Role of Body and Joint Position on lsokinetic Exercise and Testing

Transcription

1 Journal of Sport Rehabilitation, 1993, 2, O 1993 Human Kinetics Publishers, Inc. Role of Body and Joint Position on lsokinetic Exercise and Testing Donna D. Smith This paper reviews the role of body and joint position during isokinetic exercise and testing. Due to the frequent implementation of isokinetic devices, it is important to examine the methodology of their use. Positioning of the subject and the target joint is a critical component of the methodology. The literature reveals significant relationships between the position of the subject and outcome measures such as torque, agonist-antagonist ratios, peak torque to body weight ratios, and reliability. These relationships are evidenced at the larger joints of the lower extremity, such as the hip, knee, and ankle, in addition to the shoulder joint of the upper extremity. Therefore, it behooves clinicians to review research regarding the effect of varied body and joint positions on outcome measures and regarding the relevance of specific positions to the predetermined goals. The use of isokinetic training and testing devices has become quite commonplace in the clinical setting. Clinicians use these machines daily, often adhering to the manufacturer's recommendations for the procedural setup and implementation. Included in the latter is the aspect of joint and body positioning. In the majority of situations I have witnessed, the arrangement of body and joint position has often adhered more to traditional protocols than to foundations related to functional rehabilitation or premises of improved ability to generate torque. As with any exercise and testing regime, the clinician should attempt to implement a procedure that will provide the appropriate setting from which the appropriate data can be obtained. Whether the setting is appropriate will depend on the sport-specific goals for the athlete and the status of the athlete with regard to physical findings, symptoms presented, and specific diagnosis. Positioning of the patient and positioning of the target joint are important characteristics of the rehabilitation setting to address, as the relationship of joint and body positioning with measurements such as muscular force and joint force has been demonstrated (1, 3, 7, 9, 16, 23, 24). In this paper, information regarding the impact of joint and body position on isokinetic implementation will be presented with specific reference to the Donna D. Smith is a graduate student at the University of Indianapolis Krannert Graduate School of Physical Therapy and is with Physical Performance Center, 5050 N. Clinton, Fort Wayne, IN

2 142 Smith shoulder joint and specific joints of the lower extremity, that is, the knee, hip, and ankle joints. Literature Review The interest in and investigation into the role of body and joint positioning with regard to muscular activity are not new in the field of physical medicine. Historically, researchers have demonstrated a relationship between muscle length, and thus joint positioning, and the muscular tension and force developed. Gossman et al. (6) reviewed the findings of Crawford, Tabary et al., and Williams et al. (2, 20,22), who demonstrated that muscles immobilized in lengthened or shortened positions will respond by generating their peak forces at a point in the range corresponding to their newly adapted resting lengths. Thus, the lengthened muscle will generate peak force at a position of greater length than will the control muscle. Conversely, the muscle immobilized in a shortened position will generate its peak force at a shortened length in comparison to controls. Additionally, Rothstein cited literature confirming the relationship of muscle length and tension development, noting that there is an optimum length for tension development in muscle (18). Other literature supporting the length-tension relationship includes Williams and Goldspink, who concluded that the length of the muscle determines the amount of stretch to the individual sarcomeres, which then impacts the amount of maximum tension produced (22). They additionally reported that the length-tension curves obtained from normal muscles show that maximum tension is developed when the muscle length is approximately 90% of its maximum length. " Gordon et al. emphasized that the greatest tension development occurs at the sarcomere length where maximum single overlap of thin filaments with crossbridges on thick filaments occurs (5). The report additionally notes that when the thick filaments collide with the Z-band there is a sharp decrease in tension development. The impact of body and joint positioning on muscular activity has been attributed not only to the length-tension relationship but also to the influence of primitive neurological reflexes (8, 10, 21). Hellebrandt et al. reported a strong association between neck positioning