Tendon Tap Research Articles

A new method to determine stretch reflex latency.

Motion artifact signals (MASs) created by the relative movement of intramuscular wire electrodes are an indicator of the mechanical stimulus arrival time to the muscle belly. This study proposes a method that uses wire electrodes as an intramuscular mechanosensor to determine the stretch reflex (SR) latency without lag time. Gastrocnemius SR was induced by tendon tap, heel tap, and forefoot tap. The MASs recorded by intramuscular wire electrodes were extracted from background electromyographic activity using the spike-triggered averaging technique. Simultaneous recordings were obtained from multiple sites to validate the MAS technique. Using intramuscular wire electrodes, the MASs were successfully determined and extracted for all stimulus sites. In the records from the rectus femoris, MASs were also successfully extracted; thus, the reflex latency could be calculated. Wire electrodes can be used as an intramuscular mechanosensor to determine the mechanical stimulus arrival time to the muscle belly.

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.

Stretch reflexes

Many of us know about stretch reflexes from the doctor's office, when a physician taps the tendon near our kneecap to elicit a quick knee extension. This procedure is used as a diagnostic tool to determine the integrity of the spinal cord and the extension response it elicits may seem otherwise useless. In fact, the tendon tap taps into one aspect of a critical building block of mammalian motor control, the stretch reflexes. Stretch reflexes are often thought to quickly resist unexpected changes in muscle length via a very simple circuit in the spinal cord, and this is one circuit that the tendon tap engages. It turns out, however, that stretch reflexes support a myriad of functions and are highly flexible. Under naturalistic conditions, stretch reflexes are shaped by peripheral physiology and engage neural circuits spanning the spinal cord, brainstem and cerebral cortex. In this Primer, we outline what is currently known about stretch reflex function and its underlying mechanisms, with a specific focus on how the cascade of nested responses collectively known as stretch reflexes interact with and build off of one another to support real-world motor behavior.

Characterization of Differences in the Time Course of Reflex and Voluntary Responses Following Botulinum Toxin Injections in Chronic Stroke Survivors.

Spasticity is a major impairment that can occur following a hemispheric stroke and is often treated with injections of botulinum toxin, a neurotoxin that impairs transmission at the neuromuscular junction. Hyperreflexia is a defining feature of spasticity. Our main objective here was to quantify the time course of changes in the deep tendon reflex (DTR) responses and voluntary activation capacity following BT injection as well as to track changes in a clinical assessment of spasticity. Four chronic stroke survivors, scheduled to receive BT in their Biceps Brachii(BB) as part of their clinical care plan, were recruited for repeated testing sessions over the course of 4 months post injection. Both surface BB EMG reflex response to bicipital tendon taps as well as signals of applied tendon tap forces were recorded before and up to 18 weeks post-BT. Voluntary force and biceps EMG signals were also recorded during maximum voluntary (isometric) contractions (MVC) at each testing session. Our results show major reductions (up to 75%) in voluntary sEMG and force arising between 11 to 35 days post-BT-injection. The stretch reflex gain declined two weeks after the maximal reductions in voluntary EMG and force. Paradoxically, there was a short-term increase in stretch reflex gain, in three out of four participants, approximately 11-35 days post BT. The time course of recovery of voluntary MVC and reflex responses varied considerably with a longer recovery time for the reflex responses.

Quantifying The Relationship Between Contraction Efficiency And Muscle Size Across The Adult Lifespan

