Tendon Tap Reflexes Research Articles

Plantar flexor muscle stretching depresses the soleus late response but not tendon tap reflexes.

The purpose of this study was to investigate changes in muscle spindle sensitivity with early and late soleus reflex responses via tendon taps and transcranial magnetic stimulation, respectively, after an acute bout of prolonged static plantar flexor muscle stretching. Seventeen healthy males were tested before and after 5min (5×60-s stretches) of passive static stretching of the plantar flexor muscles. Maximal voluntary isometric torque and M wave-normalized triceps surae muscle surface electromyographic activity were recorded. Both soleus tendon reflexes, evoked by percussion of the Achilles tendon during rest and transcranial magnetic stimulation-evoked soleus late responses during submaximal isometric dorsiflexion were also quantified. Significant decreases in maximal voluntary isometric plantar flexion torque (-19.2±13.6%, p=.002) and soleus electromyographic activity (-20.1±11.4%, p<.001) were observed immediately after stretching, and these changes were highly correlated (r=0.76, p<.001). No changes were observed in tendon reflex amplitude or latency or peak muscle twitch torque (p>.05). Significant reductions in soleus late response amplitudes (-46.9±36.0%, p=.002) were detected, although these changes were not correlated with changes in maximal electromyographic activity, torque or tendon reflex amplitudes. No changes in soleus late response latency were detected. In conclusion, impaired neural drive was implicated in the stretch-induced force loss; however, no evidence was found that this loss was related to changes in muscle spindle sensitivity. We hypothesize that the decrease in soleus late response indicates a stretch-induced reduction in a polysynaptic postural reflex rather than spindle reflex sensitivity.

Modulation of tendon tap reflex activation of soleus motor neurons with reduced stability tandem stance

Reduced stability while standing typically decreases the soleus muscle Hoffmann (H-) reflex amplitude, purportedly to prevent the Ia afferent signal from excessively activating spinal motor neurons during the unstable stance. H-reflex measures, however, by excluding the spindle do not reflect the actual effect of the Ia pathway (i.e. the combined effects of spindle sensitivity and Ia presynaptic inhibition) on motor neuron activation, as tendon tap reflex measures can. But the effect of stance stability on soleus muscle tendon tap reflex amplitude is largely unknown. This study examined 30 young adults (mean(s), 21(2) years) as they stood in a wide stable stance position and an unstable tandem stance with a reduced base of support. Standing body sway, the amplitude of the soleus muscle tendon tap reflex, background EMG and tap force were measured in both stances. A repeated measured design t-test was calculated for each variable. Most subjects (69%) decreased tendon tap reflex amplitude when in the tandem stance position (mean decrease 11.6%), compared to the wide stance (wide stance 0.248(0.124) mV, tandem stance 0.219(0.119) mV, p < 0.05, Cohen’s d = 0.24 small) with no significant differences in background soleus and tibialis anterior EMG, and tap force across the stances. There was no relationship between the modulation of the tendon tap reflex amplitude across the stances and standing body sway in the tandem stance. Results support the idea that for most subjects examined, during a less stable stance the Ia excitation of motor neurons is decreased, likely by presynaptic inhibition, thereby avoiding potential instability in the reflex loop or saturating the reflex pathway and possibly interfering with descending control of the involved spinal motor neurons.

Increased human stretch reflex dynamic sensitivity with height-induced postural threat.

