate entropy (ApEn) of the anterior-posterior (ApEn-AP) and medial-lateral (ApEn-ML) displacement of CoP were also calculated. The results showed that dual-task costs for the total excursion, displacement in the anterior-posterior direction, mean total velocity, and mean anterior-posterior velocity of CoP were greater during the cog-DT than the mot-DT (p 0.05) between the cog-DT and mot-DT for ApEn values of the anterior-posterior and medial-lateral time series of the CoP. Both linear and nonlinear analyses showed differences between the cog-DT and ST (p < 0.05), revealing a decline in postural control during the cog-DT compared with the ST. In conclusion, performing a cog-DT causes sway impairments and lower postural control efficacy compared with motor single and dual-tasks. Furthermore, both linear and nonlinear analyses were able to distinguish between conditions

Respuestas agudas al entrenamiento de fuerza con cargas pesadas y al entrenamiento mediante estiramiento sobre el rendimiento en squat jump y countermovement jump

El objetivo de este estudio es examinar los efectos agudos del entrenamiento con cargas pesadas, y del estiramiento estático sobre sujetos no entrenados y determinar si tiene un efecto positivo sobre el rendimiento en SJ y CMJ. 20 sujetos divididos en dos grupos (grupo de fuerza n:10 y grupo de estiramientos n:10). El grupo de fuerza realizó 3 series de 3 repeticiones con la máxima carga que puede soportar en 3RM y 3 min descanso entre serie. En el grupo de estiramientos los sujetos realizaban 3 series de 3 ejercicios de estiramientos correspondientes a flexores de rodilla, extensores de cadera y gemelos manteniendo el estiramiento pasivo durante 15 segundos en cada ejercicio. SJ y CMJ fueron medidos antes y después del ejercicio. La altura de salto se incrementó significativamente en el SJ después de los ejercicios de estiramiento (p<0.05). No hubo diferencias significativas en el resto de variables

Respuestas agudas al entrenamiento de fuerza con cargas pesadas y al entrenamiento mediante estiramiento sobre el rendimiento en squat jump y countermovement jump

El objetivo de este estudio es examinar los efectos agudos del entrenamiento con cargas pesadas, y del estiramiento estático sobre sujetos no entrenados y determinar si tiene un efecto positivo sobre el rendimiento en SJ y CMJ. 20 sujetos divididos en dos grupos (grupo de fuerza n:10 y grupo de estiramientos n:10). El grupo de fuerza realizó 3 series de 3 repeticiones con la máxima carga que puede soportar en 3RM y 3 min descanso entre serie. En el grupo de estiramientos los sujetos realizaban 3 series de 3 ejercicios de estiramientos correspondientes a flexores de rodilla, extensores de cadera y gemelos manteniendo el estiramiento pasivo durante 15 segundos en cada ejercicio. SJ y CMJ fueron medidos antes y después del ejercicio. La altura de salto se incrementó significativamente en el SJ después de los ejercicios de estiramiento (p<0.05). No hubo diferencias significativas en el resto de variables

Different Profiles of the Aerial Start Phase in Front Crawl

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