The neuromuscular system undergoes a natural structural and functional degradation associated with aging. Since the size of a muscle affects its stiffness, the age-related reduction in muscle mass may result in decreased contraction speed and efficiency. PURPOSE: To quantify the relationship between muscle size and contraction efficiency, as measured by electromechanical delay (EMD), across the adult lifespan. METHODS: Seventy-five adults between 18 and 84 yrs. old were included in this study. Panoramic ultrasound images were taken from each participants’ rectus femoris (RF). Muscle cross-sectional area was defined and measured as the area of interest that included as much muscle as possible (mCSA; cm2). In addition, surface electromyographical (EMG) signals were recorded from the RF while ten tendon taps were delivered to the patellar tendon. EMD was calculated as the time (s) between EMG onset and torque onset during the evoked reflex contractions. Bin widths were utilized to condense data, where subjects were grouped based on their age as follows: 18 - 29 yrs. (n = 37), 30 - 39 (n = 7), 40 - 49 (n = 4), 50 - 59 (n = 9), 60 - 69 (n = 5) and > 70 (n = 4). Polynomial regression (2nd order) was performed to fit the apparent curvilinear relationship between EMD and mCSA. RESULTS: As can be appreciated in the figure below, EMD slowed and mCSA decreased with age. However, the relationship between EMD and mCSA was not significant (r = -0.57, p-value = 0.55). CONCLUSION: Surprisingly, EMD was not significantly related to mCSA. It is possible that this may be due to the middle-aged groups being underpowered, which led to an outlier bin (40-49 yrs. old). Additionally, a reflex contraction was used to measure EMD which might differ from the properties of a voluntary contraction. Further analyses might be needed to study the relationship between EMD and mCSA.

Neural and non-neural contributions to ankle spasticity in children with cerebral palsy.

To assess the neural and non-neural contributions to spasticity in the impaired ankle of children with cerebral palsy (CP). Instrumented tapping of the Achilles tendon was done isometrically to minimize non-neural contributions and elicit neural contributions. Robot-controlled ankle stretching was done at various velocities, including slow stretching, with minimized neural contributions. Spasticity was assessed as having neural (phasic and tonic stretch reflex torque, tendon reflex gain, contraction rate, and half relaxation rate) and non-neural origin (elastic stiffness and viscous damping) in 17 children with CP (six females and 11 males; mean age [SD] 10y 8mo [3y 11mo], range 4y-18y) and 17 typically developing children (six females and 11 males; mean age [SD] 12y 7mo [2y 9mo], range 7y-18y). All torques were normalized to weight×height. Children with CP showed increased phasic and tonic stretch reflex torque (p=0.004 and p=0.001 respectively), tendon reflex gain (p=0.02), contraction rate (p=0.038), half relaxation rate (p=0.02), elastic stiffness (p=0.01), and viscous damping (p=0.01) compared to typically developing children. Controlled stretching and instrumented tendon tapping allow the systematic quantification of various neural and non-neural changes in CP, which can be used to guide impairment-specific treatment. Ankle spasticity is associated with increased phasic and tonic stretch reflexes, tendon reflex gain, and contraction and half relaxation rates. Ankle spasticity is also associated with increased elastic stiffness and viscous damping.

The peripheral origin of tap-induced muscle contraction revealed by multi-electrode surface electromyography in human vastus medialis

It is well established that muscle percussion may lead to the excitation of muscle fibres. It is still debated, however, whether the excitation arises directly at the percussion site or reflexively, at the end plates. Here we sampled surface electromyograms (EMGs) from multiple locations along human vastus medialis fibres to address this issue. In five healthy subjects, contractions were elicited by percussing the distal fibre endings at different intensities (5–50 N), and the patellar tendon. EMGs were detected with two 32-electrode arrays, positioned longitudinally and transversally to the percussed fibres, to detect the origin and the propagation of action potentials and their spatial distribution across vastus medialis. During muscle percussion, compound action potentials were first observed at the electrode closest to the tapping site with latency smaller than 5 ms, and spatial extension confined to the percussed strip. Conversely, during tendon tap (and voluntary contractions), action potentials were first detected by electrodes closest to end plates and at a greater latency (mean ± s.d., 28.2 ± 1.7 ms, p < 0.001). No evidence of reflex responses to muscle tap was observed. Multi-electrode surface EMGs allowed for the first time to unequivocally and quantitatively describe the non-reflex nature of the response evoked by a muscle tap.

Statistical Inter-stimulus Interval Window Estimation for Transient Neuromodulation via Paired Mechanical and Brain Stimulation.