Threats to standing balance (postural threat) are known to facilitate soleus tendon-tap reflexes, yet the mechanisms driving reflex changes are unknown. Scaling of ramp-and-hold dorsiflexion stretch reflexes to stretch velocity and amplitude were examined as indirect measures of changes to muscle spindle dynamic and static function with height-induced postural threat. Overall, stretch reflexes were larger with threat. Furthermore, the slope (gain) of the stretch-velocity vs. short-latency reflex amplitude relationship was increased with threat. These findings are interpreted as indirect evidence for increased muscle spindle dynamic sensitivity, independent of changes in background muscle activity levels, with a threat to standing balance. We argue that context-dependent scaling of stretch reflexes forms part of a multisensory tuning process where acquisition and/or processing of balance-relevant sensory information is continuously primed to facilitate feedback control of standing balance in challenging balance scenarios. Postural threat increases soleus tendon-tap (t-) reflexes. However, it is not known whether t-reflex changes are a result of central modulation, altered muscle spindle dynamic sensitivity or combined spindle static and dynamic sensitization. Ramp-and-hold dorsiflexion stretches of varying velocities and amplitudes were used to examine velocity- and amplitude-dependent scaling of short- (SLR) and medium-latency (MLR) stretch reflexes as an indirect indicator of spindle sensitivity. t-reflexes were also performed to replicate previous work. In the present study, we examined the effects of postural threat on SLR, MLR and t-reflex amplitude, as well as SLR-stretch velocity scaling. Forty young-healthy adults stood with one foot on a servo-controlled tilting platform and the other on a stable surface. The platform was positioned on a hydraulic lift. Threat was manipulated by having participants stand in low (height 1.1m; away from edge) then high (height 3.5m; at the edge) threat conditions. Soleus stretch reflexes were recorded with surface electromyography and SLRs and MLRs were probed with fixed-amplitude variable-velocity stretches. t-reflexes were evoked with Achilles tendon taps using a linear motor. SLR, MLR and t-reflexes were 11%, 9.5% and 16.9% larger, respectively, in the high compared to low threat condition. In 22 out of 40 participants, SLR amplitude was correlated to stretch velocity at both threat levels. In these participants, the gain of the SLR-velocity relationship was increased by 36.1% with high postural threat. These findings provide new supportive evidence for increased muscle spindle dynamic sensitivity with postural threat and provide further support for the context-dependent modulation of human somatosensory pathways.

Standardization of the Jendrassik maneuver in Achilles tendon tap reflex

ObjectiveFor many decades, the Jendrassik maneuver (JM) has been used as a reinforcement for stretch reflexes, although the underlying mechanism of this reinforcement is still not fully understood. Moreover, the term JM has been used for many different muscle contraction strategies as there is no fixed movement for the maneuver in the literature. In this study, we aimed to investigate the effects of clenched hand pull, teeth clenching, and their combined effects to reach standardization. MethodsAchilles tendon tap reflex responses in the soleus were recorded during rest (R), hand pull (HP), teeth clench (TC), and HP + TC combined, hereafter referred to as the JM. ResultsReflex response amplitudes significantly increased during JM, HP, and TC in the soleus. HP and JM significantly changed the background activity in the soleus, but TC alone did not. ConclusionThese results suggest that dominantly presynaptic disinhibitory mechanisms may be responsible for the increase in the tendon tap reflex during HP, TC, and JM. SignificanceBecause the findings indicate that HP increases the background activity of the soleus, we suggest that researchers should use only TC during the Jendrassik maneuver to avoid any confounding background activity change.

One minute static stretch of plantar flexors transiently increases Hreflex excitability and exerts no effect on corticospinal pathways.

What is the central question of this study? What mediates neural responses following static stretching, and how long do these influences last? What is the main finding and its importance? This study shows that 1 min of static stretching inhibits the tendon tap reflex and facilitates the Hreflex without influencing motor-evoked potentials. The results indicate that at least two different mechanisms mediate neural responses after static stretching. The purpose of this study was to determine whether the neural responses observed after static stretching are mediated by sensitivity of muscle spindles, spinal excitability or cortical excitability and how long these influences last. Nineteen volunteers (25.7±5.6years old) were tested for the tendon tap reflex (T-reflex), Hreflex and motor-evoked potentials on ankle flexors and extensors immediately, 5 and 10min after 1 min static stretching applied at individual maximal ankle dorsiflexion, as well as immediately, 5 and 10min after a control period of the same duration. Comparison of measurements collected immediately after stretching or control conditions revealed that the T-reflex was weaker after stretching than after control (-59.2% P=0.000). The T-reflex showed a slow recovery rate within the first 150s after stretching, but 5 min after the inhibition had disappeared. The Hreflex increased immediately after stretching (+18.3%, P=0.036), showed a quick tendency to recover and returned to control values within 5min from stretching. Motor-evoked potentials were not affected by the procedure. These results suggest that 1min of static stretching primarily decreases muscle spindle sensitivity and facilitates the Hreflex, whereas effects on the motor cortex can be excluded.

