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Official Journal of the American College of Sports Medicine and-restart in the re-go trials with a PI of 150 ms while they execute two processes for stop and restart separately in the re-go trials with a PI of 250 ms. Moreover, this second EEG phase-locking weakened in slow re-go response trials compared with fast re-go response trials, indicating that stop-and-restart difficulty with a PI of 250 ms might be associated with an insufficient re-go-signal perception. CONCLusIONs: These results suggest that difficulty to restart 250 ms after stopping a movement is related to the presence of the second processes for re-go-signal perception. 1541 Board #133 May 30, 2:00 PM - 3:30 PM The acute Effects of static stretching on the Passive Muscle Properties of the Leg Extensors Jake A. Deckert, Trent J. Herda, Phil Vardiman, Phil M. Gallagher, Michael A. Cooper. The University of Kansas, Lawrence, KS. (Sponsor: Joseph P. Weir, FACSM) (No relationships reported) PurPOsE: The purpose of this study was to examine the effects of static stretching on the passive range of motion (PROM) and musculotendinous stiffness (MTS) of the leg extensors. METhOds: Six individuals (mean ± SD; age = 24.5 ± 6.6 yr, height = 143.7 ± 29.8 cm, weight = 66.3 ± 7.3 kg) performed a PROM assessment with the isokinetic dynamometer (Biodex Medical Systems, Inc., Shirley, New York) programed in passive mode, which extended the right leg at an angular velocity of 5°s-1. The hip was hyperextended at an angle of 148° to 152° during all range of motion assessments. The maximal ROM was determined as the point of discomfort but not pain, as acknowledged by the subject. MTS of the leg extensors was quantified using a fourthorder polynomial regression model that was fitted to the passive angle-torque curves for each subject. MTS (Nm°-1) was calculated for each degree increment in the passive angle-torque relationship. For analysis, MTS was determined at the second to last joint angle for the pre-stretching assessment and the same common joint angle selected during the post-stretching assessment. MTS was calculated offline using a customwritten software (LabVIEW 8.5, National Instruments, Austin, TX), which included a gravity correction of the limb. Surface electromyography (EMG) (Ag-AgCL, Quinton Quik Prep, Quinton Instruments Co., Bothell, WA) was monitored to ensure the movement was passive. If EMG activity was above baseline during the PROM assessment, the trial was removed from further analysis. For the stretching of the right leg extensors, subjects completed four repetitions of four stretches lasting 30 seconds with 10 seconds rest between stretches, which included three assisted stretches and one unassisted stretch. Paired samples t-tests were used to examine possible differences pre- to post-stretching for PROM and MTS. rEsuLTs: There were no significant differences for PROM (P = 0.099) or MTS (P = 0.470) between pre- and post-stretching. CONCLusION: In contrast to previous studies testing other muscle groups, there were no differences between pre- and post-stretching for PROM and MTS. The subject position in the isokinetic dynamometer may have not allowed for an accurate assessment of PROM or MTS. Future studies may want to further hyperextend the hip past the range used in the present study (148° – 152°). 1542 Board #134 May 30, 2:00 PM - 3:30 PM Contributions of Neural Excitability and Voluntary activation to Quadriceps Muscle strength Adam S. Lepley, Nael O. Bahhur, Amanda M. Murray, Brian G. Pietrosimone. University of Toledo, Toledo, OH. (No relationships reported) Previous investigations have suggested that both morphological and neural adaptations are responsible for modifying muscle strength. New rehabilitative strategies targeting neural excitability and voluntary activation have been proposed to improve muscle strength. Understanding how neural excitability and voluntary activation contribute to muscle strength is critical in developing new therapeutic techniques. PurPOsE: Determine if spinal-reflexive excitability, corticospinal excitability, and voluntary activation predict quadriceps strength. METhOds: Twenty healthy participants (12 