Abnormality in re-programing of preparatory muscle activity for landing following unpredictable events in patients with anterior cruciate ligament injury.

BACKGROUND: Anterior cruciate ligament deficiency (ACL-D) causes dysfunction in the quadriceps femoris muscle, and this dysfunction hampers a safe return to sports. However, how the dysfunctional quadriceps femoris muscle affects instantaneous re-programming of motor command in response to unpredictable events remains unknown. This study aimed to examine the effects of ACL-D on re-programming of preparatory muscle activity during an unpredictable landing task. METHODS: Eighteen patients with ACL-D and 20 healthy participants (controls) performed normal landing and surprise landing tasks. In the surprise landing task, a false floor, designed to dislodge easily under load, was positioned in the middle of the descent path. This setup causes participants to unpredictably fall through the false floor onto the actual landing surface. Electromyography data collected during the period after passing through the false floor until landing was segmented into two equal halves. The average electromyography amplitude for each muscle in each period was compared between patients and controls. RESULTS: In the vastus medialis and rectus femoris during the surprise landing task, the average electromyography amplitude during only the second half period in patients with ACL-D was significantly smaller than that in controls (p = 0.011 and 0.004, respectively). CONCLUSIONS: Abnormalities were detected in the re-programming of preparatory muscle activation during an unpredictable landing task in the vastus medialis and rectus femoris of patients with ACL-D. The surprise landing task used in the present study has the potential to become a diagnostic tool to evaluate readiness for safely returning to sports.

Tactile stimulation restores inhibited stretch reflex attributable to attenuation of Ia afferents during surprise landing.

Arthrogenic muscle inhibition (AMI) is induced by pathological knee conditions. The present study aimed to investigate the effect of tactile stimulation on reflex changes induced by simulated AMI during unpredictable landing performances. Twenty participants performed six unilateral landing tasks: 15 cm normal landing (15NL), 30 cm normal landing (30NL), surprise landing (SL), 30 cm normal landing following vibration (30NLV), SL following vibration (SLV), and SL following vibration with Kinesiology tape (SLK). For SL, the solid landing platform (15 cm) was removed and replaced by a false floor. Since the false floor dislodged easily under load, participants unpredictably fell through the platform to the actual landing surface 15 cm below. After completing 15NL, 30NL, and SL, vibration was applied to participants' knees to induce neurological changes similar to AMI. After vibration, participants performed 30NLV, SLV, and SLK in a random order. EMG signals in the post-landing short latency (31-60 ms) and medium latency (61-90 ms) periods were examined. EMG signals from the vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF) were recorded and compared between tasks. EMG signals of all muscles in SL were significantly enhanced in the medium latency period as compared with 30NL. Enhanced EMG signals in SL were suppressed by vibration stimulation in the VL, but the suppressed EMG signals were restored after cutaneous stimulation with Kinesiology tape (p < 0.01). Our findings suggest that AMI could alter motor control patterns during unpredictable landing and that tactile stimulation could restore the altered motor control to a normal state.

Effects of 8-Week Exhausting Deep Knee Flexion Flywheel Training on Persistent Quadriceps Weakness in Well-Trained Athletes Following Anterior Cruciate Ligament Reconstruction.

Persistent quadriceps weakness after anterior cruciate ligament (ACL) reconstruction is a common hurdle to efficient rehabilitation. Therefore, we evaluated a new treatment strategy for athletes with ACL reconstruction. Eleven athletes with unilateral ACL reconstruction performed one set of flywheel Bulgarian split squats to exhaustion with a maximum knee extension of 60°, over 16 sessions, on their reconstructed limb. Quadriceps rate of force development (RFD) 0-50 ms (RFD0-50 ms), and 0-150 ms (RFD0-150 ms), maximum voluntary isometric contraction (MVIC), and central activation ratio (CAR) were measured bilaterally on the week before and after the intervention. In the reconstructed limb, the RFD0-50 ms (p = 0.04; Cohen's d = 0.8) and RFD0-150 ms (p = 0.03; d = 0.9) increased after training. Before-after changes in MVIC and CAR were not significant (p > 0.05), but the lower the baseline MVIC, the greater the gain in MVIC (r = -0.71, p = 0.02). The between-leg difference in MVIC changed from large before (p = 0.01; d = 0.8) to small after training (p = 0.04; d = 0.4). One set of deep knee flexion flywheel Bulgarian split squats to exhaustion improved quadriceps deficits in well-trained athletes with ACL-reconstruction, particularly those with relatively low quadriceps force production.

