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Cochrane KC, Housh TJ, Jenkins NDM, Bergstrom HC, Smith CM, Hill EC, Johnson GO, Schmidt RJ, Cramer JT. Electromyographic, mechanomyographic, and metabolic responses during cycle ergometry at a constant rating of perceived exertion. Appl Physiol Nutr Metab 2015; 40:1178-85. [PMID: 26481288 DOI: 10.1139/apnm-2015-0144] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ten subjects performed four 8-min rides (65%-80% peak oxygen consumption) to determine the physical working capacity at the OMNI rating of perceived exertion (RPE) threshold (PWCOMNI). Polynomial regression analyses were used to examine the patterns of responses for surface electromyographic (EMG) amplitude (EMG AMP), EMG mean power frequency (EMG MPF), mechanomyographic (MMG) AMP, and MMG MPF of the vastus lateralis as well as oxygen consumption rate, respiratory exchange ratio (RER), and power output (PO) were examined during a 1-h ride on a cycle ergometer at a constant RPE that corresponded to the PWCOMNI. EMG AMP and MMG MPF tracked the decreases in oxygen consumption rate, RER, and PO, while EMG MPF and MMG AMP tracked RPE. The decreases in EMG AMP and MMG MPF were likely attributable to decreases in motor unit (MU) recruitment and firing rate, while the lack of change in MMG AMP may have resulted from a balance between MU de-recruitment as PO decreased, and an increase in the ability of activated fibers to oscillate. The current findings suggested that during submaximal cycle ergometry at a constant RPE, MU de-recruitment and mechanical changes within the muscle may influence the perception of effort via feedback from group III and IV afferents.
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Jenkins NDM, Housh TJ, Palmer TB, Cochrane KC, Bergstrom HC, Johnson GO, Schmidt RJ, Cramer JT. Relative differences in strength and power from slow to fast isokinetic velocities may reflect dynapenia. Muscle Nerve 2015; 52:120-30. [PMID: 25363299 DOI: 10.1002/mus.24505] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 10/27/2014] [Accepted: 10/29/2014] [Indexed: 12/25/2022]
Abstract
INTRODUCTION We compared absolute and normalized values for peak torque (PT), mean power (MP), rate of velocity development, and electromyography (EMG) amplitude during maximal isometric and concentric isokinetic leg extension muscle actions, as well as the %decrease in PT and %increase in MP from 1.05 to 3.14 rad·s(-1) in younger versus older men. METHODS Measurements were performed twice for reliability. Isokinetic measurements were normalized to the isometric muscle actions. RESULTS Absolute isometric PT, isokinetic PT and MP, and EMG amplitudes at 1.05 and 3.14 rad·s(-1) were greater in the younger men, although normalizing to isometric PT eliminated the age differences. The older men exhibited greater %decrease in PT (37.2% vs. 31.3%) and lower %increase in MP (87.6% vs. 126.4%) regardless of normalization. CONCLUSIONS Normalization eliminated absolute differences in isokinetic strength and power, but the relative differences from slow to fast velocities may reflect dynapenia characterized by age-related decreases in fast-twitch fiber function.
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Jenkins NDM, Housh TJ, Bergstrom HC, Cochrane KC, Hill EC, Smith CM, Johnson GO, Schmidt RJ, Cramer JT. Muscle activation during three sets to failure at 80 vs. 30% 1RM resistance exercise. Eur J Appl Physiol 2015; 115:2335-47. [PMID: 26159316 DOI: 10.1007/s00421-015-3214-9] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 06/28/2015] [Indexed: 10/23/2022]
Abstract
PURPOSE The purpose of this study was to investigate electromyographic amplitude (EMG AMP), EMG mean power frequency (MPF), exercise volume (VOL), total work and muscle activation (iEMG), and time under concentric load (TUCL) during, and muscle cross-sectional area (mCSA) before and after 3 sets to failure at 80 vs. 30 % 1RM resistance exercise. METHODS Nine men (mean ± SD, age 21.0 ± 2.4 years, resistance training week(-1) 6.0 ± 3.7 h) and 9 women (age 22.8 ± 3.8 years, resistance training week(-1) 3.4 ± 3.5 h) completed 1RM testing, followed by 2 experimental sessions during which they completed 3 sets to failure of leg extension exercise at 80 or 30 % 1RM. EMG signals were collected to quantify EMG AMP and MPF during the initial, middle, and last repetition of each set. Ultrasound was used to assess mCSA pre- and post-exercise, and VOL, total work, iEMG, and TUCL were calculated. RESULTS EMG AMP remained greater at 80 % than 30 % 1RM across all reps and sets, despite increasing 74 and 147 % across reps at 80 and 30 % 1RM, respectively. EMG MPF decreased across reps at 80 and 30 % 1RM, but decreased more and was lower for the last reps at 30 than 80 % 1RM (71.6 vs. 78.1 % MVIC). mCSA increased more from pre- to post-exercise for 30 % (20.2-24.1 cm(2)) than 80 % 1RM (20.3-22.8 cm(2)). VOL, total work, iEMG and TUCL were greater for 30 % than 80 % 1RM. CONCLUSION Muscle activation was greater at 80 % 1RM. However, differences in volume, metabolic byproduct accumulation, and muscle swelling may help explain the unexpected adaptations in hypertrophy vs. strength observed in previous studies.