and activity of the upper and lower extremities in the normal mature human (8). Rotational movements of the head were associated with responses of flexion of the arm on the skull side with pronation, and extension of the arm on the chin side with supination, responding in a manner similar to the asymmetrical tonic neck reflex (ATNR). Hellebrandt et al. (8) also observed that with subjects in the quadruped position, sagittal plane movements of the head resulted in extremity movements corresponding to the symmetrical tonic neck reflex (STNR). Though this latter research has not specifically involved the use of isokinetic devices, it may be important for a clinician to consider when examining the results of an athlete's performance during forceful isokinetic training and testing. Clinicians have additionally acknowledged the relationship of body and joint positioning to the production of joint force during muscular activity (12, 16,17). Joint angles between 60 and 90" at the knee, during isokinetic open kinetic chain testing, have been associated with greater patellofem6ral compression forces

3 lsokinetic Exercise and Testing 143 (12). Therefore, clinicians have been advised to limit the amount of activity performed in this range by individuals experiencing patellofemoral problems. Palmitier et al. and Ohkoshi et al. have further supported the existence of a relationship between joint and body positioning and the production of joint forces (16, 17). Palmitier et al. supported the use of closed kinetic chain exercises for individuals with anterior cruciate ligament deficiency, stating that the closed kinetic chain enhances activation of both the hamstrings and quadriceps musculature and thus decreases the tendency for anterior shear forces at the tibiofemoral articulation. In conjunction with such reports, clinicians have attempted to employ isokinetic devices in the closed kinetic chain (4, 13). Authors additionally recognize the important role of closed kinetic chain positioning in attempts to enhance functional performance. As stated previously, the methodology of isokinetic implementation has often adhered more to the recommendations of the manufacturer and to traditional models than to the status of the athlete and his or her sport-specific needs. Rothstein emphasized that the results of isokinetic testing should not be utilized to infer functional abilities of the athlete (18). This is in part due to the position of the joints during isokinetic training and testing; the extremity is predominately positioned in the open kinetic chain. Due in part to the findings and conclusions of the aforementioned literature, clinicians have sought to examine the impact of body and joint positioning during isokinetic implementation. The predominance of isokinetic-related literature focuses attention on the quantity of torque produced and ratios such as the agonist-antagonist and peak torque-body weight ratios (1, 3, 7, 9, 14, 15, 23, 24). Literature has additionally reported statistics regarding reliability as it relates to isokinetic testing during varying joint and body positions (7, 9, 13). As with any research topic, varying results and conclusions have been reported with regard to the optimal positions for both joint and body during training and testing. Yet important data have been obtained through these research endeavors, and it behooves clinicians to more closely examine this information. The implementation of any training program, whether isokinetic, isotonic, or isometric, should consider the role of body and joint position. Positional Impact-Knee Joint The assessment of hamstring and quadriceps function has often included isokinetic testing. The outcome is often assessed by measurement of the peak torque produced. The traditional isokinetic testing position for assessing hamstring and quadriceps torque is the seated position. However, some clinicians have assessed torque with the trunk positioned supine and prone, and with varying degrees of hip flexion (15, 23, 24). Lunnen et al. studied the effects of four different hip positions on hamstring torque and electromyographic (EMG) activity of the biceps femoris musculature (15). The positions of 0, 45, 90 and 135" hip flexion were implemented during isometric knee flexion at 60". The authors determined that the EMG activity of the biceps femoris at 135" hip flexion was significantly less than at the 0 and 45" hip positions. It was additionally found that significantly less torque was developed at the 0" hip position than at the 90 and 135" hip positions. Further analysis of Lunnen et al.'s study demonstrated that greater EMG activity was necessary for the subjects to develop the same torque with the hip

