Evaluation of reflex- and nonreflex-induced muscle resistance to stretch in adults with spinal cord injury using hand-held and isokinetic dynamometry.

Key Words: Hand-held dynamometer, Isokinetic dynamometer, Plantar flexors, Spasticity, Spinal cord injury.

Spastic hypertonia (SH), a syndrome common to upper motoneuron lesions, is defined as an increased resistance to stretch that results from reflex hyperexcitability[1] and also from changes in the physiological properties of the muscle.[2-4] Because the response to muscle stretching is velocity-dependent,[5] applying muscle stretches at different velocities makes it possible to differentiate resistance that originates from the reflex components from resistance that originates from the nonreflex components.

The use of computerized dynamometers to assess reflex and nonreflex components of SH is costly and time consuming and requires much space. Computerized dynamometers, therefore, are used mainly for research purposes. In a clinical setting, SH is usually assessed using scales such as the Ashworth scale[6] or the modified Ashworth scale.[7] These scales give a rating based on 2 factors: (1) the presence of a sudden increase of resistance (catch) felt by the evaluator and (2) the angle at which the catch is felt. Operational definitions for the 6-level modified Ashworth scale (from "normal resistance" to "unable to move the limb") were reported by Bohannon and Smith.[7] Thus, based on their operational definitions, both the Ashworth scale and the modified Ashworth scale assess the reflex-induced response to stretch. These scales, however, are not appropriate for assessing nonreflex-induced muscle resistance to stretch associated with muscle contractures or fibrosis that develops after the spinal cord lesion. In light of recent findings about the changes in muscle and connective tissue properties after central nervous system (CNS) lesions and their contribution to motor disability,[2-4] we believe it is critical to separate the nonreflex components from the reflex components in the measurement of SH in order to select appropriate therapeutic interventions. The assessment of the nonreflex components requires a quantitative measurement of the resistive torque during muscle stretches imposed at a velocity that will not elicit a reflex response[2-4] such as that provided with the hand-held dynamometer method.[8-12] Although ordinal scales are easy to use and yield reliable measurements,[7] they are expected to be less sensitive to change[13] compared with quantitative and continuous types of measurement, such as that recorded with force tranducers.

Recently, the use of hand-held dynamometers has been proposed for measuring SH.[8-12] The purported advantage of this method is that quantitative measurements of the resistive torque can be obtained during passive movements, without the disadvantages associated with complex computerized dynamometers (ie, time, cost, and space). The test-retest reproducibility of the resistive torque recorded by the hand-held dynamometry method has been repeatedly demonstrated tar various muscle groups of the upper and lower extremities of adults[8,9] and children[10] with CNS lesions. For instance, the resistive forces of the ankle plantar flexors and elbow flexors recorded with a hand-held dynamometer in 30 adults with hemiparesis by the same rater at 24-hour intervals (intrarater reliability) yielded intraclass correlation coefficients (ICCs) ranging from .89 to .92.[8] A comparable level of reproducibility (ICC=.82) was reported for the resistive forces measured with a hand-held dynamometer during passive hip abductions repeated at 30-minute intervals in 10 adults with paraparesis.[9] In the study by Claude et al,[9] the velocity during slow (18[degrees]/s) and faster (108 [degrees]/s) passive hip movements was also found to the highly reproducible (ICC=.85 and .95, respectively). Comparisons between resistive forces recorded with a hand-held dynamometer and resistive forces recorded with an isokinetic dynamometer in 10 children at 1-month intervals further revealed a similar level of reproducibility (ICC=.85 and .84, respectively).[10] The hand-held dynamometry method has also been used recently, in a group of 22 patients, to disclose a 39% increase in the nonreflex components of SH as early as 2 months after stroke.[12]

The interrater reliability of measurements obtained with the hand-held dynamometry method has been reported for 2 studies.[8,11] The reproducibility of the resistive force measured in the elbow flexors of 30 adults with hemiparesis, by 3 raters, proved to be high (ICC=.88) in contrast to that obtained in the plantar flexors (ICC=.59). A variation in the direction of force transmission at the ankle, a complex multijoint system, has been suggested to explain the poor interrater reliability of these measurements at this joint. The lower interrater reliability for the ankle joint in the study by Malouin et al[8] disagrees with the results of Dvir et al,[11] who reported high ICCs ([is greater than] .89) for measurements taken by 2 raters in the plantar flexors of children with cerebral palsy. These contrasting results can likely be explained by differences in the way passive stretches were applied by Dvir et al.[11] Indeed, the stretch end point of the passive dorsiflexions was maintained for 5 seconds. The very high force values obtained by this method (about twice as high as those normally obtained in children with cerebral palsy[10]) may reflect the strength of the evaluators rather than the resistance provided by the muscles being tested. These results suggest that measurements at the ankle joint require special attention and that measurements obtained with hand-held dynamometry should be repeated by the same rater.

