Ground reaction force differences in the countermovement jump in girls with different levels of performance

Purpose: The aim of this study was to ascertain the biomechanical differences between better and poorer performers of the vertical jump in a homogeneous group of children. Method: Twenty-four girls were divided into low-scoring (LOW; M age = 6.3 ± 0.8 years) and high-scoring (HIGH; M age = 6.6 ± 0.8 years) groups based on their performance on the vertical jump. The force-, velocity-, displacement-, and rate of force development (RFD)-time curves of vertical jumps were analyzed to determine the differences between groups. Results: The analysis of the data showed differences in the pattern of the ensemble mean curves of the HIGH and LOW groups, although the majority of the differences occurred during the eccentric contraction phase of the jump. The differences in the HIGH group with respect to the LOW group were: lower force at the beginning of the movement, higher speed and RFD during the eccentric phase, high force at the beginning of the concentric phase, higher velocity during the concentric phase, and a higher position at takeoff. Conclusion: The results showed that the HIGH group achieved a higher jump height than did the LOW group by increasing the effectiveness of the countermovement and achieving a more advantageous position at takeoff.Centro de Investigación en Rendimiento Físico y Deportiv

Relação dos saltos vertical, horizontal e sêxtuplo com a agilidade e velocidade em crianças

The aim of the present study were: 1) To verify the relationship of vertical, horizontal and sextuple jumps with agility and velocity of 5, 10 and 25 m; 2) To verify the capacity of these jumps to predict the agility and 5, 10 and 25 m velocity performance in children. Twenty eight boys (9.47 ± 0.64 years) and thirty girls (9.69 ± 0.70 years) were evaluated. The correlation values between agility and velocity on 5, 10 and 25 m velocity were, respectively, r = 0.63, 0.51, 0.44 and 0.64 with vertical jump, r = 0.68, 0.62, 0.28 and 0.62 with sextuple jump, and r = 0.60, 0.50, 0.26 and 0.57 with horizontal jump. The vertical and sextuple jumps were able to predict the agility and 25 m velocity performance (p < 0.05). Furthermore, they demonstrated capacity to predict 5 and 10 m velocity, respectively (p < 0.05). The vertical and sextuple jump tests may be used for assessment and control of training with children practicing activities that require agility and velocity, since both jumps predicted the agility and velocity performance, which did not occur with the horizontal jump.Os objetivos do presente estudo foram: 1) verifi car a relação dos saltos vertical, horizontal e sêxtuplo com a agilidade e velocidade de 5, 10 e 25 m; 2) verifi car a capacidade desses saltos em predizer o desempenho da agilidade e velocidade de 5, 10 e 25 m em crianças. Vinte e oito meninos (9,47 ± 0,64 anos) e 30 meninas (9,69 ± 0,70 anos) foram avaliados. Os valores de correlação entre a agilidade, velocidade de 5, 10 e 25 m foram, respectivamente, r = 0,63, 0,51, 0,44 e 0,64 com o salto vertical, r = 0,68, 0,62, 0,28 e 0,62 com o salto sêxtuplo, e r = 0,60, 0,50, 0,26 e 0,57 com o salto horizontal. O salto vertical e o salto sêxtuplo foram capazes de predizer o desempenho da agilidade e da velocidade de 25 m (p < 0,05). Além disso, demonstraram capacidade de predizer a velocidade de 5 e 10 m, respectivamente (p < 0,05). Os testes de salto vertical e sêxtuplo podem ser utilizados para avaliação e controle do treinamento com crianças praticantes de atividades que demandam agilidade e velocidade, uma vez que ambos os saltos predisseram o desempenho da agilidade e velocidade, o que não ocorreu com o salto horizontal

