A MECHANICAL MODEL FOR LEG STIFFNESS AND AVERAGE AND MAXIMUM FORCE ESTIMATIONS IN SPRINTERS

In running the leg's complex system of muscle, tendon and ligament has a spring like behaviour, which can be considered as a single non-linear spring. A single spring-mass model, consisting of a single non-linear leg spring and a mass in running has been considered to estimate the leg stiffness and muscle force in running remarkably well. The model has shown that in running, the stiffness of the leg spring is proportional to the squared cosine of the leg angle relative to the axis perpendicular to ground and also to the displacement of CG (centre of gravity) and finally to the squared vertical velocity component. The variation of the leg stiffness with CG displacement and the angle swept by the leg spring, when sprinters alter their supporting leg from braking phase to propulsive phase, at their maximal speed. A 20m-switch pad in conjunction with an electronic interface and a laptop computer has been used for touch down time measurement. The angle swept by sprinter's leg was determined by video filming. The proposed mathematical model enabled us to estimate leg stiffness and muscle force satisfactorily

DETERMINATION OF ARMS AND LEGS CONTRIBUTION TO PROPULSION AND PERCENTAGE OF COORDINATION IN BACKSTROKE SWIMMING

In the present study, the Indirect Measurement of Active Drag (IMAD) was used to study the contribution of the legs and arms to propulsion in backstroke swimming. Contrary to MAD (Measuring of Active Drag) system, the IMAD can be used for all strokes and enabled us to study the backstroke and to estimate not only the percentage of legs’ contribution to propulsion but also the arms contribution and whereas the percentage of swimmers’ arms and legs co- ordinations. The method revealed that there were good correlations between arms and full strokes forces and velocities. The swimmers’ mass did not much correlate with swimmers’ velocities but with the forces

A NEW BIOMECHANICAL ASPECT FOR ASSESSING MECHANICAL PARAMETERS IN LONG JUMP

INTRODUCTION: In order to make a comparison between Iranian jumpers with the world champions, in the absence of Motion Analyzer, we made a Biomechanical Model with which we were able to assess the mechanical parameters such as : final run-up velocity, initial take off velocity and angle , initial velocity components, time of the last touch - down, force applied by jumpers and their height of flight. This could be feasible just by measuring run-up time tr, flight time tf, total flight distance R and the total time of run-up, and flight , tt. METHOD: The subjects were ten male jumpers belonging to Iranian track team. Each jumper, ran his run-up distance which with measured run-up time and mechanics formulae, we could obtain the final run-up velocity. By measuring the total range of flight and its time of flight and combining the formulae , we got for the angle of take off : q = Arctan gt2 f / 2R Knowing q, R and tf , we can get , not only the flight mechanical parameters but also the force applied for jumping. This force can be achieved by measuring the total run-up and flight time and make the difference with the sum of the tr and tr separately measured, and then dividing difference momentum to difference of time , we obtain with F = dp/dt the force in question. In fact, this force is applied by the jumper, in order to change the direction of the final run-up velocity, which is horizontal to a velocity with an angle of q, previously obtained. RESULTS: Most of our jumpers could reach velocities more than 10 m/s as final run-up velocity, but at take off they lost about 2 m/s, although their take of velocity components are comparable. CONCLUSION: Our biomechanical model can easily be , in the absence of expensive 2D or 3D, used and would help to achieve effective mechanical parameters. [table

A NEW SIMPLE BIOMECHANICAL METHOD FOR INVESTIGATING HORSES JUMPING KINEMATICS

The purpose of present study was to use a simple mathematical model to investigate horses’ kinematical parameters such as initial CG angle and velocity components, horizontal distance to fence and to leading hind limb at take-off and jump height during jumping a spread fences of 100 and 140 cm high. A digital cam- coder was used (25 Hz) along with Ulead Studio program in order to get time and related distance data. The total jump distance and time of flight for each horse were measured to 10-2m and 10-2s respectively. Biomechanical formulae have been established in order to evaluate the kinematic parameters. The results obtained by this simple method agreed well with the results obtained by other researchers with sofisticated method. The simplicity of the method may permit the riders and trainers to to improve fast the jumping techniques for successful jumping

CORRELATIONS BETWEEN JUMP HEIGHT AND VELOCITY COMPONENTS OF DIFFERENT APPROACH STRIDES IN POWER SPIKING

The aim of present work was to find correlations between approach velocity components and jump height in power spike. Fourteen top elite volleyball players have been served for this study. A Mikro-Mak Motion Analyzer with Win-Analyze program has been used for 2D study. A Kodak video camera with 240 frames per second has also been used to better trace the markers on the shoulder, hip, knee, ankle, and toe. The program enabled us to find out the displacement and velocity of all parts and especially the hip in order to estimate subjects CG velocity components. Our findings showed that there were significant correlations between vertical component and jump height in all strides; short (r=0.71, ), normal (r=0.70, ), and long strides (r=0.88, ). The highest correlation was achieved for long stride, where the CG of players is more displaced horizontally as well as vertically. There were no meaningful correlations between Height jump and horizontal velocity component and deviation

