David M. Koceja

Postural modulation of the soleus H reflex in young and old subjects

The influence of different static postures on the soleus H reflex was assessed in 15 old (mean age = 76.3 years) and 10 young (mean age = 24.2 years) subjects. H reflex and M wave recruitment curves were obtained under 2 randomly administered conditions: (1) standing; and (2) prone. Once in place, the recording and stimulating electrodes were not removed until the completion of testing, to ensure that exact placement was maintained. A 1 msec current pulse was given transcutaneously to elicit the H reflex and M response. Static postural sway area (cm2) was assessed on a Kistler force platform using custom software (sample rate = 50 Hz/15 sec trials). Results demonstrated that the young subjects reduced the amplitude of the H reflex from the prone (Hmax/Mmax = 73.6%) to the standing (Hmax/Mmax = 59.9%) condition, whereas the old subjects did not (prone = 32.4%, standing = 38.2%). However, within the old group, 2 subgroups emerged--those who depressed the reflex similar to the young subjects (O-D, n = 6) and those who did not depress the reflex (O-ND, n = 9). Furthermore, there were significant differences in postural sway scores between the young and old, between the O-D and O-ND, but not between the O-D and young groups. These results suggest differences in the manner in which young and old subjects modulate the soleus H reflex when standing, and support the view that modulation of the stretch reflex may be important in the control of static posture.

Inhibition of the soleus H-reflex in standing man

There exists evidence to support the notion that the segmental reflex system is not fixed and inflexible, but rather is highly modifiable under a variety of circumstances. In this study the H-wave and M-wave recruitment curves were obtained from 19 subjects, utilizing the procedures outlined by Hugon. Each subject was tested on one day under two randomly administered conditions: (1) standing; and (2) prone. Once in place, the recording and stimulating electrodes were not removed until the completion of the study, to ensure that exact placement was maintained. A percutaneous electrical stimulus (1 ms pulse) was utilized to elicit the pulse. The current was monitored with a current probe, and was increased in 2 mA increments from zero until a maximal M-wave was obtained. An analysis of variance revealed significant increases in the amplitude of the H-wave (P < 0.05) when the subject was prone with no significant increases in the M-wave. The results indicate significantly higher H/M ratios with the subjects in the prone position. Therefore, it is concluded that H-reflex amplitude is tonically depressed when the subject is maintaining a standing position.

Effect of a 12-Week Yoga Intervention on Fear of Falling and Balance in Older Adults: A Pilot Study

OBJECTIVE To determine whether fear of falling (FoF) and balance improved after a 12-week yoga intervention among older adults. DESIGN A 12-week yoga intervention single-armed pilot study. SETTING A retirement community in a medium-sized university town in the Midwest. PARTICIPANTS A convenience sample of adults (N=14) over the age of 65 years who all endorsed an FoF. INTERVENTION Each participant took part in a biweekly 12-week yoga intervention. The yoga sessions included both physical postures and breathing exercises. Postures were completed in sitting and standing positions. MAIN OUTCOME MEASURES We measured FoF with the Illinois FoF Measure and balance with the Berg Balance Scale. Upper- and lower-body flexibility were measured with the back scratch test and chair sit and reach test, respectively. RESULTS FoF decreased by 6%, static balance increased by 4% (P=.045), and lower-body flexibility increased by 34%. CONCLUSIONS The results indicate that yoga may be a promising intervention to manage FoF and improve balance, thereby reducing fall risk for older adults. Rehabilitation therapists may wish to explore yoga as a modality for balance and falls programming; however, future research is needed to confirm the use of yoga in such programming.

Modulation of the Triceps Surae H-Reflex with Training

Thirteen neurologically healthy adults were asked to balance on a specially designed balance board. This board allowed rotation in the sagittal plane only. Muscle activity of the triceps surae and tibialis anterior was sampled at 2 kHz and recorded. When the subject was balanced, soleus H-reflexes were elicited in the right leg with a constant-current stimulus pulse. The peak to peak amplitude of the soleus H-reflex served as the perturbation to the subjects balance as well as the dependent variable in question. Subjects performed three blocks (7 H-reflexes/block) of standing control trials with the balance board supported, and seven blocks of balancing trials. Prior to each block, maximal M-waves were recorded to ensure electrode stability across blocks. Results indicated that the subjects were able to significantly reduce (p < .001) the gain the soleus H-reflex while balancing and after the balance training. As a group, the subjects decreased their peak to peak amplitude of the soleus H-reflex by 26.2 percent from the initial standing block to the last balancing block. Moreover, subjects were also able to significantly reduce the gain of their standing control H-reflexes, supporting the notion of longer-term adaptability of the spinal stretch reflex. It is concluded that the progressive reduction in the H-reflex gain with short-term training may represent functional adaptation in the central nervous system.

