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Context: Arthrogenic muscle inhibition (AMI) continues to be a limiting factor in joint rehabilitation as the inability to volitionally activate muscle significantly dampens recovery. New evidence acquired at higher brain centers and in clinical populations continues to reshape our perspective of what AMI is and how to treat it. This review aims to stimulate discussion about the far-reaching effects of AMI by exploring the interconnected pathways by which it evolves. Objectives: To discuss how reflexive inhibition can lead to adaptations in brain activity, to illustrate how changes in descending motor pathways limit our ability to contract muscle following injury, and to summarize the emerging literature on the wide-reaching effects of AMI on other interconnected systems. Data Sources: The databases PubMed, SPORTDiscus, and Web of Science were searched for articles pertaining to AMI. Reference lists from appropriate articles were cross-referenced. Conclusion: AMI is a sequential and cumulative neurological process that leads to complex clinical impairments. Originating with altered afferent information arising from an injured joint, patients experience changes in afferent information, reflexive muscle inhibition, deficiencies in somatosensation, neuroplastic compensations in higher brain centers, and ultimately decreased motor output to the muscle surrounding the joint. Other aspects of clinical function, like muscle structure and psychological responses to injury, are also impaired and influenced by AMI. Removing, or reducing, AMI should continue to be a focus of rehabilitation programs to assist in the optimization of health after joint injury. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of surgery on the gamma loop of the quadriceps on the side with an intact knee in patients with anterior cruciate ligament (ACL) injuries. We compared longitudinally the response of alpha motor neurons to vibration stimulation of the quadriceps on the side with an intact knee before and after ACL reconstruction. To evaluate alpha motor neuron response, we measured the maximal knee extension strength and integrated electromyography of the vastus medialis, vastus lateralis, and rectus femoris. After obtaining pre‐vibration data from each subject, vibration stimulation was applied to the infrapatellar tendon, and the same measurements were performed immediately after stimulation. The results of this study showed that the response to prolonged vibration stimulation on the intact side of the quadriceps did not differ pre‐ and post‐surgery. As vibration stimuli normally elicit a decrease in alpha motor neuron activity in normal individuals, abnormal responses to prolonged vibration stimulation of the quadriceps on the side with an intact knee might be observed in patients with ACL injuries. The abnormality of the gamma loop of the quadriceps on the side with an intact knee was probably induced by the rupture. Based on these results, we conclude that surgery does not induce further gamma loop abnormalities on the intact side of the quadriceps. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate whether training aimed at inhibiting primitive reflexes in children, may have an influence on their motor skills. The training method is The INPP Method, developed by The Institute for Neuro-Physiological Psychology. Methods: The design is quasi-experimental were Neuro-Developmental Diagnostic Assessment and Movement Assessment Battery for Children were used to collect quantitative data from 87 children (aged 5-16) before and after intervention. All the participants showed traces of primitive reflexes prior to the tests. To analyze the data, Paired Samples T-test and Wilcoxon Matched-pairs Signed-rank test were used. Results: The results showed a significant improvement of the reflex status. Upon completion of training aimed at inhibiting primitive reflexes, their motor skills were also significantly improved. Conclusions: This study indicates that primitive reflexes can be inhibited using the INPP-method and this can create improvement in their motor skills. Because of weak validity of the study, the results have to be interpreted carefully.

Painful stimulation of the hand results in an inhibitory response in the hand muscles known as the cutaneous silent period (CSP). In this study, we employed probability- and frequency-based analysis methods to examine the CSP induced by laser stimuli. Subjects were asked to contract their first dorsal interosseous muscle so that selected motor units discharged at a rate of about 8Hz. Laser pulses were delivered to the palm of the hand, and reflex responses were recorded. The stimuli generated CSP in all test subjects. We found that the latency of the CSP evoked using laser stimulation was longer than that the previously published latency values of the CSP evoked using electrical stimulation. Using only the presently generated laser induced CSP data, the CSP duration was longer when analyzed via peristimulus frequencygram method compared to the probability-based methods such as peristimulus time histogram and surface electromyogram. In the light of the current results, we suggest that laser stimulation could be used when studying pain pathways in human subjects and the frequency-based analysis methods can be preferred because they are previously shown to be more reliable for obtaining the synaptic activity profile. These results can be used to standardize the CSP methods in basic and clinical research. [ABSTRACT FROM AUTHOR]