Gamma Loop Dysfunction as a Possible Neurophysiological Mechanism of Arthrogenic Muscle Inhibition: A Narrative Review of the Literature.

CONTEXT: Quadriceps activation failure has been observed following various pathological conditions in a knee joint such as knee surgery, pain, effusion in knee, and osteoarthritis also could be aging matter. Those patients are unable to attain maximal quadriceps strength for a long period of time although their quadriceps itself is not damaged. This impairment is termed arthrogenic muscle inhibition (AMI). AMI has been of concern to clinicians because this weakness hinders the rehabilitation process considerably and delays recovery because strengthening protocols for the AMI could be largely ineffective. Clinically, it is important to understand neurophysiological mechanisms of the AMI to treat patients with the impairment. OBJECTIVES: This is a narrative review of the literature. The purpose of this review is to understand the following: (1) Why investigations of only peripheral spinal reflexive pathways are not enough for elucidation of the mechanisms of the AMI? (2) What we know about the role of the gamma spindle system in AMI so far? (3) Could a dysfunctional gamma spindle system contribute to AMI lead neural changes in upper central nervous system? and (4) Concerns that a clinician should take into consideration when deciding whether to apply therapeutic interventions for AMI. DATA SOURCES: The databases PubMed, MEDLINE, SPORTDiscus, and CINAHL were searched with the terms arthrogenic muscle inhibition (AMI), reflex inhibition, joint mechanoreceptor, gamma loop, corticospinal pathway, spinal reflex, effusion, and joint injury. The remaining citations were collected from references of similar papers. CONCLUSIONS: AMI is a limiting factor in the rehabilitation of joint injury. Motor unit recruitment could be hindered in patients with AMI as a result of a dysfunctional gamma spindle system. Clinicians should understand the mechanism of AMI well in order to establish effective rehabilitation programs for AMI. Indeed, AMI is not caused by a single factor, but rather, multiple neural factors can change over time following the appearance of AMI. Therefore, multiple interventions targeting different neural pathways should be combined to achieve the ideal therapeutic goal for the treatment of AMI.

Predictive ability of neonatal illness severity scores for early death in extremely premature infants.

BACKGROUND: The predictive ability of neonatal illness severity scores for mortality or morbidity in extremely premature infants has not been extensively studied. We aimed to evaluate the ability of neonatal illness severity scores [Clinical Risk Index for Babies II (CRIB II), Score for Neonatal Acute Physiology II (SNAP-II), and SNAP-Perinatal Extension II (SNAPPE-II)] in predicting mortality and short-term morbidity of extremely premature infants. METHODS: This retrospective study involved 171 infants with gestational age (GA) between 22 and 27 weeks who were admitted to the NICU during 2010-2017. Predictive ability of neonatal illness severity scores for mortality and short-term morbidity (bronchopulmonary dysplasia, retinopathy of prematurity, intraventricular hemorrhage, necrotizing enterocolitis, and gastrointestinal perforation) was assessed by comparing their area under the receiver operating characteristic curve. RESULTS: The overall mortality rate was 11.1%. Mortality at 23 weeks' gestation was higher than that at 24-27 weeks' gestation (p < .01, adjusted residual 4.5). Neonatal illness severity scores were significantly higher in infants who died than in those who survived (p < .01). CRIB II (AUC 0.93, 95% CI 0.85-1.00), SNAP-II (AUC 0.90, 95% CI 0.76-1.00), and SNAPPE-II (AUC 0.95, 95% CI 0.91-0.99) appeared to be excellent predictors and were superior to birth weight (AUC 0.88, 95% CI 0.80-0.95) or GA (AUC 0.84, 95% CI 0.72-0.96) alone in predicting early death (died on <28th postnatal day). CRIB II, SNAP-II, and SNAPPE-II were better predictors of early death than mortality in extremely premature infants. Neonatal illness severity score and short-term morbidity were not strongly associated. CONCLUSIONS: The neonatal illness severity scores were excellent predictors of early death in extremely premature infants and might be useful for selecting extremely preterm infants who need intervention.

