Abstract:
An isometric strength testing device includes a base for selectively supporting either a chair or a wheelchair for the subject to be tested. A pair of limb supports are positioned on the base, one to immobilize an arm and the other a leg of the subject. Each support includes a band carrying a load cell for generating a signal measurement of the force applied to the cell. Goniometers are associated with the supports for establishing appropriate angles of the subject&#39;s limbs at the knee and elbow. A computer connected to the force plates processes and displays data generated by the load cells.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention relates to isometric strength testing apparatus and method, and more particularly relates to isometric strength testing for measuring disease progression in ALS patients. 
         [0003]    2. Background 
         [0004]    In the past decade, the number of candidate therapeutic agents for the treatment of ALS has greatly increased, and the ability of the clinical trial community to test these agents is limited due to cost, time, and especially resource constraints. Muscle strength is an important determinant of function in ALS and thus is a valuable outcome measure in clinical trials. Establishing a disease progression rate for each individual provides an extremely accurate method to determine even modest therapeutic effects. The equipment heretofore available to perform such tests is expensive and/or requires a highly trained evaluator. 
         [0005]    Sample size determination is largely dependent on the variance of both the measurement system and the between-subject variation. Therefore, selection of the precise outcome measures is a critically important component of clinical trial design. Because strength loss within each subject is very linear, the variation of loss in a particular patient is very small. However, the differences in disease progression rates can be ten-fold or greater between subjects. By establishing each subject&#39;s rate of strength loss and comparing each subject to themselves, the sample size requirements are a fraction of the size needed to compare groups of subjects due to the variance of both the measurement system and the between subject variation employed in clinical trials today. Precise, accurate testing of muscle strength may allow much more efficient outcome measure and enable clinical trials to be significantly shorter, less expensive and require considerably less resources. 
         [0006]    In accordance with one ALS testing protocol presently used, strength measurement of  18  muscle groups use maximal voluntary isometric contraction (MVIC). A measurement utilizes a strain gage attached to uprights and the subject pulls against a strap attached to the uprights to measure force output of several muscles in the arms and legs. However, this protocol is time intensive, requires the subject to be moved onto a treatment table and undergo multiple position changes during the testing procedure. The equipment used is large consuming substantial floor space, is very difficult to relocate and the cost of the equipment is substantial. Moreover, the testing protocol requires a highly trained evaluator. Furthermore, many subjects discontinue testing due to the difficulty with transfers and positioning as their disease worsens. As a result, many subjects are not tested in the later stages of the disease. 
         [0007]    An alternative method to measure muscle strength uses hand-held dynamometry. This method uses a hand-held force gage to measure the force of the subject&#39;s muscular resistance. Holding the force gage in his hand, the evaluator attempts to break the subject&#39;s resistance. This method is relatively inexpensive, is portable and can be performed in the sitting position in a short time. However, because the force output is dependent on the evaluator overpowering the subject&#39;s strength and because many muscles are tested in an anti-gravity position, there are potentially extraneous factors reflected in the measurement. Moreover, testing positions and stabilization by the evaluator make standardization difficult to achieve. 