4 144 Smith flexed at 0" than for any of the other hip positions. Additionally, when EMG activity of the biceps femoris was held constant, the greater degree of hip flexion was associated with greater torque. Worrell et al. also investigated the effects of hip positioning on hamstring and quadriceps torque production in addition to the effect on the hamstringquadriceps ratio (23). The subjects in this study performed concentric contractions of the knee flexors and extensors with the hip at both 110" of flexion (seated) and 10" of hip flexion (supine). Testing velocities of 60, 80, 180, and 240'1s were incorporated. The results of the testing exhibited greater peak torque values for both hamstring and quadriceps musculature in the seated position for all testing velocities. With regard to the hamstring-quadriceps ratio, the data revealed an increase of the ratio with increasing velocities. An increase of the ratio was also found in the seated testing position. In a later study by Worrell et al., both concentric and eccentric hamstring torques were assessed in relation to the prone and supine positions (24). The prone position incorporated approximately 10 to 20" of hip flexion with the head extended approximately 30 to 45O. The results of this unique study found significantly greater torque production for both concentric and eccentric modes of contraction in the prone position versus the supine position. Each of these studies points to the impact of joint and body position on torque production. Inquiry as to why joint and body positions affect torque and tension development is the next logical step in the analysis of the current literature. Authors refer to the length-tension relationship as being a significant factor in the aforementioned results (15, 23). However, the aspects of moment a m and the number of motor units activated as well as the connective tissue contribution also have been cited as factors affecting torque production (15). As previously discussed, it has been proposed that there is a certain length of a muscle, and thus a certain joint position, at which optimal cross-bridging of the actin and myosin filaments will occur. At this optimal muscle length it is believed a muscle can generate its maximum force. In the research previously cited it was evident that higher hamstring torque was generated in the seated position than in the supine position. Worrell et al. proposed that the position of hip flexion between 110 and 130" was optimal for actin and myosin crossbridging for both the knee flexors and extensors (23). Lunnen et al. concurred with this impression (15). However, Lunnen et al. found improved torque of the biceps femoris with the hip at the 135" angle, yet this was simultaneously a position of decreased EMG activity in comparison to the 0" hip flexion position. Therefore, it is important to recognize that torque production cannot be simplistically associated with equivalent EMG recordings. Lunnen et al. theorized that the connective tissue may have been responsible for the increased torque when the tissue was placed in the lengthened position, thereby reducing the need for increased motor unit activation. Thus, when motor unit discharge is reduced, so too will the EMG activity be reduced. Another proposed reason for the presence of decreased EMG activity during the lengthened position of the muscle involves the influence of the Golgi tendon organs (GTO). It is hypothesized by some that when the tendons are in a lengthened position the inhibitory afferent impulses in the region of the tendon decrease the autogenic muscle activity (15). Though the seated position was associated with greater torque output as compared to the supine position, Worrell et al. demonstrated that the prone

5 lsokinetic Exercise and Testing 145 position allowed the hamstrings to generate greater torque than the supine posture. The authors deduced no specific reason for the latter but proposed an interesting hypothesis (24). The hypothesis highlights the role that primitive reflexes may serve in facilitating certain postures and thus certain movement directions. Primitive reflexes such as the tonic labyrinthine reflex (TLR) and the symmetrical tonic neck reflex (STNR) are believed to facilitate flexion of the lower extremities when the body is in the prone position and when the head is in the extended position, respectively. The primitive reflexes become more influential in the mature nervous system at times when the individual is exerting great effort (8). Therefore, clinicians are encouraged to be mindful of the possible influence of the primitive reflexes, which may be integrated in the mature nervous system but are never completely eliminated. In an attempt to assess the role of body and joint positioning as it relates to many functional and sport-specific activities, Levine et al. examined the use of an isokinetic device in the closed kinetic chain for the lower extremity (13). Nineteen healthy subjects performed simultaneous hip and knee extension through a range of 110" hip and knee flexion, while the trunk was positioned in supine. Subjects performed