Male, 8 Female; 22.1±2.4yrs; 173.4±7.5cm, 71.6±8.2kg) were included. Quadriceps strength was assessed via maximal voluntary isometric contractions (MVIC) performed at 90° of knee flexion. Spinal-reflexive excitability was assessed using Hoffmann reflexes normalized to maximal muscle responses (H:M ratio). Corticospinal excitability was evaluated with active motor thresholds (AMT), which were elicited by stimulating specific areas on the motor cortex using Transcranial Magnetic Stimulation during a standardized contraction at 5% of MVIC. Voluntary activation was measured via a superimposed burst technique and the central activation ratio (CAR). A hierarchal multiple Linear Regression model was used to determine the ability of H:M, AMT and CAR to predict MVIC. The change in R2 to the model from the addition of each predictor variable was also analyzed. rEsuLTs: The overall multiple regression model significantly predicted 45% of the variance in MVIC (R2 = 0.45, P=0.01; MVIC = 2.3H:M -.03AMT + 3.3CAR + 1.2). Initial imputation of H:M into the model accounted for 24% (R2=0.24, P=0.02) of the variance in MVIC. The subsequent addition of AMT accounted for a significant Vol. 45 No. 5 Supplement S301 increase of 16% (Δ R2 = 0.16, P=0.04) in the prediction capability of the model. Lastly, CAR contributed an insignificant increase of 5%(Δ R2 = 0.05, P=0.23) to the prediction capability of the model, and was therefore removed. CONCLusION: Neural excitability predicted nearly half of the variance in quadriceps strength. This may be interpreted as evidence that neural pathways are essential in maintaining and increasing quadriceps strength. Interventions targeting neural pathways may be beneficial to gain and restore optimal quadriceps strength. 1543 Board #135 May 30, 2:00 PM - 3:30 PM The Effect of Massed versus distributed Practice on the Variability of Muscle activity and Force Jessica McGuire 1 , Lara Green 1 , Kristina M. Calder 2 , Jae Patterson 1 , David A. Gabriel, FACSM 1 . 1 Brock University, St. Catharines, ON, Canada. 2 McMaster University, Hamilton, ON, Canada. (No relationships reported) PurPOsE: The purpose of this study was to determine if the initial phase of learning a resistive exercise task is affected by the structure of the practice (i.e., contraction) schedule. METhOds: Twenty-six female university students were recruited. Participants were randomly assigned to one of two experimental groups: massed, which performed 15 isometric elbow flexion contractions on one day, or distributed, which performed the 15 contractions across three days (5 per day). All participants performed two retention tests, each consisting of 5 contractions, which occurred two weeks and three months after the final test session. Each contraction was 5-sec in length with a 3-minute intertrial period. Surface electromyographic (sEMG) activity and force were recorded concurrently. Mean amplitude values (MAV) and variance ratios (VR) were calculated for the biceps and triceps sEMG data and force. rEsuLTs: There was a significant increase in force (∆27.7 N, or 26%) and biceps brachii sEMG (∆77 µV, or 29.6%) in both groups (p’s0.05). In contrast, the pattern of change in force variability was different between the two practice schedules (p=0.05). Force variability for the massed group decreased but plateaued after the first block of trials, whereas the distributed group exhibited a more gradual reduction of similar magnitude. Both groups maintained a nearly 60% decrease in force variability across the two retention tests. The variability in biceps and triceps sEMG mirrored the variability in force but the F-ratios were non-significant (p’s>0.05). CONCLusION: The magnitude of force and sEMG revealed no difference between practice schedules, but the force variability data followed the classic findings for massed versus distributed practice. The initial phase of learning a resistive exercise task was, therefore, affected by the type of practice schedule. This work was supported by the Natural Sciences and Engineering Research Council of Canada. 1544 Board #136 May 30, 2:00 PM - 3:30 PM h-index Measurement Is Important In Persons With Peripheral Neuropathy Matthew Homles 1 , Shuqi Zhang 2 , Duckchan Jang 3 , Li Li, FACSM 1 . 