Resistive Eccentric Exercise: Effects of Visual

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1 Resistive Eccentric Exercise: Effects of Visual Feed back on Maximum Moment of Knee Extensors and Flexors Eleftherios Kellis, BScl Vasilios Baltzopoulos, Ph D, M Phil, BSc2 Copyright All rights reserved. sokinetic dynamometers are widely used in the assessment and improvement of muscular function for both rehabilitation and training purposes (1,lO). Their widespread applications relate to their ability to quantify accurately muscular function through the total range of movement at a constant velocity (1). The development of active dynamometers has enabled the isokinetic assessment of the muscular ability to produce tension under eccentric conditions. The tension development during isokinetic eccentric activation is greater compared with other types of muscle action (10). Several factors may influence the accuracy of the moments obtained by an isokinetic dynamometer. The positive effects of knowledge of strength performance during isometric activations are well documented (3,4,13,15). Furthermore, the influence of visual feedback (VF) on isokinetic concentric moments has also been investigated (2,7,9). It was found that VF improves the moment output of both knee flexors and extensors at slow angular velocities (2, 7), whereas there are conflicting results on the influence of VF on moment output at fast angular velocities (2,7,9). In addition, the angle of peak moment is shifted later in the range of motion when VF is implemented at concentric slow angular velocities. whereas the knee flexor to One of the most important features of isokinetic dynamometry is the accurate assessment of muscular function. One of the main factors affecting the accuracy of isokinetic parameters during maximum activation efforts is visual feedback. The purpose of this study was the examination of the effects of visual feedback on maximum moment measurements of the knee extensors and flexors during isokinetic eccentric activations. Twenty-five males performed five maximal efforts at angular velocities of 3O'Ysec and I5Oo/sec with and without visual feedback on a Biodex dynamometer. Visual feedback was provided as real time display of the moment output. A three-factor analysis of variance test revealed significant differences between the moments recorded with visual feedback and the nonvisual feedback maximum moments of knee extensors and flexors at both speeds. The mean extension peak moments at 30Ysec and 150'Ysec under visual feedback condition were approximately 7.2 and 6.4% higher than the nonvisual feedback moments, respectively. The increase for the knee flexor moment was 8.7 and 9% for slow and fast speeds, respectively. These findings suggest that visual feedback can improve maximum eccentric output and should be provided during assessment of maximum eccentric strength on an isokinetic dynamometer. Key Words: resistive exercise, eccentric, knee, visual feedback ' Doctoral Student, Department of Movement Science, University of Liverpool, Liverpool, 169 3BX, United Kingdom Reader in Biomechanics, Division of Sport Science, Manchester Metropolitan University, Alsager, United Kingdom extensor ratio is not affected by VF (2) - Most of the research in isokinetic dynamometry has focused on the isokinetic eccentric moment output of the knee flexors and extensors relative to concentric at a particular velocity and over a range of velocities (8,10,14,19,20). In these studies, the presence of VF during testing procedure is not indicated. Information concerning the effects of VF on moment measurements during isokinetic eccentric exercise is very limited (5) and reported significant knee extensor moment improvements when VF was implemented. However, the effect of VF on maximum knee flexor moment has not been examined. Therefore, the purpose of this study was to examine the effects of VF on maximum moments during resisted eccentric knee extension and flexion at slow and fast angular velocities. METHODS Subjects Twenty-five males (age = years; mass = kg; height = m) volunteered to participate in this study after signing informed consent forms. The subjects had no previous musculoskeletal injury of the lower limbs. Volume 23 Number 2 February 1996 JOSPT