National Rugby League athletes and tendon tap reflex assessment: a matched cohort clinical study

BackgroundLimited research suggests elite athletes may differ from non-athletes in clinical tendon tap reflex responses.MethodsIn this matched cohort study, 25 elite rugby league athletes were compared with 29 non-athletes to examine differences in tendon reflex responses. Relationships between reflex responses and lengths of players’ careers were also examined. Biceps, triceps, patellar and Achilles tendon reflexes were clinically assessed.ResultsRight and left reflexes were well correlated for each tendon (rS = 0.7–0.9). The elite rugby league athletes exhibited significantly weaker reflex responses than non-athletes in all four tendons (p < 0.005). Biceps reflexes demonstrated the largest difference and Achilles reflexes the smallest difference. Moderate negative correlations (rS = −0.3–0.6) were observed between reflex responses and lengths of players’ careers.ConclusionsFuture research is required to further elucidate mechanisms resulting in the observed differences in tendon reflexes and to ensure clinical tendon tap examinations and findings can be interpreted appropriately in this athletic population.

Reliability of the Achilles tendon tap reflex evoked during stance using a pendulum hammer

The tendon tap reflex (T-reflex) is often evoked in relaxed muscles to assess spinal reflex circuitry. Factors contributing to reflex excitability are modulated to accommodate specific postural demands. Thus, there is a need to be able to assess this reflex in a state where spinal reflex circuitry is engaged in maintaining posture. The aim of this study was to determine whether a pendulum hammer could provide controlled stimuli to the Achilles tendon and evoke reliable muscle responses during normal stance. A second aim was to establish appropriate stimulus parameters for experimental use. Fifteen healthy young adults stood on a forceplate while taps were applied to the Achilles tendon under conditions in which postural sway was constrained (by providing centre of pressure feedback) or unconstrained (no feedback) from an invariant release angle (50°). Twelve participants repeated this testing approximately six months later. Within one experimental session, tap force and T-reflex amplitude were found to be reliable regardless of whether postural sway was constrained (tap force ICC=0.982; T-reflex ICC=0.979) or unconstrained (tap force ICC=0.968; T-reflex ICC=0.964). T-reflex amplitude was also reliable between experimental sessions (constrained ICC=0.894; unconstrained ICC=0.890). When a T-reflex recruitment curve was constructed, optimal mid-range responses were observed using a 50° release angle. These results demonstrate that reliable Achilles T-reflexes can be evoked in standing participants without the need to constrain posture. The pendulum hammer provides a simple method to allow researchers and clinicians to gather information about reflex circuitry in a state where it is involved in postural control.

EMG spectral differences among the quadriceps femoris during the stretch reflex

The purpose of this study was to examine the electromyographic (EMG) spectral characteristics of the quadriceps femoris muscles during tendon tap stretch reflexes. Sixteen healthy subjects (mean ± SD age = 21.2 ± 2.8 years) performed tendon tap reflexes of the leg extensors as surface EMG signals were detected from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles of the dominant thigh. All EMG signals were processed with a wavelet analysis, and the resulting spectra were decomposed with nonparametric spectral decomposition. The results showed that the spectra for the VL had significantly more high-frequency power than those for the RF and VM, with similar spectral shapes for the RF and VM. These findings could be due to differences in the width of the innervation zone, or the fiber type composition of the muscles, although the latter seems to be more likely.

The effects of body position and muscle activation on patellar tendon reflex properties

Our purpose was to examine the effects of body position and a low-intensity voluntary contraction on patellar tendon tap reflex properties.Surface electromyography, torque, and accelerometry signals were obtained from 30 subjects (25.0 ± 4.6 years) during patellar tendon taps. These signals were used to quantify reflex magnitude and the subcomponents of reflex latency for each subject in the upright position (i.e. control), supine position, and during α–γ coactivation (i.e. a low-intensity contraction). The Jendrassik maneuver was also performed to examine any potential benefits beyond that of standard reinforcement.Neither experimental condition significantly altered reflex magnitude. However, the supine body position condition resulted in a significant decrease in reflex latency (p = 0.037) which appears largely attributable to a decreased electromechanical delay. Interestingly, the low-intensity contraction had no effect on any of the latency components.The assessment of reflex latency can be improved by utilizing a supine body position. This effect may be due to the presence of slack within musculotendinous structures during the traditional upright position. A voluntary contraction, however, does not enhance the reflex response beyond that of standard reinforcement. Limitations regarding the use of a light contraction during tendon taps are discussed for future investigations.

