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Joel T Cramer - One of the best experts on this subject based on the ideXlab platform.
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the effects of interelectrode distance over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus concentric eccentric and isometric torque relationships for the vastus lateralis muscle
Journal of Electromyography and Kinesiology, 2009Co-Authors: Travis W Beck, Joel T Cramer, Terry J Housh, Joseph P. WeirAbstract:Abstract The purpose of this study was to examine the influence of interelectrode distance (IED) over the estimated innervation zone (IZ) for the vastus lateralis muscle and normalization on the torque-related patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the leg extensors. Eight men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously with two bipolar electrode arrangements in single differential configuration (20 and 40mm IEDs) placed over the estimated IZ for the vastus lateralis muscle and a third electrode arrangement in single differential configuration (20mm IED) placed distal to the estimated IZ. The results indicated that there were only a few (six of 90 statistical comparisons) significant ( p
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acute effects of static stretching on characteristics of the isokinetic angle torque relationship surface electromyography and mechanomyography
Journal of Sports Sciences, 2007Co-Authors: Joel T Cramer, Terry J Housh, Travis W Beck, Laurie L Massey, Sarah M Marek, Suzanne Danglemeier, Sushmita Purkayastha, Julie Culbertson, Kristi A Fitz, Alison D EganAbstract:Abstract The aims of this study were to examine the acute effects of static stretching on peak torque, work, the joint angle at peak torque, acceleration time, isokinetic range of motion, mechanomyographic amplitude, and electromyographic amplitude of the rectus femoris during maximal concentric isokinetic leg extensions at 1.04 and 5.23 rad · s−1 in men and women. Ten women (mean ± s: age 23.0 ± 2.9 years, stature 1.61 ± 0.12 m, mass 63.3 ± 9.9 kg) and eight men (age 21.4 ± 3.0 years, stature 1.83 ± 0.11 m, mass 83.1 ± 15.2 kg) performed maximal voluntary concentric isokinetic leg extensions at 1.04 and 5.23 rad · s−1. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. Peak torque, acceleration time, and electromyographic amplitude decreased (P≤ 0.05) from pre- to post-stretching at 1.04 and 5.23 rad · s−1; there were no changes (P > 0.05) in work, joint angle at peak torque, i...
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an acute bout of static stretching does not affect maximal eccentric isokinetic peak torque the joint angle at peak torque mean power electromyography or mechanomyography
Journal of Orthopaedic & Sports Physical Therapy, 2007Co-Authors: Joel T Cramer, Terry J Housh, Travis W Beck, Joseph P. Weir, Glen O Johnson, Jared W CoburnAbstract:Study Design Repeated-measures experimental design. Objective To examine the acute effects of static stretching on peak torque, the joint angle at peak torque, mean power output, and electromyographic and mechanomyographic amplitudes and mean power frequency of the vastus lateralis and rectus femoris muscles during maximal eccentric isokinetic muscle actions. Background A bout of static stretching may impair muscle strength during isometric and concentric muscle actions, but it is unclear how static stretching may affect eccentric force production. Methods and Measures Fifteen men (mean ± SD age, 23.4 ± 2.4 years) performed maximal eccentric isokinetic muscle actions of the dominant and nondominant knee extensor muscles at 60°·s−1 and 180°·s−1 on an isokinetic dynamometer, while electromyographic and mechanomyographic amplitudes (root-mean-square) and mean power frequency were calculated for the vastus lateralis and rectus femoris muscles. Peak torque (Nm), the joint angle at peak torque (°), and mean pow...