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Bergstrom HC, Housh TJ, Cochrane KC, Jenkins NDM, Zuniga JM, Buckner SL, Goldsmith JA, Schmidt RJ, Johnson GO, Cramer JT. Factors underlying the perception of effort during constant heart rate running above and below the critical heart rate. Eur J Appl Physiol 2015; 115:2231-41. [DOI: 10.1007/s00421-015-3204-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2015] [Accepted: 06/15/2015] [Indexed: 10/23/2022]
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Jenkins NDM, Miller JM, Buckner SL, Cochrane KC, Bergstrom HC, Hill EC, Smith CM, Housh TJ, Cramer JT. Test-Retest Reliability of Single Transverse versus Panoramic Ultrasound Imaging for Muscle Size and Echo Intensity of the Biceps Brachii. ULTRASOUND IN MEDICINE & BIOLOGY 2015; 41:1584-1591. [PMID: 25746907 DOI: 10.1016/j.ultrasmedbio.2015.01.017] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Revised: 01/12/2015] [Accepted: 01/21/2015] [Indexed: 06/04/2023]
Abstract
This study compared test-retest reliability and sensitivity to change for muscle size and echo intensity (EI) measurements from single transverse (EIST) versus panoramic (EIP) ultrasound (US) images of the biceps brachii. Forearm flexor muscle thickness and EIST and biceps brachii muscle cross-sectional area and EIP were quantified from single transverse and panoramic US images in 14 men (age = 21.8 ± 2.5 y [mean ± standard deviation]) on two separate days. The intra-class correlation coefficients, coefficients of variation, and minimum differences for muscle thickness, EIST, muscle cross-sectional area and EIP ranged from 0.78 to 0.99, from 2.26% to 3.29%, and from 6.26% to 9.12%, respectively. These findings suggested that single transverse imaging and panoramic US imaging are comparable, reliable techniques for quantifying muscle size and EI of the biceps brachii. Single transverse images may be simpler to obtain; thus, future studies may choose to quantify muscle size and EI from a single transverse US image in the biceps brachii.
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Cochrane KC, Housh TJ, Smith CM, Hill EC, Jenkins ND, Johnson GO, Housh DJ, Schmidt RJ, Cramer JT. Relative Contributions of Strength, Anthropometric, and Body Composition Characteristics to Estimated Propulsive Force in Young Male Swimmers. J Strength Cond Res 2015; 29:1473-9. [DOI: 10.1519/jsc.0000000000000942] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Smith CM, Housh TJ, Herda TJ, Zuniga JM, Ryan ED, Camic CL, Bergstrom HC, Smith DB, Weir JP, Cramer JT, Hill EC, Cochrane KC, Jenkins NDM, Schmidt RJ, Johnson GO. Effects of the innervation zone on the time and frequency domain parameters of the surface electromyographic signal. J Electromyogr Kinesiol 2015; 25:565-70. [PMID: 26014918 DOI: 10.1016/j.jelekin.2015.04.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Revised: 03/26/2015] [Accepted: 04/27/2015] [Indexed: 11/17/2022] Open
Abstract
The purposes of the present study were to examine the effects of electrode placements over, proximal, and distal to the innervation zone (IZ) on electromyographic (EMG) amplitude (RMS) and frequency (MPF) responses during: (1) a maximal voluntary isometric contraction (MVIC), and; (2) a sustained, submaximal isometric muscle action. A linear array was used to record EMG signals from the vastus lateralis over the IZ, 30mm proximal, and 30mm distal to the IZ during an MVIC and a sustained isometric muscle action of the leg extensors at 50% MVIC. During the MVIC, lower EMG RMS (p>0.05) and greater EMG MPF (p<0.05) values were recorded over the IZ compared to away from the IZ, however, no differences in slope coefficients for the EMG RMS and MPF versus time relationships over, proximal, and distal to the IZ occurred. Thus, the results of the present study indicated that during an MVIC, EMG RMS and MPF values recorded over the IZ are not comparable to those away from the IZ. However, the rates of fatigue-induced changes in EMG RMS and MPF during sustained, submaximal isometric muscle actions of the leg extensors were the same regardless of the electrode placement locations relative to the IZ.