Comparison of heteronymous monosynaptic ia facilitation in young and elderly subjects in supine and standing positions

Background The control of posture and balance is a primary concern among the elderly. Postural instability has been identified as a contributor to the greater incidence of falling among this segment of the population. One important neuromuscular mechanism identified as important in the control of posture and balance is the segmental reflex system. The purpose of this study was to examine the role of presynaptic inhibition in modulating the reflex system in young and elderly subjects. Methods To estimate the influence of body position on presynaptic inhibition to the soleus motor pool between young and elderly subjects, 11 young (mean age = 23.9 yrs.) and 9 elderly (mean age = 72.1 yrs.) subjects were examined in two different body positions: supine and standing. This study utilized the heteronymous facilitation protocol, as described by Hultborn et at. (1987). to estimate presynaptic inhibition of the la afferent pathway onto the soleus o-motoneuron pool. Maximal soleus H-reflex (H-max) and motor response (M-max) amplitudes were determined prior to testing at each condition, and the H-max/M-max ratio at each body position was determined. To estimate presynaptic inhibition at each body position, subjects received 24 test soleus H-reflex stimuli (~15% M-max), and 24 soleus H-reflexes conditioned by stimulation of the ipsilateral femoral nerve. Results Results demonstrated a significant decrease in H-max/M-max ratio from supine (66.1%) to standing (56.8%) for the young subjects, whereas the elderly subjects demonstrated no changes in the H-max/M-max ratio between body positions (39.8% supine; 39.8% standing). The conditioning stimulus produced a significant change in the test reflex for the young subjects during supine testing (51.1% increase) but not standing (3.4% increase). The elderly subjects demonstrated no significant changes in the test reflex produced by the heteronymous conditioning at either condition (17.6% increase supine; 4.9% increase standing). Conclusions These results demonstrate differential effects of both H-reflex modulation and heteronymous conditioning for elderly subjects when compared with young adults. These differences may be an adaptive phenomenon of the aging neuromuscular system, exemplified by a decreased ability to modulate the reflex system in the elderly group.

Age-dependent effects of muscle vibration and the Jendrassik maneuver on the patellar tendon reflex response☆

OBJECTIVE To explore possible effects of aging on the excitability of spinal reflexes. DESIGN Using a cross-sectional design, the influences of muscle vibration and the Jendrassik maneuver on patellar tendon reflex function were compared between 30 young adults and 15 older adults. SETTING Motor control research laboratory. SUBJECTS The young adults were volunteers of college age. The older adults (74.5 +/- 4.14 yr) were volunteers from the local community. All subjects were free of medications and neurological conditions that would affect normal neuromuscular responses. MAIN OUTCOME MEASURES A force-time curve analysis of the patellar tendon reflex response was used to assess the inhibition and facilitation of spinal reflexes. In the experimental protocol to assess spinal reflex inhibition, 100 Hz vibration was applied to the right quadriceps muscle. In another experimental protocol, spinal reflex facilitation was assessed using the Jendrassik maneuver. To perform the Jendrassik maneuver, subjects were instructed to grasp their hands together and to pull as hard as possible while breathing normally. After a 2-second count, the tendon tap was delivered to the right leg and the subject was instructed to relax. In both experimental protocols, control patellar tendon reflexes were collected. RESULTS Analysis of variance for reflex peak force revealed a significant 30% reduction in the amount of vibration-induced reflex inhibition with increasing age, and a similar 33% reduction in the amount of Jendrassik maneuver facilitation observed for the older adults as compared with the younger adults. CONCLUSION These results support the hypothesis that inhibitory and excitatory influences acting on the alpha motoneuron pool are different in young and older adults.

Regulation of motor output between young and elderly subjects

OBJECTIVES Considerable information exists concerning the differences in motoneuron pool (MP) excitability between young and elderly subjects. A recent study demonstrated decreased heteronymous Ia facilitation with aging, suggesting increased presynaptic inhibition (PI) with increasing age as a mechanism for this change (Morita et al., Exp Brain Res 104 (1995) 167). It has been suggested that during voluntary movement, supraspinal, and possibly, segmental mechanisms (Hultborn et al., J Physiol 389 (1987) 757) modulate this inhibition. It is theorized that PI can modulate the recruitment gain of the MP during movement without altering the excitability of the motoneurons. Therefore, the purpose of this study was to examine the roles of PI and volitional volleys in modulating MP output in young and elderly subjects. METHODS Twenty apparently healthy females participated in this study, 10 college aged (mean age, 22.4+/-2.8 years) and 10 independent, community dwelling elderly (mean age, 77.6+/-5.4 years). All subjects were tested in a semi-recumbent position. H-reflexes were elicited at rest, and at 10 and 20% of maximal voluntary contraction. To assess MP output, background electromyography (EMG) was monitored prior to stimulation. The stimulus intensity was adjusted during volitional contractions to ensure similar control reflexes (25% of the maximal motor response (M-max)) at each level of contraction. RESULTS Control reflexes at each level of volitional contraction (rest, 10 and 20%) were similar for both groups. To assess PI and to estimate the extent to which a change in the H-reflex amplitude reflects a change in MP gating, the common peroneal nerve was stimulated at 1.5 times the motor threshold 100 ms prior to stimulation of the tibial nerve. Significantly greater PI was observed for the young subjects at rest (5 vs. 13% M-max). At both 10 and 20% levels of voluntary contraction, the conditioned reflex was significantly different from rest for the young subjects. The elderly subjects, in contrast, failed to modulate the conditioned reflex until the 20% of maximal voluntary contraction (MVC) condition. When examining the recruitment gain in the MP during the PI condition (H-reflex amplitude as a function of EMG levels), a significant group effect was observed, with the young subjects demonstrating significantly higher PI gain. CONCLUSIONS These results indicate differential control of MP output (e.g. PI vs. volitional volleys) in young and elderly subjects.