2 Visual feedback appears to be a motivating factor for maximum muscular moment exerted. Extension Flexion NVF = Nonvisual feedback. Test I 6.0 t ? TABLE 1. Maximum (i + SDj eccentric moment (Nmj measurements of knee extensors and flexors at two angular velocities during test and retest (N = 13). Copyright All rights reserved. Instrumentation All tests were performed on a Biodex (Biodex Corp., Shirley. NY) dynamometer. The Biodex computer software (V.3.2, Biodex Corp., Shirley, NY) was used for data recording. The system permits isokinetic eccentric movements (maximum angular velocity 150 /sec) and was interfaced to a PC compatible computer. Procedure All subject.. performed a familiarization and warm-up 5 minutes prior to testing. The warm-up consisted of three submaximal and two maximal eccentric repetitions at both testing speeds. The testing protocol consisted of five maximal reciprocal rep etitions of the knee extensors and flexors at the "eccentric/eccentric" mode of the dynamometer. The test was performed at angular velocities of 30 /sec and 150 /sec with and without VF. The total range of motion for all tests was 80" (from 10 to 90" of knee flexion). The testing order was randomized. A 5minute rest was given between each of the four different tests. During the testing, the subject was seated on the Biodex in a position of approximately 70" of hip flexion. The subjects were secured with two velcrob straps crossed on the chest, one strap was secured over the waist, and one stabilized the thigh. The subjects were also instructed to cross their arms on the chest. The resistance pad was placed proximal to the ankle joint. The axis of rotation of the lever arm was carefully aligned with the medial femoral epicondyle of the knee. The system was calibrated an hour before each testing session according to the Biodex clinical manual. he "scaling" mode on the Biodex test protocol was set at approximately 500 Nm in order to permit the subjects to observe the differences between the moment graphs from one VF repetition to another during the test. The gravitational moment was estimated automatically using the Biodex computer software. During the testing, the computer monitor was positioned 1 m from the subject at eye level. During the VF tests, real time display of the gravity-corrected moment output was provided. All subjects were given written instructions to work as hard as possible at each test. During VF efforts, the sub jects were instructed to observe the monitor and try to overcome the moment graph from the previous repetition whereas the monitor was covered (blank) during non VF (NVF) efforts. The maximum moment from the five repetitions was used for further analysis. Thirteen subjects were retested 1 week after the first test at approximately the same time to establish the reliability of eccentric moment measurements. The retest consisted of three submaximal and two maximal eccentric repetitions followed by five maximal reciprocal repetitions of the knee extensors and flexors with VF at both angular velocities. Data Analysis One-way repeated measures analysis of variance (ANOVA) was used for the determination of the testretest reliability coefficients for knee extension and flexion at each angular velocity. The reliability coeffkients were calculated using the formula proposed by Thomas and Nelson (18). A three-factor (2 X 2 X 2) ANOVA design was used to examine the differences between the VF and NVF maximum moments at two different velocities (30 /sec and 150 / sec) and different muscle groups (knee flexors-extensors). The level of significance was set at p < RESULTS The maximum test-retest moments are presented in Table 1. The reliability coefficients ranged from 0.93 to 0.98, indicating appropriate test-retest reliability (Table 2). The mean and standard deviations of the moment measurements ranged from to Nm for the knee extensors and from to Nm for the flexors and are presented in Table 3 and graphically in the Figure. There was a significant F ratio for VF (F,,,, = 77.02, p < 0.05), muscle group Extension Flexion TABLE 2. Reliability coefficients of maximum eccenhic moments at slow and fast angular velocities (N = 13). JOSPT Volume 23 Number 2 February 1996

3 Copyright All rights reserved. FIGURE. Maximum moment fnm) of knee extensors and flexors under different visual feedback WF) and angular velocity conditions (N = 25, NVF = Nonvisual feedback). 3O0/sec 1 50 /sec VF NVF VF NVF Extension t t t t 48.1 Flexion t NVF = Nonvisual feedback. TABLE 3. Maximum (,f t SD) eccentric moment (Nm) measurements of knee extensors and flexors at two angular velocities under different testing conditions (N = 25). Source of Variation df SS MS F VF speed Direction VF x Speed VF X Direction Speed X Direction VF x Speed x Direction - * F ratio significant at the a = 0.05 level. TABLE 4. Repeated measures analysis of variance table used to determine differences between maximum moments during knee extension and flexion at two speeds under different conditions (N = 25). (F,,,, = , p < 0.05). and speed (F,,,, = 11.50, P < 0.05) (Table 4). DISCUSSION The results of this study demonstrate that VF improves gravitycorrected eccentric