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Cramer JT, Jenkins NDM, Mustad VA, Weir JP. Isokinetic Dynamometry in Healthy Versus Sarcopenic and Malnourished Elderly: Beyond Simple Measurements of Muscle Strength. J Appl Gerontol 2015; 36:709-732. [DOI: 10.1177/0733464815584669] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
This study quantified systematic and intraindividual variability among three repetitions of concentric isokinetic knee extension and flexion tests to determine velocity-related differences in peak torque (PT) and mean power (MP) in healthy elderly (HE) versus sarcopenic and malnourished elderly (SME). In total, 107 HE ( n = 54 men, n = 53 women) and 261 SME ( n = 101 men, n = 160 women) performed three maximal concentric isokinetic knee extension and flexion repetitions at 60°·s−1 and 180°·s−1. PT for Repetition 3 was lower than Repetitions 1 and 2, while MP for Repetition 1 was lower than Repetitions 2 and 3 in SME. Intraindividual variability among repetitions was correlated with strength, but not age, and was greater in SME, during knee flexion, and at 180°·s−1. Velocity-related decreases in PT from 60°·s−1 to 180°·s−1 were more pronounced in SME. In summary, (a) the repetition with the highest PT value may be the best indicator of maximal strength, while the average may indicate strength maintenance in SME; (b) intraindividual variability among repetitions reflects functional decrements from HE to SME; and (c) decreases in PT from 60°·s−1 to 180°·s−1 may reflect greater losses of fast-twitch (type II) fiber function.
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Bergstrom HC, Housh TJ, Cochrane KC, Jenkins ND, Buckner SL, Goldsmith JA, Schmidt RJ, Johnson GO, Cramer JT. Factors Underlying the Perception of Effort during Constant Heart Rate Running. Med Sci Sports Exerc 2015. [DOI: 10.1249/01.mss.0000478891.45051.d6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Smith CM, Herda TJ, Zuniga JM, Ryan ED, Camic CL, Bergstrom HC, Smith DB, Weir JP, Cramer JT, Cochrane KC, Hill EC, Jenkins ND, Housh TJ, Schmidt RJ, Johnson GO. Effects of the Innervation Zone on Electromyographic Responses during Fatiguing Isometric Muscle Actions. Med Sci Sports Exerc 2015. [DOI: 10.1249/01.mss.0000477296.51731.b6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Costa PB, Herda TJ, Herda AA, Cramer JT. Effects Of Resistance Exercise Mode On Rating Of Perceived Exertion During Short-term Training. Med Sci Sports Exerc 2015. [DOI: 10.1249/01.mss.0000479257.36806.f7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Hill EC, Camic CL, Housh TJ, Monaghan MM, Jenkins ND, Cochrane KC, Smith CM, Cramer JT, Schmidt RJ, Johnson GO. Effects of Velocity on Peak Torque and Neuromuscular Responses during Repeated, Maximal, Eccentric Muscle Actions. Med Sci Sports Exerc 2015. [DOI: 10.1249/01.mss.0000477298.36484.f0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Jenkins ND, Miller JM, Yeo N, Smith CM, Hill EC, Cochrane KC, Bergstrom HC, Housh TJ, Cramer JT. Electromyographic And Mechanomyographic Responses During Three Sets To Failure Of Low- Versus High-load Resistance Training. Med Sci Sports Exerc 2015. [DOI: 10.1249/01.mss.0000479271.43536.30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Cochrane K, Housh T, Jenkins ND, Bergstrom HC, Smith CM, Hill EC, Johnson GO, Schmidt RJ, Cramer JT. Electromyographic, Mechanomyographic, And Metabolic Responses During Cycle Ergometry At A Constant Rating Of Perceived Exertion. Med Sci Sports Exerc 2015. [DOI: 10.1249/01.mss.0000478888.71072.47] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Jenkins NDM, Buckner SL, Baker RB, Bergstrom