In obstructive sleep apnea (OSA), the short-latency inhibitory reflex (IR) of inspiratory muscles to airway occlusion is prolonged in proportion to the severity of the OSA. The mechanism underlying the prolongation may relate to chronic inspiratory muscle loading due to upper airway obstruction or sensory changes due to chronic OSA-mediated inflammation. Continuous positive airway pressure (CPAP) therapy prevents upper airway obstruction and reverses inflammation. We therefore tested whether CPAP therapy normalized the IR abnormality in OSA. The IR responses of scalene muscles to brief airway occlusion were measured in 37 adult participants with untreated, mostly severe, OSA, of whom 13 were restudied after the initiation of CPAP therapy (usage >4 h/night). Participants received CPAP treatment as standard clinical care, and the mean CPAP usage between initial and subsequent studies was 6.5 h/night (range 4.1-8.8 h/night) for a mean of 19 mo (range 4-41 mo). The duration of the IR in scalene muscles in response to brief (250 ms) inspiratory loading was confirmed to be prolonged in the participants with OSA. The IR was assessed before and after CPAP therapy. CPAP treatment did not normalize the prolonged duration of the IR to airway occlusion (60 ± 21 ms pretreatment vs. 59 ± 18 ms posttreatment, means ± SD) observed in participants with severe OSA. This suggests that the prolongation of IR reflects alterations in the reflex pathway that may be irreversible, or a specific disease trait. [ABSTRACT FROM AUTHOR]

In all but the simplest monosynaptic reflex arcs, sensory stimuli are encoded by sensory neurons that transmit a signal via sensory interneurons to downstream partners in order to elicit a response. In the embryonic zebrafish (Danio rerio), cutaneous Rohon-Beard (RB) sensory neurons fire in response to mechanical stimuli and excite downstream glutamatergic commissural primary ascending (CoPA) interneurons to produce a flexion response contralateral to the site of stimulus. In the absence of sensory stimuli, zebrafish spinal locomotor circuits are spontaneously active during development due to pacemaker activity resulting in repetitive coiling of the trunk. Self-generated movement must therefore be distinguishable from external stimuli in order to ensure the appropriate activation of touch reflexes. Here, we recorded from CoPAs during spontaneous and evoked fictive motor behaviors in order to examine howresponses to self-movement are gated in sensory interneurons. During spontaneous coiling, CoPAs received glycinergic inputs coincident with contralateral flexions that shunted firing for the duration of the coiling event. Shunting inactivation of CoPAs was caused by a slowly deactivating chloride conductance that resulted in lowered membrane resistance and increased action potential threshold. During spontaneous burst swimming, which develops later, CoPAs received glycinergic inputs that arrived in phase with excitation to ipsilateral motoneurons and provided persistent shunting. During a touch stimulus, short latency glutamatergic inputs produced cationic currents through AMPA receptors that drove a single, large amplitude action potential in the CoPA before shunting inhibition began, providing a brief window for the activation of downstream neurons. We compared the properties of CoPAs to those of other spinal neurons and propose that glycinergic signaling onto CoPAs acts as a corollary discharge signal for reflex inhibition during movement. [ABSTRACT FROM AUTHOR]

As early as 1969, the role of retained or residual primitive reflexes was discovered, by one of the authors of this paper (Blythe), to play a significant role in specific learning difficulties, agoraphobia and panic disorder. At the same time, a protocol for neuro-diagnostic assessment based on standard medical tests was devised to detect the presence of aberrant reflexes (neuromotor immaturity) in older children and adults, and developmental movement programmes were devised to inhibit and integrate aberrant reflexes. This system, now known as The INPP Method, has been shown in peer reviewed journals to bring about remission of presenting difficulties both educational and medico-psychological. Evidence has emerged showing that a number of behavioural optometrists and practitioners of vision therapy are using clinically unknown diagnostic procedures to test for the presence of aberrant reflexes, misinterpreting obser-vations during the assessment of primitive reflexes, and applying clinically unproven reflex inhibition programmes without a clear understanding of the developmental basis for some of the exercises used in relation to primitive re-flexes. These failures appear to be the result of inadequate and misleading training which is being communicated to others through various publications, training courses, seminars, and information given out to patients and families of patients. This viewpoint article highlights some of the issues involved. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effect of surgery on the gamma-loop in the quadriceps of patients with ACL injuries. We compared the response to vibration stimulation in subjects with ACL repair, subjects with ACL rupture, and normal subjects, by measuring the maximal strength and integrated electromyography (I-EMG) of the quadriceps. Pre-vibration data were obtained from each subject by measuring the MVC of the knee extension and the I-EMG from the vastus medialis, vastus lateralis, and rectus femoris. Vibration stimulation was applied to the infrapatellar tendon, followed immediately by repeating maximal strength and I-EMG recording. The results of this study indicated that alpha motor neuron activity of the intact side of the vastus lateralis in response to prolonged vibration stimulation was altered by surgery, but no effect was detected in the injured side. The results could suggest that abnormality of the gammaloop existed even in the quadriceps of patients with ACL rupture since the vibration stimulus failed to elicit changes in ACL-rupture group as compared with those of normal subjects. In comparison, abnormality of the gamma-loop in the intact side of the QF was probably induced by the rupture, and further abnormality of gamma-loop was induced by surgery. [ABSTRACT FROM AUTHOR]