1 Georgia Southern University, Statesboro, GA. 2 Louisiana State University, Baton Rouge, LA. 3 Keimyung University, Daegu, Republic of Korea. (No relationships reported) Peripheral neuropathy (PN) is a neurodegenerative disease that damages the peripheral nervous system. The presentation of PN is usually symmetrical sensory nerve damage to distal extremities but progresses proximally. Strength, sensitivity, and endurance measures are useful tools in understanding effectiveness of interventions. However, nerve function measures should be considered for this population. H-index is measure used in many neurological studies and can provide new insight to peripheral neuropathy. PurPOsE: To better understand nerve function, as measured by H-index, and its relation to functional motor output in people with PN. METhOds: H-index, standing balance, Timed up-and-go (TUG), 6-min walk test, peak knee flexion/extension torque were measured from 12 participants with PN. H-index was determined by eliciting electrical stimulation at the posterior tibial nerve and recording latency of M- and H-waves by EMG on the lateral gastrocnemius. H-index was calculated as (Height (cm) / (latency (ms))^2* 2. Participants were seated and asked to walk as quickly and safely as possible around a cone placed 3 m away then return to their seat, TUG was the average time of three trials. For the 6 min walk test, participants were encouraged to walk as far as possible in 6 min. Peak knee flexion/extension was performed on a Biodex. Pearson correlation was performed between H-index and other measures of interest. rEsuLTs: 12 participants (8 women, 4 men) age (72.5 ± 9.2), height (163.0 ± 11.9), body mass (171.8 ± 46.2) diagnosed with PN were tested. Causes of PN included diabetes (n=2), trauma (n=1), and idiopathic (n=9). Duration of PN was 10.0 ± 1.7 (Mean ± SD) years. Mean and standard error of mean for our measures of interest were as follows: H-index (61.21 ± 4.52); TUG (9.22±0.41); 6 min walk (429.58 ± Abstracts were prepared by the authors and printed as submitted. Thursday, May 30, 2013
Thursday, May 30, 2013 S302 Vol. 45 No. 5 Supplement 26.37); 95% area (0.82 ± 0.13); peak flexion (37.15 ± 6.43); and peak extension (64.73 ± 6.52). H-index was correlated with 95% area (R²=.26), TUG (R²=.51), 6 min walk (R²=.27), but not peak flexion (R²=.04) or peak extension (R²=.002). CONCLusIONs: H-index as a measure of nerve function in people with PN is related to functional outcomes but not strength measures. H-index could be useful in understanding functional impairments in gait and standing balance among people with PN. 1545 Board #137 May 30, 2:00 PM - 3:30 PM h-index Is Independent From Other sensory Measures among People With Peripheral Neuropathy Shuqi Zhang1 , Matthew Homles2 , Duckchan Jang3 , Li Li, FACSM4 . 1Louisiana State University, Baton Rouge, LA. 2 3 Georgia Southern University, Statesboro, GA. Keimyung University, Daegu, Republic of Korea. 4Goergia Southern University, Statesboro, GA. (No relationships reported) The balance problem in people with peripheral neuropathy (PN) is believed to be from deteriorated function of afferent information collection and transition. Nerve transmission speed in peripheral and central nervous system is critical for movement control. H-index, as a representative measure of transmit speed in nervous system, is a potential measure to explain neurological impairments among people with PN. PurPOsE: This study was to examine if H-index is an independent measure from other common sensory measures of people with PN. METhOds: 12 participants (8 women, 4 men) age (72.5 ± 9.2), height (163.0 ± 11.9), body mass (171.8 ± 46.2) diagnosed with PN were tested. Causes of PN included diabetes (n=2), trauma (n=1), and idiopathic (n=9). Duration of PN was 10.0 ± 1.7 (Mean ± SD) years. The foot sole sensitivity was tested at big toe (BT), 1st and 5th metatarsal (M1 and M5), midfoot (MF) and medial heel (MH) with a 5.07 monofilament. The overall score of one foot is the number of its sensitive sites, ranged from 0 to 5. H-index is based on the linear relationship between participant height and the latency between H- and M-wave. H- and