On the Effectiveness of Force Application in Guided Leg Movements

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<ul><li><p>This article was downloaded by: [McGill University Library]On: 08 October 2014, At: 02:26Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK</p><p>Journal of Motor BehaviorPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/vjmb20</p><p>On the Effectiveness of Force Application in GuidedLeg MovementsCaroline A. M. Doorenbosch a , Dirkjan H. E. J. Veeger a , Jan Peter van Zandwijk a &amp; GerritJan van Ingen Schenau aa Institute of Fundamental and Clinical Human Movement Studies Vrije UniversiteitAmsterdam , The NetherlandsPublished online: 01 Apr 2010.</p><p>To cite this article: Caroline A. M. Doorenbosch , Dirkjan H. E. J. Veeger , Jan Peter van Zandwijk &amp; Gerrit Jan van IngenSchenau (1997) On the Effectiveness of Force Application in Guided Leg Movements, Journal of Motor Behavior, 29:1, 27-34</p><p>To link to this article: http://dx.doi.org/10.1080/00222899709603467</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (the Content) containedin the publications on our platform. However, Taylor &amp; Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.</p><p>This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms &amp; Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions</p><p>http://www.tandfonline.com/loi/vjmb20http://dx.doi.org/10.1080/00222899709603467http://www.tandfonline.com/page/terms-and-conditionshttp://www.tandfonline.com/page/terms-and-conditions</p></li><li><p>Journal of Motor Behavior, 1997, Vol. 29, No. 1, 27-34 </p><p>On the Effectiveness of Force Application in Guided Leg Movements </p><p>Caroline A. M. Doorenbosch DirkJan (H. E. J.) Veeger Jan Peter van Zandwijk Gerrit Jan van lngen Schenau Institute of Fundamental and Clinical </p><p>Human Movement Studies Vrije Universiteit Amsterdam, The Netherlands </p><p>ABSTRACT. In guided leg movements (e.g., in cycling or wheel- chair propulsion), the kinematics of a limb are determined by the object on which a force is applied. As a consequence, the force direction can vary and may deviate from the movement direction, that is, the effective direction. In the present study, the relation of effective force application and maximal power output was exam- ined. Subjects (n = 5 ) performed guided leg tasks on a special dy- namometer. They were instructed to exert a maximal force against a moving forceplate in the direction of the movement, as if they were pushing the plate away. Three different movement directions were tested: perpendicular to the horizontal, rotated 30" backward, and rotated 30" forward. For each trial, force and position data were recorded. The results of the experiments showed that in the extreme movement directions (both 30' conditions), the force vec- tor deviated significantly from the direction of the movement. Apparently, maximal power output was achieved with a low force effectiveness in these tasks. The background of this phenomenon was revealed by using the kinematics of one of these tasks in a simulation model. The stimulation level of 6 leg muscles was opti- mized toward a maximal effective force component (a) without a constraint on the direction of the total force or (b) with a constraint on the force component perpendicular to the effective force. The muscle stimulation pattern that resulted in the highest effective force coincided with a low force effectiveness. Apparently, this is a prerequisite for maximal power transfer from the muscles to the plate in these guided movements. </p><p>Key words: contact control, force control, force effectiveness, humans, leg tasks </p><p>he problem of how the central nervous system controls T all the degrees of freedom of the musculoskeletal sys- tem so that motor behavior can be harmonious and func- tional is a major issue in the various disciplines that consti- tute the human movement sciences. In spite of the seemingly infinite number of possibilities, different </p><p>(skilled) subjects execute a particular motor task with little variation (Ingen Schenau, 1989). This suggests that there are structural or functional constraints that limit the set of possible movement and activation patterns. </p><p>The so-called guided movements are a specific type of complex movements. In guided movements, the trajectory of the foot or hand is determined by the object on which a force is applied, as, for example, is the case during cycling and wheelchair propulsion. In contrast to a free movement along a predefined trajectory (Miller, Gielen, Theeuwen, &amp; Doorenbosch, 1992; Theeuwen, 1994), the direction of the pushing force during a guided movement is not prescribed. </p><p>It has often been argued that, from a mechanical point of view, the force should be directed in the direction of the movement because, in that case, the total force