For achieving motor recovery in individuals with sensorimotor deficits, augmented activation of the appropriate sensorimotor system, and facilitated induction of neural plasticity are essential. An emerging procedure that combines peripheral nerve stimulation and its associative stimulation with central brain stimulation is known to enhance the excitability of the motor cortex. In order to effectively apply this paired stimulation technique, timing between central and peripheral stimuli must be individually adjusted. There is a small range of effective timings between two stimuli, or the inter-stimulus interval window (ISI-W). Properties of ISI-W from neuromodulation in response to mechanical stimulation (Mstim) of muscles have been understudied because of the absence of a versatile and reliable mechanical stimulator. This paper adopted a combination of transcranial magnetic stimulation (TMS) and Mstim by using a high-precision robotic mechanical stimulator. A pneumatically operated robotic tendon tapping device was applied. A low-friction linear cylinder achieved high stimulation precision in time and low electromagnetic artifacts in physiological measurements. This paper describes a procedure to effectively estimate an individual ISI-W from the transiently enhanced motor evoked potential (MEP) with a reduced number of paired Mstim and sub-threshold TMS trials by applying statistical sampling and regression technique. This paper applied a total of four parametric and non-parametric statistical regression methods for ISI-W estimation. The developed procedure helps to reduce time for individually adjusting effective ISI, reducing physical burden on the subject.

Wrestle while you learn: EMG as a teaching tool for undergraduate skeletal muscle physiology teaching.

Wrestle while you learn: EMG as a teaching tool for undergraduate skeletal muscle physiology teaching.

Automated Variable Stimulus Tendon Tapping Modulates Somatosensory Evoked Potentials.

Somatosensory Evoked Potentials (SSEPs) are an important tool for both basic neuroscience research and evaluation of therapeutic techniques. While a large body of work exists in the study of electrically induced SSEPs both as a metric for therapeutic performance and tool for physiological research, comparatively little work has explored stretch response SSEPs evoked via tendon tapping. The measurement of SSEPs necessitates both timing and stimulation intensity consistency. This work presents an evaluation of a simple tapping device for automating this procedure and a comparison to manual tendon tapping demonstrating significantly reduced variability in both timing and intensity. The variable intensity nature of automated tapping is then used to measure SSEPs in a single subject, with apparent modulation of peak-peak amplitude by stimulation intensity.

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.

Influence of mass and velocity of the tendon tap on the stretch reflex response

This article assesses the utility of small group interviews comprised of two or more interviewers and two or more interviewees as a selection tool for entrance into allied health educational programs. The article also suggests reasons for lack of predictive utility of the traditional admissions interview, examines data on decision-making processes in small group selection interviews, and makes specific recommendations on the use of small group selection interviews in allied health education programs.

F166. Quantifying the tendon hammer tap

Introduction The myotatic reflex is a common neurological test performed at the bedside. This monosynaptic reflex provides a subjective assessment of the central and peripheral nervous system. The assessment of this reflex is based on the clinician’s expertise in performing and interpreting the test. It is difficult for a student or inexperienced clinician to perform and interpret the subtleties of this reflex. Even in expert hands quantification is poor, making it a limited tool for diagnosis and staging of disease. Several factors like the intervening soft-tissue, the exact location of contact and the position of the leg, make it difficult to determine how the administered tap is translated to the stretch of the tendon. We propose a simple addition to a standard tendon hammer that provides feedback to the clinician on the quality of the performed tap. This can be an useful teaching and learning tool. Methods In a freely swinging hammer of known mass, if the acceleration is known, the exact force during the tendon tap can be determined. We used an accelerometer on the head of the hammer to measure the linear acceleration during the tendon tap. Using the data from this we can plot and analyse the entire swing of the hammer along with the deceleration at the point of contact with the tendon. During use, the tendon hammer is held pivoted between thumb and forefinger and the hammer is allowed to freely swing. In this process the only external force on the hammer is the tap on the target tendon. Therefore the force of tap can be calculated accurately. Prior settings can be used for the range of forces that are deemed as adequate to produce a good response. Surface EMG electrodes on the agonist record the electrical response from the muscle which indicates a successful tap. Feedback can be provided to the user to indicate a good tap or a poor tap. Results Using this hammer, we can distinguish a good tap from a poor tap. This is quantified based on the following: magnitude and temporal course of tap force, electrical response from the muscle. Custom written software analyses the characteristics of the hammer accelerometer data to identify strike of the tendon, then confirms an electrical response on the EMG. The force of the tap is then calculated and the software checks if these fall within the preset parameters for the same. A good tap in a normal subject is one where the hammer stretches the tendon of interest with adequate force to elicit an adequate electrical response in the agonist muscle. Preliminary data support such quantitative assessment of the tendon tap. Conclusion Feedback on the quality of a tendon tap will greatly improve the interpretation and reduce the inter-person variability of interpretation of the deep tendon reflexes. Apart from being a tool that can be used for training of students, feedback of quality of tap will help in interpretation of deep tendon reflexes at the bedside.

