WHY DO YOU JUMP HIGHER WITH A FLEXIBLE VAULTING POLE?

A computer simulation study revealed why athletes are able to vault higher with a flexible fibre glass pole than with the old-style bamboo poles and steel poles. The crucial feature of the pole vault model was the inclusion of the energy losses associated with the pole plant and takeoff. The simulations showed that a flexible pole reduces the energy dissipated in the vaulter's body when the pole is planted into the takeoff box (as had been suggested previously). Also, a flexible pole lowers the optimum takeoff angle, and so the athlete loses less energy in jumping off the ground. This pole vault model could be combined with previous models to produce a computer simulation program that would allow sports scientists to provide correct biomechanical advice to athletes and coaches

Superconducting re-entrant cavity transducer for a resonant bar gravitational radiation antenna

Copyright @ American Institute of PhysicsA 10‐GHz superconducting niobium re‐entrant cavity parametric transducer was developed for use in a cryogenic 1.5‐tonne Nb resonant bar gravitational radiation antenna. The transducer has a very high electrical Q (6×105 at 4.2 K), and was operated at high cavity fields without degrading the Q. A very high electromechanical coupling between the antenna and the transducer was therefore achieved. The highest coupling attained, constrained by the available pump power, was 0.11. If the transducer were to be operated in conjunction with a wideband impedance matching element, an antenna bandwidth comparable to the frequency of the antenna would be attained. The temperature dependence of the Q of the transducer was in good agreement with theory. At temperatures above about 6 K the Q was degraded by the increase in the BCS surface resistance, while at lower temperatures the Q was limited by radiative losses

Assessing rugby place kick performance from initial ball flight kinematics: development, validation and application of a new measure

The appropriate determination of performance outcome is critical when appraising a performer’s technique. Previous studies of rugby place kicking technique have typically assessed performance based on ball velocity, but this is not the sole requirement. Therefore, a mathematical model of rugby place kick ball flight was developed to yield a single measure more representative of true performance. The model, which requires only initial ball flight kinematics, was calibrated and validated using empirical place kick data, and found to predict ball position with a mean error of 4.0% after 22 m of ball flight. The model was then applied to the performances of 33 place kickers. The predicted maximum distance, a single performance measure which accounted for initial ball velocity magnitude and direction, and spin, was determined using the model and was compared against ball velocity magnitude. A moderate association in the rank-order of the kicks between these two measures (ρ = 0.52) revealed that the relative success of the kicks would be assessed differently with each measure. The developed model provides a representative measure of place kick performance that is understandable for coaches, and can be used to predict changes in performance outcome under different ball launch or environmental conditions

Determination of the gravitational constant at an effective mass separation of 22 m

Copyright @ 1988 The American Physical SocietyA vacuum balance that compares the weights of 10-kg stainless-steel masses suspended in evacuated tubes at different levels in a hydroelectric reservoir is being used to measure the gravitational attractions of layers of lake water up to 10 m in depth. The mean effective distance between interacting masses in this experiment is 22 m, making it the largest-scale measurement of G using precisely controlled moving masses. The experiment extends laboratory-type measurements into the range previously explored only by geophysical methods. Assuming purely Newtonian physics the value of the gravitational constant determined from data obtained so far is G=6.689(57)×10-11 m3 kg-1s-2, which agrees with laboratory estimates. The data admit at a 0.6 standard deviation level the parameters of non-Newtonian gravity inferred from geophysical measurements in mines and a tower. These measurements push the estimated ranges of non-Newtonian forces down to a scale accessible to our reservoir experiment, so that experimental improvements now at hand may provide a critical test of non-Newtonian effects

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

Improvement in 100-m sprint performance at an altitude of 2250 m

© 2016 by the author. A fair system of recognizing records in athletics should consider the influence of environmental conditions on performance. The aim of this study was to determine the effect of an altitude of 2250 m on the time for a 100-m sprint. Competition results from the 13 Olympic Games between 1964 and 2012 were corrected for the effects of wind and de-trended for the historical improvement in performance. The time advantage due to competing at an altitude of 2250 m was calculated from the difference between the mean race time at the 1968 Olympic Games in Mexico City and the mean race times at the low-altitude competition venues. The observed time advantage of Mexico City was 0.19 (±0.02) s for men and 0.21 (±0.05) s for women (±90% confidence interval). These results indicate that 100-m sprinters derive a substantial performance advantage when competing at a high-altitude venue and that an altitude of 1000 m provides an advantage equivalent to a 2 m/s assisting wind (0.10 s). Therefore, the altitude of the competition venue as well as the wind speed during the race should be considered when recognizing record performances