will con- tribute to the work needed to accomplish the task. Deviation from this direction would mean that part of the exerted force does not contribute to the external work. The latter is con- sidered to be ineffective (e.g., Davis &amp; Hull, 1981; Ericson &amp; Nisell, 1988; Faria, 1992; Zschorlich, 1989). </p><p>Remarkably, measurements of forces in handrim wheel- chair propulsion (Roeleveld, Lute, Veeger, Gwinn, &amp; Woude, 1994; Veeger, Woude, &amp; Rozendal, 1991a, 1991b) and in cycling (Coyle et al., 1991; Davis &amp; Hull, 1981; Ericson &amp; Nisell, 1988; Faria, 1992; Hull &amp; Davis, 1981; Ingen Schenau, Boots, Groot, hackers, &amp; Woensel, 1992; </p><p>Correspondence address: Caroline A. M . Doarenbosch, D- epartment of Rehabilitation, Free University Hospital, Vrije Uni- versiteit, PO. Box 7057, 1007 MB Amsterdam, The Netherlands. E-mail address: cdoor@knoware.nl </p><p>27 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>McG</p><p>ill U</p><p>nive</p><p>rsity</p><p> Lib</p><p>rary</p><p>] at</p><p> 02:</p><p>26 0</p><p>8 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>C. A. M. Doorenbosch, H. E. J. Veeger, J. P. van Zandwijk, &amp; G. J. van lngen Schenau </p><p>Lafortune &amp; Cavanagh, 1983; Redfield &amp; Hull, 1986a, 1986b) have shown that subjects do not apply the propul- sive force in line with the trajectory of the hand or foot. In cycling, the ratio of effective force to total force, referred to as pedal force effectiveness (Faria, 1992), did not appear to be larger than 76% for elite cyclists. Faria (1992) used the term wasted force suggesting that the force component in the direction of the crank axis is wasted. However, in exper- iments aimed at increasing the effectiveness of the exerted force by using feedback during cycling, higher power out- puts on the pedal did not occur (Faria, 1992; Lafortune &amp; Cavanagh, 1983). </p><p>As argued before (Ingen Schenau, Koning, &amp; Groot, 1994), the force component in the direction of the crank axis is not necessarily associated with any waste of meta- bolic energy. Rather, pedal force effectiveness is related to the force and work distribution among the hip and knee extensors. Apparently, muscle coordination during these guided movements results in a seemingly ineffective force component on the pedal or wheelchair rim. </p><p>Our aim in this study was to illustrate why the phenome- non of such an ineffective force is the most optimal with respect to the goal of the (standardized) guided leg tasks, that is, maximal power output. We will demonstrate that power output is not related to force effectiveness. </p><p>To get insight into the underlying muscle coordination pat- tern, one of the tasks was simulated with a model of the lower extremity by optimizing the muscle stimulation of each mod- eled muscle to a maximal effective force component. </p><p>Method </p><p>Subjects </p><p>Five healthy subjects (1 woman and 4 men; aged 29 k 2 years; height, 1.81 f .03 m; weight, 74.8 f 6.4 kg) partic- ipated in the experiments. </p><p>Protocol </p><p>The subjects were seated in a dynamometer on a bike sad- dle, such that the right foot was placed on the forceplate (Fig- ure 1). The dynamometer consisted of a rail along which a forceplate could move in a straight line over 1 m, placed within a frame. The rail could be mechanically rotated about an axis at the lower side of the rail as well as translated over a double bar at the bottom of the frame (see arrows in Figure l), which allowed adjustment of different movement direc- tions. The movement of the forceplate was controlled by a servo-motor (SEM, MT30U4-36, London, Great Britain) via a ball-rotation spindle, using a motion control software pack- age (GALL DMC-710, Sunnyvale, CA). </p><p>Subjects were first placed in a reference position, with the hip angle at 1 15" and a knee angle of 100" (for both joints, 180" is full extension). The ankle angle differed, depending on the position of the forceplate. Before the actu- al experiments started, anthropometric parameters were obtained from each subject. </p><p>FIGURE 1. Outline of the dynamometer. The right foot of the subject was placed on a forceplate, which moved in an up- and downward direction along a rail. The rail could be rotated and translated (see arrows) so that different move- ment directions could be obtained. </p><p>During the experiments, subjects were instructed to exert a maximal force in the movement direction of the moving forceplate, as if they were pushing the plate away. No movements of the foot relative to the forceplate were allowed. Three different movement directions were imposed: one in which the forceplate moved away from the subjects in a downward neutral direction ($ = 0), one in which the rail was placed in a 30" forward position (Q = -30), and one in which the rail was rotated 30" backward ($ = 30) (see