       SUMMARY OF INVENTION 
       [0008]    The strength-testing apparatus of the present invention measures, records, and analyzes maximal isometric muscle force readings from various muscle groups in all four limbs. The apparatus includes of a platform carrying a chair for the subject and separate leg and arm restraints along with load cells, a microprocessor and a personal computer. The platform preferably is provided with a ramp to enable a wheelchair to be used when the subject cannot be easily transferred to the chair. Restraints separately stabilize an arm and leg of the subject, load cells engage a wrist and lower leg of the subject, apparatus measures the joint angles of the arm and leg to assure that the limbs are at the appropriate angle, and a single test for each limb will measure strength as a raw score and/or a percent of predicted normal and may also provide a cumulative test report showing disease progression over time and calculate the rate of disease progression over a period of time. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings: 
           [0010]      FIG. 1  is a perspective view of many of the major components of the assembled apparatus shown in a collapsed state for storage; 
           [0011]      FIG. 2  is a similar view of the apparatus with the base unfolded to the open or useable position; 
           [0012]      FIG. 3  is a perspective view of the unfolded apparatus with a chair attached and positioned for easy access by a subject; 
           [0013]      FIG. 4  is a perspective view of the apparatus with the attached chair removed and replaced by a wheelchair; 
           [0014]      FIG. 5  is a side view of the apparatus of  FIG. 3  with the subject to be tested seated in the chair and facing in a direction to be engaged by the limb restraints; 
           [0015]      FIG. 5A  is a side view similar to  FIG. 5  but showing the leg rest in position to support the knees of the subject; 
           [0016]      FIG. 6  is a side view of the chair with the arm restraint extended and supporting the left arm of a subject and with the chair tilted; 
           [0017]      FIG. 7  is a side view similar to  FIG. 5A  but showing the leg restraints extended and immobilizing the subject&#39;s left leg immediately above the ankle; and 
           [0018]      FIG. 8  is a fragmentary perspective view with the subject seated as in  FIG. 7  but showing use of the apparatus to measure the force generated by the subject&#39;s foot. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
         [0020]      FIGS. 1-3  show the apparatus folded in stored position and in position to accept a subject to be tested. The strength testing apparatus shown in accordance with one embodiment of the invention includes a base  10  intended to rest on the floor or other surface when the apparatus is in use. The base in turn carries a platform  11  that supports a chair  12  in which the subject sits for testing. The base also carries a column  14  to which a pair of limb supports  16  and  18  are connected. The platform  11  may also be used to support a conventional chair or a wheelchair  12   a  (see  FIG. 4 ) in place of the attached chair  12  as described in detail below. 
         [0021]    In accordance with one embodiment of the invention, the platform  11  carries an adjustable post  28  that supports the chair  12  and enables the chair to rotate to provide easier access for the subject (compare  FIGS. 3 and 5 ). The position of the chair may also be varied to accommodate subjects of different size particularly when the limb supports  16  and  18  are utilized. In accordance with one embodiment of the present invention, the platform  11  is carried by a U-shaped frame  22  pivotally mounted on the base  10 , which enables the platform to be raised to the position shown in  FIG. 1  to facilitate storage of the apparatus. For use, the U-shaped frame  22  is pivoted about the connections at the end of the legs  27  that join it to the base  10 , placing the platform  11  in the horizontal position of  FIG. 2 . 
         [0022]    The platform  11  in accordance with one embodiment of the invention is mounted on the frame  22  by two pairs of scissor jacks  24  disposed beneath the platform. Each pair of scissor jacks in this embodiment preferably includes a connector  26  that accepts a crank handle or other means to operate the scissor jacks to vary the height of the platform. The scissor jacks  24  may also orient the platform at any desired angle with respect to the horizontal, as described below in connection with the use of the apparatus. 
         [0023]    As shown in  FIGS. 3 and 5 , the platform  11  and post  28  carry an adjusting mechanism  30  that in turn supports the chair  12 . The mechanism may be operated by the handle  31 . The post  28  enables the adjusting mechanism  30  to be rotated about the post axis so as to change the direction in which the chair faces (see  FIGS. 3 and 5 ), and the adjusting mechanism  30  enables the chair  12  to be moved radially with respect to the post axis, all to accommodate the subject&#39;s size when a leg or arm is to be engaged by one of the limb supports  16  or  18  on column  14 . 
         [0024]    While one specific means of mounting the chair  12  is shown, it should be appreciated that the chair may be mounted in many different ways on the platform and it is most advantageous that when the column mounted chair is used, the chair may be moved with respect to the column  14  so that the subject is comfortable and in the precise position appropriate for the tests to be performed. It is also contemplated that the post  28  may be disconnected from or withdrawn into the platform if a free standing chair or a wheelchair is to be used for the subject. 