Brain motor control assessment of upper limb function in patients with spinal cord injury

Background: The brain motor control assessment (BMCA) for the upper limb has been developed to add resolution to the clinical evaluation in patients with spinal cord injury (SCI). BMCA is a surface electromyography (sEMG)-based measure of motor output from the central nervous system during a variety of reflex and voluntary motor tasks performed under strictly controlled conditions.Method: Nine participants were recruited and assessed four times over a period of 1 year in a prospective cohort study design. The sEMG of 15 muscles (7 muscles from each upper limb and rectus abdominis) were recorded throughout the following stages of the BMCA protocol: (i) relaxation, (ii) reinforcement maneuvers, (iii) voluntary tasks, (iv) tendon-tap reflex responses, (v) vibration responses.Results: Similarity index (SI) values were significantly lower in the SCI group for unilateral shoulder abduction (P = 0.006) and adduction (P = 0.021), elbow extension (P = 0.038), wrist flexion/extension with palm up (P < 0.001; P < 0.001) and wrist flexion with palm down (P = 0.016). sEMG magnitudes were also significantly lower in the SCI group for wrist flexion/extension with palm up (P < 0.001; P = 0.042). SI changes over time were significant for tasks related to wrist joint (P = 0.002).Conclusion: Clinicians who are involved in rehabilitation of patients with SCI can use the BMCA to assess their patients’ motor control abilities and monitor their progression throughout their rehabilitation process. The results of this type of neurophysiological assessment might be useful to tailor therapeutic strategies for each patient.

Afferent control of walking: Are there distinct deficits associated to loss of fibres of different diameter?

ObjectivesTo compare the gait pattern in patients affected by different types of neuropathy. MethodsWe recruited healthy subjects (HS, n=38), patients with Charcot–Marie–Tooth disease type 1A (CMT1A) (n=10) and patients with diabetic neuropathy (DNP) (n=12). Neuropathy impairment score and neuropathy score were assessed. Body sway during quiet stance, and spatio-temporal gait parameters were recorded. ResultsMost patients had reduced or absent tendon-tap reflexes. Strength of foot dorsiflexor muscles (p<0.05) and conduction velocity (CV) of leg nerves (p<0.0001) were more impaired in CMT1A than DNP, whereas joint-position sense was more affected (p<0.05) in DNP. Body sway while standing was larger in DNP compared to CMT1A and HS (p<0.01 and p<0.0001 respectively). During gait, the distribution of foot sole contact pressure was abnormal in CMT1A (p<0.05) but not in DNP. Velocity and step length were decreased, and foot yaw angle at foot flat increased, in DNP with respect to CMT1A and HS (both variables, p<0.001). Gait velocity and step length were decreased (p<0.005) also in CMT1A, but to a smaller extent than in DNP, so that the difference between patient groups was significant (p<0.0005). Duration of the double support was protracted in DNP compared to CMT1A and HS (p<0.0005). For DNP only, velocity of gait and duration of single support were correlated (p<0.05) both to sway path and lower limb muscle strength. ConclusionsChanges in both body sway and stance phase of gait were larger in DNP than CMT1A, indicating more impaired static and dynamic control of balance when neuropathy affects the small in addition to the large afferent fibres. Diminished somatosensory input from the smaller fibres rather than muscle weakness or foot deformity plays a critical role in the modulation of the support phase of gait. SignificanceThe analysis of balance and gait in patients with neuropathy can offer a tool for understanding the nature and functional impact of the neuropathy and should be included in their functional evaluation.

EMG analysis tuned for determining the timing and level of activation in different motor units

Recruitment patterns and activation dynamics of different motor units greatly influence the temporal pattern and magnitude of muscle force development, yet these features are not often considered in muscle models. The purpose of this study was to characterize the recruitment and activation dynamics of slow and fast motor units from electromyographic (EMG) recordings and twitch force profiles recorded directly from animal muscles. EMG and force data from the gastrocnemius muscles of seven goats were recorded during in vivo tendon-tap reflex and in situ nerve stimulation experiments. These experiments elicited EMG signals with significant differences in frequency content ( p < 0.001). The frequency content was characterized using wavelet and principal components analysis, and optimized wavelets with centre frequencies, 149.94 Hz and 323.13 Hz, were obtained. The optimized wavelets were used to calculate the EMG intensities and, with the reconstructed twitch force profiles, to derive transfer functions for slow and fast motor units that estimate the activation state of the muscle from the EMG signal. The resulting activation–deactivation time constants gave r values of 0.98–0.99 between the activation state and the force profiles. This work establishes a framework for developing improved muscle models that consider the intrinsic properties of slow and fast fibres within a mixed muscle, and that can more accurately predict muscle force output from EMG.