F157. Presynaptic inhibition of the soleus H reflex and gating of event-related potentials by ankle taps

Introduction A single tendon tap may cause at the same time inhibition of reflex responses through post-activation depression and reduction of the afferent volley reaching the cortex through sensory gating. We aimed at characterizing the temporal profile of the two effects and establish the differences in the timing and degree of inhibition between them. Methods In 10 healthy subjects aged 22–65 years we recorded both the H reflex from the soleus muscle and the long-latency evoked potentials (LLEPs) from Cz to electrical stimuli to the posterior tibial nerve at the popliteal fossa. Stimulus intensity was appropriate to induce an H reflex with a small or absent M wave. In test trials, the responses were conditioned by an Achilles tendon tap at interstimulus intervals 60, 80, 100, 200, 400, 800, 1200, 1600 and 2000 ms. Results The H reflex was inhibited test trials at short intervals with progressive recovery at long inte, reaching 72% of control values at the longest interval tested (2000 ms). The LLEPs were inhibited at short intervals, reaching 90% of control values at 200 ms. The M wave remained unmodified in all control and test trials. Conclusion Homosynaptic depression of the H reflex is far more powerful than gating of the same sensory volley by mechanical taps. The long lasting inhibition of the H reflex may imply the activation of inhibitory circuits that do not participate in afferent gating.

F189. Reciprocal excitation: A hidden component of the myotatic stretch reflex

Introduction The Myotatic Reflex (MR) and Reciprocal Inhibition (RI) are well documented phenomena. They fit well into the framework of negative feedback control of muscle length and complementary control of movement by opposite groups of muscles. Reciprocal excitation (RE) has been reported intermittently and controversially, only in patients with spasticity of various forms. While using quantitative measures of the MR, we recorded clear and consistent electrical evidence of RE in normal subjects. Our experiments show that the standard textbook model of the MR is in fact incomplete. In this paper we present experimental evidence confirming the presence of RE as a spinal reflex, in normal subjects. Methods Three methods were used to elicit the MR of the quadriceps muscle: the patellar tendon tap, rapid mechanical flexion at the knee, electrical stimulation of the femoral nerve. The electrical response from the agonist and antagonist muscles were recorded simultaneously using surface EMG. Following the stretch of the quadriceps, the reflex excitation from the quadriceps and a smaller excitation from the hamstrings was recorded. Mechanical artefacts and cross-pickup from neighbouring muscles were excluded. Data from 28 normal subjects was processed and analysed with custom programs in Python. The mechanical stretch stimulus was the flexion at the knee lasting roughly 100 ms making it difficult to identify a single time-point of stretch stimulus. On electrical stimulation of the femoral nerve in the femoral triangle it was difficult to separate the reflex wave from the stimulation artefact as most subjects required strong stimulus. Results Excitation of the heteronymous group of muscles as a component of the MR in normal subjects has been clearly observed in our experiments. Though this excitation is around 10% of the primary reflex excitation, its latency and reproducibility confirm its physiological origin as a spinal reflex. The patellar tendon tap latency(ms) and amplitude(mV) ranges averaged over 25 trials for each of the 28 subjects, seen distinct from background noise are, respectively: Rectusfemoris = 15–22, 0.0473–2.1503; Bicepsfemoris = 17–33, 0.0076–0.3462, Semitendinosus = 17–33, 0.003–0.2015. The recordings with mechanical stretch and electrical stimulation of the femoral nerve confirm distinct RE in the hamstrings. Conclusion There are a few reports of RE in spasticity. We have demonstrated its presence in normal subjects. The coexcitation of the antagonist at the same time as the agonist may play an important role in providing stability around a joint to prevent injuries when there is rapid stretch of the agonist. Our data suggests that further studies are required to understand its neuronal pathway, relevance and potential clinical use in normal subjects and pathology.