To date, no study has examined the validity of the hand-held dynamometer method for the assessment of SH. For instance, although comparison of the reproducibility level between the 2 methods (hand-held dynamometry and isokinetic dynamometry) has been made,[10] the resistive forces recorded by each method could not be compared. The main reason the resistive forces could not be compared was that both the electromyographic (EMG) activity and the ankle position were not monitored during hand-held dynamometry testing, making the results difficult to interpret.

The present results originate from the baseline measures of an ongoing clinical trial in individuals with spinal cord injuries. Measurements of SH obtained with the Penny and Giles hand-held dynamometer(*) arid the Kin-Cam dynamometer([dagger]) have been compared. For both methods, muscle activity and ankle position were monitored during passive movements at low and high velocities. The first objective of the present study was to examine the intertrial reproducibility of the resistive torque measured with the 2 methods. The second objective was to validate the use of the hand-held dynamometer as a measure of the reflex and nonreflex components of SH.

Method

Subjects

Nine adults with spinal cord injuries (3 women, 6 men), aged 21 to 54 years (X=40.6, SD=10.5), consented to participate in this study. They had chronic lesions of the spinal cord (1-5 years' duration), either complete (n=7) or incomplete (n=2), of traumatic (n=8) or ischemic (n= 1) origin. All subjects had increased resistance to passive stretch of the plantar flexors, as determined by a score of at least 1 on the modified Ashworth scale.[7] This scale has 6 levels (0, 1, 1 +, 2, 3, and 4), where a score of 0 corresponds to normal tonus and a score of 4 corresponds to severe hypertonus. Exclusion criteria were fixed contractures or deformities of the lower limbs and history, of fracture or thrombophlebitis. The subject characteristics are given in Table 1. The evaluators were experienced physical therapists and physicians.

Table 1. Subject Characteristics

Subject
No.       Age (y)       Sex         Level of Injury(a)

  1       34            M           T5-T6, COM
  2       44            M           T7, COM
  3       51            F           T5, COM
  4       20            F           T5, COM
  5       48            M           T5, INC
  6       54            M           T10, COM
  7       34            M           C6, INC
  8       42            F           T8, COM
  9       38            M           T10, COM

                        Ashworth
                        Scale       Dorsiflexion
Subject   Time Since    (Plantar    Range of
No.       Injury (y)    Flexors)    Motion [degrees]

  1       4.0           2           10
  2       2.6           1+           5
  3       5.4           1+           0
  4       1.4           2            0
  5       3.0           2            3
  6       3.2           1+           0
  7       3.8           1+           5
  8       2.5           2            0
  9       1.4           2            5

(a) Based on criteria from International Standards for Neurological and Functional Classification of Spinal Cord Injury. Rev ed. Chicago, Ill: American Spinal Injury Association; 1996. COM=complete lesion, INC=incomplete lesion.

Experimental Design

This study took place in the Motor Evaluation Laboratory of the Neurobiology Research Center in Quebec City (Quebec, Canada), arid each subject was tested once. The resistive torque of the plantar flexors was evaluated during passive ankle dorsiflexions. Passive movements were imposed first with the hand-held dynamometer and second with the isokinetic dynamometer. The high-velocity (180 [degrees]/s) movements were evaluated first, followed by the low-velocity (5 [degrees]/s) movements. The order of the tests was not randomized because of the context of the study. The present study was part of a clinical trial involving a series of clinical and laboratory measures and a control group. This order was chosen for technical considerations and practical reasons pertaining to the clinical trial. The testing procedures were performed by the same rater tot all subjects, and testing was completed within 2 hours for each subject.