Figure 2). In each movement direction, the tasks were executed under isokinetic conditions at four different velocities of the forceplate: 10, 20, 30, and 40 c d s , result- ing in 12 different tasks. Additionally for each subject, 1 of the 12 tasks was randomly chosen and repeated five times. </p><p>For all trials, the forceplate was positioned 20 cm higher than the standard position. A 1.25s period was used for placing the foot on the forceplate and exerting a force on a stationary forceplate. Thereafter, the subjects had to exert a maximal force while the forceplate moved downward with a fixed velocity until it was 20 cm below the standard posi- tion. For all tasks, a trajectory of comparable joint angles was passed. Total movement time for the isokinetic trials differed for each velocity. </p><p>For each protocol, we used computer-generated audible signals to indicate the start of the trial, initiation of the movement, and end of the trial. These signals were simulta- </p><p>28 Journal of Motor Behavior </p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>McG</p><p>ill U</p><p>nive</p><p>rsity</p><p> Lib</p><p>rary</p><p>] at</p><p> 02:</p><p>26 0</p><p>8 O</p><p>ctob</p><p>er 2</p><p>014 </p></li><li><p>Force Effectiveness </p><p>30 0 - 30 </p><p>FIGURE 2. Illustration of the three movement directions of the forceplate used in the experiments. Vertical position is indicated at O", backward at -30". and forward at 30". Sub- jects were instructed to exert a maximal force while the forceplate moved in the direction of the arrow. </p><p>neously recorded as block pulses and used for synchroniza- tion in time. On each trial, joint position and reaction force were recorded. </p><p>Position and Force Markers (13 mm diameter) placed on the skin corre- </p><p>sponded with the fifth metatarsophalangeal joint, heel, lat- eral malleolus, knee joint (on the lateral collateral ligament at the height of the knee cleft), greater trochanter, top of iliac crest, and neck (at the height of the fifth cervical ver- tebra). Two markers were placed on the forceplate and three on the dynamometer frame as a reference orthogonal coor- dinate system. </p><p>The displacements of the right leg were collected at 60 Hz, using a motion analysis software system (VICON, Oxford Metrics Ltd., Oxford, Great Britain). With the VICON system, three-dimensional coordinates were calcu- lated. After proper scaling, the absolute coordinates of the anatomical landmarks in the sagittal plane were obtained and subsequently low-pass filtered (zero phase lag, net cut- off frequency 2 Hz). We chose this low cut-off frequency to minimize quantitization noise; it was adequate in these rela- tively slow isokinetic movements because the joint angles and their derivatives did not contain higher frequencies than 1 Hz. The coordinates defined four body segments: foot, lower leg, upper leg, and a part of the upper body, which we used to calculate joint angles as well as joint velocities (Lanczos, 5-point differentiation filter; Lees, 1980). To determine the positions of the mass centers of the different body segments, we combined the coordinates with anthro- pometric measurements and data from Clauser, McConville, and Young (1969) and Winter (1 979). </p><p>The reaction forces of the right foot were recorded by means of strain gauges built in a forceplate. The analog force signals were amplified, low-pass filtered (75 Hz, 24 dB/oct), and sampled (600 Hz, 12 bits) by the VICON sys- tem. From the distribution of the separate force compo- nents, the center of pressure of the force vector was calcu- lated. Combined with the points of reference of the position data, the center of application was related to the position of the foot. </p><p>We applied Newtonian equations of motion to a linked segment model of the human body in order to calculate the net torques about the hip and knee joints (Elftmann, 1939). Hip and knee extension torques were defined as positive. </p><p>Data Analysis </p><p>For each trial of each subject, the values of several vari- ables (e.g., reaction force) were calculated over the period in which the foot displacement was within 5 cm of the ref- erence position. Next, the mean values of this time period were calculated for each trial. Subsequently, for all subjects, these values of the corresponding tasks were averaged. </p><p>To test for possible differences that may have resulted from movement velocity or movement direction, we per- formed a two-way analysis of variance (ANOVA), with repeated measurements (a probability level I .05 was con- sidered to be statistically significant). </p><p>Musculoskeletal Model The musculoskeletal model used for the simulation of a </p><p>guided leg task included two parts: the skeletal and the mus- cular model (MUSK system;...</p></li></ul>


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