DRAG FORCE ,RELATED TO BODY OIMENSIONS IN BUITERFLY SWIMMING

During four last decades, a great deal of attention has been given to the presupposed relationship between body dimensions and hydrodynamic resistance related drag for actively swimming subjects to anthropometrical variables. The development of a new indirect method of determining active drag (IMAD) warranted a reevaluation of this relationship, which was the aim of present study. Twenty female swimmers with different body shape and experience ranging from 13 to 19 years and in mass from 42 to 68 kg have volunteered in this study. They were requested to swim a 10-m distance as fast as they could and three trials with enough rest in between. They have also been instructed to glide at the end of 10-m swim, by whistling. until still position. The time of 10-m swim and the glide distance were measured with reasonable precision. The variables were mass, height. upper limit length, arm, forearm, hand lengths, and torso, arm, and head circumferences. Very high and significant correlations were found between active drag and anthropometric variables. The drag force for advanced swimmers was ranging from 26 to 36 N, while for other swimmers was ranging from 16 to 32 N. The results achieved from this study agreed well with the results obtained by other researchers using direct measurement systems

AN ELECTRONIC TELEMETRY SYSTEM USING A LAPTOP FOR INVESTIGATION OF KINEMATIC AND KINETIC STUDIES OF SPRINTERS

The purpose of this study was to design an electronic telemetry system in order to investigate kinematics and kinetic characteristics of sprinters. Ten FM transmitters with the frequency range of 98-108 MHz have been designed and constructed for time interval capturing in conjunction with an adequate interface including a FM receiver and pulse shaping, and a laptop computer. With the help of C program, we could profit the internal clock of the computer. A video camera at 30 Hz was also used to capture data for investigation of reaction, stopping and take-off mean forces of each leg. The kinematics curves showed that how the sprinters ran a 100m run, when they reached their maximum speed, how long they could maintain this speed, and when the acceleration begins to be negative, while the kinetic results showed that in maximum speed, the longer the stride length is, the larger are the forces

KINEMATIC AND KINETIC COMPARISONS BElWEEN SPOT, CROSSOVER AND UPWARD JUMP THROWINGS IN HANDBALL

Throwing is one of the most important skills in handball in which two basic factors are of importance with regard to the efficiency of shots Le. accuracy and velocity. A 2Dimensional analysis of different throws Le. on the spot, with a cross-over step, and with upward jump has been undertaken. Eighteen high-performance handball players took part in this study. The average values of basic parameters of physical characteristics of subjects were: 80.2 ± 6.1 Kg (body mass), 184.8 ± 4 cm (body height), and 19.79 ± 0.63 years of age. The main aim of present study was to establish a valuable kinematic and kinetic comparison between different types of throws in handball. Statistically significant differences were found between maximal ban velocity during throws with cross-over step and ball velocity during other analyzed throws. In addition to the high velocity in this throw, the energy and power consumptions were also higher in magnitude comparing with other throws. The results obtained by this study agreed well with the results reported by other researchers

A NEW MATHEMATICAL SIMULATION TO STUDY FLIP TURN CHARACTERISTICS IN FRONT CRAWL SWIM

Swim turns represent an integral factor in determining the final outcome of a swimmer race. The aim of present study was to provide a comprehensive mathematical modelling for achieving kinematic parameters in freestyle flip (pike) turn. In proposed model all attempts have been applied to find out what swimmers should do in order that the turns are accomplished in shorter time. This new mathematical model has been adopted to flip turn but can also be adopted to tuck turn with minor change in calculations. Theoretical considerations suggest that faster upper limbs rotation could lead to a torso pressure gradient, which would induce significant axial flow along the upper limbs toward the torso. Our results demonstrate a better reality of the predicted rotational of body during front crawl swim flip turn. In this new model, we hypothesize that in flip turn the body can be considered and simulated as three thin hinged prisms; upper body, thigh, and shank

A BIOMECHANICAL APPROACH TO DRAG FORCE AND HYDRODYNAMIC COEFFICIENT ASSESSMENTS

A fundamental theoretical analysis for estimation of kinematic and kinetic characteristics of swimmers was developed. The purpose of the study was to present a simple method for data collection, to establish simple formulae for determining the swimmers characteristics and to evaluate the validity and accuracy of the model estimation against the other methods such as; direct measurements; Measurement of Active Drag, and added drag provided by hydrodynamic body. The active drag force was estimated during maximal swimming in front crawl but the method can also be applied for other strokes. The swimmers performed three 10-meter trials with enough rest in between and with zero initial velocity over which average velocity was calculated. By this method the maximum speed of swimmers in 10m swim could also be estimated. The swimmers began to swim from still position after whistling, and stopped swimming at the end of 10m again by whistling, and kept gliding until still position. The time of 10m swim and the glided distance were measured with reasonable precision and then used in the established formulae for determining the velocity, acceleration, and drag force. One of the elite swimmers was requested to perform swimming with different speeds in order to achieve different characteristic curves for proposed model