Adam Czaplicki

Estimation of the muscle force distribution in ballistic motion based on a multibody methodology

This work presents a general three-dimensional multibody procedure for studying the human body motion with emphasis on the locomotion apparatus. The methodology includes a three-dimensional biomechanical model, data acquisition techniques and an inverse dynamics approach. The biomechanical model is based on a multibody formulation using natural coordinates and consists of 16 anatomical segments modeled by 33 rigid bodies for a total of 44 degrees-of-freedom. The action of the muscles is introduced in the equations of motion of the multibody model by means of driver actuators defined as kinematic constraints. By associating a Lagrange multiplier to each muscle actuator the muscle forces became coupled with the biomechanical model through the Jacobian matrix of the underlying multibody system. A Hill type muscle model is used to calculate individual muscle forces. The model for the muscle apparatus comprises 43 muscle groups for each leg, which use the full three-dimensional lines of action for these muscles in their geometric description. The problem of the redundancy of the forces on the musculoskeletal structure is solved by using inverse dynamics and static optimization methods. In the process of describing the methodology the benefits of modeling in natural coordinates are highlighted. The methodology developed is demonstrated through its application to a case of ballistic motion, represented by the take-off to an aerial trajectory in order to estimate the joint torques and the muscle force distribution in the supporting leg. The time characteristics of the resultant net torques at the basic joints of the supporting leg and the time-varying muscle force patterns are presented and discussed. The results obtained are explained in terms of their relevance to the activity under study.

THE EFFECTS OF SINGLE VERSUS REPEATED PLYOMETRICS ON LANDING BIOMECHANICS AND JUMPING PERFORMANCE IN MEN

The aim of this study was to examine the chronic effects of single and repeated jumps training on vertical landing force (VGRF) and jump height in untrained men. The VGRF and jump height were compared after a six-week plyometric training programme containing single and repeated jumps, together with two additional parameters: landing time (LT) and range of the knee flexion during landing (KF). Thirty-six untrained physical education students with a plyometric training background were randomly assigned to a single jump group (SJG, n =12), repeated jumps group (RJG, n =12), and control group (CON, n =12). The SJG performed only single jumps, the RJG executed repeated (consecutive) jumps, whereas the CON did not perform any exercises at all. A countermovement jump (CMJ), repeated countermovement jumps (RCMJ), and a drop jump (DJ) were tested before and after the training. Only the RJG showed a significantly reduced VGRF (p < 0.05) in all tests. Both plyometric groups significantly improved (p < 0.05) their jump height in all tests. The LT was significantly greater in the RJG, compared to the SJG, in all tests. The KF was also significantly (p < 0.05) greater in the RJG than in the SJG for CMJ and RCMJ. The results suggest that repeated jumps are beneficial for simultaneous landing force reduction and jumping performance enhancement.

Contact modeling and inverse dynamics identification of the handspring front somersault in pike position

Handspring front somersaults are explosive and exciting events consisting of several distinct ballistic motion and support phases, in which the gymnast contacts the springboard/mat and the table, respectively, with his feet and hands. The purpose of this article is to develop an effective formulation for the inverse dynamics simulation of all the vaults that are suitable for analyses in two dimensions. A planar model of a jumper composed of 16 rigid segments connected by 15 hinge joints is used in the computations. The determinate inverse dynamics formulation, developed in Cartesian coordinates of the segments, allows for the explicit estimation of the resultant muscle torques in the joints and external reactions (up to three components) during the analyzed vaults. By using a projection method, the analysis is then confined to the lower limbs. A computational scheme for the indeterminate inverse dynamics is proposed to distribute the previously assessed net torques in the limbs into the respective muscle forces based on static optimization solution. The reaction forces in the lower limb joints are finally determined following the projection-based formulation. Some numerical results of the inverse dynamics simulation of the handspring front somersault in pike position are reported.

