The effects of initial conditions and takeoff technique on running jumps for height and distance

This study used a subject-specific model with eight segments driven by joint torques for forward dynamics simulation to investigate the effects of initial conditions and takeoff technique on the performance of running jumps for height and distance. The torque activation profiles were varied in order to obtain matching simulations for two jumping performances (one for height and one for distance) by an elite male high jumper, resulting in a simulated peak height of 1.98m and a simulated horizontal distance of 4.38m. The peak height reached/horizontal distance travelled by the mass centre for the same corresponding initial conditions were then maximised by varying the activation timings resulting in a peak height of 2.09m and a horizontal distance of 4.67m. In a further two optimizations the initial conditions were interchanged giving a peak height of 1.82m and a horizontal distance of 4.04m. The four optimised simulations show that even with similar approach speeds the initial conditions at touchdown have a substantial effect on the resulting performance. Whilst the takeoff phase is clearly important, unless the approach phase and the subsequent touchdown conditions are close to optimal then a jumper will be unable to compensate for touchdown condition shortcomings during the short takeoff phase to achieve a performance close to optimum.     

Determination of subject-specific model parameters for visco-elastic elements

The determination of subject-specific model parameter values is necessary in order for a computer simulation model of human motion to be evaluated quantitatively. This study used an optimisation procedure along with a kinematically driven simulation model of the contact phase in running jumps to determine the elastic parameters of segmental wobbling masses and the foot-ground interface. Kinetic and kinematic data were obtained on running jumps for height and distance performed by an elite male high jumper. Stiffness and damping coefficients of the visco-elastic elements in the model were varied until the difference between simulation and performance was minimised. Percentage differences of 6% and 9% between the simulated and recorded performances were obtained in the jumps for height and distance, respectively. When the parameters obtained from the jump for height were used in a simulation of the jump for distance (and vice versa), there was poor agreement with the recorded jump. On the other hand, a common set of visco-elastic parameters were obtained using the data from both recorded jumps resulting in a mean difference of only 8% (made up of 7% and 10%) between simulation and performance that was almost as good as the individual matches. Simulations were not overly sensitive to perturbations of the common set of visco-elastic parameters. It is concluded that subject-specific elastic parameters should be calculated from more than a single jump in order to provide a robust set of values that can be used in different simulations.     

Maximising somersault rotation in tumbling

Performing complex somersaulting skills during the flight phase of tumbling requires the generation of linear and angular momenta during the approach and takeoff phases. This paper investigates how approach characteristics and takeoff technique affect performance with a view to maximising somersault rotation in tumbling. A five-segment planar simulation model, customised to an elite gymnast, was used to produce a simulation which closely matched a recorded performance of a double layout somersault by the elite gymnast. Three optimisations were carried out to maximise somersault rotation with different sets of initial conditions. Using the same initial linear and angular momentum as the double layout somersault and varying the joint torque activation timings allowed a double straight somersault to be performed with 19% more rotation potential than the actual performance. Increasing the approach velocity to a realistic maximum of 7 ms(-1) resulted in a 42% reduction in rotation potential when the activation timings were unchanged but allowed a triple layout somersault to be performed with an increase of 31% in rotation potential when activation timings were re-optimised. Increasing also the initial angular momentum to a realistic maximum resulted in a 4% reduction in rotation potential when the activation timings were unchanged but allowed a triple straight somersault to be performed with a further increase of 9% in rotation potential when activation timings were re-optimised. It is concluded that the limiting factor to maximising somersault rotation is the ability to generate high linear and angular velocities during the approach phase coupled with the ability to adopt consonant activation timings during the takeoff phase.     

Is a single or double arm technique more advantageous in triple jumping?