Mood, neuromuscular function, and performance during training in female swimmers.

The effect of seasonal changes in training load on mood, neuromuscular function, and measures of physical power were examined in 12 collegiate women swimmers. These subjects were studied at three training stages during a competitive swim season: baseline (5,000 m.d-1), peak training (8,300 m.d-1), and taper (2,300 m.d-1). Mood was evaluated with the Profile of Mood States. Neuromuscular function was measured via the soleus Hoffmann-reflex (H-reflex). Anaerobic swimming power was assessed with a 30-s tethered swim test, and maximal aerobic power was determined following a maximal 378-m swim. Repeated measures ANOVA revealed that at peak training H-reflex and peak anaerobic swimming power were reduced (P < 0.05) below baseline values by 8.6% and 9.4%, respectively, and total mood disturbance was elevated above baseline (P < 0.01). These variables returned to baseline values at the taper assessment. H-reflex values were correlated with peak (r = 0.52, P < 0.01) and mean (r = 0.39, P < 0.05) anaerobic swimming power. Total mood disturbance was correlated (r = -0.34, P < 0.05) with mean swimming power. The results suggest that neurological mechanisms play a role in the adaptations that result from periodized training.

Effect of a Reduced Base of Support in Standing and Balance Training on the Soleus H-reflex

The present study provides evidence that a reflex at the segmental level can adapt over a two hour experiment in a functionally appropriate manner in response to a balance training task. Subjects (N = 9) received soleus (S) H-reflexes in blocks of seven trials while free standing on a normal base-of-support (NBOS) and while standing on a plafform with a reduced base-of-support (RBOS) in the sagittal plane. During the RBOS condition, the H-reflex served as a postural perturbation. Subjects were instructed to suppress the H-reflex when it was evoked, as an attempt to maintain a balanced state. Background EMG from the S and tibialis anterior muscles, the S M-wave, and stimulus current were maintained at a constant level during the experiment. Subjects initially received a block of NBOS trials, followed by 4 RBOS blocks (training), a second NBOS block, four additional RBOS blocks, and a third NBOS block with the protocol repeated on three different days (D1, D2 and D3) within the same week. The S H/M ratio was depressed 9% upon standing on the RBOS. With training the S H/M ratio decreased by 22% on Dl, 18% on D2 and 6% on D3. The ratio between the H-reflex and background S EMG (H-reflex gain) decreased 10% on D1, 40% on D2 and 23% on D3 when the first NBOS and first RBOS blocks were compared. Due to a slight increase in the S EMG across blocks, the H-reflex gain decreased considerably more across blocks than the H/M ratio. Although the S H/M ratio underwent an 7% decrease from D1 to D3, the differences were not significant. Individually, however, six of the nine subjects decreased their H/M ratios from 12–42% across days. The results may reflect the inception of longer-term adaptations of the segmental stretch reflex system.

The effects of vision and task complexity on Hoffmann reflex gain

Previous research demonstrates modulation of the Hoffmann reflex amplitude and gain during changes in environmental conditions. H-reflex gain (defined in this study as the ratio of H-reflex amplitude to average soleus background EMG) is considered a functional measure of reflex modulation. In this study the effects of manipulating visual input and surface stability were to investigated in 17 subjects under four experimental conditions: (1) vision-stable surface, (2) no vision-stable surface, (3) vision-unstable surface, and (4) no vision-unstable surface. In each condition, subjects performed fifteen trials of a single leg stance for 7 s. The H-reflex was electrically elicited at the end of each trial by delivering a 1 ms square wave stimulation to the tibial nerve in the popliteal online for each trial (sampling rate = 2 kHz). An analysis of variance revealed significant decreases in H-reflex gain for the visual (F1.16 = 4.71, P < 0.05) and, surface conditions (F1.16 = 7.67, P < 0.05), however there was no interaction (F1.16 = 0.48, P < 0.05), between these variables. These results suggest that supraspinal mechanisms, possibly presynaptic inhibition, modulate H-reflex gain across environmental conditions. We conclude that visual and possibly cutaneous inputs were responsible for driving presynaptic inhibition and thus decreasing H-reflex gain.