Neuromuscular and psychological influences on range of motion recovery in anterior cruciate ligament reconstruction patients

To identify distinguishing characteristics for knee surgery patients who experience a protracted recovery process, we sought to determine if there is an association between the neuromuscular stretch reflex and psychological factors of pain perception and anxiety on the range of motion (ROM) recovery rate of post-operative anterior cruciate ligament reconstruction (ACLR) rehabilitation patients. The ACLR participants were categorized into a slow recovery group (SRG: >6 weeks to recover 0–125° knee flexion [ n = 10]) and a normal recovery group (NRG: <6 weeks to recovery 0–125° knee flexion [ n = 12]). Control participants ( n = 22) were age, gender and activity-level matched to the surgical participants. Neuromuscular testing consisted of sagittal plane video kinematics of the Wartenberg Pendulum Test for determining lower limb stiffness indices and electromyography-monitored patellar tendon tap reflex responses. Psychological and health status assessments consisted of the State–Trait Anxiety Inventory and SF-36™ Health Survey. Data revealed that neuromuscular reflex profiles, lower limb stiffness indices, pain, anxiety and SF-36™ indices of function were not significantly different between the two surgical groups (SRG and NRG). The surgical groups exhibited significantly greater pain (2.67 ± 2.27 SRG, 1.49 ± 1.15 NRG) than the control group ( p ⩽ .05). SF-36™ indices were significantly lower for the surgical groups for total score (546.55 ± 94.70 SRG, 577.57 ± 125.58 NRG), function 69.00 ± 20.24 SRG, 67.08 ± 19.12 NRG), role physical (53.75 ± 22.85 SRG, 53.12 ± 23.15 NRG), social (76.24 ± 25.31 SRG, 65.62 ± 27.24 NRG), and emotional (82.49 ± 19.81 SRG, 81.38 ± 23.02 NRG) subscales ( p ⩽ .05). These results suggest that neuromuscular reflex responses, visual analogue scale (VAS) pain, and anxiety are not distinguishing factors for ROM recovery rate between the SRG and NRG. Decreased SF-36™ indices, including pain as it influences function, though clinically relevant factors, were not statistically associated with post-operative ROM recovery rate.

Soleus T reflex modulation in response to spinal and tendinous adaptations to unilateral lower limb suspension in humans

To investigate the influence of tendinous and synaptic changes induced by unilateral lower limb suspension (ULLS) on the tendon tap reflex. Eight young men underwent a 23-day period of ULLS. Muscle cross-sectional area (CSA), torque and electromyographic (EMG) activity of the plantar flexor muscles (normalized to the M wave), Achilles tendon-aponeurosis mechanical properties, soleus (SOL) H and T reflexes and associated peak twitch torques were measured at baseline, after 14 and 23 days of ULLS, and 1 week after resuming ambulatory activity. Significant decreases in muscle CSA (-9%), in maximal voluntary torque (-10%) and in the associated SOL EMG activity (-16%) were found after ULLS (P < 0.05). In addition to a 36% (P < 0.01) decrease in tendon-aponeurosis stiffness, normalized H reflex increased by 35% (P < 0.05). An increase in the slope (28%, P < 0.05) and intercept (85%, P < 0.05) of the T reflex recruitment curve pointed to an increase in the gain and to a decrease in the sensitivity of this reflex, possibly resulting from the decrease in the tendon-aponeurosis stiffness at low forces. Following ULLS, changes in tendinous stiffness correlated with changes in neuromuscular efficiency (peak twitch torque to reflex ratio) at higher tendon tap forces. These findings point out the dual and antagonistic influences of spinal and tendinous adaptations upon the tendon tap reflex in humans under conditions of chronic unloading. These observations have potential implications for the sensitivity of the short-latency Ia stretch response involved in rapid compensatory contractions to unexpected postural perturbations.