HC, Cochrane KC, Weir JP, Housh TJ, Cramer JT. Effects of 6 weeks of aerobic exercise combined with conjugated linoleic acid on the physical working capacity at fatigue threshold. J Strength Cond Res 2015; 28:2127-35. [PMID: 24796987 DOI: 10.1519/jsc.0000000000000513] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The purpose of this study was to examine the effects of conjugated linoleic acid (CLA) supplementation in conjunction with 6 weeks of aerobic exercise training on the physical working capacity at the fatigue threshold (PWCFT), timed sit-ups, and the standing long jump. Thirty-three untrained to moderately trained men (mean ± SD; age = 21.6 ± 2.8 years) participated in this double-blind, placebo-controlled study and were randomly assigned to either a CLA (Clarinol A-80; n = 17) or placebo (PLA; sunflower oil; n = 16) group. Before and after 6 weeks of aerobic training (50% VO2peak for 30 minutes, twice per week) and supplementation (8 ml CLA or PLA per day), each subject completed an incremental cycle ergometer test to exhaustion to determine the PWCFT, maximal number of sit-ups in 1 minute, and the standing long jump. There were no differences (all p ≥ 0.23) between the CLA and PLA groups for the analysis of covariance-adjusted posttest mean values for PWCFT, sit-ups, or standing long jump. The PWCFT increased from pre- to posttraining in the CLA (p = 0.003) and PLA (p = 0.003) groups. There were no differences (p > 0.05) from pre- to posttraining for sit-ups and standing long jump in either the CLA or PLA groups. There was no effect of CLA on the training-induced increases in PWCFT, nor were there any effects of CLA or aerobic training on the maximum number of sit-ups or standing long jump. Thus, CLA had no ergogenic benefits on this model of aerobic training-induced improvements in neuromuscular fatigue, or on field tests of muscle endurance and power.
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Herda TJ, Zuniga JM, Ryan ED, Camic CL, Bergstrom HC, Smith DB, Weir JP, Cramer JT, Housh TJ. The influence of electromyographic recording methods and the innervation zone on the mean power frequency-torque relationships. J Electromyogr Kinesiol 2015; 25:423-30. [PMID: 25851079 DOI: 10.1016/j.jelekin.2015.02.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 01/30/2015] [Accepted: 02/27/2015] [Indexed: 10/23/2022] Open
Abstract
This study examined the effects of electromyographic (EMG) recording methods and innervation zone (IZ) on the mean power frequency (MPF)-torque relationships. Nine subjects performed isometric ramp muscle actions of the leg extensors from 5% to 100% of maximal voluntary contraction with an eight channel linear electrode array over the IZ of the vastus lateralis. The slopes were calculated from the log-transformed monopolar and bipolar EMG MPF-torque relationships for each channel and subject and 95% confidence intervals (CI) were constructed around the slopes for each relationship and the composite of the slopes. Twenty-two to 55% of the subjects exhibited 95% CIs that did not include a slope of zero for the monopolar EMG MPF-torque relationships while 25-75% of the subjects exhibited 95% CIs that did not include a slope of zero for the bipolar EMG MPF-torque relationships. The composite of the slopes from the EMG MPF-torque relationships were not significantly different from zero for any method or channel, however, the method and IZ location slightly influenced the number of significant slopes on a subject-by-subject basis. The log-transform model indicated that EMG MPF-torque patterns were nonlinear regardless of recording method or distance from the IZ.