Procedure

The hand-held dynamometer used in this study was a Penny and Giles dynamometer. The experimental setup is shown in Figure 1. A plastic device was adapted at the distal end of the transducer to help maintain the handheld dynamometer in contact with the metatarsals during passive movements. Signals from the hand-held dynamometer recording system were directed to a personal computer for continuous recording of the resistive torque measurements throughout the passive movements. Ankle displacement was measured using a custom-made electrogoniometer consisting of 2 flexible polystyrene arms connected to a Spectrol potentiometer([double dagger]) (360 [degrees], 10 k[Omega]), which was aligned with the ankle's center of rotation. The proximal end was fixed to the lower leg, and the distal arm was attached to the fifth metatarsal (Fig. 1). The accuracy of the potentiometer associated with the linearity (0.5%) and the numerical conversion is about 2.5 degrees according to the manufacturer and the laboratory engineer. Similar electrogoniometers have been shown to yield reproducible angular position and velocity measurements of hip abduction[9] and spinal flexion.[14]

[Figure 1 ILLUSTRATION OMITTED]

The angular displacements were used to calculate the ankle position and the velocity of the passive movements during the use of the hand-held dynamometer. The isokinetic dynamometer used in this study was a Kin-Com dynamometer (model 500-4) modified by mechanically increasing the length of the load cell lever arm, using a stainless steel extension, to obtain a 2-fold increase in sensitivity.[15] This increased sensitivity provided a resolution of 0.5 N (about 0.15 N [multiplied by] m) and a precision of [+ or -]2 N (about 0.6 N [multiplied by] m). The Kin-Com delivered passive movements at preset velocities and, as for the hand-held dynamometer, was connected to the computer. Disposable silver-silver chloride surface electrodes (Medi-Trace pellet electrodes, model ECE 1801([sections])), placed on the upper third of the tibialis anterior muscle and on the soleus muscle below the lateral gastrocnemius muscle, posterior to the tendons of the peroneus muscles), recorded EMG activity.

For both testing methods, subjects were evaluated while seated on an adjustable chair with the hip and the knee flexed at 70 and 30 degrees relative to the rectitude of the proximal and distal segments, respectively. Stabilization was provided with belts at the chest and waist, and another strap just above the knee stabilized the lower leg during testing. For the Kin-Corn method, the foot was fixed to a footplate, with its rotational axis aligned with the ankle's center of rotation. Two adjustable straps, one located at the ankle and the other at the metatarsal level, kept the heel in place during the passive movements.

Subjects were asked to relax and to keep their head in midline during the testing. A set of 5 passive ankle dorsiflexion movements, ranging from -35 to 5 degrees of dorsiflexion, was imposed with both testing methods. The selected preset velocities for the Kin-Com method were 5 [degrees]/s (low velocity) and 180 [degrees]/s (high velocity). A high velocity of 180 [degrees]/s was selected because the maximum velocity of the Kin-Com was 210 [degrees]/s. For the hand-held dynamometry method, the evaluator manually imposed the passive movement while holding the dynamometer. The distal end of the dynamometer was held perpendicular to the sole of the foot under the distal end of the metatarsals. The velocity of the manually imposed movement was controlled by having the evaluator count silently (ie, "one thousand one," "one thousand two," and so on) so that the movement time for a 40-degree ankle displacement at 5 [degrees]/s would take 8 seconds. In a previous study in our laboratory,[9] we showed that this method of counting yields velocities of passive movement that are highly reproducible. Because some subjects did not show a reflex response at 180 [degrees]/s, we decided not to match 180 [degrees] /s with the hand-held dynamometry method but instead to impose a velocity high enough to elicit a reflex response. Therefore, the evaluator had to maintain a given cadence for successive trials, which differed across subjects.

A 1-second pause separated each passive movement and a rest period of 3 minutes, during which the foot was taken off the footplate (for the Kin-Com testing). Before each series of rapid movements, subjects were asked to perform a Jendrassik maneuver, which consisted of pulling apart, as strongly as possible, the 2 hands that were joined together at the chest level. This reinforcement maneuver was used to standardize events preceding muscle stretch and is thought to promote comparable neuronal excitability levels from test to test.[8,10]

For both the Kin-Com and hand-held dynamometer testing, the sampling frequencies (torque, EMG, angle) were set at 100 Hz at low velocity and at 1,000 Hz at high velocity. The EMG signals were preamplified and sent to the Grass polygraph (7P3 AC preamplifier)([parallel]) for initial hand-pass filtering (5-700 Hz). For movements at high velocity (for both methods), because of a greater risk of movement artifacts and in an attempt to ensure the accuracy of EMG signals, the signals were sent to a personal computer and filtered (20-Hz, fourth-order, high-pass filter), full-wave rectified, and then smoothed (50-Hz, low-pass filter). Force and angle signals were also sent to the computer and stored for later analysis.