Spasticity-spastic movement disorder

Antispastic medications that are directed to reduce clinical signs of spasticity, such as exaggerated reflexes and muscle tone, do not improve the movement disorder. Medication can even increase weakness which might interfere with functional movements, such as walking. In clinical practice, signs of exaggerated tendon tap reflexes associated with muscle hypertonia are the consequence of spinal cord injury (SCI). They are generally thought to be responsible for spastic movement disorders. Most antispastic treatments are, therefore, directed at the reduction of reflex activity. In recent years, a discrepancy between spasticity as measured in the clinic and functional spastic movement disorder was noticed, which is primarily due to the different roles of reflexes in passive and active states, respectively. We now know that central motor lesions are associated with loss of supraspinal drive and defective use of afferent input with impaired behaviour of short-latency and long-latency reflexes. These changes lead to paresis and maladaptation of the movement pattern. Secondary changes in mechanical muscle fibre, collagen tissue, and tendon properties (e.g., loss of sarcomeres, subclinical contractures) result in spastic muscle tone, which in part compensates for paresis and allows functional movements on a simpler level of organisation. Antispastic drugs should primarily be applied in complete SCI. In mobile patients they can accentuate paresis and therefore should be applied with caution.

Paradoxical modulation of tendon tap reflex during voluntary contraction in Parkinson's disease

Objective Inadequate supraspinal modulation of spinal motor control mechanisms such as α–γ coactivation is supposed to cause difficulty in maintaining proper voluntary contraction in Parkinson's disease (PD). Methods Subjects were 42 patients with PD and 20 normal volunteers. Soleus H-reflex and tendon tap reflex (T-reflex) were recorded. The maximal reflexes ( H max and T max) at rest were recorded first. Next, the stimulus intensities were fixed to obtain a reflex size of around 25% of M max at rest for both H- and T-reflexes, and the reflexes were recorded at rest, during tonic plantarflexion (TPF), and at the onset of plantarflexion. Results H max at rest was 55% and T max 30% in normal subjects, while they were 36 and 31%, respectively, in PD. The size ratio of T max and H max at rest in PD was larger than normal. In PD, the size of H-reflex increased with TPF as in normal subjects, but T-reflex decreased. These changes in T-reflex were correlated with the grade of rigidity, bradykinesia, and time for 10 m gait. H-reflex had no such correlations. Conclusions T-reflex was abnormally modulated in PD especially during tonic contraction. Significance Inappropriate supraspinal modulation of the spinal reflex pathways disturbs motor performance in PD.

Neuromuscular Characteristics of Endurance- and Power-Trained Athletes

In response to chronic physical training, the human neuromuscular system undergoes significant and specific adaptations. More importantly, these influences are the result of the type and quantity of physical activity. One of the simplest neuromuscular mechanisms is the spinal stretch reflex. The reflex system was previously viewed as inflexible, with a relatively fixed response that could vary only slightly. However, more recent data have identified an adaptive plasticity in the reflex system. In this respect, the reflex system can be used to assess training and aging adaptations of the human neuromuscular system. Due to their methodological simplicity, both the tendon-tap reflex and the electrically evoked Hoffmann reflex (H-reflex) can be used to assess training adaptations of the human neuromuscular system. The purpose of this paper is to review briefly the tendon-tap and H-reflex paradigms and delineate the research findings pertaining to changes in the reflex system with physical training. For purposes of clarity, this discussion will be divided into the following: (a) differences observed in the tendon-tap reflex, (b) differences observed in the H-reflex, and (c) role of interneurons in mediating these changes.

Chemical ablation of sensory afferents in the walking system of the cat abolishes the capacity for functional recovery after peripheral nerve lesions.