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acute effects of static stretching on peak torque and mean power output in national collegiate athletic association division i women s basketball players
Journal of Strength and Conditioning Research, 2006Co-Authors: Alison D Egan, Joel T Cramer, Laurie L Massey, Sarah M MarekAbstract:Egan, A.D., J.T. Cramer, L.L. Massey, and S.M. Marek. Acute effects of static stretching on peak torque and mean power output in National Collegiate Athletic Association Division I women's basketball players. J. Strength Cond. Res. 20(4): 778-782. 2006.-The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and mean power output (MP) during maximal, voluntary concentric isokinetic leg extensions at 60 and 300°·s?1 in National Collegiate Athletic Association Division I Women's Basketball players. Eleven members of a women's basketball team volunteered to perform maximal concentric isokinetic leg extensions at 60 and 300°·s?1 on a calibrated Biodex System 3 dynamometer. After the initial isokinetic testing, the dominant leg extensors were stretched using 1 unassisted and 3 assisted static stretching exercises. The poststretching isokinetic assessments were repeated at 5, 15, 30, and 45 minutes after the static stretching (post-5, post-15, post-30, and post-45). PT (N·m) and MP (W) were recorded by dynamometer software. The results indicated no stretching-related changes in PT (p = 0.161) or MP (p = 0.088) from pre- to poststretching for any of the testing intervals (post-5, post-15, post-30, and post-45). These findings indicated that the static stretching had no impact on PT or MP during maximal, voluntary concentric isokinetic muscle actions in collegiate women's basketball players. In conjunction with previous studies, these findings suggested that trained athletes may be less susceptible to the stretching-induced force deficit than untrained, nonathletes.
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the acute effects of static stretching on peak torque mean power output electromyography and mechanomyography
European Journal of Applied Physiology, 2005Co-Authors: Joel T Cramer, Terry J Housh, Joseph P. Weir, Glen O Johnson, Jared W Coburn, Travis W BeckAbstract:The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240°·s-1 of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3) years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240°·s-1. Surface EMG (μVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P≤0.05) from pre- to post-stretching for the stretched limb at 60 and 240°·s-1 and for the unstretched limb at 60°·s-1. EMG amplitude of the VL and RF also decreased (P≤0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.
Travis W Beck - One of the best experts on this subject based on the ideXlab platform.
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the effects of interelectrode distance over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus concentric eccentric and isometric torque relationships for the vastus lateralis muscle
Journal of Electromyography and Kinesiology, 2009Co-Authors: Travis W Beck, Joel T Cramer, Terry J Housh, Joseph P. WeirAbstract:Abstract The purpose of this study was to examine the influence of interelectrode distance (IED) over the estimated innervation zone (IZ) for the vastus lateralis muscle and normalization on the torque-related patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the leg extensors. Eight men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously with two bipolar electrode arrangements in single differential configuration (20 and 40mm IEDs) placed over the estimated IZ for the vastus lateralis muscle and a third electrode arrangement in single differential configuration (20mm IED) placed distal to the estimated IZ. The results indicated that there were only a few (six of 90 statistical comparisons) significant ( p
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acute effects of static stretching on characteristics of the isokinetic angle torque relationship surface electromyography and mechanomyography
Journal of Sports Sciences, 2007Co-Authors: Joel T Cramer, Terry J Housh, Travis W Beck, Laurie L Massey, Sarah M Marek, Suzanne Danglemeier, Sushmita Purkayastha, Julie Culbertson, Kristi A Fitz, Alison D EganAbstract:Abstract The aims of this study were to examine the acute effects of static stretching on peak torque, work, the joint angle at peak torque, acceleration time, isokinetic range of motion, mechanomyographic amplitude, and electromyographic amplitude of the rectus femoris during maximal concentric isokinetic leg extensions at 1.04 and 5.23 rad · s−1 in men and women. Ten women (mean ± s: age 23.0 ± 2.9 years, stature 1.61 ± 0.12 m, mass 63.3 ± 9.9 kg) and eight men (age 21.4 ± 3.0 years, stature 1.83 ± 0.11 m, mass 83.1 ± 15.2 kg) performed maximal voluntary concentric isokinetic leg extensions at 1.04 and 5.23 rad · s−1. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. Peak torque, acceleration time, and electromyographic amplitude decreased (P≤ 0.05) from pre- to post-stretching at 1.04 and 5.23 rad · s−1; there were no changes (P > 0.05) in work, joint angle at peak torque, i...