Data Analysis

Using software developed in our laboratory, the resistive torque measurements obtained with the Kin-Com dynamometer were corrected for the gravitational forces acting on the footplate and the foot. Three measurements of gravitational forces were recorded at the beginning of the evaluation while the subject was seated with the hip and knee in the testing position described and with the ankle positioned in -10 degrees of dorsiflexion. On-line EMG monitoring during the measurements was used to confirm the relaxation of ankle plantarflexor and dorsiflexor muscles. Each 3-second recording (100 Hz) consisted of 300 measurements of gravitational forces, which were averaged. The last recording of the 3 identical ([+ or -] 0.1 N) and consecutive recordings was retained for analysis. Corrections of resistive torque values for gravitational forces were performed a posteriori for each ankle position during the stretches. This method has been proven to yield highly reliable measurements in children with cerebral palsy (n= 10)[10] and adults with meniscal tears (n= 19).[16]

For the hand-held dynamometry method, resistive torque measurements were obtained by multiplying the force measurements by the length of a lever arm corresponding to the distance between the transducer and the ankle's center of rotation. Resistive torque measurements were obtained at -5 degrees of dorsiflexion, and 5 trials were averaged at each velocity for 8 subjects for comparison between the Kin-Com and hand-held dynamometry methods. In the remaining subject, only 3 trials were averaged for the hand-held dynamometry method at high velocity because -5 degrees of dorsiflexion could not be obtained in the other trials.

As shown in Figure 2, for all conditions except high-velocity hand-held dynamometry testing, -5 degrees of dorsiflexion occurred at a relatively constant velocity in a part of the movement that was outside the impact range of acceleration or deceleration. Measurements of velocity were also analyzed at -5 degrees of dorsiflexion, except for hand-held dynamometry tests at high velocity. During high-velocity hand-held dynamometric testing, because the position of -5 degrees of dorsiflexion often corresponded to the deceleration phase of the movement and because stretch reflex elicitation is, by definition, dependent on increasing velocity, the maximal velocity value was used in the analysis, as it was more representative of the stretch imposed on the plantar flexors during rapid movements. In the example illustrated in Figure 2C, the velocity at -5 degrees of dorsiflexion was lower than the peak velocity attained earlier. The presence of an EMG signal 2 standard deviations larger than the mean baseline level of EMG activity preceding the onset of the movement was used as a criterion to reject trials with unwanted activation at low velocity and to identify reflex responses for high-velocity movements. None of the trials had to be rejected because of reflex responses at low velocity. Typical EMG, resistive torque, and velocity-angle curves recorded with both dynamometers at low and high velocities are illustrated in Figure 2.

[Figure 2 ILLUSTRATION OMITTED]

Intraclass correlation coefficients (type 2,1)[17] based on a 1-way analysis of variance (ANOVA) for repeated measures and their respective 95% confidence intervals[18] were computed to determine the intertrial reliability of resistive torque measurements. Coefficients of variation (CVs) were computed for both resistive torque and velocity values. Although the CV is not recognized as a probabilistic measure of reliability, we calculated CVs to allow comparison with studies in which it was used. Wilcoxon matched-pairs signed-rank tests were used to compare resistive torque and velocity measurements between the hand-held dynamometer and the Kin-Com. All statistical analyses were performed on GB-STAT 4.0 software,(#) and the level of significance was set at .05.

Results

Intertrial Reliability and Variability of Resistive Torque Measurements

Mean resistive torque values for each of the 5 trials recorded with both methods at low and high velocities are illustrated in Figure 3. The ICCs (and 95% confidence limit intervals) for resistive torque measurements are reported in Table 2. With the hand-held dynamometer, the mean resistive torque values remained quite similar across the trials (Figs. 3A, 3C), and ICCs of .93 and .84 (Tab. 2) indicate high intertrial reliability for the hand-held dynamometry measurements at low velocity and high velocity, respectively. With the Kin-Com dynamometer, however, the measurements obtained during the first trial were always higher than the measurements obtained during the other trials, particularly at high velocity (Fig. 2D). The ICCs indicate a lower level of reliability at high velocity (ICC= .75) than at low velocity (ICC=.83). To determine the effect of the first trial on the intertrial reliability, calculation of the ICCs was repeated without the first trial. The results (Tab. 2) indicate that removing the first trial markedly increases the reliability of the Kin-Com measurements at both low velocity (ICC= .99) and high velocity (ICC= .93), but not that of the hand-held dynamometry measurements.