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.

An Examination of Patellar Tendon Reflex Pre-Motor Conduction Velocity across the Adult Lifespan

It is known that aging is accompanied by a loss in muscle mass and motor units. However, the direct cause for the loss of motor units has not been identified. One possible mechanism could be related to changes in the sensory input motor neurons receive. Therefore, it is important to find objective measures to quantify sensory function that are sensitive to changes with aging. PURPOSE: To determine if the conduction velocity of a patellar tendon reflex is sensitive to aging. METHODS: One hundred and one volunteers participated in this study. Tendon taps were delivered to the patellar tendon of each subject while surface electromyographic (EMG) signals were recorded from the rectus femoris. The pre-motor reflex latency was calculated as the time from the onset of the hammer-strike to the onset of EMG activity. This latency (s) was adjusted for femur length (m) to instead provide a pre-motor conduction velocity (CV; m/s). The subjects were then grouped and averaged into intervals based on age as follows: 18 - 29 yrs. (n = 50), 30 - 39 (n = 10), 40 - 49 (n = 6), 50 - 59 (n = 16), 60 - 69 (n = 13) and > 70 (n = 6). Linear regression was applied across the mean age and pre-motor CV from each interval. RESULTS: Pre-motor CV was negatively related to age (r = - 0.799; p = 0.028). The resulting regression equation was y = -0.1113x + 24.216. The group averaged data as well as the line of best fit are shown in the figure below. CONCLUSION: Our findings show that the conduction velocity of a patellar tendon reflex is significantly related to age. Therefore, this variable may be useful in future studies that wish to track changes in sensory function across age.Figure

The Effects of Muscle Damage on Muscle Spindle Function

The effects of eccentric muscle damage on extrafusal muscle fibers and motor function have been well studied. However, very few studies have examined the effects of muscle damage on sensory function, specifically, whether eccentric contractions damage the intrafusal fibers muscle spindles are wrapped around. PURPOSE: To investigate the effects of fatigue and muscle damage on the premotor latency (PML) and reflex magnitude (normalized reflex Torque; nRT) of patellar tendon reflexes. METHODS: Fifteen males (mean ± SD: age = 24.1 ± 2.9 yrs.) and fifteen females (age = 21.67 ± 2.1 yrs.) participated in a familiarization trial followed by two experimental sessions, separated by seven (±1) days. The 2 conditions consisted of either fatiguing (CON) or muscle damaging (ECC/CON) contractions at 60°· s-1 until 70% of peak torque (PT) was achieved. Patellar tendon taps were performed at a knee angle of 90° and a reflex hammer fastened to a swing arm was used to provide uniform impacts. PML was calculated as the time between the strike of the hammer to the onset of myoelectric activity in the rectus femoris, and nRT was normalized [% of Pre maximal voluntary contraction (MVC)] at all time points. Reflex assessments and MVCs were completed before (Pre) and following (Post) both the CON and ECC/CON protocols until recovery of PT to Pre values (Recov). A three-way repeated measures ANOVA [gender (males vs females) × condition (CON vs ECC/CON) × time (Pre vs Post vs Recov)] was used to analyze all reflex data. An alpha value of P ≤ 0.05 was considered statistically significant for all comparisons. RESULTS: A main effect for time (P = 0.003) was observed in which PML was greater at Recov compared to Pre (P = 0.01). Additionally, a two-way gender × time interaction was observed in which nRT was lower at Post and Recov compared to Pre (P = 0.001-0.002) for the females. No differences were observed across time for the males (P = 1.000). CONCLUSION: These findings revealed that changes in PML may not be sensitive to muscle damaging contractions but may have delayed responses as a result of exercise-induced fatigue. Furthermore, reflex magnitude deficits may be evident in females following fatiguing exercise but not likely as a result of muscle damage.