Weakening the ankle extensor muscles of cats by denervation of the synergists of the medial gastrocnemius (MG) muscle results in transient increase in yield at the ankle during early stance. Recovery of ankle function occurs over a period of 1-2 weeks, is use-dependent, and is associated with increases in the strength of reflexes from MG group I muscle afferents and an increase in the magnitude of bursts in the MG muscles during stance. These observations have led to the hypothesis that feedback from large muscle afferents is necessary for functional recovery. In this investigation we have tested this hypothesis by examining functional recovery in animals treated with pyridoxine, a drug known to destroy large muscle afferents. In four adult animals we confirmed that pyridoxine abolished the group I-mediated tendon-tap reflex in the ankle extensor muscle, and subsequently found that group I afferents from MG were either destroyed or non-conducting. Immediately after pyridoxine treatment the animals showed severe locomotor dysfunction but all recovered significantly over a period of 1 or 2 months and showed only minor kinematics deficits at the time of the muscle denervations. In all four pyridoxine-treated animals, weakening of the ankle extensors by denervation of the synergists of the MG muscle resulted in a large increase in yield at the ankle that persisted almost unchanged for a month after the operation. The magnitude of burst activity in the MG muscle during early stance of the pyridoxine-treated animals either did not increase or increased only slightly after the denervation of synergists. These observations are consistent with the hypothesis that feedback from group I afferents is necessary for functional recovery in untreated animals.

Warm-up Activities and Their Influences on Neuromuscular and Functional Indices

Introduction: Researchers show that a high intensity warm-up prior to an explosive event, can improve one's performance [Gullich and Schmidtbleicher, 1996]. Post activation potentiation (PAP) is cited as the reason for these increases in performance. It is thought that PAP causes an increase in Ca++ sensitivity within the actomyosin complex [Sweeney, Bowman, and Stull, 1993]. However, it is not known whether it is the warm-up phase occurring before or the intense activity phase of the entire pre-event protocol that causes the neuromuscular changes often cited as post activation potentiation. So, the purpose of this study was to examine neuromuscular and functional outcomes of post activation stimulation caused by distinct phases of voluntary muscular activation. Methods: This study employed two separate oneway repeated measures designs. The sessions were single leg leg extension (LE) and tendon tap reflex (TTR); characterized by performing the activity using a resistance equal to 40% 1repetition maximum (1RM) and the muscle activity recorded within the rectus femoris caused by 6 N force rapidly applied to the patellar tendon respectively. Dependent measures were average rectus femoris EMG (AEMG) during the LE session and AEMG and peak isometric force (PIF) produced during the 120-ms post stimulus period within the TTR session. Data from nine subjects (174.66 ± 10.54 cm; 76.22 ± 13.22 kg; 21.67 ± 1.58 yrs) was collected using Noraxon telemetered EMG hardware and a tensile calibrated load cell integrated by DataPac 2000 software. The EMG signal, from both sessions, was processed (passive demeaning and RMS smoothed (20-msec)). The processed AEMG and the raw PIF were then normalized to their baseline values. The warm-up phase during each session consisted of a series of submaximal high bar parallel back squats: 1 × 5 at 50% of 1RM, 1 × 5 at 65% of 1RM, 1 × 3 at 75% of 1RM, 1 × 1 at 90% of 1RM with a three minute rest interval between sets and a five minute rest interval separating the warm-up phase from the data collection. At the conclusion of the 5-minute rest interval, the subjects began the intense activity phase, which consisted of 5 × 1 at 90% 1-RM with three minutes rest in between sets and a five-minute rest interval at the conclusion of the squat activity. Data collection resumed at the conclusion of this rest interval. Results: Significance was found during the warm-up phase and the intense phase on AEMG compared to baseline during the TTR (P ≤ 0.10). No significant effect was found on the AEMG during the LE session for any phase. PIF was significantly different for the intense phase (P ≤ 0.10). Discussion: PAP can alter segmental reflexive activity via neuromuscular changes and increasing force production. Neuromuscular changes can occur within any type of warm-up activity. Our study confirms that PAP can occur in untrained as well as recreationally trained individuals. Other studies have confirmed that PAP can occur in elite athletes as well [Gullich and Schmidtbleicher, 1996]. Future studies may want to investigate if and how PAP can alter motor unit recruitment patterns.

Basic principles and therapy of spasticity

An acute central nervous system lesion is followed by a phase of "shock" with flaccid muscle tone. After some weeks the syndrome of spastic paresis develops which is characterized by increased muscle tone and exaggerated tendon tap reflexes. During the last years it could be shown that the characteristic spastic movement disorder is mainly due to secondary changes of muscle properties which require a specific treatment. Exaggerated reflexes do only little contribute to the movement disorder.