Morphological and behavioural changes in back muscles are common in back pain and injury. Recent data indicate a rapid reduction in the size of the multifidus, a deep back muscle, within 3 days of experimental intervertebral disc (IVD) injury in pigs. A reduced neural drive may contribute to this. We investigated changes in corticomotor excitability following IVD lesion by evaluation of the response of back muscles to electrical stimulation of the motor cortex. Motor evoked potentials (MEPs) were studied in 12 Swedish landrace pigs before injury, immediately after abdominal incision, immediately after L3-4 IVD lesion with a scalpel, and 15 min later. In two animals, responses were also evoked by descending volleys excited at the level of the mastoid processes (cervicomedullary evoked potentials) without motor cortex activation. In five animals, a sham procedure was followed without IVD lesion. MEPs were recorded in short (deep) and long (superficial) fibres of the multifidus at L3-5 on the lesioned side and at L4 contralaterally with intramuscular wire electrodes. Although the MEP amplitude increased in several muscles after incision, at 15 min after IVD lesion only the MEP amplitude of the deep L4 multifidus on the lesioned side was increased [36% (SD 15%), P < 0.05]. There were no changes in MEP amplitude after 15 min at adjacent or contralateral levels. The response to cervicomedullary stimulation reduced slightly. This suggests that the increased MEP amplitude was due to changes in cortical excitability. These data indicate that IVD lesion induces localized increases, and not decreases, in the excitability of cortical inputs to the deep paraspinal muscles that cross a lesioned disc. [ABSTRACT FROM AUTHOR]

Introduction: Neuronal reflex inhibition of gastrointestinal motility is a key mechanism in the development of postoperative ileus (POI). The aim of our study was to determine whether intestinal afferent nerve fibers are sensitized during the first hours after surgery contributing to this mechanism.Methods: Under enflurane anesthesia, C57BL/6 mice underwent laparotomy followed by sham treatment or standardized small bowel manipulation to induce POI. After 1, 3, or 9 h, extracellular multi-unit mesenteric afferent nerve recordings were performed in vitro from 2 cm segments of jejunum (subgroups n = 6) superfused with Kreb's buffer (32 degrees C, gassed with O(2)/CO(2) mixture). Segments were cannulated to monitor luminal pressure and intestinal motility. Afferent impulses as response to bradykinin (0.5 microM) and to mechanical ramp distension of the intestinal lumen from 0 to 80 cmH(2)O were recorded.Results: At 1 h, amplitudes of intestinal contractions were 0.8 +/- 0.2 cmH(2)O after induction of POI and 5.0 +/- 0.8 cmH(2)O in sham controls (mean +/- SEM; p < 0.01). A similar difference was observed for segments harvested at 3 and 9 h. Afferent firing to serosal bradykinin was increased at 1, 3, and 9 h in POI segments compared to sham controls (p < 0.05 at 1 h, p < 0.01 at 3 and 9 h). During distension with high pressures, afferent firing rate was increased at 1 and 3 h in segments after induction of POI compared to sham controls. Nine hours postoperatively, contracted and dilated segments were observed during POI that were investigated separately. While afferent firing in dilated segments was increased to 176 +/- 16 imp s(-1) at 80 cmH(2)O luminal distension (p < 0.01), it was 46 +/- 5 imp s(-1) in contracted segments (p < 0.001) compared to 77 +/- 4 imp s(-1) in sham controls.Conclusions: Afferent firing to bradykinin and high threshold distension is augmented in the early phase of POI. As these stimuli are known to sensitize predominantly spinal afferents, this mechanism may contribute to reflex inhibition of intestinal motility during POI. [ABSTRACT FROM AUTHOR]