Comparing risk factors associated with the late detection of critical congenital heart disease at different facility levels.

AIMS: Critical congenital heart disease (CCHD) requires surgery or catheter intervention within the first year of life; delayed diagnoses result in worsened outcomes. In Japan, there are few reports of delayed CCHD diagnosis. We investigated the diagnoses and factors associated with the late detection of CCHD. METHODS: This retrospective cohort study evaluated 88 CCHD infants admitted to a level IV facility. We compared the late detection rates across facility levels of neonatal care and CCHD characteristics. RESULTS: Critical congenital heart disease was identified prenatally in 46 (52%) infants: early (≤3 days postnatally) in 29 (33%) and late (≥4 days postnatally) in 13 (15%). The oxygen saturation of 27 of 29 infants with early detection and 7 of 13 infants with late detection was measured using pulse oximetry within 3 days postnatally. Factors associated with the late detection of CCHD were lack of clinical recognition of symptoms in five infants, referral to higher-level facilities after discharge in four infants, and definitive diagnosis not confirmed using echocardiography in four infants. The most common factors associated with late detection were referral to higher-level facilities after discharge in level I facilities and definitive diagnosis not confirmed using echocardiography in level II facilities. CONCLUSION: Critical congenital heart disease may require advanced knowledge and echocardiographic techniques for diagnosis. Pulse oximetry and telemedicine should also be incorporated in the diagnostic algorithm. Improvement in these factors might contribute to reducing the late detection of CCHD.

Stretch reflex changes in ACL-deficient individuals and healthy controls during normal and surprise landings.

No studies in ACL-D individuals have examined neuromuscular adaptations during landing from a jump where an unexpected mechanical event changes the pre-programmed course of movement. The purpose of this study was to compare pre- and post-landing muscle activation in ACL-D individuals and uninjured controls during normal and surprise landings. Nineteen ACL-D and 17 uninjured volunteered. Participants performed repeated single leg landings from 30 and 15 cm heights. During 15 cm landings, a single surprise landing was performed where participants unexpectedly fell through a false surface at 15 cm to the solid floor a further 15 cm below. Electromyography (EMG) amplitude from vastus lateralis (VL), lateral hamstrings (LH), and soleus (Sol) was recorded. Pre-landing (-60 to 0 ms), post-landing short latency (31-60 ms), and post-landing medium latency (61-90 ms) periods were examined. Comparisons in EMG amplitudes were made across limbs (ACL-D, ACL intact, and control) in 30 cm landings. Additionally, the ratio of EMG amplitude in surprise:30 cm normal landings was analyzed. Post-landing LH EMG was reduced in the ACL-D compared to control limbs at short latencies (P < 0.05). Post-landing VL EMG was reduced in the ACL-D and ACL intact compared to the control limb at both latencies (P < 0.05). Surprise landings notably increased post-landing EMG in all muscles, across all limbs (P < 0.001). However, the gain in VL EMG was significantly greater in ACL-D and ACL intact limbs (P < 0.05). These changes in neuromuscular control of ACL-D individuals during expected and surprise landings may have important implications for rehabilitation, instability, and the risk of secondary injury.

Effect of Subcutaneous Tissue on Changes in Thigh Circumference Following Anterior Cruciate Ligament Reconstruction.