concentric contractions at speeds of 30, 120, and 210 /s. This study specifically investigated the intrarater test-retest reliability of torque measurements, that is, peak torque, average torque, and angle-specific torque. The study found that torque measurements were highly reliable at speeds of 120 and 210 /s. The authors additionally concluded that the intraclass correlation coefficients (ICC) for peak and average torque of all subjects were comparable in reliability to previously cited, open kinetic chain test findings. Though the study provided the measurements of torque for the varying velocities, these should not be simplistically compared to the findings of open kinetic chain testing, because the closed kinetic chain incorporates multijoint activity. The study does, however, suggest that due to high reliability, the closed kinetic chain can be incorporated into isokinetic training and testing and may provide a more functional means of measuring an individual's progress. Positional Impact-Hip Joint The movements of the hip joint have also been isokinetically assessed, though the volume of literature is significantly less than that of the knee joint. The effect of body and joint position on the torque produced at the hip was assessed by Lindsay et al. (14), who specifically assessed the torque produced by the hip internal and external rotators relative to three varying body and joint positions. The study employed the following positions: supine with the knee extended (dynamometer attached to the subject's foot), supine with the knee flexed to 90, and seated with the hip and knee both flexed to 90" (subjects facing the isokinetic unit). Similar to those studies involving the knee joint, the Lindsay et al. study also demonstrated a significant relationship between torque output and testing position. Results indicated that the seated position with 90' of hip and knee flexion produced significantly greater rotational torques (both internal and external) than either of the supine positions. Data additionally determined that torque produced with the knee flexed and the trunk supine proved to be greater than torque generated in the supine position with the knee extended. The length-tension relationship is once again proposed as a specific reason why the external rotation torque improved during the seated position; the position

6 1 46 Smith of hip flexion caused increased length of the external rotators and thus improved their ability to generate torque. The authors attempt to explain the reason for the simultaneous improvement in the internal rotational torque by reviewing the function of the pelvic and hip musculature and more specifically the functions of the gluteus medius and the piriformis muscles. Of specific interest and relevance is the impact of the hip angle on the function of the piriformis and gluteus medius musculature. It is reported that with the hip positioned at 15" of extension, the gluteus medius provides an external rotation force, but as the hip flexes beyond 30" the muscle possesses an internal rotation moment arm. The piriformis is similarly affected by the position of the hip; that is, at 0" of hip flexion the piriformis contributes to external rotation, but at flexion greater than 60" the muscle develops an internal rotation function. Based upon this explanation, the study concluded that the gluteus medius and piriformis musculature contributed to improved internal rotational torque in the seated testing position. The effect of the moment arm is also highlighted by Lindsay et al. with specific attention to the testing position incorporating a supine trunk and an extended knee (14). In this position, the moment arm is obviously decreased in comparison to the alternate testing positions and may contribute significantly to the decreased torque produced. Positional Impact-Ankle Joint To further corroborate the concepts presented thus far, research involving isokinetic assessment of the ankle joint has examined the impact of body and joint position on torque production. Cawthom et al. analyzed the effect of three varying ankle positions on the production of inversion and eversion torque (1). The subjects were positioned with angles of 10" of dorsiflexion, neutral dorsiflexion, and 10" of plantar flexion. In each of these positions the subjects' knees were positioned at 20" with the trunk supine. The position associated with maximal invertor and evertor torque was determined to be that with the ankle positioned in 10" of plantar flexion. The position of 10" of dorsiflexion elicited the lowest torque values for both eversion and inversion. The authors further assessed the invertor-evertor ratio and determined that this did not demonstrate a significant change between the various testing positions. The length-tension relationship is reiterated once more in Cawthom et al.'s study as the authors note that the invertors and evertors simultaneously