Purpose of this study was to investigate the effects of anterior cruciate ligament (ACL) repair on the γ loop of the bilateral quadriceps femoris (QF). Maximal voluntary contraction (MVC) of knee extension and integrated electromyogram (I-EMG) of vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) were examined in uninjured and injured limbs of 18 patients and 10 normal subjects, before and after 20-min vibration applied to the QF. Mean percentage changes were calculated as: (pre-vibration value−post-vibration value)/pre-vibration value × 100. Patients were divided into two groups: short-term-group (tested ≤12 months after ACL repair, n=8), long-term-group (tested ≥18 months after ACL repair, n=10). Mean percentage changes of the four groups were compared with those of controls. Results indicated that changes of MVC and I-EMG on the uninjured and injured sides in short-term-group in response to vibration were significantly different from those of controls. There were no significant differences between uninjured sides in long-term and control groups. MVC and I-EMG of VM and RF of injured side in patients in the long-term-group in response to vibration were not different from those of controls. From these results, we concluded that this abnormality of the γ loop in both injured and uninjured sides did not recover despite ACL reconstruction. However, the abnormality in uninjured side might recover ≥18 months after repair. [ABSTRACT FROM AUTHOR]

Pain, atrophy and dysfunction of the longissimus dorsi in the equine back can lead to poor performance and altered biomechanics. Back problems are often treated by manipulative therapy to this muscle. The purpose of this study was to identify if manipulative therapy resulted in changes to muscle tone or electromyographic (EMG) activity immediately after treatment. We measured the muscle tone during standing using a mechanical tissue indenter and the EMG activity (both at the T16 level in the longissimus dorsi) during walking around a figure-of-eight course in 26 horses. The horses were randomly assigned into three groups that received: (a) spinal (McTimoney) manipulations, (b) reflex inhibition therapy or (c) a control group that was not manipulated. The muscle tone and activity were measured immediately after treatment. Both the McTimoney and the reflex inhibition groups showed significant decreases in muscle tone (c. 12%) and walking EMG activity (c. 19%). The control group showed no significant change in tone or EMG activity. These results document how the longissimus dorsi muscle responds immediately after manipulative therapy. Further studies would be needed to identify how long such changes persist or if such changes caused a reduction in pain or an increase in performance. [ABSTRACT FROM PUBLISHER]

Twenty-four college students served as subjects in a study that examined the effect of a prototypical abdominal muscle strengthening device (AbVice) compared with other devices currently on the market. The purpose of the present study was to investigate a prototypical device (AbVice) that incorporates contraction of the hamstring and gluteal musculature in conjunction with the abdominals, which may assist in decreasing activation of the hip flexors by allowing greater activity levels of the abdominal musculature via the theory of reflex inhibition, compared with other devices currently available on the market (AbRoller and Ab-Rocker). The repeated-measures study included 17 women and 7 men who ranged in age from 20-23 years (mean ± SD age, 21.3 ± 1.5 years). Each subject underwent a single session of data collection during which they completed 10 repetitions of abdominal crunches per device. Subjects completed 4 different crunch sets (AbRocker, AbRoller, standard crunch, AbVice). Counterbalancing of the device was used to negate the effect of fatigue. Speed of repetitions was ensured via use of a metronome set at 40 b·min-1 to permit similar contraction times and rest periods between repetitions. Rest between conditions was 3 minutes. Mean activation levels of surface electromyography (EMG) were recorded for each condition at the following locations on the right side of the body: rectus abdominis 2.5 cm superior to the umbilicus, rectus abdominis 2.5 cm inferior to the umbilicus, external oblique abdominis 1.0 cm medial to the anterior superior iliac spine, and external oblique abdominis less than 1.0 cm superior to the inguinal ligament. Mean (SD) activation was 1,165.21 mV (634.60 mV) with the AbVice, 242.92 mV (263.03 mV) with the AbRocker, 753.29 mV (514.80 mV) with the standard crunch, and 757.67 mV (542.85 mV) with the AbRoller. Broken down by sex, women had the following mean (SD) EMG values: 1,079.76 mV (705.02 mV) with the AbVice, 680.35 mV (535.35 mV) with the standard crunch, 262.70 mV (305.89 mV) with the AbRocker, and 636.88 mV (502.82 mV) with the Ab-Roller. Men demonstrated mean (SD) values of 1,372 mV (383.87 mV) with the AbVice, 1,051 mV (560.09 mV) with the AbRoller, 930.43 mV (447.17 mV) with the standard crunch, and 194.86 mV (109.05 mV) with the AbRocker. Two-way analysis of variance with factor 1 (person) and factor 2 (condition) had F values of 11.73 and 36.04, respectively. Post hoc analysis using the Tukey test indicated that all comparisons between conditions were significant at the p = 0.01 level except for the standard crunch vs. the AbRoller. The AbVice activated the selected abdominal musculature more effectively than the other conditions. [ABSTRACT FROM AUTHOR]