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an acute bout of static stretching does not affect maximal eccentric isokinetic peak torque the joint angle at peak torque mean power electromyography or mechanomyography
Journal of Orthopaedic & Sports Physical Therapy, 2007Co-Authors: Joel T Cramer, Terry J Housh, Travis W Beck, Joseph P. Weir, Glen O Johnson, Jared W CoburnAbstract:Study Design Repeated-measures experimental design. Objective To examine the acute effects of static stretching on peak torque, the joint angle at peak torque, mean power output, and electromyographic and mechanomyographic amplitudes and mean power frequency of the vastus lateralis and rectus femoris muscles during maximal eccentric isokinetic muscle actions. Background A bout of static stretching may impair muscle strength during isometric and concentric muscle actions, but it is unclear how static stretching may affect eccentric force production. Methods and Measures Fifteen men (mean ± SD age, 23.4 ± 2.4 years) performed maximal eccentric isokinetic muscle actions of the dominant and nondominant knee extensor muscles at 60°·s−1 and 180°·s−1 on an isokinetic dynamometer, while electromyographic and mechanomyographic amplitudes (root-mean-square) and mean power frequency were calculated for the vastus lateralis and rectus femoris muscles. Peak torque (Nm), the joint angle at peak torque (°), and mean pow...
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the acute effects of static stretching on peak torque mean power output electromyography and mechanomyography
European Journal of Applied Physiology, 2005Co-Authors: Joel T Cramer, Terry J Housh, Joseph P. Weir, Glen O Johnson, Jared W Coburn, Travis W BeckAbstract:The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240°·s-1 of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3) years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240°·s-1. Surface EMG (μVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P≤0.05) from pre- to post-stretching for the stretched limb at 60 and 240°·s-1 and for the unstretched limb at 60°·s-1. EMG amplitude of the VL and RF also decreased (P≤0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.
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mechanomyographic responses of the vastus medialis to isometric and eccentric muscle actions
Medicine and Science in Sports and Exercise, 2004Co-Authors: Jared W Coburn, Joel T Cramer, Terry J Housh, Travis W Beck, Joseph P. Weir, Moh H Malek, Glen O JohnsonAbstract:Purpose: The mechanomyographic (MMG) signal may he used to examine the motor control strategies used to modulate torque during various types of muscle actions. Therefore, the purpose of this study was to examine the MMG amplitude and mean power frequency (MPF) versus torque relationships during isometric and eccentric isokinetic muscle actions. Methods: Eleven adults (mean age ± SD = 20.8 ± 1.4 yr) volunteered to perform isometric and eccentric isokinetic leg extension muscle actions at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of peak torque on a Cyhex 6000 dynamometer. A piezoelectric crystal contact sensor was placed on the vastus medialis to detect the MMG signal. Results: Polynomial regression analyses indicated that for the isometric muscle actions the relationships for MMG amplitude (r 2 = 0.984) and MPF (r 2 = 0.989) versus torque were linear. For the eccentric isokinetic muscle actions, the relationships for MMG amplitude (r 2 = 0.580) and MPF (r 2 = 0.961) versus torque were also linear. Conclusion: The patterns for MMG amplitude and MPF may reflect the motor control strategies that modulate torque production for isometric and eccentric isokinetic muscle actions. Based on the results of this and previous studies, it appears that for the vastus medialis, torque is modulated in a similar manner for isometric, concentric, and eccentric isokinetic muscle actions. Specifically, these findings suggest that gradation of torque involves increases in recruitment and firing rate to 100% voluntary torque production.
P Rochcongar - One of the best experts on this subject based on the ideXlab platform.