Table 2. Intraclass Correlation Coefficients Computed for the
Hand-held Dynamometry and Kin-Com Methods for All Trials
(n=5) and Without the First Trial (n=4)

                 Low Velocity
                 (5 [degrees]/s)

No. of trials   5                        4
Hand-held
  dynamometer   .93 (.86)(a)             .94 (.86)
Kin-Com
  dynamometer   .83 (.62)                .99 (.96)

                High Velocity
                (180 [degrees]/s)(b)

No. of trials   5                        4
Hand-held
  dynamometer   .84 (.70)                .81 (.63)
Kin-Com
  dynamometer   .75 (.54)                .93 (.84)

(a) Lower limits of 95% confidence intervals shown in parentheses.

(b) 180 [degrees] /s or faster for the hand-held dynamometer.

[Figure 3 ILLUSTRATION OMITTED]

Intertrial variability for the last 4 trials was also estimated by calculation of CVs for resistive torque and velocity measurements. For the resistive torque measurements at low velocity, the intertrial variability was slightly higher with the hand-held dynamometry method, as shown in Table 3. At high velocity, however, the hand-held dynamometer showed greater variability (CV=16.11%) than did the Kin--Com (CV=6.43%). For the velocity measurements, as expected, the CVs were larger for the hand-held dynamometry method, particularly at low velocity (CV=40.43%).

Table 3. Mean Intertrial Coefficients of Variation (Expressed as a
Percentage) for Resistive Torque and Velocity Measurements
Calculated for 4 Trials

             Hand-held
             Dynamometer

             Low                High
             Velocity           Velocity
Variable     (5 [degrees]/s)    (180 [degrees]/s)(a)

Resistive
torque              7.98       16.11
Velocity           40.43       12.74

            Kin-Com
            Dynamometer

            Low                High
            Velocity           Velocity
Variable    (5 [degrees] /s)   (180 [degrees] /s)

Resistive
torque      3.14               6.43
Velocity    7.84               0.47

(a) 180 [degrees] /s or faster for the hand-held dynamometer.

Comparison of Velocity and Resistive Torque Measurements Between the 2 Methods

Mean (n=8) velocity and resistive torque measurements for the Kin-Com and hand-held dynamometry methods at low and high velocities are illustrated in Figure 4. As mentioned in the "Method" section, the evaluator attempted to match the velocity imposed with the Kin--Com only for the low-velocity condition with the hand-held dynamometer. The mean velocity measured at -5 degrees of dorsiflexion with the Kin-Com was 4.5 [degrees]/s, thus slightly lower than the preset velocity of 5 [degrees]/s. The mean velocity of the manually imposed movement was 3.3 [degrees]/s, which is about 2 [degrees]/s lower than that expected with the mental cadence. Both testing methods allowed, at this slow velocity, the evaluation of resistive torques that were not reflex induced, as confirmed by EM(; monitoring. At high velocity, the velocity measurements obtained with the Kin--Com were again slightly lower (177.4 [degrees] /s) than the preset value (180 [degrees] / s). The mean maximal velocity of the manually imposed movement with the hand-held dynamometer was 311.1 [degrees]/s (range=187.3 [degrees] -393.5 [degrees]/s), which is more than 130o/s higher than the maximal velocity of the movement with the Kin-Com method.

[Figure 4 ILLUSTRATION OMITTED]

Comparison of mean resistive torque measurements between the 2 testing methods revealed that the handheld dynamometry method underestimated resistive torque values at both low and high Velocities. Although the difference in resistive torque measurements at low velocity (0.8 N [multiplied by] m) was significant (P [is less than] .05), it did not attain statistical significance (P [is greater than] .05) at high velocity (1.2 N [multiplied by] m). Because of the higher velocities attained with the hand-held dynamometer (311.1 [degrees] /s), more subjects (7 of the 8 subjects) displayed reflex responses in the soleus muscle, as compared with the Kin-Com method, which elicited a reflex response in only 3 subjects. Moreover, clonus was elicited in 4 subjects with the hand-held dynamometer (Fig. 5) for all 5 trials. In contrast, clonus was not elicited in any subjects during the Kin-Com testing.