Anthropometric and Physical Qualities of Elite Male Youth Rugby League Players

Rugby league is a collision team sport played at junior and senior levels worldwide, whereby players require highly developed anthropometric and physical qualities (i.e., speed, change of direction speed, aerobic capacity, muscular strength and power). Within junior levels, professional clubs and national governing bodies implement talent identification and development programmes to support the development of youth (i.e., 13-20 years) rugby league players into professional athletes. This review presents and critically appraises the anthropometric and physical qualities of elite male youth rugby league players aged between 13 and 20 years by age category, playing standard and playing position. Height, body mass, body composition, linear speed, change of direction speed, aerobic capacity, muscular strength and power characteristics are presented and demonstrate that qualities develop with age and differentiate between playing standard and playing position. This highlights the importance of anthropometric and physical qualities for the identification and development of youth rugby league players. However, factors such as maturity status, variability in development, longitudinal monitoring and career attainment should be considered to help understand, identify and develop the physical qualities of youth players. Further extensive research is required into the anthropometric and physical qualities of youth rugby league players, specifically considering national standardized testing batteries, links between physical qualities and match performance, together with intervention studies, to inform the physical development of youth rugby league players for talent identification and development purposes

Are there differences in performance, metabolism, and quadriceps muscle activity in black African and Caucasian athletes during brief intermittent and intense exercise?

The purpose of the present study was to determine whether there are any differences in power output (PO) and/or quadriceps muscle (Quad) activity between black African and Caucasian football players during a force-velocity (fv) exercise test, which consisted of performing maximal 6-s sprints against an increasing load. Each subject started the test with a load of 2 kg and then recovered for 5 min before repeating the same test with a load increased by 2 kg. When the pedal frequency did not exceed 130 rev x min(-1), the load was increased by only 1 kg. Each subject attained the load corresponding to his maximal power if an additional increase in load (+1 kg) induced a power decrease. Nine black Africans (mean age 24.2 +/- 3.3 years) and nine Caucasians (24.7 +/- 4.2 years) (matched for stature and aerobic fitness) participated in the fv exercise test. During the test, PO, blood lactate, and the quadriceps electromyography (EMG) root mean square (Quad RMS) were assessed. Higher blood lactate was observed in Caucasians than in black Africans for POs over the load range from 4 kg up to the maximal power. However, PO and Quad RMS values were similar in Caucasians and black Africans. They also had similar lean leg volume (LLV) and consequently produced similar PO/LLV and Quad RMS/LLV values. Overall, our results suggest that Caucasians and black Africans matched for stature, VO(2max), and training background have similar PO and Quad RMS values, but different blood lactate concentrations during brief, intermittent, intense exercise performed on a cycloergometer

Effects of prior exercise on force-velocity test performance and quadriceps EMG

This study investigated the effects of prior exercise on performance during a subsequent force-velocity (FV) exercise test. After determination of the individual maximal aerobic power (MAP) during maximal graded exercise testing, fifteen trained male subjects (age: 25 ± 3 y) were randomly assigned to perform the FV exercise test without prior exercise (NPE) or preceded by prior exercise (PE) (10 min at 60 % of MAP, followed after 1-min rest interval by four intervals of 30-s cycling at 100 % MAP with 15-s rest intervals, then 10 min recovery). Blood samples were drawn at rest, and then for each work load at the 3rd minute of recovery. Skin temperature (Tsk) from the rectus femoris and heart rate (HR) were measured continuously during prior exercise, the FV test, and during the 5-min recovery period at the end of each FV test. The Root Mean Square (RMS) of the surface electromyogram (EMG) signals obtained from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) were calculated during each sprint for each FV test. The lactate increase for each load (ΔLa) during the FV test was significantly less following PE than NPE. However, the lactate concentration (La) was significantly higher in the FV test following PE than NPE. There was an improvement in power output during the first two sprints (2 and 4 kg) following PE compared to NPE. There was also a more pronounced decrease in VL, VM, and RF RMS in PE compared to NPE. Our results showed that the first few sprints may provide sufficient prior exercise for the FV test. The higher lactate concentration following PE than NPE, despite no difference in maximum power, suggests that a large lactate accumulation may not be detrimental to FV test performance. However, a greater lactate concentration and Tsk may be associated with a decrease in RMS

Aptitudes cardiorespiratoires à l'exercice et fonction musculaire périphérique chez des enfants infirmes moteurs d'origine cérébrale

Les enfants IMOC présentent des aptitudes cardiorespiratoires diminuées à l'exercice, associées à une force maximale isométrique et une endurance musculaire du quadriceps déficiente par rapport aux enfants sain