The analysis of saccadic eye movements has assumed an important role as a pathophysiological approach in neuropsychiatric diseases. However, before abnormal cognitive saccade behavior can be fully understood, some basic psychophysiological aspects have to be further investigated. Previous studies have demonstrated a shortening of saccade latency when the fixation stimulus was removed prior to the appearance of a peripheral visual target. This gap effect is smaller for antisaccades (AS; away from the target) than for reflexive saccades (RS; towards the target). Apart from the generation of an intentional eye movement, AS rely on different processes including reflex inhibition and spatial reversal of the saccade direction. We wondered whether intentional prosaccades (IpS) that do not rely on these additional processes also show a reduced gap effect. Therefore, we compared the gap effect in a saccade paradigm for RS and IpS in healthy subjects. We found a smaller gap effect in IpS than in RS and suggest that this reduction reflects endogenous strategic processes. Our findings further imply that reflex inhibition is not the unique cause for the smaller gap effect in AS than in RS and suggest that an endogenous component may be involved. We hypothesize that frontal control on the superior colliculus fixation cell activity may continue even after the fixation stimulus has disappeared, thus inhibiting a fixation offset and reducing the gap effect. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Stretch-shortening cycle (SSC)-type fatigue is associated with acute and delayed functional defects, and appears to be a useful model to reveal the flexibility of both central and reflex adjustments to the contractile failure. SSC fatigue was induced in an experimental (EXP) group (n=6) on a sledge ergometer with an exhaustive rebound exercise with submaximal effort. The acute (POST) and 2-day delayed (2D) neuromuscular changes with fatigue were examined in a short submaximal rebound task (REBOUND) and in a maximal isometric plantarflexion test (ISOM). The EXP group results were compared to those of a control group (n=6) who did not perform the exhaustive SSC exercise and did not present any change in the tests. In the EXP group, the ISOM test revealed mostly a large decrease in maximal plantarflexion force at 2D that was correlated with the reduced mean soleus muscle (SOL) activation. Indicating "task-dependent" fatigue effects on the neural changes, the REBOUND test revealed both acute and delayed increases in SOL activation. Supporting central neural changes, SOL preactivation increased in POST and 2D. The neural flexibility along time and across muscles was demonstrated by the shifted increase in SOL activation from the braking phase in POST to the push-off phase in 2D, and associated increased gastrocnemius medialis preactivation in 2D. In contrast, activation during the stretch-reflex period was constant in POST, and decreased in 2D. These results would support the influence of musculotendinous afferents on the flexible neural adjustments to the SSC-induced contractile failure. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate gamma loop function in the quadriceps femoris muscle in patients who with less than 6 month-history of anterior cruciate ligament ACL) reconstruction. For this purpose, we compared the response to vibration stimulation in 10 patients with ACL repair and 12 normal healthy subjects, by measuring the maximal voluntary isometric contraction MVC) and integrated electromyograms I-EMG) of the quadriceps muscles. Pre-vibration data were obtained from each subject by measuring the MVC of the knee extension and the I-EMG from the vastus medialis, vastus lateralis, and rectus femoris muscles. Vibration stimulation was applied to the infrapate!!ar tendons, followed immediately by repeating the MVC and I-EMG recording. Prolonged vibration resulted in a significant decrease of both MVC and I-EMG in the control group. In contrast, the same stimulus failed to elicit changes in ACL-repair group. Our results suggest the presence of abnormal gamma loop function in the quadriceps femoris muscle of patients with ACL repair, which may explain the muscle weakness often described in such patients. [ABSTRACT FROM AUTHOR]

Reflex inhibition was investigated in young and elderly subjects as a function of prestimulus duration. In Experiment 1, tone prestimuli of 20 and 200 msec duration were presented at ISIs of 60, 120, 240, and 420 msec before the reflex-eliciting, periorbital airpuff. Both age groups evidenced more eyeblink inhibition with the longer prestimulus. The heart rate response was primarily decelerative in both age groups. In young subjects, the initial deceleration was augmented by the prestimulus, particularly for the 200-msec prestimulus, whereas the elderly heart rate response was unaffected. In Experiment 2, a gap in a continuous tone served as the prestimulus. In both young and elderly subjects, eyeblink inhibition increased as gap duration increased from 10 to 80 msec. The longest gap (120 msec) produced the most inhibition in the elderly, while inhibition decreased somewhat in young subjects between the 80 and 120 msec gaps. Heart rate was not affected by the gap prestimuli in either group. It was proposed that reflex inhibition is, in part, a function of the onset and offset transients of the prestimulus. As prestimulus duration is increased and, consequently, the two transients become more separated in time, their effects upon the reflex may become progressively more independent. The discrepancy between the PS effects upon eyeblink and HR in the elderly is probably due to a decline in HR response plasticity rather than central nervous system processes involved in reflex inhibition. [ABSTRACT FROM AUTHOR]