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Buckner SL, Jenkins NDM, Costa PB, Ryan ED, Herda TJ, Cramer JT. Comparing passive angle-torque curves recorded simultaneously with a load cell versus an isokinetic dynamometer during dorsiflexion stretch tolerance assessments. Med Eng Phys 2015; 37:494-8. [PMID: 25782330 DOI: 10.1016/j.medengphy.2015.02.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 10/28/2014] [Accepted: 02/16/2015] [Indexed: 11/19/2022]
Abstract
The purpose of the present study was to compare the passive angle-torque curves and the passive stiffness (PS, N m °(-)(1)) values recorded simultaneously from a load cell versus an isokinetic dynamometer during dorsiflexion stretch tolerance assessments in vivo. Nine healthy men (mean ± SD age = 21.4 ± 1.6 years) completed stretch tolerance assessments on a custom-built apparatus where passive torque was measured simultaneously from an isokinetic dynamometer and a load cell. Passive torque values that corresponded with the last 10° of dorsiflexion, verified by surface electromyographic amplitude, were analyzed for each device (θ1, θ2, θ3, …, θ10). Passive torque values measured with the load cell were greater (p ≤ 0.05) than the dynamometer torque values for θ4 through θ10. There were more statistical differentiations among joint angles for passive torque measured by the load cell, and the load cell measured a greater (p ≤ 0.01) increase in passive torque and PS than the isokinetic dynamometer. These findings suggested that when examining the angle-torque curves from passive dorsiflexion stretch tolerance tests, a load cell placed under the distal end of the foot may be more sensitive than the torque recorded from an isokinetic dynamometer.
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Cochrane KC, Housh TJ, Bergstrom HC, Jenkins NDM, Johnson G, Schmidt RJ, Cramer JT. Physiological Responses during Cycle Ergometry at a Constant Perception of Effort. Int J Sports Med 2015; 36:466-73. [PMID: 25700102 DOI: 10.1055/s-0034-1396826] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
13 subjects performed an incremental test to exhaustion, 4, 8-min submaximal rides, and a 1-h ride at the rating of perceived exertion (RPE) that corresponded to the physical working capacity at the OMNI threshold (PWC(OMNI)) to examine: 1) the oxygen consumption (V̇O2), heart rate (HR), minute ventilation (+V̇(E)), respiratory frequency (FR), and power output responses during 1-h work bouts at a constant RPE that corresponded to the PWC(OMNI); and 2) the ability of current models to explain the responses for physiological and perceptual parameters during the 1-h work bouts. The RPE that corresponded to the PWC(OMNI) represented a sustainable exercise intensity (56±5% (V̇O(2Peak)) within the moderate-intensity domain. The mean, normalized slope coefficients for the V̇O2, +V̇(E), and power output vs. time relationships during the 1-h rides were significantly less than zero. The mean, normalized slope coefficient for the FR vs. time relationship during the 1-h rides, however, was not significantly different from zero. Thus, RPE most clearly tracked FR responses during the 1-h rides. It was hypothesized that afferent feedback from respiratory muscles may have mediated the perception of effort during cycle ergometry at a constant RPE in the moderate-intensity domain.
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Bergstrom HC, Housh TJ, Cochrane KC, Jenkins NDM, Buckner SL, Goldsmith JA, Zuniga JM, Schmidt RJ, Johnson GO, Cramer JT. Application of the Critical Heart Model to Treadmill Running. J Strength Cond Res 2015; 29:2237-48. [PMID: 25647653 DOI: 10.1519/jsc.0000000000000869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The mathematical model used to estimate critical power has been applied to heart rate (HR) measurements during cycle ergometry to derive a fatigue threshold called the critical heart rate (CHR). This study had 2 purposes: (a) determine if the CHR model for cycle ergometry could be applied to treadmill running and (b) examine the times to exhaustion (Tlim) and the VO2 responses during constant HR runs at the CHR. Thirteen runners (mean ± SD; age = 23 ± 3 years) performed an incremental treadmill test to exhaustion. On separate days, 4 constant velocity runs to exhaustion were performed. The total number of heart beats (HBlim) for each velocity was calculated as the product of the average 5-second HR and Tlim. The CHR was the slope coefficient of the HBlim vs. Tlim relationship. The Tlim and VO2 responses were recorded during a constant HR run at the CHR. Polynomial regression analyses were used to examine the patterns of responses for VO2 and velocity. The HBlim vs. Tlim relationship (r = 0.995-1.000) was described by the linear equation: HBlim = a + CHR (Tlim). The CHR (176 ± 7 b·min, 91 ± 3% HRpeak) was maintained for 47.84 ± 11.04 minutes. There was no change in HR but quadratic decreases in velocity and VO2. These findings indicated that the CHR model for cycle ergometry was applicable to treadmill running and represented a sustainable (30-60 minutes) intensity but cannot be used to demarcate exercise intensity domains.