Triple jumpers employ either an asymmetrical ‘single-arm’ action or symmetrical ‘double-arm’ action in the takeoff of each phase of the jump. This study investigated which technique is more beneficial in each phase using computer simulation. Kinematic data were obtained from an entire triple jump using a Vicon automatic motion capture system. A planar 13-segment torque-driven subject-specific computer simulation model was evaluated by varying torque generator activation timings using a genetic algorithm in order to match performance data. The matching produced a close agreement between simulation and performance, with differences of 3.8%, 2.7%, and 3.1% for the hop, step, and jump phases, respectively. Each phase was optimised for jump distance and an increase in jump distance beyond the matched simulations of 3.3%, 11.1%, and 8.2% was obtained for the hop, step, and jump, respectively. The optimised technique used symmetrical shoulder flexion whereas the triple jumper had used an asymmetrical arm technique. This arm action put the leg extensors into slower concentric conditions allowing greater extensor torques to be produced. The main increases in work came at the joints of the stance leg but the largest increases in angular impulse came at the shoulder joints, indicating the importance of both measures when assessing the impact of individual joint actions on changes in technique. Possible benefits of the double-arm technique include: cushioning the stance leg during impact; raising the centre of mass of the body at takeoff; facilitating an increase in kinetic energy at takeoff; allowing a re-orientation of the body during flight.     

Coping with perturbations to a layout somersault in tumbling

Tumbling is a dynamic movement requiring control of the linear and angular momenta generated during the approach and takeoff phases. Both of these phases are subject to some variability even when the gymnast is trying to perform a given movement repeatedly. This paper used a simulation model of tumbling takeoff to establish how well gymnasts can cope with perturbations of the approach and takeoff phases. A five segment planar simulation model with torque generators at each joint was developed to simulate tumbling takeoffs. The model was customised to an elite gymnast by determining subject specific inertia and torque parameters and a simulation was produced which closely matched a performance of a layout somersault by the gymnast. The performance of a layout somersault was found to be sensitive to the approach characteristics and the activation timings but relatively insensitive to the elasticity of the track and maximum muscle strength. Appropriate variation of the activation timings used during the takeoff phase was capable of coping with moderate perturbations of the approach characteristics. A model of aerial movement established that variation of body configuration in the flight phase was capable of adjusting for takeoff perturbations that would lead to rotation errors of up to 8%. Providing the errors in perceiving approach characteristics are less than 5% or 5 degrees and the errors in timing activations are less than 7ms, perturbations in the approach can be accommodated using adjustments during takeoff and flight.     

Maximising forward somersault rotation in springboard diving

Performance in the flight phase of springboard diving is limited by the amounts of linear and angular momentum generated during the takeoff phase. A planar 8-segment torque-driven simulation model combined with a springboard model was used to investigate optimum takeoff technique for maximising rotation in forward dives from the one metre springboard. Optimisations were run by varying the torque activation parameters to maximise forward rotation potential (angular momentum × flight time) while allowing for movement constraints, anatomical constraints, and execution variability. With a constraint to ensure realistic board clearance and anatomical constraints to prevent joint hyperextension, the optimised simulation produced 24% more rotation potential than a simulation matching a 2½ somersault piked dive. When 2 ms perturbations to the torque onset timings were included for the ankle, knee and hip torques within the optimisation process, the model was only able to produce 87% of the rotation potential achieved in the matching simulation. This implies that a pre-planned technique cannot produce a sufficiently good takeoff and that adjustments must be made during takeoff. When the initial onset timings of the torque generators were unperturbed and 10 ms perturbations were introduced into the torque onset timings in the board recoil phase, the optimisation produced 8% more rotation potential than the matching simulation. The optimised simulation had more hip flexion and less shoulder extension at takeoff than the matching simulation. This study illustrates the difficulty of including movement variability within performance optimisation when the movement duration is sufficiently long to allow feedback corrections.     