M-waves were elicited by stimulating tibial nerve at back of right knee joint and signals were picked up at calf muscle in all participations. H-index is calculated by [(Height (cm))/(latency(ms)) ]^2*2. Active ankle proprioception, measured from maximal inversion to the target positions at inversion of -15°, 0° and eversion of 10°. Proprioception was represented by the errors between the stop positions and target positions. Pearson correlation analysis examined the relationship between H-index and plantar sensitivity as well as proprioception of ankle at three target positions separately. rEsuLTs: H-index is not correlated with ankle proprioception at 0°, inversion of -15°, and eversion of 10°, nor with foot sole sensation (R-square = 0.0253, =7E-05, =0.1914, =0.1233, and =0.0189, respectively). CONCLusIONs: These results indicate H-index is a neurological parameter can be measured in nervous system, independently from plantar tactile sensation and ankle joint proprioception, among this population. In further study, H-index should be employed to explain how PN affects the nerve system in addition to the deterioration of proprioception and tactile sensation. 1546 Board #138 May 30, 2:00 PM - 3:30 PM Corticospinal and spinal Variability during Lengthening and shortening Contractions Performed by Trained and untrained Males Glyn Howatson, FACSM1 , Jamie Tallent1 , Stuart Goodall1 , Alan St Clair Gibson1 , Tibor Hortobagyi, FACSM2 . 1Northumbria University, Newcastle-upon-Tyne, United Kingdom. 2University of Groningen, Groningen, Netherlands. (No relationships reported) There is a controversy concerning the mechanism and pathways involved in the neural adaptations to resistance training. Here we examined the hypothesis that corticospinal and spinal excitability differs between previously strength trained (ST) and untrained (UT) males. PurPOsE: To compare corticospinal and spinal excitability measured during dynamic muscle contractions in ST and UT males and to determine the impact of training status on the variability in motor evoked potentials (MEPs). METhOds: Nine UT and 10 ST male volunteers reported to the laboratory on two occasions separated by 24 h. On each visit, MEPs and the cortical silent period were evoked by transcranial magnetic brain stimulation applied to the left primary motor cortex and recorded from the tibialis anterior at the instant when the dominant, right ankle was at 90° during shortening and lengthening contractions. The H-reflex and V-waves were also evoked during contractions by peripheral nerve stimulation. Differences in MEP variability were investigated between groups on day 1 and changes within groups from days 1 to 2. rEsuLTs: Although the ST vs. UT group was 24% stronger (P = 0.02), there were no differences in corticospinal or spinal excitability between the groups. MEP variability was similar in the two groups on day 1 (39.1 and 40.9%, respectively) but variability of the resting MEPs was significantly lower on day 2 in ST (25%, P < 0.005). MEDICINE & SCIENCE IN SPORTS & EXERCISE ® CONCLusION: Against expectations, corticospinal and spinal excitability were similar in ST and UT, the decrease in resting MEP variability from day 1 to day 2 in the ST compared with UT suggests that chronic resistance training may produce a greater degree of acute plasticity of the CNS under the present experimental conditions. 1547 Board #139 May 30, 2:00 PM - 3:30 PM stiffness Quantification of human Calf Muscle during standing Wall stretching using ultrasound shear-wave Elastography Keigo Taniguchi1 , Minoru Shinohara, FACSM2 , Shuhei Nozaki1 , Masaki Katayose1 . 1Sapporo Medical University, Sapporo, Japan. 