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isokinetic and anterior cruciate ligament reconstruction with hamstrings or patella tendon graft analysis of literature
International Journal of Sports Medicine, 2005Co-Authors: M Dauty, L Tortellier, P RochcongarAbstract:: We report isokinetic results of anterior cruciate ligament reconstruction with patellar tendon or hamstring graft from the literature analysis. The literature was defined from two search "textwords": Isokinetic and Anterior cruciate ligament reconstruction, and from three databases: Medline, Pascal, and Herasmus. Two independent physicians (Physical Medicine and Rehabilitation) carried out an analysis according to the French National Accreditation and Health Evaluation Agency recommendations. Fifty-three studies were selected: 29 reported isokinetic results after anterior cruciate ligament reconstruction with patellar tendon graft, 15 reported isokinetic results after anterior cruciate ligament reconstruction with hamstring graft, and 9 studies compared the two surgical procedures. After discussing different bias and in reference to prospective randomised and comparative studies, the anterior cruciate ligament reconstruction with patellar tendon graft involves a knee extensors deficit during several months. The hamstring surgical procedure involves a less important knee extensor deficit (from 6 to 19 % against 8 to 21 %). Knee sprain and intra-articular surgery involve a long-lasting knee extensors deficit. Anterior cruciate ligament reconstruction with hamstrings graft involves a knee flexors deficit over several months. The patellar tendon surgical procedure involves a less important knee flexors deficit (from 1 to 15 % against 5 to 17 %). In reference to isokinetic parameters, no difference between the two surgical procedures (patellar tendon graft or hamstring graft) is shown after more than twenty-four post-surgical months.
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reproducibility of concentric and eccentric isokinetic strength of the knee flexors in elite volleyball players
Isokinetics and Exercise Science, 2001Co-Authors: M Dauty, P RochcongarAbstract:The aim of this study is to define the test-retest reproducibility for measuring the peak torque of the knee flexors according to the isokinetic concentric and eccentric muscle action. The tests were done in two sessions at a 21 day interval. Ten healthy national-level volleyball players, 24.3 years old ± 3.9 were included. Tests took place after the competition season. Evaluation was carried out with a Cybex 6000 dynamometer and the reliability was calculated according to the intraclass correlation coefficient (ICC 2.1). The protocol consisted of 5 isokinetic concentric contractions at 180°/s followed by 5 isokinetic eccentric contractions at 30 and 60°/s. Results show an excellent reproducibility for isokinetic concentric peak torque at 180°/s. (ICC: 0.94) and very good reproducibility for isokinetic eccentric peak torque at 30 and 60°/s. (ICC: 0.86; 0.83). These results indicate that knee flexion strength at these velocities may be used to estimate the performance of volleyball players.
Ufuk Sekir - One of the best experts on this subject based on the ideXlab platform.
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early versus late start of isokinetic hamstring strengthening exercise after anterior cruciate ligament reconstruction with patellar tendon graft
American Journal of Sports Medicine, 2010Co-Authors: Ufuk Sekir, Hakan Gur, Bedrettin AkovaAbstract:BackgoundHamstring strengthening after anterior cruciate ligament reconstruction is a vital component of the rehabilitation program.PurposeThe objective of this trial was to investigate the effects of hamstring isokinetic training used in the early phase of the rehabilitation program on the stability, strength, symptoms, and functional outcomes of patients throughout 12 months after anterior cruciate ligament surgery.Study DesignRandomized controlled clinical trial; Level of evidence, 2.MethodsForty-eight men underwent anterior cruciate ligament reconstruction with an ipsilateral bone—patellar tendon—bone autograft. The patients were randomly assigned to perform daily isokinetic hamstring exercises at postoperative 3 weeks (group I) or to perform daily isokinetic hamstring exercises at postoperative 9 weeks (group II). The patients were evaluated monthly for the first 4 months and at the 12th month for postoperative hamstring and quadriceps strength, as well as for knee function via the Cincinnati Knee Ra...