Circumference measurements have been used to estimate muscle cross-sectional area (CSA) in clinical settings. Measurements of thigh circumference are affected by muscle and subcutaneous fat (SF). In fact, SF could increase over a short period. Therefore, clarifying the relationship between thigh circumference and muscle and SF following ACL reconstruction is important. This study's primary purpose was to examine pre- and post-operative changes in thigh circumference, thigh muscles and SF CSAs in both legs. Secondary, the relationship between thigh circumference and muscle and SF CSAs was examined to demonstrate that circumference measurements could be used to detect atrophy. Quadriceps, hamstrings, and SF CSAs at 15, 10, and 5 cm proximal to the patella were measured by MRI pre- and 4 weeks postoperatively to examine how reconstruction affected those tissues in the thighs. The results showed increases in SF CSA (r=0.72 at 10 cm, r=0.67 at 15 cm) greatly affected thigh circumference in females on the surgical side. In males, increases in SF CSA (r=0.83) at 15- and 5-cm and decreases in quadriceps muscle CSA (r=0.73) at 5 cm affected thigh circumference on the surgical side. Thigh circumference measurements might not reflect actual muscle CSA in ACL patients.

Complications During Continuous Renal Replacement Therapy in Critically Ill Neonates.

Background/ Aims: Owing to practical and technical developments, continuous renal replacement therapy (CRRT) has been administered even in critically ill neonates. In this study, the complications in CRRT for neonates were examined to establish a safe CRRT. METHODS: This retrospective study reviewed the clinical records of neonates who underwent CRRT at our neonatal intensive care unit between 2009 and 2017. RESULTS: Eight neonates with a body weight of 1,462-3,288 g were treated by 70 CRRT sessions with blood priming. Intradialytic hypotension (IDH) was observed in 39 sessions (55.7%), most of which occurred soon after the start of the CRRT. Body temperature decreased in 48 sessions (70.5%), and thrombocytopenia during CRRT occurred 30 times (42.9%). CONCLUSION: Complications during CRRT in neonates comprised IDH at the start of the CRRT, body temperature decline, and thrombocytopenia. These complications need to be analyzed for a safe neonatal CRRT.

Fetal intracranial hemorrhage due to maternal subclinical vitamin K deficiency associated with long-term eating disorder.

Vitamin K deficiency in pregnant women causes intracranial hemorrhage (ICH) in fetuses. Fetal ICH frequently causes life-threatening and persistent neurological damage. However, indicators for preventing fetal ICH are not established. Two pregnant women developed long-term eating disorders caused by psychosis. They were administered intravenous fluid and vitamin supplementation, excluding vitamin K. The intracranial low-hypoechoic area on fetal ultrasound was suggestive of fetal ICH due to vitamin K deficiency. Their neonates showed severe developmental delay. Laboratory analysis revealed a normal prothrombin time, but elevated protein induced by vitamin K absence II. Pregnant women who have eating disorders more than 3 weeks could develop fetal ICH due to maternal subclinical vitamin K deficiency. Illness duration and protein induced by vitamin K absence II of pregnant woman may be indicators for vitamin K administration to prevent fetal intracranial hemorrhage.

Temporal brain metabolite changes in preterm infants with normal development.

OBJECTIVE: Preterm infants are at high risk for developmental delay, epilepsy, and autism spectrum disorders. Some reports have described associations between these conditions and gamma-aminobutyric acid (GABA) dysfunction; however, no study has evaluated temporal changes in GABA in preterm infants. Therefore, we assessed temporal changes in brain metabolites including GABA using single-voxel 3-Tesla (T) proton magnetic resonance spectroscopy (1H-MRS) in preterm infants with normal development. METHODS: We performed 3T 1H-MRS at 37-46 postmenstrual weeks (PMWs, period A) and 64-73PMWs (period B). GABA was assessed with the MEGA-PRESS method. N-acetyl aspartate (NAA), glutamate-glutamine complex (Glx), creatine (Cr), choline (Cho), and myo-inositol (Ins) were assessed with the PRESS method. Metabolite concentrations were automatically calculated using LCModel. RESULTS: Data were collected from 20 preterm infants for periods A and B (medians [ranges], 30 [24-34] gestational weeks, 1281 [486-2030]g birth weight). GABA/Cr ratio decreased significantly in period B (p=0.03), but there was no significant difference in GABA/Cho ratios (p=0.58) between the two periods. In period B, NAA/Cr, Glx/Cr, NAA/Cho, and Glx/Cho ratios were significantly increased (p<0.01), whereas Cho/Cr, Ins/Cr, and Ins/Cho ratios were significantly decreased (p<0.01). There was no significant difference for GABA or Cho concentrations (p=0.52, p=0.22, respectively). NAA, Glx, and Cr concentrations were significantly increased (p<0.01), whereas Ins was significantly decreased (p<0.01). CONCLUSIONS: Our results provide new information on normative values of brain metabolites in preterm infants.