2Georgia Institute of Technology, Atlanta, GA. (No relationships reported) Stretching for calf muscle is commonly prescribed to increase the range of motion for ankle dorsiflexion. The magnitude of changes in the stiffness of muscle belly during stretching in a weight-bearing position is unknown. Recent development of shear-wave elastography has opened the possibility for objectively quantifying muscle stiffness (Shinohara et al. 2010). PurPOsE: To quantify the changes in muscle stiffness of the triceps surae belly during standing wall stretching with the novel ultrasound shear-wave elastography. METhOds: Eleven healthy young adults performed standing wall stretching that consisted of 10 and 20 deg of ankle dorsiflexion while maintaining the right hip and knee in an extended position. Longitudinal ultrasonic images of the medial (MG) and lateral (LG) gastrocnemius and soleus (SOL) muscles of the right leg were obtained while the subjects maintained 50% of their body weight on the foot. Shear-wave elastography was applied with the ankle joint angle in neutral position (0 deg) during standing and at 10 and 20 deg dorsiflexion during stretching. Based on shear-wave propagation velocity, muscle stiffness was quantified as shear modulus in the muscle fascicular area. rEsuLTs: The reproducibility of shear modulus was confirmed by the intra-rater intraclass correlation coefficient (0.95 for MG, 0.94 for LG, 0.72 for SOL) between measurements. Shear modulus increased as the ankle joint angle changed from 0 to 20 deg: 25.7 ± 9.2 vs. 90.9 ± 27.9 kPa (3.5-fold) in MG, 17.3 ± 3.9 vs. 51.0 ± 11.6 kPa (2.9-fold) in LG, and 24.7 ± 5.6 vs. 38.2 ± 8.2 kPa (1.5-fold) in SOL. Furthermore, shear modulus of MG was significantly higher than that of LG and SOL at 20 deg dorsiflexion (p < 0.05). CONCLusION: The findings indicated that the stiffness of triceps surae belly progressively increased by 1.5 to 3.5-fold in response to progressive dorsiflexion. Variability in the index of stiffness between muscles may be related to variability in passive tension between muscles during standing wall stretching. Quantification of muscle stiffness during stretching with ultrasound elastography would provide useful information to develop effective therapeutic exercise for improving joint flexibility. 1548 Board #140 May 30, 2:00 PM - 3:30 PM Is Neuromuscular activation Of Vastus Intermedius Muscle Induced By hip Flexion Movement? Akira Saito, Hiroshi Akima. Nagoya University, Nagoya, Japan. (Sponsor: Katsumi Asano, FACSM) (No relationships reported) The quadriceps femoris (QF) composed of four knee extensor muscles, i.e. vastus intermedius (VI), vastus lateralis, vastus medialis (VM) and rectus femoris (RF). The RF acts as not only the knee extensor but also hip flexor. Montgomery et al. (1994) found out that activation of VI was similar to that of RF during hip and knee flexion phase of running, which reached to 17% of maximal knee extension. However, it is unclear whether the activation of VI was actually induced by the hip flexion movements. A neural pathway from the sensory nerves in the cruciate ligament to the thigh muscles was reported in humans. If the VI activity is elicited by hip flexion movement, it would be one of the factors. PurPOsE: The purpose of this study is to examine the neuromuscular activation of VI during isometric hip flexion at different hip joint angles. METhOds: Ten healthy men (age 25.3 ± 6.9 years, height 174.6 ± 6.3 cm and weight 67.2 ± 10.3 kg) performed 25%, 50%, 75%, 100% of maximal voluntary contraction (MVC) of isometric hip flexion at 90°, 110° and 130° of hip joint angles (180° is fully extended). We recorded the surface electromyography (EMG) of four individual muscles of the QF as previous study (Watanabe & Akima 2009). The root mean square (RMS) of individual muscles of the QF was normalized by the RMS of MVC during isometric knee extension. Onsets of muscle activation for VI and RF were defined as 5%RMS deviation from baselines during isometric knee extension MVC, and we calculated the time lag between both muscles. rEsuLTs: Normalized EMG of the RF was significantly higher than other three synergists of the QF (all P < 0.05) and normalized EMG of the VI was significantly higher than that of the VM during MVC at 110° and 130° of hip joint angles (all P < 0.05). During hip flexion tasks, activation delay comparing to the RF was observed in the VI at three hip joint angles (230 to 240 msec), and these were significantly later than during knee extensions (-19 to 6 msec) at each hip joint angle (all P < 0.05). CONCLusIONs: Neuromuscular activation of the VI appears during isometric hip ACSM May 28 - June 1, 2013 Indianapolis, Indiana
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