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Smith-Ryan AE, Ryan ED, Fukuda DH, Costa PB, Cramer JT, Stout JR. The effect of creatine loading on neuromuscular fatigue in women. Med Sci Sports Exerc 2014; 46:990-7. [PMID: 24152706 DOI: 10.1249/mss.0000000000000194] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PURPOSE This study aimed to examine the effects of intermittent isometric fatigue on maximal voluntary contraction (MVC) strength, percent voluntary activation (%VA), peak twitch force (PTF), peak rate of force development (PRFD), half relaxation time (HRT), and maximal compound action potential (M-wave) amplitude of the soleus and medial gastrocnemius muscles before and after creatine (Cr) loading. METHODS Using a double-blinded, placebo-controlled, randomized design, 12 women were assigned to a Cr (n = 6; mean age ± SD = 23.3 ± 3.0 yr) or placebo (PL; n = 6; mean age ± SD = 21.3 ± 1.6 yr) group. Participants supplemented four times daily for 5 d with 5 g of Cr + 10 g of fructose or 10 g of fructose. At baseline and after testing, an isometric MVC and the twitch interpolation procedure were used before and after a 4-min isometric fatigue protocol of the plantarflexor muscles, which consisted of six intermittent duty cycles per minute (7-s contraction, 3-s relaxation) at 70% MVC. RESULTS There were no interactions between the Cr and PL groups (P > 0.05) for any dependent variable. The fatigue protocol reduced voluntary strength (-17.8%, P < 0.001) and %VA (-3.7%, P = 0.005). Baseline PTF (P < 0.005) and PRFD (P < 0.001) values were less than those of all respective time points, but PTF value decreased from 3 min to 4 min and after testing (P < 0.005). HRT increased from baseline to minutes 1 and 2 and then returned to baseline at minutes 3 and 4 and after testing. The M-wave did not change (P > 0.05). CONCLUSIONS Five days of Cr loading did not influence isometric force, %VA, evoked twitch properties, or the central and peripheral aspects of fatigue measured in this study.
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Herda AA, Herda TJ, Costa PB, Ryan ED, Stout JR, Cramer JT. Muscle performance, size, and safety responses after eight weeks of resistance training and protein supplementation: a randomized, double-blinded, placebo-controlled clinical trial. J Strength Cond Res 2014; 27:3091-100. [PMID: 23442287 DOI: 10.1519/jsc.0b013e31828c289f] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The purpose of this study was to examine the effects of 2 different types of protein supplementation on thigh muscle cross-sectional area (CSA), blood markers, muscular strength, endurance, and body composition after 8 weeks of low- or moderate-volume resistance training in healthy, recreationally trained, college-aged men. One hundred and six men were randomized into 5 groups: low-volume resistance training with bioenhanced whey protein (BWPLV; n = 22), moderate-volume resistance training with BWP (BWPMV; n = 20), moderate-volume resistance training with standard whey protein (SWPMV; n = 22), moderate-volume resistance training with a placebo (PLA; n = 21), or moderate-volume resistance training with no supplementation (CON; n = 21). Except for CON, all groups consumed 1 shake before and after each exercise session and one each on the nontraining day. The BWPLV, BWPMV, and SWPMV groups received approximately 20 g of whey protein per shake, whereas the BWP groups received 5 g of additional polyethylene glycosylated (PEG) leucine. Resistance training sessions were performed 3 times per week for 8 weeks. There were no interactions (p > 0.05) for muscle strength and endurance variables, body composition, muscle CSA, and safety blood markers, but the main effects for training were observed (p ≤ 0.05). However, the Albumin:Globulin ratio for SWPMV was lower (p = 0.037) than BWPLV and BWPMV. Relative protein intake (PROREL) indicated a significant interaction (p < 0.001) with no differences across groups at pre; however, BWPLV, BWPMV, and SWPMV had a greater intake than did PLA or CON at post (p < 0.001). This study indicated that 8 weeks of resistance training improved muscle performance and size similarly among groups regardless of supplementation.