Fabrication of Vertical Molecular Junction Devices with Conductive Polymer Contacts Using a Peeling Method.

We present a simple technique for patterning Au top electrodes in vertical molecular junction devices that have the conductive polymer, poly(3,4-ethylene dioxythiophene)-poly(4-styrene sulfonate) ( PEDOT: PSS), as a contact layer between the self-assembled monolayer and the Au top electrode. In this method, a thermally curable photoresist of SU-8 is used to define the areas where the top electrodes are formed. The hydrophobicity and low surface energy of the cured SU-8 facilitates selective deposition of PEDOT: PSS onto the defined top electrode areas of the device through solution dewetting, and also enables the physical peeling of the Au top electrodes deposited on the SU-8 layers using an adhesion tape. Through this approach, vertical molecular junctions with patterned Au top electrodes can be fabricated without employing the shadow mask evaporation process used in the conventional approach. We processed vertical molecular tunneling devices based on self-assembled alkanedithiol monolayers with an active area of 100 µm2.

Assessing Temporal Brain Metabolite Changes in Preterm Infants Using Multivoxel Magnetic Resonance Spectroscopy.

PURPOSE: To investigate temporal changes in brain metabolites during the first year of life in preterm infants using multivoxel proton magnetic resonance spectroscopy ((1)H-MRS). METHODS: Seventeen infants born at 29 (25-33) gestational week (median, range) weighing 1104 (628-1836) g underwent 1.5-T multivoxel (1)H-MRS at 42 postconceptional week (PCW) and at 3, 6, 9, and 12 months after. We measured N-acetyl aspartate (NAA)/creatine (Cr), choline (Cho)/Cr, myo-inositol (Ins)/Cr, NAA/Cho, and Ins/Cho ratios in the frontal lobe (FL) and basal ganglia and thalamus (BG + Th). Linear regression analyses were performed to identify longitudinal changes in infants showing normal imaging findings and normal development. We also evaluated ratios of subjects with abnormal imaging findings and/or development using the 95% confidence intervals (CIs) of regression equations in normal subjects. RESULTS: In the 13 infants with normal development, NAA/Cr and NAA/Cho ratios showed significant positive correlations with PCWs in the FL (r = 0.64 and 0.83, respectively, both P < 0.01) and BG + Th (r = 0.79 and 0.87, respectively, both P < 0.01), while Cho/Cr and Ins/Cr ratios revealed significant negative correlations with PCWs in the FL (r =-0.69 and -0.58, respectively, both P < 0.01) and BG + Th (r =-0.74 and -0.72, respectively, both P < 0.01). Ins/Cho ratios in the FL did not significantly correlate with PCWs (r =-0.19, P = 0.18), while those in the BG + Th showed significant negative correlation with PCWs (r =-0.44, P < 0.01). The metrics in the abnormal group were within the normal group 95% CIs in all periods except a few exceptions. CONCLUSIONS: Longitudinal multivoxel MRS is able to detect temporal changes in major brain metabolites during the first year of life in preterm infants.

Tactile stimulation with kinesiology tape alleviates muscle weakness attributable to attenuation of Ia afferents.