lengthen during dorsiflexion and shorten during plantar flexion. Thus, the ratio of invertor to evertor torque will not change significantly. Although the muscle length for both invertors and evertors is increased in the dorsiflexed position, it is apparent from Cawthom et al.'s study that the position of 10" of plantar flexion allowed a stronger contraction and greater torque to be produced. This latter position is believed to approximate the midrange position more than the alternate testing positions and may therefore contribute to a more efficient length-tension relationship. Positional Impact-Shoulder Joint Of all the isokinetic-related literature I read, the material discussing the shoulder joint was particularly enlightening. Of special relevance was the concept of appropriate semantics regarding biomechanics of the shoulder joint complex (1 1, 19). For example, the shoulder joint movements are predominately named

7 lsokinetic Exercise and Testing 147 according to their direction in relationship to the trunk. Yet, it seems more appropriate to utilize the proximal skeletal component of the joint as the reference point rather than the trunk of the body. In conjunction with the latter, clinicians are encouraged to review the normal resting position and mechanics of the glenohumeral joint. Authors note that for movements of flexion and abduction in the cardinal planes, the humerus must undergo medial and lateral rotation, respectively. However, once full elevation is achieved, the position of the humerus is similar-that of the medial epicondyle facing forward and slightly medial (7, 9, 1 1, 19). This position correlates with a plane of motion termed the plane of the scapula (POS). Studies have demonstrated that in contrast to movement in the cardinal planes, movement in the POS requires no additional rotation of the humerus in either direction. The POS has been defined as reorientation of the humerus to a position 30 to 45" anterior to the frontal plane. Authors have further noted that movement done in the POS places less stress on the fibers of the inferior joint capsule and enhances glenohumeral joint stability via increased congruency of the joint surfaces (7). Being mindful of this information, various clinicians have investigated the function of the shoulder joint in various planes of movement. Both Greenfield et al. (7) and Hellwig and Perrin (9) examined the impact of shoulder and body position on shoulder internal and external rotation torque values. Both studies compared and contrasted the torque values with reference to movements performed in the scapular plane versus the frontal plane. However, the results of the studies vary to some degree. Greenfield et al. determined external rotational torque to be significantly higher when performed in the POS versus the frontal plane. It was also reported that the reliability correlation coefficient was highest for the external rotation movement in the POS (r =.94). In contrast to Greenfield et al., Hellwig and Perrin found no significant differences between peak rotational torques obtained in the frontal and scapular planes (9). Additionally, Hellwig and Perrin revealed higher reliability correlation coefficient values for movements in the frontal plane (r =.93) versus the scapular plane (r = 35). Although the data vary between these studies, each study should be examined more closely, for it is apparent that their methodologies differed. The most obvious difference is that the subjects were seated during Hellwig and Perrin's study, whereas in Greenfield et al.'s study the subjects were standing with no external stabilization. A second and possibly more important difference between the two studies is the position of the scapular plane. In Hellwig and Perrin's study the scapular plane was defined at 40" anterior to the frontal plane, whereas in Greenfield et al.'s study the position of 30' anterior to the frontal plane was employed. The methodologies of these two studies additionally varied with regard to the manner in which contractions were performed and the amount of time permitted for rest between contractions. Though the relationship of joint position to the quantity of torque produced is an important factor to consider during the rehabilitation of the shoulder joint, it is important to inquire as to whether the joint position enhances more functionally relevant processes. Those authors investigating the impact of the plane of the scapula are credited with acknowledging the importance of the scapular plane with regard to its functional significance.