Effects of Assisted and Traditional Drop Jumps on Jumping Performance

The purpose of the present study was to evaluate the effects of assisted and traditional drop jumps on fast stretch-shortening cycle exercises in collegiate athletes. Participants were selected into one of three groups: 1) the assisted drop jump (n=11); the traditional drop jump (n=11); and 3) the control (n=11). The assisted drop jump training involved drop jumps (DJs) with assistance of tubing, whereas the traditional DJ training was performed without any assistance. Prior to and at the completion of 5-week training programs, DJs from heights of both 30 (DJ30) and 60 cm (DJ60) were conducted to determine jump height, drop jump reactivity coefficient, contact time and peak ground reaction force. Both the assisted DJ and traditional DJ training programs resulted in significant (p< 0.05) improvement in jump height, DJ reactivity coefficient and decreased contact time for DJ30. Although both the assisted DJ and traditional DJ modes also increased jump height and DJ reactivity coefficient for DJ60, an enhancement of the assisted DJ training in DJ reactivity coefficient was significantly greater compared to the traditional DJ training. In addition, the assisted DJ mode allowed for a significant reduction of ground reaction force, while the traditional DJ did not change the ground reaction force. The results of this study support the inclusion of assisted DJ training into jumping sports like basketball, volleyball, and track and field jumps. Our results further suggest that incorporating assisted DJ training may be appropriate for highly trained adult athletes due to jumping performance improvement and impact landing forces reduction simultaneously.

Biomechanical Assessment of Strength and Jumping Ability in Male Volleyball Players During the Annual Training Macrocycle

Abstract Introduction. The aim of the study was to determine the changes in the peak torque of the knee extensors and flexors of the dominant lower limb, the shoulder internal and external rotators of the dominant upper limb, and the shoulder extensors and flexors of the dominant upper limb as well as the changes in jump height in volleyball players during the annual training macrocycle. Material and methods. The study involved 13 volleyball players from a Polish second-league team. The measurements were performed five times: before the preparation period (T1), at the beginning of the competitive season (T2), in the middle (T3) and at the end of the first competition period (T4), and after the competitive season (T5). The torque of the knee muscles and shoulder rotators was measured in isokinetic conditions, and the torque of the shoulder extensors and flexors was assessed in isometric conditions. Jumping ability was tested using a piezoelectric platform. Results. We observed statistically significant differences (p < 0.05) in jump height and relative peak torque between the measurements, except for the torque of the shoulder external rotators and flexors. The results of multiple factor analysis based on 5 sets composed of 5 strength variables revealed differences between subjects and measurement sessions. Conclusions. The results obtained indicate that strength and jumping ability should be assessed regularly during the competitive season. The findings of the study suggest that it is necessary to modify the training methods used during the preparation period and individualize the training in the final phase of the competition period.

Biomechanical Assessment of Motor Abilities in Male Handball Players During the Annual Training Macrocycle

Abstract Introduction. The aim of the study was to determine the torque of the knee extensors and flexors of the lead lower limb, the torque of the shoulder extensors and flexors of the dominant upper limb, and the torque generated by the muscles of the kinematic chain going from the trail lower limb to the hand of the dominant limb in male handball players during the annual training macrocycle. Changes in jump height and throwing velocity were also investigated. Material and methods. The study involved 13 handball players from a Polish second-league team. The measurements were performed four times: at the beginning of the preparation period, at the beginning of the season, at the end of the first part of the season, and at the end of the second part of the season. Torque was measured in isokinetic and isometric conditions. Jumping ability was tested using a piezoelectric platform, and throwing velocity was measured with a speed radar gun. Results. The study found statistically significant differences between the relative torque values of the knee extensors (p < 0.002) and flexors (p < 0.003) of the lead leg measured in isokinetic conditions between the first three measurements and the final one. Isokinetic measurement of the torque of the muscles of the kinematic chain going from the trail leg to the hand of the dominant arm decreased in a statistically significant way at the end of the season. As for the results of the measurement of the torque of the shoulder extensors and flexors in static conditions, no statistically significant differences were observed between the four measurements. However, statistically significant differences were noted in jumping ability and throwing velocity in the annual training macrocycle. Conclusions. The results of the study indicate that there is a need to perform regular assessments of players’ strength and jumping ability during the competition period. There is a need to modify the training methods used during the preparation period and in the second part of the season as well as to individualise training at the end of the competition period.

Inverse Simulation Study of Trampoline-Performed Somersaults*

Front and back somersaults on the trampoline are modeled. The developed mathematical models are used to solve the inverse dynamics problem, in which the applied moments of muscle forces at the joints that result in an actual (recorded) motion are determined. The nature of the stunts, the way the human body is maneuvered and controlled can be studied. The calculated torques are then used as control signals for the dynamic simulation. This provides a way to check the inverse dynamics procedures. The influence of typical control errors on somersault performance can be studied as well. Some examples of numerical calculations are reported.