moment output of knee flexors and extensors at both slow and fast angular velocities. This is in agreement with other findings (5) during eccentric knee extensions at 3O0/sec and 12O0/sec. There are no previous studies examining the effects of VF on isokinetic eccentric moment of the knee flexors. Hald and Bottjen (9) reported significant improvement of concentric strength of both muscle groups of 3.0 and 6.0% at 30 /sec and 180 / sec, respectively. Baltzopoulos et a1 (2) found significant increases of 8.0 and 6.0% for knee extensors and flexors only at a slow speed, whereas Figoni and Morris (7) reported an increase of 12.0% for both muscle groups at slow speed only (15O/sec). Carlson et a1 (5) found increases of 14 and 9% at slow and fast eccentric angular velocities, respectively. The effects of VF on isometric knee extension or elbow flexion moments were found to be greater (3,4,13). The present findings indicate that the mean eccentric extension peak moments at 30 /sec and 15O0/sec under VF condition are approximately 7.2 and 6.4% higher than the NVF moments, respectively. Similarly, the average peak moments of flexors with VF at slow and fast velocities were 8.7 and 9.0% higher than the NVF moments, respectively (Table 3). Baltzopoulos et al (2) found differences between VF and NVF moments, ranging from 1.4 Nm for knee flexors to 17 Nm for knee extensors, whereas Hald and Bottjen (9) found differences ranging from 2.1 to 5.1 ft-lbs. The absolute differences between VF and NVF moments in this study were significantly greater, ranging from 13 Nm for knee flexion to 23 Nm for knee extension. Carlson et al (5) reported greater differences Volume 23 Number 2 February 1996 JOSPT

4 Copyright All rights reserved. ranging from 50.9 N to 36.2 N for eccentric and concentric knee extension moments, respectively. This indicates the significant effect of VF on eccentric moment measurements due to the higher magnitude of eccentric relative to concentric or isometric moments. The assessment of the actual maximum performance is very important in physical therapy and training. Westing et al (20) found significantly greater isokinetic eccentric moments obtained during electrical stimulation efforts compared with maximal voluntary trials. It was concluded that maximum voluntary eccentric tests do not indicate actual maximum performance. The results of this study demonstrate that the presence of visual information during testing affects the mechanism responsible for force development under eccentric isokinetic conditions. The behavior of the central and peripheral nervous.system may be different when feedback is present or not. Control of voluntary movements is a complex process that involves a variety of structures and organs. Many forms of feedback are used for the control of human motion (1 6). Types of information that play an important role in this process are the feedback provided by muscle spindles, tendon organs, and joint receptors, and information provided by sensor organs (11,12). The proprioceptors of the involved musculotendinous unit5 and joints provide information for controlling the movement and tend to reduce the amplitude of the stimulus that led to their activation (6,11,12). This neural mechanism may be activated during eccentric activations when the force tends to exceed a limit to prevent injury of the muscular and joint structures (1 7). As a consequence, fewer motor units are activated, resulting in lower force development (20). Therefore, maximum strength capability should be higher compared with the recorded This neural mechanism may be activated during eccentric activations when the force tends to exceed a limit to prevent injury of the muscular and joint structures. strength during both VF and NVF conditions. Information provided by sensor organs is also used for planning and controlling the movement of the limb relative to the environment ( 1 1). During NVF isokinetic testing, the subjects had visual information on the direction of the movement at a constant angular velocity. On the contrary, during VF testing, information was provided on strength and direction of the movement. It a p pears that the quantity of visual information contributes to higher strength output. Furthermore, the time available for the central nervous system to process and respond to visual information can range from 160 to 180 msec (16). The time required for the completion of the 80" angular motion was approximately 2.7 sec at 30 /sec and 750 msec at 150 /sec. Consequently, the percentage of movement time available for the sub jects to react to visual information was approximately 93 and 73% at the fast and slow speed, respectively. This indicates that there was enough time for the