8 Smith Conclusion In the practice of physical medicine and rehabilitation the use of instrumentation is often employed in order to improve the accuracy and reliability of the clinician's findings. Yet, it is imperative that the practitioner continually question the effectiveness of the tool, that is, whether the tool is measuring what the clinician seeks to know. Thus it is vitally important that the clinician review the needs and goals of the athlete and thus the appropriate setting from which to perform training and testing. For if we are to continue to utilize machinery for our treatment and testing, then we must optimize the conditions and methodology such that the ultimate functional and sport-specific goals can be obtained. The literature reviewed in this report supports the existence of a relationship between body and joint positioning and objective measures of torque, force, EMG activity, agonist-antagonist ratios, and reliability. An important factor to consider is whether these findings are relevant to the needs of the athlete. In many instances, clinicians are seeking to determine the muscle's maximum force ability, so it will be beneficial for the clinician to know which positions will facilitate greater force and torque output. Yet clinicians must additionally consider whether the position of testing and training corresponds well with the established goals and needs of the athlete, as well as his or her present physical status. Ultimately all of these factors should direct the therapeutic approach. References 1. Cawthom, M., G. Cummings, J.R. Walker Jr., and R. Donatelli. Isokinetic measurement of foot invertor and evertor force in three positions of plantarflexion and dorsiflexion. J. Orthop. Sports Phys. Ther. 14(2):75-81, Crawford, G.N.C. The growth of striated muscle immobilized in extension. J. Anat. 114(2): , Currier, D.P. Positioning for knee strengthening exercises. Phys. Ther. 57(2): , Engle, B. Suggestions from the clinic: Clinical use of an isokinetic leg press. J. Orthop. Sports Phys. Ther. Nov./Dec.: , Gordon, A.M., A.F. Huxley, and F.J. Julian. The variation in isometric tension with sarcomere length in vertebrate muscle fibers. J. Physiol. (Lond.) 184: , Gossman, M.R., S.A. Sahrmann, and S.J. Rose. Review of length-associated changes in muscle: Experimental evidence and clinical implications. Phys. Ther. 62(12): , Greenfield, B.H., R. Donatelli, M.J. Wooden, and J. Wilkes. Isokinetic evaluation of shoulder rotational strength between the plane of scapula and the frontal plane. Am. J. Sports Med. 18(2): , Hellebrandt, F.A., S.J. Houtz, M.J. Partridge, and C.E. Walters. Tonic neck reflexes in exercises of stress in man. Am. J. Phys. Med. 35: , Hellwig, E.V., and D.H. Perrin. A comparison of two positions for assessing shoulder rotator peak torque: The traditional frontal plane versus the plane of the scapula. Isokin. Exer. Sci. 1(4): , Hirt, S. The tonic neck reflex mechanism in the normal human adult. Am. J. Phys. Med. 46(1): , Johnston, T.B. The movements of the shoulder-joint: A plea for the use of the "plane

9 lsokinetic Exercise and Testing 149 of the scapula" as the plane of reference for movements occurring at the humeroscapular joint. Brit. J. Surg. 25: , Kaufman, K.R., A. Kai-nan, W.J. Litchy, B.F. Morrey, and E.Y.S. Chao. Dynamic joint forces during knee isokinetic exercise. Am. J. Sports Med. 19(3): , Levine, D., A. Klein, and M. Morrissey. Reliability of isokinetic concentric closed kinematic chain testing of the hip and knee extensors. Isokin. Exer. Sci. 1(3): , Lindsay, D.M., M.E. Maitland, R.C. Lowe, and T.J. Kane. Comparison of isokinetic internal and external hip rotation torques using different testing positions. J. Orthop. Sports Phys. Ther. 16(1):43-50, Lunnen, J.D., J. Yack, and B.F. LeVeau. Relationship between muscle length, muscle activity, and torque of the hamstring muscles. Phys. Ther. 61(2): , Ohkoshi, Y., K. Yasuda, K. Kaned, T. Wada, and A.M. Yamanaka. Biomechanical analysis of rehabilitation in standing position. Am. J. Sports Med. 19(6): , Palmitier, R.A., A. Kai-nan, S.G. Scott, and E.Y.S. Chao. Kinetic chain exercise in knee rehabilitation. Sports Med. 1 1 (6): , Rothstein, J.M. Muscle biology: Clinical considerations. Phys. Ther. 62(12): , Saha, A.K. Mechanism of shoulder movements and a plea for the recognition of "zero position" of glenohumeral joint. Clin. Orthop. 173:3-10, Tabary, J.C., C. Tabary, C. Tardieu, G. Tardieu, and G. Goldspink. Physiological and structural changes in the cat's soleus muscle due to immobilization at different lengths by plaster casts. J. Physiol. (Lond.) 224: , Tokizane, T., M. Murao, T. Ogata, and T. Kendo. Electromyographic studies of tonic neck, lumbar, and labyrynthine reflexes in normal persons. Jap. J. Physiol. 2: , Williams, P.E., and G. Goldspink. Changes in sarcomere length and physiological properties in immobilized muscle. J. Anat. 127(3): , Worrell, T.W., D.H. Pemn, and C.R. Denegar. The influence of hip position on quadriceps and hamstring peak torque and reciprocal muscle group ratio values. J. Orthop. Sports Phys. Ther. 11(3): , Worrell, T.W., C.R. Denegar, S.L. Armstrong, and D.H. Perrin. Effect of body position on hamstring muscle group average torque. J. Orthop. Sports Phys. Ther. 11(10): , 1990.