Petar Bačić

Biomechanical Differences in the Sprint Start Between Faster and Slower High-Level Sprinters

Abstract The purpose of this study was to examine the kinematic and kinetic differences of the sprint start and first two steps between faster and slower high-level sprinters. Twelve male sprinters were dichotomized according to personal best 60- and 100-m times. Each participant performed five starts under constant conditions. An eight-camera system was used for 3-D kinematic analysis. Dynamic forces at the start were determined with starting blocks mounted on bipedal force plates. Measures of front and rear block total force, front and rear block maximal force, time to front and rear block peak force, total force impulse, total horizontal and vertical impulse, front and rear block force impulse, time of block clearance, block leaving velocity and block leaving acceleration were collected. Between-group comparisons were made using independent samples t tests (p < 0.05) and by calculating effect sizes (Cohen’s d). Spearman’s correlation coefficients were used to examine the relationships between sprint start kinematics, kinetic measures and sprint performance. Significant between-group differences were observed in rear block total force (p = 0.0059), rear block maximal vertical force (p = 0.0037) and total force impulse (p = 0.0493). Only front block total force significantly correlated with 100 m sprint performance in both the slower and faster groups (r = 0.94 and 0.54, respectively; p = 0.05). Our findings suggest that faster sprinters show enhanced sprint start motor performance with greater force development than slower sprinters.

Effect of glenohumeral forward flexion on upper limb myoelectric activity during simulated mills manipulation; relations to peripheral nerve biomechanics

BackgroundIt is generally accepted that muscles may activate via the common nociceptive flexion reflex (NFR) in response to painful stimuli associated with tensile or compressive forces on peripheral nerves. Following the basic assumption that the radial nerve may be stressed around the elbow during the execution of the Mills manipulation, t wo positions considered to have different mechanical effects on the radial nerve and the brachial plexus were tested in order to i) explore whether muscles are activated in certain patterns with concomitant changes in nerve tension, ii) establish whether muscle responses can be modified with mechanical unloading of the brachial plexus.MethodsMuscle responses were quantified bilaterally in eight subjects (N = 16) during Mills Manipulation (MM) pre-manipulative positioning and a Varied position that putatively produces less mechanical tension in the brachial plexus. End range pre-manipulative stretch was used in order to simulate the effects of Mills manipulation. Electromyographic signals were recorded with a 16 channel portable EMG unit and correlated with kinematic data from three charge-coupled device adjustable cameras which allowed for precise movement tracking.ResultsCompared with the Standard Mills manipulation position, the Varied position produced significantly reduced myoelectric activity (P ≤ .001) in all test muscles. Additional subjective data support the notion that certain muscle activity patterns were protective.ConclusionIt seems that protective muscles are selectively activated in a specific pattern in order to protect the radial nerve from mechanical tension by shortening its pathway, suggesting integration of muscle and neural mechanisms. Furthermore, the significantly decreased myoelectric activity with reduced mechanical tension in the brachial plexus may help controlling collateral effects of the Mills manipulation itself, making it potentially safer and more specific.

Low extremity body model for large scale purposes

There is a lot of body models used in Biomechanical laboratory worldwide. Some of them are product of particular Research Laboratories but mostly they are bound together with various hardware/software system vendors. Especially wide spread are models for Gait analysis and among them body models for low extremities. Among existing models we can found various advantages and disadvantages. Laboratories choices depend on their major purposes for which they are ground for. Better equipped laboratories can afford use of more complex models for more reliable data. But there are also a lot of practical conditions that influence a particular model choice. Duration of acquisition sequence together with patient preparation can influence the data and also patient readiness to participate in testing. Factors that can prolong testing are number of used markers, model sensitivity on accurate marker placement, furthermore number of direct taken anthropometric variables etc. A Goal of model presented with this paper is in first order its usability for fast gait analysis and especially for sport. Testing with this model can be proceed in short pants and even wearing shoes. In this work, presented model and gait parameters calculated on it will be compared with parameters gathered from the same acquisitions using well known Helen Hayes model. HH model is chosen as one of the most acceptable and practical model today. Use of model presented with this paper asks for two acquisitions sets - static and dynamic set. Dynamic set need only 9 optical marker and static set need additional 14 marker for calculating anthropometric relations. Also there remain 5 anthropometric measures to take directly. Helen Hayes model asks for 15 optical marker for both, static and dynamic acquisition and also 19 directly taken anthropometric measures. Model is very fast for patient testing and optical data reconstruction. Patient has not impression of wearing some technical equipment on himself and also feels free for all kind of complex movement.

A human body model for movement analysis using optoelectronic system

Human motion analysis asks frequently for determination of kinetic and kinematic data. This work proposes method to model human body as a linkage of rigid segments and to compute so called body segment parameters (BSP). Calculated BSP combined with 3D optoelectronic (kinematic) system data allow also kinetic analysis of human motion. Proposed body model is based on Helen-Hayes protocol. Modifications are introduced which makes it more robust to analyze movements where ASIS markers are usually hidden from camera, such as running, jumping etc. Moreover, alternative way of computing anthropometric measurements, needed for computation of BSP, is suggested via additional marker set. It is believed that these extra markers are acceptable compromise which in turn saves preparation time for patient in comparison where anthropometric measurements are obtained with various tape measures and calipers. Ultimate accuracy of inverse dynamic values is highly dependent on accuracy of BSP and 3D reconstruction. The later one is in turn greatly influenced by system calibration, i.e. cameras parameters computation. Another part of this work brings up the issue of calibration. A method to calibrate 3D optoelectronic system was proposed which exploits certain geometric entities defined within it, i.e. it takes advantage of orthogonal calibration tools. Proposed method simplifies typical camera calibration procedure of 3D kinematic systems. Validation of proposed body model has been successfully undertaken by comparing results with widely accepted model which uses Helen-Hayes protocol. Additionally validation is preformed through check of segments power calculation in two different ways: direct computation and derivation of total segment energies. Validation of proposed camera calibration has been carried out through reconstruction and analysis of points in space which position, i.e. mutual distance was known with high degree of accuracy in advance. Obtained accuracy is quite comparable, if not even better, with commercially available 3D kinematic systems.