Considerations that affect optimised simulation in a running jump for height

This study used a computer simulation model to investigate various considerations that affect optimum peak height in a running jump. A planar eight-segment computer simulation model with extensor and flexor torque generators at five joints was formulated and customised to an elite male high jumper. A simulation was matched to a recorded high jumping performance by varying the activation profiles of each of the torque generators giving a simulated peak height of 1.99m compared to the recorded performance of 2.01 m. In order to maximise the peak height reached by the mass centre in the flight phase, the activation profiles were varied, keeping the same initial conditions as in the matching simulation. Optimisations were carried out without any constraints, with constraints on the angular momentum at take-off, with further constraints on joint angles, and with additional requirements of robustness to perturbations of activation timings. A peak height of 2.37 m was achieved in the optimisation without constraints. Introducing the three constraints in turn resulted in peak heights of 2.21, 2.14 and 1.99m. With all three types of constraints included, the peak height was similar to that achieved in the recorded performance. It is concluded that such considerations have a substantial influence on optimum technique and must be included in studies using optimised simulations.     

A kinematic examination of wild sockeye salmon jumping up natural waterfalls

Wild Alaskan sockeye salmon Oncorhynchus nerka jumping natural waterfalls were observed and photographed to obtain insight into factors important to the fish in dealing with obstacles during their upstream spawning migrations. The fish showed preferences for specific sets of conditions related to heights of waterfalls and depths in pools below waterfalls. Successful jumps appeared to result from running starts, not standing fast starts. The proportion of observed jumps that were successful was low (10% at Brooks Falls, Katmai National Park, Alaska, U.S.A.). Successful jumping behaviour was modelled mathematically and predictions were compared to measured kinematic variables of successful and unsuccessful jumping obtained from analyses of digital video photographs. There were statistically significant differences between the two data sets, but the model identified takeoff velocities and angles, and distances between takeoffs and successful landings as important variables.     

The mechanisms that enable arm motion to enhance vertical jump performance-a simulation study

The reasons why using the arms can increase standing vertical jump height are investigated by computer simulations. The human models consist of four/five segments connected by frictionless joints. The head-trunk-arms act as a fourth segment in the first model while the arms become a fifth segment in the second model. Planar model movement is actuated by joint torque generators. Each joint torque is the product of three variable functions of activation level, angular velocity dependence, and maximum isometric torque varying with joint angle. Simulations start from a balanced initial posture and end at jump takeoff. Jump height is maximized by finding the optimal combination of joint activation timings. Arm motion enhances jumping performance by increasing mass center height and vertical takeoff velocity. The former and latter contribute about 1/3 and 2/3 to the increased height, respectively. Durations in hip torque generation and ground contact period are lengthened by swinging the arms. Theories explaining the performance enhancement caused by arms are examined. The force transmission theory is questionable because shoulder joint force due to arm motion does not precisely reflect the change in vertical ground reaction force. The joint torque/work augmentation theory is acceptable only at the hips but not at the knees and ankles because only hip joint work is considerably increased. The pull/impart energy theory is also acceptable because shoulder joint work is responsible for about half of the additional energy created by arm swings.     

Effect of arm motion on standing lateral jumps

The role of arm swing in jumping has been examined in numerous studies of standing jumps for height and forward distance, but no prior studies have explored its effect on lateral jumping. The purpose of the present study was to investigate the effect of arm motion on standing lateral jump performance and to examine the biomechanical mechanisms that may explain differences in jump distance. Six participants executed a series of jumps for maximum lateral distance from two in-ground force platforms for two jump cases (free and restricted arms) while an eight-camera, passive-reflector, motion capture system collected 3D position data throughout the movements. Inverse kinematics and dynamics analyses were performed for all jumps using three-dimensional (3D) link models to calculate segment angular velocities, joint moments, joint powers, and joint work. Free arm motion improved standing lateral jump performance by 29% on average. This improvement was due to increased takeoff velocity and improved lateral and vertical positions of the center of gravity (CG) at takeoff and touchdown. Improved velocity and position of the CG at takeoff resulted from a 33% increase in the work done by the body. This increase in work in free arm jumps compared to restricted arm jumps was found in both upper and lower body joints with the largest improvements (>30 J) occurring at the lower back, right hip, and right shoulder.     