[Figure 5 ILLUSTRATION OMITTED]

Discussion

The results of our study show that, when measuring resistance of the plantar flexors to passive movement at either low or high velocity, the hand-held dynamometer yielded reliable intertrial measurements of resistive torque, as shown by the ICCs of .93 and .84 computed for the low- and high-velocity tests. These high reliability values were greater than those computed for the Kin-Com method when all 5 trials were considered. When the first trial was removed from the ICC calculation, however, the Kin-Com resistive torque measurements showed better reproducibility, with ICCs of .99 and .93. Only Boiteau et al[10] have also examined the reproducibility of force measurements recorded with a hand-held dynamometer and the Kin-Com. They reported ICCs of .79 and .90 for force measurements obtained initially and after a 1-month interval with the hand-held dynamometer at low and high velocities and of .84 for measurements obtained with the Kin-Com at both velocities. Thus, in the present study, as in that of Boiteau et al,[10] the reliability of resistive torque (or force) measurements recorded with the hand-held dynamometer resembles that of measurements recorded with the Kin-Com dynamometer. Moreover, the ICCs calculated for the hand-held dynamometry values in the present study are in the same range as those reported by Boiteau et al.[10]

The results also show that the first trials yielded larger resistive torque values than did the subsequent 4 trials with the Kin-Com dynamometer, but not with the handheld dynamometer (Figs. 3B, 3D). The larger resistive torque values obtained during tire first trials have a physiological explanation, namely, hysteresis or muscle thixotropy. What some authors[19,20] called thixotropy is a behavior that changes muscle stiffness, depending on the muscle's history of lengthening or contraction. Thixotropy is thought to be related to the residual cross-bridges in the resting muscle.[21] according to Proske et al,[22] in a review of the effect of muscle thixotropy, the residual crossbridges bind within a few seconds at the length at which the muscle is left undisturbed and can be detached by a large stretch. The fact that the testing order was not randomized cannot account for our findings, because a similar phenomenon (larger resistive torque values in the first trials) was also reported even when the testing order was randomized.[23] This finding was demonstrated in 18 subjects, where passive ankle dorsiflexions, applied at 6 different velocities ranging from 5 [degrees] to 180 [degrees]/s, resulted consistently in a first resistive torque that was larger than the following responses.

We can question, however, whether the nonrandomization of the testing order (hand-held dynamometry testing preceding Kin-Com testing) could be responsible for not observing the phenomenon of thixotropy with handheld dynamometry testing? We believe this possibility is unlikely because the time separating each series (3 minutes) was similar for both testing methods. The factor that could explain why the resistance for the first trial was not greater than the resistance for next trial would be a shorter duration of the period during which the muscle was left undisturbed,[19,20,24] which was not the case here. One alternative explanation for our findings with the hand-held dynamometry method is the difference in the way muscle stretches were elicited by the 2 testing methods. Constant stimuli from trial to trial, such as those delivered by an isokinetic device, are required for the expression of thixotropy. Manually applied passive movements (Fig. 2C) do not appear to have yielded consistent acceleration and deceleration from trial to trial, which may have contributed to masking the thixotropic element during testing with the hand-held dynamometer.

At both low and high velocities, the resistive torque values obtained with the hand-held dynamometer were lower than the values obtained with the Kin-Com. At low velocity, both the resistive torque values and the velocity were lower with the hand-held dynamometry method than with the Kin-Com method. Although the nonreflex muscle response to stretch is velocity-sensitive[15,23,25] due to the viscoelastic properties of skeletal muscle, it cannot account for the difference in resistive torque between the 2 methods at low velocity. The difference in movement velocity between the 2 testing methods was very small (1.2 [degrees]/s). In addition, Hufschmidt and Mauritz[3] reported that no velocity-sensitive behavior was present for the plantar flexors at movement velocities ranging from 2 [degrees] to 20 [degrees]/s in either subjects with or without CNS damage. At high velocity, the resistive torque values tended to be lower with the hand-held dynamometer, despite the fact that the mean maximal velocity was larger than 180 [degrees]/s. Higher resistive torques would have been expected because of the higher velocities attained and because of the larger incidence of reflex responses with the hand-held dynamometry method.