         [0025]    In accordance with one embodiment of the invention, the chair  12  mounted on the post  28  includes a seat  40  with a seat cushion  42 , a backrest  44  and a headrest  46  that preferably is height adjustable by means of a slide connection or some other suitable mechanism for connecting the headrest to the backrest. In accordance with another embodiment of the invention, the angular relationship between the seat  40  and backrest  44  may be varied to provide for the comfort of the subject and to facilitate tests performed separately on the arms and legs (see  FIGS. 6-8 ). The backrest adjustment typically may be accomplished by providing an adjusting mechanism in the frame connecting the backrest to the seat. Such mechanisms are well-known in the furniture and automotive arts. 
         [0026]    In accordance with yet another aspect of the invention a ramp  50  may be provided along an edge of the platform  11  (see  FIG. 2 ) to facilitate rolling a wheelchair onto the platform if the subject being tested cannot or should not be seated in the chair  12 . If the subject does not require a wheelchair and for some reason chooses not to use the seat  12 , the seat  12  may be removed with or without the post  28 , and a conventional chair may be used instead. In  FIG. 4  a barrier  51  is shown connected to the platform  11  to prevent the wheelchair  12   a  from rolling off it when the platform is tilted to place the wheelchair in an appropriate position for the particular test to be performed. Many different expedients may be used for the same purpose. 
         [0027]    The limb supports  16  and  18  are each adjustably mounted on the column  14  by means of separate sleeves  60  and  62 , each secured in fixed position on the column by means of the set screw type fasteners  64  that extend through a wall of each sleeve and engage the column. Other locking devices such as clamps, cam catches or split blocks may be used as well. The limb support  16  for immobilizing the arm of the subject is joined to the sleeve  60  by a hinge mechanism  66 . As shown in  FIGS. 3 ,  4  and  6 , in accordance with this embodiment of the invention, the limb support  16  is composed of three sections  70 ,  72  and  74  connected end-to-end by hinge mechanisms  76 ,  78  and  80 . The end section  74  of the support is designed to directly engage the forearm  82  of the subject and for that purpose a collar  84  is carried on its free end against which the elbow of the subject is positioned when tests are to be performed. The hinges  76 ,  78  and  80  provide three degrees of freedom so that the section  74  may be positioned to comfortably and separately accommodate the forearm  82  of either arm of the subject seated in any position on the platform with the upper arm and forearm being specifically oriented as prescribed for the tests to be performed. It will be noted that the hinge mechanism  80  provides pivotal motion about a horizontal axis while hinges  66 ,  76  and  78  provide pivotal motion about vertical axes. This enables arm restraint  16  to restrain either arm of the subject. Height adjustment is also facilitated by the ability to raise and lower the sleeve  60  on column  14 . 
         [0028]    The mechanism for making the strength measurements may take many different forms, but typically may include load cells carried on the section  74  and appropriate restraints such as a brace or bands that encircle the forearm so as to immobilize the arm. The mechanism may for example include a wrist clamp  73  as shown in  FIGS. 4 and 6  that is lightly padded and carries the load cells  77  such as, strain gages, force plates or any other well-known device. Most commonly, the arm section  74  and wrist clamp or other means employed to immobilize the forearm holds the forearm at right angles to the upper arm. It should be appreciated that the limb support  16  may take many different forms, but the illustrated embodiment is the preferred form. Restraints may also be employed engaging the upper arm near the elbow of the subject, and a pad may also be placed under the elbow on the section  74  for the subject&#39;s comfort. 
         [0029]    The limb support  18 , which is specifically intended to immobilize the leg and/or foot, in the embodiment illustrated, is constructed in a fashion similar to that of the limb support  16 . As shown in  FIGS. 2 and 3 , the leg support may include three sections,  89 ,  90  and  92  hingedly connected end-to-end by hinge mechanisms  93  and  94 . The section  89  of the support is connected to the sleeve  62  by hinge mechanism  96 . In other embodiments more or fewer sections with a corresponding member of hinge mechanisms may be employed. Height adjustment of the free end  100  of section  92  is afforded by the slidably mounted sleeve  62  on column  14 . The hinges  94  and  96  provide adjustment of the position of the end  100  about vertical axes. Although not shown, an additional hinge mechanism like mechanism  80  shown in  FIG. 6  may also be incorporated into the limb support  18  to adjust the height of the support. Preferably each hinge mechanism includes or has an associated latching device to enable the leg and arm restraints to be locked in a fixed position as each test is performed. 