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effect of isokinetic training on strength functionality and proprioception in athletes with functional ankle instability
Knee Surgery Sports Traumatology Arthroscopy, 2007Co-Authors: Ufuk Sekir, Bulent Hazneci, Yavuz Yildiz, Fatih Ors, Taner AydinAbstract:The purpose of this study was to investigate the effects of isokinetic exercise on strength, joint position sense and functionality in recreational athletes with functional ankle instability (FAI). Strength, proprioception and balance of 24 recreational athletes with unilateral FAI were evaluated by using isokinetic muscle strength measurement, ankle joint position sense and one leg standing test. The functional ability was evaluated using five different tests. These were; single limb hopping course (SLHC), one legged and triple legged hop for distance (OLHD–TLHD), and six and cross six meter hop for time (SMHT–CSMHT). Isokinetic peak torque of the ankle invertor and evertor muscles were assessed eccentrically and concentrically at test speeds of 120°/s. Isokinetic exercise protocol was carried out at an angular velocity of 120°/s. The exercise session was repeated three times a week and lasted after 6 weeks. At baseline, concentric invertor strength was found to be significantly lower in the functionally unstable ankles compared to the opposite healthy ankles (p 0.05). Ankle joint position sense in the injured ankles declined significantly from 2.35 ± 1.16 to 1.33 ± 0.62° for 10° of inversion angle (p < 0.001) and from 3.10 ± 2.16 to 2.19 ± 0.98° for 20° of inversion angle (p < 0.05) following the isokinetic exercise. One leg standing test score decreased significantly from 15.17 ± 8.50 to 11.79 ± 7.81 in the injured ankles (p < 0.001). Following the isokinetic exercise protocol, all of the worsened functional test scores in the injured ankles as compared to the opposite healthy ankles displayed a significant improvement (p < 0.01 for OLHD and CSMHT, p < 0.001 for SLHC, TLHD, and SMHT). These results substantiate the deficits of strength, proprioception, balance and functionality in recreational athletes with FAI. The isokinetic exercise program used in this study had a positive effect on these parameters.
Terry J Housh - One of the best experts on this subject based on the ideXlab platform.
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the effects of interelectrode distance over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus concentric eccentric and isometric torque relationships for the vastus lateralis muscle
Journal of Electromyography and Kinesiology, 2009Co-Authors: Travis W Beck, Joel T Cramer, Terry J Housh, Joseph P. WeirAbstract:Abstract The purpose of this study was to examine the influence of interelectrode distance (IED) over the estimated innervation zone (IZ) for the vastus lateralis muscle and normalization on the torque-related patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the leg extensors. Eight men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously with two bipolar electrode arrangements in single differential configuration (20 and 40mm IEDs) placed over the estimated IZ for the vastus lateralis muscle and a third electrode arrangement in single differential configuration (20mm IED) placed distal to the estimated IZ. The results indicated that there were only a few (six of 90 statistical comparisons) significant ( p
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acute effects of static stretching on characteristics of the isokinetic angle torque relationship surface electromyography and mechanomyography
Journal of Sports Sciences, 2007Co-Authors: Joel T Cramer, Terry J Housh, Travis W Beck, Laurie L Massey, Sarah M Marek, Suzanne Danglemeier, Sushmita Purkayastha, Julie Culbertson, Kristi A Fitz, Alison D EganAbstract:Abstract The aims of this study were to examine the acute effects of static stretching on peak torque, work, the joint angle at peak torque, acceleration time, isokinetic range of motion, mechanomyographic amplitude, and electromyographic amplitude of the rectus femoris during maximal concentric isokinetic leg extensions at 1.04 and 5.23 rad · s−1 in men and women. Ten women (mean ± s: age 23.0 ± 2.9 years, stature 1.61 ± 0.12 m, mass 63.3 ± 9.9 kg) and eight men (age 21.4 ± 3.0 years, stature 1.83 ± 0.11 m, mass 83.1 ± 15.2 kg) performed maximal voluntary concentric isokinetic leg extensions at 1.04 and 5.23 rad · s−1. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. Peak torque, acceleration time, and electromyographic amplitude decreased (P≤ 0.05) from pre- to post-stretching at 1.04 and 5.23 rad · s−1; there were no changes (P > 0.05) in work, joint angle at peak torque, i...