Optimal compliant-surface jumping: a multi-segment model of springboard standing jumps

A multi-segment model is used to investigate optimal compliant-surface jumping strategies and is applied to springboard standing jumps. The human model has four segments representing the feet, shanks, thighs, and trunk-head-arms. A rigid bar with a rotational spring on one end and a point mass on the other end (the tip) models the springboard. Board tip mass, length, and stiffness are functions of the fulcrum setting. Body segments and board tip are connected by frictionless hinge joints and are driven by joint torque actuators at the ankle, knee, and hip. One constant (maximum isometric torque) and three variable functions (of instantaneous joint angle, angular velocity, and activation level) determine each joint torque. Movement from a nearly straight motionless initial posture to jump takeoff is simulated. The objective is to find joint torque activation patterns during board contact so that jump height can be maximized. Minimum and maximum joint angles, rates of change of normalized activation levels, and contact duration are constrained. Optimal springboard jumping simulations can reasonably predict jumper vertical velocity and jump height. Qualitatively similar joint torque activation patterns are found over different fulcrum settings. Different from rigid-surface jumping where maximal activation is maintained until takeoff, joint activation decreases near takeoff in compliant-surface jumping. The fulcrum-height relations in experimental data were predicted by the models. However, lack of practice at non-preferred fulcrum settings might have caused less jump height than the models' prediction. Larger fulcrum numbers are beneficial for taller/heavier jumpers because they need more time to extend joints.     

Behaviour of triceps surae muscle-tendon complex in different jump conditions

The force-length relationship of the human muscle-tendon complex (MTC) of the triceps surae and the achilles tendon was investigated in various stretch load conditions. Six male subjects performed various vertical jumps with maximal effort: squat jumps (SJ), counter movement jumps (CMJ) and drop jumps (DJ) from a height of 24 cm, 40 cm and 56 cm. The force-length relationship was calculated from the signals of the components of the ground reaction forces and the kinematic data obtained from the high-speed film records. Surface electromyograms (EMG) of the soleus, gastrocnemius and tibialis anterior muscles were also recorded. The force-length diagrams showed individually high sensitivity to the imposed stretch load. In conditions with relatively low stretch load requirements there was a counter-clockwise direction observable, indicating that the energy absorbed during the eccentric, or lengthening phase was lower than the energy delivered during the concentric, or shortening phase. In high load conditions this relationship was reversed indicating a negative energy balance. The EMG-length diagrams of SJ and CMJ consisted of an initial isometric loading of the muscle, followed by a shortening phase with only slightly reduced EMG amplitudes. In DJ, however, the diagrams showed an initial lengthening of the MTC with fairly constant activation amplitudes. After 40 ms an isometric loading of the muscle, lasting for approximately 80 ms, was followed by a shortening phase. It was concluded that segmental stretch reflex activation represented the predominant activation process during the isometric loading phase, to meet the adequate stiffness properties of the MTC.     

Kinetic quantification of plyometric exercise intensity

Ebben, WP, Fauth, ML, Garceau, LR, and Petushek, EJ. Kinetic quantification of plyometric exercise intensity. J Strength Cond Res 25(12): 3288-3298, 2011-Quantification of plyometric exercise intensity is necessary to understand the characteristics of these exercises and the proper progression of this mode of exercise. The purpose of this study was to assess the kinetic characteristics of a variety of plyometric exercises. This study also sought to assess gender differences in these variables. Twenty-six men and 23 women with previous experience in performing plyometric training served as subjects. The subjects performed a variety of plyometric exercises including line hops, 15.24-cm cone hops, squat jumps, tuck jumps, countermovement jumps (CMJs), loaded CMJs equal to 30% of 1 repetition maximum squat, depth jumps normalized to the subject's jump height (JH), and single leg jumps. All plyometric exercises were assessed with a force platform. Outcome variables associated with the takeoff, airborne, and landing phase of each plyometric exercise were evaluated. These variables included the peak vertical ground reaction force (GRF) during takeoff, the time to takeoff, flight time, JH, peak power, landing rate of force development, and peak vertical GRF during landing. A 2-way mixed analysis of variance with repeated measures for plyometric exercise type demonstrated main effects for exercise type and all outcome variables (p ≤ 0.05) and for the interaction between gender and peak vertical GRF during takeoff (p ≤ 0.05). Bonferroni-adjusted pairwise comparisons identified a number of differences between the plyometric exercises for the outcome variables assessed (p ≤ 0.05). These findings can be used to guide the progression of plyometric training by incorporating exercises of increasing intensity over the course of a program.     