An underestimation of resistive torque with the hand-held dynamometer at both low and high velocities may, in part, be explained by the ankle position measurement. Because the distal end of the electrogoniometer was fixed at the level of the head of the fifth metatarsal, the angles measured were influenced by forefoot movements taking place in the sagittal and frontal planes. With the hand-held dynamometer being applied under the forefoot, the occurrence of forefoot movements could have resulted in an overestimation of the ankle dorsiflexion position. Thus, the position of -5 degrees of dorsiflexion may have corresponded to a less dorsiflexed position, and, as resistive torque increased with dorsiflexion (Fig. 2), it may have yielded lower resistive torque values. Malouin et al,[8] in a study using the hand-held dynamometer at the ankle, suggested that the transmission of forces may be affected by the multijoint system at the ankle and may, in part, explain the lower interrater reliability computed for the plantar flexors as compared with the elbow flexors. With Kin-Com testing, however, the effect of forefoot movements were eliminated by the rigid footplate and fixation system. Thus, because it is not possible to ascertain that resistive torque values were measured at the same ankle position, our data cannot be used to confirm the concurrent validity of the resistive torque measurements obtained with the hand-held dynamometry and Kin-Com methods.

The monitoring of EMG signals during low- and high-velocity passive movements showed an absence of reflex responses at low velocity for both the hand-held dynamometry and Kin-Com methods. Thus, both methods can be used to assess the nonreflex components of SH. Although only 3 subjects displayed reflex responses (based on EMG data) in the soleus muscle with the Kin-Com testing at high velocity, passive movements with the hand-held dynamometer elicited reflex responses in all subjects except one. This larger incidence of reflex responses is likely related to the higher velocities (187 [degrees] - 394 [degrees]/s) applied with the hand-held dynamometer. This observation indicates one advantage of the hand-held dynamometry method: it allows the velocity of the manually imposed movements to be increased in order to reach the threshold of the reflex responses.

Another observation associated with the hand-held dynamometry method was the occurrence of clonic responses, consisting of 2 bursts or more, in 50% of the subjects. During these clonic responses, both the velocity and angular position curves showed oscillations near the end of the dorsiflexion movement (Fig. 5). For instance, during the fastest movement, there was a sudden drop in velocity at -10 degrees of dorsiflexion, and a change of direction of the movement followed the reflex activation of the soleus muscle. This drop in velocity and the change of movement direction are likely due to the inability of the evaluator to match the sudden increase in resistive torque resulting from the soleus muscle activation. Burke has stated that the ease of elicitation of clonus depends on 2 factors: "First, a critical degree of muscle stretch must be maintained so that muscle relaxation can trigger a synchronized spindle discharge. Second, the reflex pathway must be in a high state of excitability."[1(p409)] Thus, features of the manual stretch, namely, the large acceleration phases and the high peaks of velocity, as it induced reflex responses, may set the reflex loop at a high excitability level. Furthermore, the fact that the evaluator attempted to reach the end position and the muscle relaxed after the reflex contraction may have resulted in successive muscle stretches that were likely to induce repeated EMG bursts in the soleus muscle. The Kin-Com dynamometer, however, moves at a lower velocity (177.4 [degrees]/s) and at a constant rate that does not always reach the reflex threshold. The Kin-Com also does not allow oscillating movements at the ankle. Thus, the repetition of the stimuli cannot occur, reducing the likelihood of eliciting clonus. For these reasons, clonic responses may have not been elicited with the use of the Kin-Com. Malouin et al,[8] in their study of adults with hemiparesis, also observed clonic responses in the plantar flexors when imposing rapid dorsiflexions with a hand-held dynamometer. They recorded peak resistive force values, and, even if the final position (0 [degrees]) of the stretch was controlled with a visual marker, this did not affect their intrarater reliability (ICC=.89-.90).