OBJECTIVE: Prolonged vibration stimulation to normal individuals could lead to muscle weakness attributable to attenuation of afferent feedback. This weakness is neurophysiologically similar to that seen in patients with knee injury. Theoretically, increasing input to gamma motor neurons could reverse this weakness. Sensory input to these neurons from skin could indirectly increase Ia afferent feedback. The present study examined the effect of this tactile stimulation in the form of Kinesiology tape on muscle weakness attributable to attenuation of afferent feedback. DESIGN: Randomized, crossover design. METHODS: All participants were measured their eccentric maximal voluntary contractions under the 2 conditions (taping and non-taping). First, maximal voluntary contraction during eccentric contraction was measured as baseline. For the taping condition, Kinesiology tape was applied around each subject's knee joint during maximal voluntary contraction measurement after vibration. For the non-taping condition, tape was not applied during maximal voluntary contraction measurement after vibration. Mean percentage changes between pre- and post-vibration stimulation were compared between two conditions. RESULTS: Maximal voluntary contraction and average electromyography of taping condition was significantly larger than that of non-taping condition. CONCLUSIONS: Our results suggest that tactile stimulation in the form of Kinesiology tape inhibits the decline of both strength and electromyography. Alpha motor neuron activity attenuated by prolonged vibration would thus be partially rescued by tactile stimulation. These results indirectly suggest that stimulation of skin around the knee could counter quadriceps femoris weakness due to attenuated Ia afferent activity.

Relationship between muscle volume and muscle torque of the hamstrings after anterior cruciate ligament lesion.

PURPOSE: This study was conducted to identify factors other than morphological muscle strength factors that affect injured and uninjured sides of knee flexors with anterior cruciate ligament (ACL) lesions. METHODS: The study population consisted of 22 patients with ACL lesions. Their hamstring muscle volume was measured on MRI, and muscle torque per muscle volume was calculated as the peak torque of knee flexion divided by hamstring muscle volume. RESULTS: The mean muscle torque per unit volume of hamstrings in patients with ACL rupture was 0.09 ± 0.02 Nm/cm(3) at 60°/s and 0.08 ± 0.01 Nm/cm(3) at 180°/s on the injured side, and 0.11 ± 0.02 Nm/cm(3) at 60°/s and 0.08 ± 0.01 Nm/cm(3) at 180°/s on the uninjured side. The mean muscle torque per unit volume of hamstrings in control subjects was 0.11 ± 0.02 Nm/cm(3) at 60°/s and 0.08 ± 0.03 Nm/cm(3) at 180°/s. One-factor ANOVA analysis found no significant differences between the three groups at either flexion velocity. CONCLUSIONS: Neurological dysfunction does not appear to exist in knee flexor muscles after ACL injury, unlike the quadriceps. Since the mechanism of muscle weakness will differ depending on the muscle, it is important for clinicians to take this discrepancy into consideration. LEVEL OF EVIDENCE: II.

Relationship between quadriceps femoris muscle volume and muscle torque after anterior cruciate ligament rupture.

PURPOSE: The purpose of this study was to obtain evidence to support the hypothesis that motor unit recruitment is reduced in the quadriceps femoris (QF) of patients with ACL rupture. METHODS: We compared muscle torque per unit volume in the QF from injured and uninjured sides to normal subjects. If high-threshold motor unit recruitment is reduced in patients with ACL rupture, this reduction will theoretically lead to a reduction in muscle torque per unit volume compared to the control group. The subjects included 22 patients with ACL rupture and 22 subjects with no history of knee injury. To identify the muscle torque per unit volume, the isokinetic peak torque was divided by QF volume which was obtained by MRI. RESULTS: Tests revealed that the mean muscle torque per unit volume of the uninjured and injured sides was significantly lower than those of the control group. CONCLUSION: This study demonstrated that the values of the muscle torque per unit volume of both injured and uninjured sides of patients with ACL rupture were significantly lower than those of the control group, thereby providing indirect evidence of the hindrance of motor unit recruitment in these patients. The results of the present study also indicate that there may be bilateral QF weakness in patients with ACL rupture. Since persistent QF weakness is a significant barrier to effective rehabilitation in patients with ACL injuries, a better understanding of the underlying mechanisms will allow clinicians and scientists to develop more effective therapeutic strategies for patient rehabilitation.

Left coronary artery ostial stenosis from Takayasu's arteritis diagnosed using transthoracic color flow and pulsed Doppler echocardiography.

Coronary artery stenosis is seen in 10-45% of patients with Takayasu's arteritis (TA) and coronary ostia are most frequently involved. It may cause angina pectoris and sudden death during the early course of the disease. We describe a 14-year-old girl who first presented with exertional angina and syncope and was diagnosed as having left coronary artery ostial stenosis from TA by using transthoracic echocardiography. This is the first report showing the important role of color flow and pulsed Doppler echocardiography to detect coronary artery stenosis caused by TA.