         [0030]    In accordance with one embodiment of the invention shown in  FIG. 7 , the free end of support section  92  carries a collar  101  that engages the ankle  103  of the subject and includes load cells  102  against which the subject will exert extension and flexion forces during performance of the tests. As an alternative test, the subject may place his/her foot beneath a load cell  104  and exert a lifting force against it by trying to bend the ankle upwardly against it. In  FIG. 8  the cell  104  is shown held by restraint  105  that opposes the force exerted by the foot. Alternatively, a strap about the forepart of the foot may carry the load cell  104  and restrain the foot. 
         [0031]    Additional mechanisms provided by the apparatus to position the legs comprise a pair of braces  110 , one mounted on each side of the seat  40  (see  FIG. 3 ). Each brace  110  includes a pad  112  mounted on its forward end and a handle  116  at its back end. The braces are mounted on the support mechanism  30  on each side of the seat  40 , and each may separately be moved to several different positions to support the legs of the subject. In  FIGS. 5 and 6  both legs  117  of the subject are shown supported by the braces  110  slightly above the ankle (the legs are not being tested) and the braces serve as a leg rest to comfort the subject whether or not tests are being performed on an arm of the subject. In  FIGS. 7-8 , the brace  110  is shown in an elevated position wherein the pad  112  is disposed immediately behind the knee  118  so as to hold the leg in a fixed position as strength tests are being performed on a subject&#39;s leg or foot. 
         [0032]    The additional apparatus and equipment to conduct the valuations of the subject may include a display  150  connected to the various load cells through a microprocessor  152 . The load cells may be in the form of pressure gages, strain gages, or other known devices that will respond to the force applied against them and generate a signal that is a function of the force imposed. The display  150  may provide a single test report by expressing the strength as a raw score and/or a percent of a predicted normal. Alternatively, the display may graph disease progression over time and calculate the rate of disease progression based on percent of strength change expressed for example, per year. 
         [0033]    In accordance with the present invention, it is contemplated that the limbs of the subject are tested one at a time. Because of the adjustability of each of the limb supports  16  and  18  and of the position of the seat  12 , the arm support  16  is capable of serving effectively to immobilize, one at a time, both the left and right arm of the subject, and similarly the leg support  18  may be used one at a time with the left and right leg of the subject in the strength measurement of the leg and foot. The apparatus enables the use of a separate wheelchair or a fully adjustable specially designed chair for subjects depending upon their condition. 
         [0034]    To insure that the limbs are disposed at the proper angle for each test being performed and so that repeated test results may be compared, in accordance with another aspect of the invention, goniometers  160  (see  FIG. 7 ) are provided on each limb support to measure the angular disposition of each limb. These instruments may take many different forms and for convenience in this setting may reference the angle from the limbs themselves or from various portions of the limb supports. 
         [0035]    The present invention greatly facilitates the measuring, testing and monitoring of maximal isometric muscle force in all four limbs and reduces the time required to perform these functions. Once seated in the equipment, the subject need not be moved from the seat until all of the procedures have been completed. The arms and legs are connected to the restraints one at a time and the load cells are positioned with respect to the limbs so as to respond to the forces exerted by the subject, and only after all of the procedures have been completed is the subject removed from the apparatus. The apparatus is not large and can conveniently be stored, and the cost of the apparatus is not prohibitive. The storage is further facilitated by the ability to collapse the limb supports about the base  10  and column  14 . The apparatus when folded for storage as shown in  FIG. 1  has a footprint approximately 3 ft.×3 ft., and when opened as in  FIG. 2 , approximately 3 ft.×6 ft. 
         [0036]    While the apparatus has been described in terms of tests for measuring the loss of muscle strength as it relates to ALS patients, the apparatus has much broader applications including neurology, orthopedic and rehabilitation research and clinical practice, as well as for the fitness industry. Moreover, within the purview of the present invention the apparatus may permit the testing of many additional muscle groups including shoulder and hip flexion, extension, abduction adduction, etc. 
         [0037]    Having thus described several aspects of several embodiments of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.