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an acute bout of static stretching does not affect maximal eccentric isokinetic peak torque the joint angle at peak torque mean power electromyography or mechanomyography
Journal of Orthopaedic & Sports Physical Therapy, 2007Co-Authors: Joel T Cramer, Terry J Housh, Travis W Beck, Joseph P. Weir, Glen O Johnson, Jared W CoburnAbstract:Study Design Repeated-measures experimental design. Objective To examine the acute effects of static stretching on peak torque, the joint angle at peak torque, mean power output, and electromyographic and mechanomyographic amplitudes and mean power frequency of the vastus lateralis and rectus femoris muscles during maximal eccentric isokinetic muscle actions. Background A bout of static stretching may impair muscle strength during isometric and concentric muscle actions, but it is unclear how static stretching may affect eccentric force production. Methods and Measures Fifteen men (mean ± SD age, 23.4 ± 2.4 years) performed maximal eccentric isokinetic muscle actions of the dominant and nondominant knee extensor muscles at 60°·s−1 and 180°·s−1 on an isokinetic dynamometer, while electromyographic and mechanomyographic amplitudes (root-mean-square) and mean power frequency were calculated for the vastus lateralis and rectus femoris muscles. Peak torque (Nm), the joint angle at peak torque (°), and mean pow...
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the acute effects of static stretching on peak torque mean power output electromyography and mechanomyography
European Journal of Applied Physiology, 2005Co-Authors: Joel T Cramer, Terry J Housh, Joseph P. Weir, Glen O Johnson, Jared W Coburn, Travis W BeckAbstract:The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240°·s-1 of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3) years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240°·s-1. Surface EMG (μVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P≤0.05) from pre- to post-stretching for the stretched limb at 60 and 240°·s-1 and for the unstretched limb at 60°·s-1. EMG amplitude of the VL and RF also decreased (P≤0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.
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mechanomyographic responses of the vastus medialis to isometric and eccentric muscle actions
Medicine and Science in Sports and Exercise, 2004Co-Authors: Jared W Coburn, Joel T Cramer, Terry J Housh, Travis W Beck, Joseph P. Weir, Moh H Malek, Glen O JohnsonAbstract:Purpose: The mechanomyographic (MMG) signal may he used to examine the motor control strategies used to modulate torque during various types of muscle actions. Therefore, the purpose of this study was to examine the MMG amplitude and mean power frequency (MPF) versus torque relationships during isometric and eccentric isokinetic muscle actions. Methods: Eleven adults (mean age ± SD = 20.8 ± 1.4 yr) volunteered to perform isometric and eccentric isokinetic leg extension muscle actions at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of peak torque on a Cyhex 6000 dynamometer. A piezoelectric crystal contact sensor was placed on the vastus medialis to detect the MMG signal. Results: Polynomial regression analyses indicated that for the isometric muscle actions the relationships for MMG amplitude (r 2 = 0.984) and MPF (r 2 = 0.989) versus torque were linear. For the eccentric isokinetic muscle actions, the relationships for MMG amplitude (r 2 = 0.580) and MPF (r 2 = 0.961) versus torque were also linear. Conclusion: The patterns for MMG amplitude and MPF may reflect the motor control strategies that modulate torque production for isometric and eccentric isokinetic muscle actions. Based on the results of this and previous studies, it appears that for the vastus medialis, torque is modulated in a similar manner for isometric, concentric, and eccentric isokinetic muscle actions. Specifically, these findings suggest that gradation of torque involves increases in recruitment and firing rate to 100% voluntary torque production.