subjects to respond to visual stimuli and use this information to improve their performance. The learning or motivational effects of feedback are not always the same. The type of feedback provided, the interval between trials, the effects of other types of motivation that may be provided simultaneously, and the amount and quality of information are some of the factors that affect its effectiveness (12.16). The subjects in this study had no verbal encouragement that could affect their performance. Further research should compare the effect5 of verbal encouragement and VF on maximum isokinetic moments. All environmental conditions were adjusted in order to eliminate all possible factors that could distract the attention of the subjects. Furthermore, the real time display of the moment output was presented over the entire monitor without additional information. The curve from the previous to the next repetition was superimposed using different colors from repetition to repetition. This allowed easier and direct comparisons between the repetitions during the test. The results of this study indicated that VF does not affect the eccentric moment-velocity relationship. The peak eccentric flexor and extensor moments decreased from slow to fast angular velocity under both VF and NVF conditions. A decrease of 5.0% for both conditions was o h served. A neural inhibition mechanism that prevents the increase of maximum eccentric moment as velocity increases may be a factor responsible for this phenomenon (10,l 7,l9, 20). The above findings indicate a significant effect of VF on different isokinetic parameters. Consequently, the use of VF as a standard procedure in isokinetic testing protocols is recommended. Furthermore, the use or not of VF during the assessment of isokinetic maximum eccentric m e ment should always be reported to allow valid comparisons between different studies. CONCLUSION The results of this study demonstrate that real time display of muscular moment output generates greater maximum moments of both knee JOSPT Volume 23 Number 2 Fehnlary 1W6 123

5 Copyright All rights reserved. muscle groups at fast and slow eccentric angular velocities relative to the nonvisual feedback condition. Consequently, visual feedback appears to be a motivating factor for maximum muscular moment exerted during isokinetic eccentric activations. JOSPT REFERENCES 1. Baltzopoulos V, Brodie DA: lsokinetic dynamometry: Applications and limitations. Sports Med 8: , Baltzopoulos V, Williams JG, Brodie DA: Sources of error in isokinetic dynamometry: Effects of visual feedback on maximum torque measurements. J Orthopspom Phys Ther 13: , Berger RA: Effects of knowledge of isometric strength during performance on recorded strength. Res Q 38: , Brown BS, Daniel M, Gorman OR: Visual feedback and strength improvement. Natl Strength Cond Assoc J 22-24, Carlson A), Bennet G, Metcalf 1: The effects of visual feedback in isokinetic testing. Isokin Exerc Sci 2:60-64, Enoka RM: Neuromuscular Basis of Kinesiology, Publishers, Figoni SF, Morris AF: Effects of knowledge of results on reciprocal, isokinetic strength, and fatigue. J Orthop Sports Ph ys Ther 6: , Ghena DR, Kurth AL, Thomas M, Mayhew /: Torque characteristics of the quadriceps and hamstrings muscles during eccentric and concentric loading. J Orthop Sports Phys Ther l4:l49-154, Hald RD, Bottjen El: Effects of visual feedback on maximal and submaximal isokinetic test measurements of normal quadriceps and hamstrings. J Orthop Sports Phys Ther 6: , Kellis E, Baltzopoulos V: lsokinetic eccentric exercise: A review. Sports Med 19(3): , Lee DN: The functions of vision. In: Pick HL, Saltzman E (eds), Modes of Perceiving and Processing Information, pp Hillsdale, NJ: Lawrence Erlbaum Associates, Magill RA: Motor Learning. Concepts and Applications (3rd Ed), Dubuque, /A: William C. Brown Publishers, Manzer CW: The effects of knowledge of output on muscular work. J Exp Psychol 18:80-90, Perrin DH: Isokinetic Exercise and Assessment, Publishers, Pierson WR, Rasch PJ: Effects of knowledge of results on isometric strength scores. Res Q 35: , Schmidt R: Motor Control and Learning, Publishers, Stauber Wl: Eccentric action of muscles: Physiology, injury, and adaptation. Exerc Sport Sci Rev 17:157-l85, Thomas JR, Nelson JK: Research Methods in Physical Activity (2nd Ed), Publishers, Westing SH, Seger JY, Karlson E, Ekblom B: Eccentric and concentric torque-velocity characteristics of the quadriceps femoris muscle in man. Eur J Appl Ph YS 58: , I Westing SH, Seger JY, Thorstensson A: Effects of electrical stimulation on eccentric and concentric torque-velocity relationships during knee extension in man. Acta Ph ysiol Scand 140: 17-22, 1990 Volume 23 Number 2 Febn~a~ JOSF'T