The EMG activity and mechanics of the running jump as a function of takeoff angle.

To characterize the electromyographic (EMG) activity, ground reaction forces, and kinematics were used in the running jump with different takeoff angles. Two male long jumpers volunteered to perform running jumps at different approach speeds by varying the number of steps (from 3 to 9) in the run-up. Subject TM achieved a greater vertical velocity of the center of gravity (CG) at takeoff for all approach distances. This jumping strategy was associated with greater backward trunk lean at touchdown and takeoff, a lesser range of motion for the thigh during the support phase, more extended knee and ankle angles at touchdown, and a more flexed knee angle at takeoff. Accompanying these differences in kinematics, TM experienced greater braking impulses and lesser propulsion impulses for the forward-backward component of the ground reaction force. Furthermore, TM activated mainly the rectus femoris, vastus medialis, lateral gastrocnemius, and tibialis anterior, while if rarely activated the biceps femoris from just before contact to roughly the first two-thirds of the support phase. These results indicate that TM used a greater takeoff angle in the running jump because he enabled and sustained a greater blocking effect via the coordination patterns of the muscles relative to the hip, knee, and ankle joints. These findings also suggest that the muscle activities recorded in the present experiment are reflected in kinematics and kinetics. Further, the possible influence of these muscle activities on joint movements in the takeoff leg, and their effect on the vertical and/or horizontal velocity of the jump are discussed.     

The effect of drop jump starting height and contact time on power, work performed, and moment of force

The purposes of this study are (a) to examine the effects of contact time manipulation on jump parameters and (b) to examine the interaction between starting height changes and contact time changes on important jump parameters. Fifteen male athletes performed a series of drop jumps from heights of 20, 40, and 60 cm. The instructions given to the subjects were (a) "jump as high as you can" and (b) "jump high a little faster than your previous jump." Jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The data were divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and groups 2-4 were composed of progressively shorter contact times, with group 5 having the shortest contact times. The jumps of group 3 produced the highest maximum and mean mechanical power (p <0.05) during the positive phase of the drop jumps regardless of starting jump height. The vertical takeoff velocities for the first 3 groups did not show significant (p < 0.05) differences. These results indicate that the manipulation of jump technique plays larger role than jump height in the manipulation of important jump parameters.     

Pelvic kinematic method for determining vertical jump height

Sacral marker and pelvis reconstruction methods have been proposed to approximate total body center of mass during relatively low intensity gait and hopping tasks, but not during a maximum effort vertical jumping task. In this study, center of mass displacement was calculated using the pelvic kinematic method and compared with center of mass displacement using the ground-reaction force-impulse method, in experienced athletes (n = 13) performing restricted countermovement vertical jumps. Maximal vertical jumps were performed in a biomechanics laboratory, with data collected using an 8-camera motion analysis system and two force platforms. The pelvis center of mass was reconstructed from retro-reflective markers placed on the pelvis. Jump height was determined from the peak height of the pelvis center of mass minus the standing height. Strong linear relationships were observed between the pelvic kinematic and impulse methods (R2 = .86; p < .01). The pelvic kinematic method underestimated jump height versus the impulse method, however, the difference was small (CV = 4.34%). This investigation demonstrates concurrent validity for the pelvic kinematic method to determine vertical jump height.     

