load of competitive matches. Therefore, the aims of this study were to: (1) confirm the reliability of these measurements in the context of relevant analytical goals and (2) compare the locomotive and physiological responses to modified physical contact during the rugby league movement simulation
Jonathan P. Norris, Jamie Highton, and Craig Twist
Mark Waldron, Jamie Highton, and Craig Twist
This study assessed the reliability of a rugby league movement-simulation protocol, relative to interchanged players (RLMSP-i).
Fifteen male participants completed 2 trials of the RLMSP-i, separated by 1 wk. The RLMSP-i comprised low- to moderate-intensity running, interspersed by high-intensity sprinting and tackling activity, based on global positioning system (GPS) data recorded during Super League performances.
The lowest coefficient of variation (CV ± 95% CI) was observed for total m/min during both interchange bout 1 (1.1% ± 0.2%) and bout 2 (1.0% ± 0.2%). The percentage of heart rate peak and ratings of perceived exertion demonstrated CVs of 1.2–2.0% and 2.9–3.5%, respectively. The poorest agreement between trials was found for blood lactate concentration (16.2% ± 2.8%). In no case was the CV smaller than the smallest worthwhile change, yet in every case the moderate changes were larger than the CV.
The RLMSP-i’s reliability is sufficient to enable the detection of moderate changes in various performance and physiological measurements that accurately simulate some, but not all, aspects of rugby league matches.
Tom G. Welter and Maarten F. Bobbert
It has been shown in previous research that the initial phase of EMG for a punching movement remained almost unchanged regardless of whether an external force was applied to the arm. The purpose of the present study was to explain this finding with the help of simulations. A two-dimensional model of me arm actuated by 6 Hill-type muscles was used to simulate a punching movement in the horizontal plane from a prescribed starting position with 90° elbow flexion. Input to the model was the stimulation of me muscles, and output were, among others, muscle forces and segmental accelerations. A genetic algorithm was used to determine the muscle onset times mat minimized movement duration and targeting error. In a subsequent forward simulation, the optimized muscle onset times for an unloaded punching movement were superimposed on the isometric stimulation necessary to hold me arm in the starting position while an external force was applied to the arm. The resulting movement was only slightly different from the unloaded movement. It appeared that because of the low level of isometric muscle force prior to the movement, and the high level of stimulation during the movement, muscle force was increased at a rate mat was almost independent of the prior force level. These results confirmed the suggestion that the initial phase of EMG in ballistic movements is more related to the rate of change of force than to the absolute force level. It is hypothesized mat this may simplify the task of the nervous system in the choice of initial muscle activity in ballistic arm movements because no adjustments to varying external forces are required.
Thomas Mullen, Craig Twist, and Jamie Highton
. Furthermore, physiological and perceptual responses can be measured regularly in a controlled environment, which would not be feasible in competition. Accordingly, in rugby league, various iterations of the Rugby League Movement Simulation Protocol (RLMSP) have successfully been used to examine changes in
L.J. Richard Casius, Maarten F. Bobbert, and Arthur J. van Soest
Mathematical modeling and computer simulation play an increasingly important role in the search for answers to questions that cannot be addressed experimentally. One of the biggest challenges in forward simulation of the movements of the musculoskeletal system is finding an optimal control strategy. It is not uncommon for this type of optimization problem that the segment dynamics need to be calculated millions of times. In addition, these calculations typically consume a large part of the CPU time during forward movement simulations. As numerous human movements are two-dimensional (2-D) to a reasonable approximation, it is extremely convenient to have a dedicated, computational efficient method for 2-D movements. In this paper we shall present such a method. The main goal is to show that a systematic approach can be adopted which allows for both automatic formulation and solution of the equations of kinematics and dynamics, and to provide some fundamental insight in the mechanical theory behind forward dynamics problems in general. To illustrate matters, we provide for download an example implementation of the main segment dynamics algorithm, as well as a complete implementation of a model of human sprint cycling.
Thomas Mullen, Craig Twist, Matthew Daniels, Nicholas Dobbin, and Jamie Highton
. Waldron M , Highton J , Twist C . The reliability of a rugby league movement-simulation protocol designed to replicate the performance of interchanged players . Int J Sports Physiol Perform . 2013 ; 8 ( 5 ): 483 – 489 . 10.1123/ijspp.8.5.483 23238019 24. Kempton T , Sirotic AC