Stretch reflex adaptation in elbow flexors during repeated passive movements in unilateral brain-injured patients  Brian D. Schmit, PhD, Julius P.A. Dewald, PhD, PT, W.Zev Rymer, MD, PhD  Archives of Physical Medicine and Rehabilitation  Volume 81, Issue 3, Pages 269-278 (March 2000) DOI: 10.1016/S0003-9993(00)90070-4 Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 1 Experimental preparation for quantifying elbow spasticity using constant velocity ramp stretches. The subject was seated adjacent to the motor with the elbow axis of rotation aligned with the motor axis. The hand and wrist were cast and attached to the manipulandum of the motor as shown. EMG electrodes were placed over the biceps, brachioradialis, and lateral head of the triceps. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 2 Calculation of the reflex torque was made by fitting a fifth-order polynomial to the passive trial and subtracting the passive torque from the measured torque. The data are from elbow extension only. Measured torque was made at 30°/sec. The parameters θq and τq for this subject (subject G) are shown. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 3 A single trial for subject C is shown. The upper trace is the measured torque for elbow flexion, 10-sec hold, and return extension. The elbow was held in the extended position between trials. The EMGs were filtered (comb filter for 60Hz and harmonics) and rectified. The flexor EMGs were positive rectified and extensor negative rectified for display purposes. Elbow position and velocity are shown below. The data were partitioned into flexion and extension for further analysis. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 4 Sequential flexor reflex measurements for subject D show the adaptation of the stretch reflex across the 30 test trials. Reflex torques are offset from left to right as the experiment proceeds. The parameter τq is shown for each trial (gray, solid circles) and declines with increasing trial number. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 5 The slope and intercept for each test session is shown. (A) Estimated spasticity was identified as the intercept of the linear regression. Initial spasticity appeared to be both subject and session dependent. (B) Adaptation was identified as the slope of the regression. Adaptation also appeared to have dependence on session. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 6 The estimated mean and SD of initial level of spasticity and extent of adaptation for each subject. (A) Spasticity was defined as the intercept parameter of the linear regression analysis. The error bars represent ± 1 SD. Spasticity mean and SD estimates were based on individual analysis of each session (not pooled data). (B) Adaptation was defined as the slope parameter of the regression analysis. Note that subject G did not show significant adaptation. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 7 Estimates of adaptation for subjects E, C, and G for each session are shown. The error bars demarcate the 95% confidence interval of the linear regression slope. Note that these are the same subjects shown for the pooled data of figure 5. Subject E always produced a significant adaptation. Subject C showed significant adaptation (p <.05) for five of the seven sessions, and subject G produced mixed results although six of nine sessions had no significant trend. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 8 Pooled data for three subjects are shown. Because of the large trial-to-trial variation, data were normalized by subtraction of the mean of the first 20 trials and pooled across sessions for each subject. A linear regression analysis was conducted for each subject to identify the extent of adaptation. These examples show two levels of significant adaptation and the one subject (subject G) that did not show adaptation. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 9 Stretch reflex torque adaptation was accompanied by changes in EMG. (A) The EMG from trials 1 and 30 are shown for the biceps and brachioradialis for subject C. The EMGs from trial 30 were lower in amplitude and delayed slightly compared with those from trial 1. The position trace is shown for reference. (B) The RMS power of the EMG signal 0.5sec before θq was correlated with the decrease in reflex torque as shown for a session for subject F (p <.05, Pearson's correlation coefficient). Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 10 An analysis of the number of trials required to estimate spasticity within 1.0Nm suggests that spasticity can be estimated with less than 10 stretches in 74% of cases. The majority of cases requiring more than 10 trials were for subject G. The SD used for the calculations for each session was obtained from all trials of that session. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 11 One session of subject B was extended for an additional 30 trials to obtain additional information regarding the nature of the adaptation process. A linear regression line using the first 30 trials is superimposed on the data (thin black line). In addition, an exponential model is also shown (thick gray line), with parameters estimated from all 60 trials. It is apparent that the exponential model fits the long-term trend in the data better than the linear model. Archives of Physical Medicine and Rehabilitation 2000 81, 269-278DOI: (10.1016/S0003-9993(00)90070-4) Copyright © 2000 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions