Introduction to Sports Biomechanics: Analysing Human Movement ...

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EXPERIMENTAL PROCEDURES IN ELECTROMYOGRAPHY THE ANATOMY OF HUMAN MOVEMENT The results of an electromyographic investigation can only be as good as the preparation of the electrode attachment sites. Although skin resistance ceases to be a problem if active electrodes are used, many EMG studies in sports biomechanics currently use passive surface electrodes, and good surface preparation is, therefore, still beneficial. The location of the electrodes is the first consideration. For the muscles covered by their recommendations, the advice on electrode placements in the SENIAM report are well illustrated and simple (see Box 6.5 for a few examples). The separation of the electrodes was discussed above. For muscles not covered by those recommendations, simple advice is that: The two detector electrodes – or the detector pair – should be placed over the mid-point of the muscle belly. The orientation of the electrode pair should be on a line parallel to the direction of the muscle fibres (for example Box 6.5). If the muscle fibres are neither linear nor have a parallel arrangement, the line between the two electrodes should point to the origin and insertion of the muscle for consistency. The following are good experimental practice for skin preparation to improve the electrode-to-skin contact, thereby reducing noise and artefacts: The area of the skin on which the electrodes are to be placed is shaved if necessary. The attachment area is then cleaned and degreased using an alcohol wipe, the alcohol being allowed to evaporate before the electrodes are attached to the skin. None of the procedures used historically, requiring abrasion with sandpaper or a lancet to scratch the skin surface, is recommended by SENIAM; such procedures raise ethical, or health and safety, issues at many institutions and are not necessary if the amplifier input impedance conforms to that recommended in the previous section. Preferentially, the electrodes should be pre-gelled; if they are not then, after the electrodes have been attached, electrode gel should be injected into the electrodes; any excess gel should be removed. It should not normally be necessary to check the skin resistance; however, if using older equipment, a simple DC ohmmeter reading of skin resistance should be taken. The resistance should be less than 10 kΩ and, preferably, less than 5 kΩ. If the resistance exceeds the former value, the electrodes should be removed and the preparation repeated. The reference electrode, also known as the earth or ground electrode, should be placed on electrically inactive tissue near the site of the recording electrodes or electrode pair. These sites are specific to each electrode (see examples in Box 6.5) and are usually on a bony prominence. 265
INTRODUCTION TO SPORTS BIOMECHANICS BOX 6.5 SOME ELECTRODE PLACEMENTS (ADAPTED FROM SENIAM) Biceps brachii Starting posture: Seated on a chair; elbow at a right angle; palm facing up. Electrode location: On a line between the medial aspect of the acromion process and the cubit fossa at 1/3 of the distance from the latter (Figure 6.22(a)) in the direction of the muscle fibres. Reference electrode: On or around the wrist. Clinical test: With one hand under the elbow, flex the elbow slightly below, or at, a right angle with the forearm supinated, and press against the forearm to extend the elbow. Triceps brachii – long head Starting posture: Seated on a chair; shoulder about 90° abducted; elbow flexed at a right angle; palm facing down. Electrode location: Midway along a line between the posterior crest of the acromion process and the olecranon process at two-finger widths medial to that line (Figure 6.22(b)) in the direction of the muscle fibres. Reference electrode: On or around the wrist. Clinical test: Extend the elbow while applying pressure that would tend to flex it. Rectus femoris Starting posture: Seated on a table; knees slightly flexed; upper body slightly bent backwards. Electrode location: Midway along the line from the anterior superior iliac spine to the superior aspect of the patella (Figure 6.22(c)) in the direction of the muscle fibres. Reference electrode: On or around the ankle or on the spinous process of the seventh cervical vertebra. Clinical test: Extend the knee – with no rotation of the thigh – against pressure. Biceps femoris Starting posture: Lying prone with thighs on table; knees flexed by less than 90° from fully extended position; thigh and shank both slightly rotated externally. Electrode location: Midway along the line from the ischial tuberosity to the lateral epicondyle of the tibia (Figure 6.22(d)) in the direction of that line. Reference electrode: On or around the ankle or on the spinous process of the seventh cervical vertebra. Clinical test: Extend the knee against pressure applied to the leg proximal to the ankle. 266
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Introduction to Sports Biomechanics
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First edition published 1997 This e
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Contents List of figures x List of
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Study tasks 216 Glossary of importa
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FIGURES 1.26 Underarm throw - femal
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FIGURES 5.9 Typical path of a swimm
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Tables 2.1 Examples of slowest sati
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Preface Why have I changed the cove
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Introduction MISSING TEXT The first
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INTRODUCTION principal movements in
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INTRODUCTION TO SPORTS BIOMECHANICS
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Figure 2.2 ‘Principles’ approac
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Figure 2.13 Identifying critical fe
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Page 237 and 238: INTRODUCTION TO SPORTS BIOMECHANICS
Page 265 and 266: Figure 6.8 Main skeletal muscles: (
Page 287: INTRODUCTION TO SPORTS BIOMECHANICS
Page 305 and 306: INDEX 282 balls air flow past 173 b
Page 307 and 308: INDEX 284 energy 219 kinetic 219 mi
Page 309 and 310: INDEX 286 isokinetic contraction 24
Page 311 and 312: INDEX 288 muscle length-tension rel
Page 313 and 314: INDEX 290 three-dimensional 146-7,
Page 315: INDEX 292 validity 220 vantage poin
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