Relationship between muscle volume and muscle torque of the hamstrings after anterior cruciate ligament reconstruction.

The muscle torque per unit volume of the hamstrings on the injured and uninjured sides in patients with ACL reconstruction were compared with participants with no history of knee injury to examine whether a similar mechanism leading to quadriceps weakness exists in the hamstrings of these patients. The study population consisted of 18 and 52 patients at

Effects of prolonged tendon vibration stimulation on eccentric and concentric maximal torque and emgs of the knee extensors.

The purpose of present study was to compare the effect of Ia afferent attenuation on the activity of alpha motor neuron (MN) during concentric and eccentric action. Eight male subjects were enrolled in the present study. The experiments consisted of two sessions of MVC measurements, since all subjects performed both maximal concentric and eccentric action. EMG signals were simultaneously measured. To establish the baseline of strength, subjects were asked to perform MVC of knee extension in each session. After finishing the measurements, 20 min of vibration stimulation was applied. Immediately after finishing vibration stimulation, the MVC and AEMG were again measured. The means of MVC for concentric knee extension at pre and post- vibration stimulation were 192.2 ± 49.3 Nm and 162.3 ± 47.9 Nm, respectively. The means of MVC for eccentric knee extension at pre and post-vibration stimulation were 299.7 ± 77.0 Nm and 247.3 ± 88. 6 Nm, respectively. Two-factor repeated ANOVA detected significant differences in the MVC. Both main effects for pre-post condition (F(1,7)=, p = 0.0033) and action (F(1,7)=26.35, p = 0.0013) were noted. No interaction effect (action x condition) was noted. The means of AEMG (vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF)) at pre and post -vibration stimulation were decreased. Two-factor repeated ANOVA detected significant differences in AEMG (VM and VL). Both main effects for pre-post condition (VL;F(1,7)=7.27, p = 0.0308, VM; F(1,7)=9.55, p = 0.0175) and action (F(1,7)=12.40, p = 0.0097) were noted in the VL and the VM but not in the RF. Furthermore, significant interaction (action x condition) effect was noted in the VM (F(1,7)=7.03, p = 0.0328) but not in the VL. The MVC and the EMG activity of the VL in response to the prolonged vibration stimulation were significantly reduced in eccentric contraction over concentric contraction. These results represented that a deactivation effect on the alpha MN of the VL during eccentric action was greater than that of concentric action. Key pointsA deactivation effect on the alpha motor neuron of the vastus lateralis during eccentric action was greater than that of maximal concentric action.

Gamma loop dysfunction of the quadriceps femoris of elderly patients hospitalized after fall injury.

BACKGROUND AND PURPOSE: Gamma loop dysfunction may increase the risk of falls. Therefore, we evaluated gamma loop function in subjects hospitalized after fall injury and examined whether aging affects the gamma loop. METHODS: Maximal voluntary contraction (strength) of knee extension and integrated electromyography (I-EMG) of the quadriceps femoris were examined to evaluate the activities of alpha motoneurons before and after 20-min vibration applied to the quadriceps femoris. Mean percentage changes were calculated as: (previbration value-postvibration value)/previbration valuex100). As strength and I-EMG of both uninjured (UG) and injured limbs (IG) of patients with a history of falls resulting in hospitalization were examined in each group, the mean percentage changes of the 4 groups were compared with those of controls [young control group (YCG) and elderly control group (ECG)]. RESULTS: Mean percentage changes in strength of UG and IG were significantly different from YCG but not the ECG. Mean percentage changes in I-EMG for VL (vastus lateralis) and VM (vastus medialis)in IG were significantly different from YCG. However, I-EMG of RF of IG were not significantly different from YCG. Although mean percentage changes in I-EMG of UG were not significantly different from ECG, those for VL and VM of IG were different from ECG. CONCLUSIONS: As the gamma loop dysfunction exited in the uninjured limbs of subjects with a history of falls resulting in hospitalization, a dysfunctional gamma loop could be a risk factor for falling. Further studies are needed to identify the effects of aging on gamma loop function.