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Costa PB, Herda TJ, Herda AA, Cramer JT. Effects of dynamic stretching on strength, muscle imbalance, and muscle activation. Med Sci Sports Exerc 2014; 46:586-93. [PMID: 24042312 DOI: 10.1249/mss.0000000000000138] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
PURPOSE This study aimed to examine the acute effects of dynamic stretching on concentric leg extensor and flexor peak torque, eccentric leg flexor peak torque, and the conventional and functional hamstring-quadriceps (H:Q) ratios. METHODS Twenty-one women (mean ± SD age = 20.6 ± 2.0 yr, body mass = 64.5 ± 9.3 kg, height = 164.7 ± 6.5 cm) performed maximal voluntary isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60°·s and 180°·s before and after a bout of dynamic hamstring and quadriceps stretching as well as a control condition. RESULTS Leg flexion peak torque decreased under both control (mean ± SE for 60°s = 75.8 ± 4.0 to 72.4 ± 3.7 N·m, 180°·s = 62.1 ± 3.2 to 59.1 ± 3.1 N·m) and stretching (60°·s = 73.1 ± 3.9 to 65.8 ± 3.3 N·m, 180°·s = 61.2 ± 3.3 to 54.7 ± 2.6 N·m) conditions, whereas eccentric hamstring peak torque decreased only after the stretching (60°·s = 87.3 ± 5.1 to 73.3 ± 3.6 N·m, 180°·s = 89.2 ± 4.4 to 77.0 ± 3.4 N·m) intervention (P ≤ 0.05). Stretching also caused a decrease in conventional H:Q (60°·s = 0.58 ± 0.02 to 0.54 ± 0.02, 180°·s = 0.67 ± 0.02 to 0.61 ± 0.03) and functional H:Q ratios (60°·s = 0.69 ± 0.03 to 0.60 ± 0.03, 180°·s = 1.00 ± 0.06 to 0.60 ± 0.03) (P ≤ 0.05). CONCLUSIONS Because dynamic stretching reduced concentric and eccentric hamstring strength as well as the conventional and functional H:Q ratios, fitness and allied-health professionals may need to be cautious when recommending dynamic rather than static stretching to maintain muscle force.
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Jenkins ND, Buckner SL, Bergstrom HC, Cochrane KC, Goldsmith JA, Housh TJ, Johnson GO, Schmidt RJ, Cramer JT. Reliability and relationships among handgrip strength, leg extensor strength and power, and balance in older men. Exp Gerontol 2014; 58:47-50. [DOI: 10.1016/j.exger.2014.07.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 07/03/2014] [Accepted: 07/11/2014] [Indexed: 11/17/2022]
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Jenkins NDM, Housh TJ, Traylor DA, Cochrane KC, Bergstrom HC, Lewis RW, Schmidt RJ, Johnson GO, Cramer JT. The rate of torque development: a unique, non-invasive indicator of eccentric-induced muscle damage? Int J Sports Med 2014; 35:1190-5. [PMID: 25259592 DOI: 10.1055/s-0034-1375696] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
This study examined the time courses of recovery for isometric peak torque and rate of torque development (RTD) after eccentric-induced muscle damage. 18 men completed 6 sets of 10 maximal eccentric isokinetic muscle actions at 30° · s(-1). Peak torque, peak RTD and RTD at 10 (RTD10), 50 (RTD50), 100 (RTD100) and 200 ms (RTD200), serum creatine kinase and lactate dehydrogenase were measured before (PRE), immediately after (POST), 24, 48 and 72 h after eccentric exercise. Creatine kinase and lactate dehydrogenase increased from 139 to 6 457 and from 116 to 199 IU · L(-1) from PRE to 72 h, respectively. Peak torque and all RTDs decreased at POST. Peak torque and RTD200 remained lower than PRE through 72 h. Peak RTD remained lower than PRE through 48 h, but was not different from PRE at 72 h. RTD10 and RTD100 were lower than PRE through 24 h, but were not different from PRE at 48 and 72 h. RTD50 decreased at POST, but was not different from PRE at 24 h. Early phase RTDs recovered more quickly than PT and RTD200. Early phase RTDs may reflect neural mechanisms underlying eccentric-induced force decrements, while late RTDs may describe the same physiological mechanisms as PT.
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Jenkins ND, Buckner SL, Cochrane KC, Bergstrom HC, Palmer TB, Johnson GO, Schmidt RJ, Housh TJ, Cramer JT. Age-related differences in rates of torque development and rise in EMG are eliminated by normalization. Exp Gerontol 2014; 57:18-28. [DOI: 10.1016/j.exger.2014.04.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 04/22/2014] [Accepted: 04/28/2014] [Indexed: 11/24/2022]
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