Finally, examination of the CVs revealed that the intertrial variability of resistive torque was similar between the 2 testing methods at low velocity, whereas at high velocity that of the hand-held dynamometer was 10% higher (Tab. 3). This higher variability likely has physiological and methodological explanations. First, hand-held dynamometer testing elicited reflex responses more frequently than the Kin-Com testing did. Second, at high velocity, it is more difficult to maintain the hand-held dynamometer perpendicular to the forefoot throughout the muscle stretching. Lastly, the lower resistive torque values (37%) recorded with the dynamometer (Fig. 4) can also contribute to the larger CV. For the velocity values, as expected, at both low and high velocities, the intertrial variability was lower for the Kin-Com than for the hand-held dynamometer. Despite the fact, however, that the evaluator applied a wide range of velocities (187-394 J/s) across the subjects to elicit reflex responses at high velocity, the intertrial variability for velocity measures was less than 13%. This relatively low intertrial variability is consistent with the reproducibility of resistive torque measurements at high velocity (ICC=.84) obtained with the myometer method. It is also consistent with the results of Claude et al,[9] who found high intrasubject reliability of movement velocity measurements, at a 30-minute interval, when assessing SH of hip adductors with the hand-held dynamometer method. Thus, our results indicate that when using a standardized protocol, an evaluator is able to manually impose reproducible velocities of stretch to measure reproducible resistive torque values with a hand-held dynamometer.

Conclusion

Within the limits of this study (eg, small sample size), we demonstrated that a hand-held dynamometer, when used in a standardized protocol, yields intertrial resistive torque measures as reliable as those obtained with a computerized device such as the Kin-Com dynamometer, for either low- or high-velocity movements. At low velocity, EMG recordings validate the use of the handheld dynamometer for the evaluation of the nonreflex components of SH because, based on EMG data, no reflex-induced muscle activation occurred. At high velocity, as the velocity of movement with the hand-held dynamometer has a higher upper limit than the Kin-Com dynamometer, reflex responses could be elicited in most individuals. Thus, the hand-held dynamometer appears to be potentially useful for assessing the reflex components of SH in persons with a spinal cord injury because they can have a wide range of reflex excitability. The appropriate velocity for a given individual call be selected by the evaluator based on the catch felt during the passive movement. The hand-held dynamometry method, therefore, provides a measure of resistive torque that reflects not only the reflex components but also the nonreflex components of SH, which is not possible with the Ashworth scale. Moreover, because hand-held dynamometry provides a reliable and easily available measure, we believe that it can be used by clinicians as an outcome measure.

The results also indicate that resistive torque measurements at a given ankle position were underestimated with the hand-held dynamometer, possibly due to forefoot movements. Because muscles with increased SH often have contractures, controlling forefoot movements during hand-held dynamometry testing is important as resistance from tarsal joints may interfere with the measurement of muscle resistance. These measures might be improved by using a light, but rigid, footplate fixed to the foot to control tarsal movements during the ankle displacements.

Acknowledgments

We thank Nicole Roger, PT, and Richard Beaupre, MD, (Institut de Readaptation en Deficience Physique de Quebec, Quebec City, Canada) for the screening of the patients, as well as Francois Comeau and Daniel Tardif for technical assistance.

(*) LAM Associates, 1001 Sierra Blvd, Missisauga, Ontario, Canada L4Y 2E3.

([dagger]) Chattanooga Group Inc, 4717 Adams Rd PO Box 489 Hixson TN 37343.

([double dagger]) Spectrol Electronics Corp. 1707 E Gale Ave, city of Industry, CA 91745.

([sections]) Graphic Controls Canada Ltd, 215 Herbert: Gananoque, Ontario, Canada K1G 2Y7.

([parallel]) Grass Instrument Co, 101 Old Colony Ave, PO Box 516, Quincy, MA 02169.

(#) Dynamic Microsystems, 13003 Buccaneer Rd, Silver Spring, MI) 20904.

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A Lamontagne, PT, is a doctoral student in neurobiology (rehabilitation), Department of Rehabilitation, Faculty of Medicine, Laval University, Quebec City, Quebec, Canada G1K 7P4.

F Malouin, PhD, PT, is Professor, Department of Rehabilitation, Faculty of Medicine, Laval University. Address all correspondence to Dr Malouin at Rehabilitation Research Group, Quebec Rehabilitation Institute, 525, Blvd Wilfrid-Hamel, Bureau B-77, Quebec, Quebec, Canada G1M 2S8 ([e-mail]).

CL Richards, PhD, PT, is Professor, Department of Rehabilitation, Faculty of Medicine, Laval University.

F Dumas, PT, is Research Therapist, Department of Rehabilitation, Faculty of Medicine, Laval University.

This study was part of a project supported by grants from The Medical Research Council of Canada and Health Canada. Ms Lamontagne was the recipient of studentships from the Rick Hansen Man in Motion Foundation and from Health Canada.

This study was approved by the Research Ethics Board of Quebec Rehabilitation Institute.

This article was submitted March 10, 1997, and was accepted April 1, 1998.