The reliability of jump kinematics and kinetics in children of different maturity status

The purpose of this study was to determine the reliability of eccentric (ECC) and concentric (CON) kinematic and kinetic variables thought to be critical to jump performance during bilateral vertical countermovement jump (VCMJ) and horizontal countermovement jump (HCMJ) across children of different maturity status. Forty-two athletic male and female participants between 9 and 16 years of age were divided into 3 maturity groups according to peak height velocity (PHV) offset (Post-PHV, At-PHV, and Pre-PHV) and percent of predicted adult stature. All the participants performed 3 VCMJ and HCMJ trials and the kinematics, and kinetics of these jumps were measured via a force plate over 3 testing sessions. In both jumps, vertical CON mean and peak power and jump height or distance were the most reliable measures across all groups (change in the mean [CM] = -5.4 to 6.2%; coefficient of variation [CV] = 2.1-9.4%; Intraclass correlation coefficient [ICC] = 0.82-0.98), whereas vertical ECC mean power was the only ECC variable with acceptable reliability for both jumps (CM = -0.7 to 10.1%; CV = 5.2-15.6%; ICC = 0.74-0.97). A less mature state was "likely" to "very likely" to reduce the reliability of the HCMJ ECC kinetics and kinematics. These findings suggested that movement variability is associated with the ECC phase of CMJs, especially in Pre-PHV during the HCMJ. Vertical CON mean and peak power and ECC mean power were deemed reliable and appropriate to be used in children as indicators of jump and stretch-shortening cycle performance.     

Effects of Isometric Scaling on Vertical Jumping Performance

Jump height, defined as vertical displacement in the airborne phase, depends on vertical takeoff velocity. For centuries, researchers have speculated on how jump height is affected by body size and many have adhered to what has come to be known as Borelli’s law, which states that jump height does not depend on body size per se. The underlying assumption is that the amount of work produced per kg body mass during the push-off is independent of size. However, if a big body is isometrically downscaled to a small body, the latter requires higher joint angular velocities to achieve a given takeoff velocity and work production will be more impaired by the force-velocity relationship of muscle. In the present study, the effects of pure isometric scaling on vertical jumping performance were investigated using a biologically realistic model of the human musculoskeletal system. The input of the model, muscle stimulation over time, was optimized using jump height as criterion. It was found that when the human model was miniaturized to the size of a mouse lemur, with a mass of about one-thousandth that of a human, jump height dropped from 40 cm to only 6 cm, mainly because of the force-velocity relationship. In reality, mouse lemurs achieve jump heights of about 33 cm. By implication, the unfavourable effects of the small body size of mouse lemurs on jumping performance must be counteracted by favourable effects of morphological and physiological adaptations. The same holds true for other small jumping animals. The simulations for the first time expose and explain the sheer magnitude of the isolated effects of isometric downscaling on jumping performance, to be counteracted by morphological and physiological adaptations.     

Muscle performance during maximal isometric and dynamic contractions is influenced by the stiffness of the tendinous structures.

Contractile force is transmitted to the skeleton through tendons and aponeuroses, and, although it is appreciated that the mechanocharacteristics of these tissues play an important role for movement performance with respect to energy storage, the association between tendon mechanical properties and the contractile muscle output during high-force movement tasks remains elusive. The purpose of the study was to investigate the relation between the mechanical properties of the connective tissue and muscle performance in maximal isometric and dynamic muscle actions. Sixteen trained men participated in the study. The mechanical properties of the vastus lateralis tendon-aponeurosis complex were assessed by ultrasonography. Maximal isometric knee extensor force and rate of torque development (RTD) were determined. Dynamic performance was assessed by maximal squat jumps and countermovement jumps on a force plate. From the vertical ground reaction force, maximal jump height, jump power, and force-/velocity-related determinants of jump performance were obtained. RTD was positively related to the stiffness of the tendinous structures (r = 0.55, P < 0.05), indicating that tendon mechanical properties may account for up to 30% of the variance in RTD. A correlation was observed between stiffness and maximal jump height in squat jumps and countermovement jumps (r = 0.64, P < 0.05 and r = 0.55, P < 0.05). Power, force, and velocity parameters obtained during the jumps were significantly correlated to tendon stiffness. These data indicate that muscle output in high-force isometric and dynamic muscle actions is positively related to the stiffness of the tendinous structures, possibly by means of a more effective force transmission from the contractile elements to the bone.