Torque and Neuromuscular Responses are not Joint Angle Dependent During a Sustained, Isometric Task Anchored to a High Perceptual Intensity

Smith, R. Scott; Housh, Terry J.; Anders, John Paul V.; Neltner, Tyler J.; Arnett, Jocelyn E.; Ortega, Dolores G.; Schmidt, Richard J.; Johnson, Glen O.

doi:10.12691/ajssm-10-2-1

Cited by 4 publications

(16 citation statements)

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“…The amplitude of the EMG signal was used to estimate muscle activation (5) and is influenced by motor unit recruitment, firing rate, and synchronization (8). Furthermore, normalized EMG AMP has previously been used to calculate NME (normalized MVIC torque/normalized EMG AMP) (20,39), a parameter used to describe how a muscle responds to neural excitation (10). In this study, NME decreased at JA100 and JA125 but remained unchanged at JA75.…”

Section: Discussionmentioning

confidence: 99%

“…The amplitude (AMP) of the EMG signal reflects muscle activation (5) while the EMG MPF provides information about the motor unit action potential conduction velocity (MUAP CV) (2). Neuromuscular efficiency (NME) describes how a muscle responds to neural excitation (10) and is estimated by using the ratio of normalized MVIC torque to normalized EMG AMP (20,39). Although there are differences of opinion regarding the applicability of NME (13), decreases in NME have been associated with excitation-contraction coupling failure (10,31) due to peripheral fatigue (39).…”

Section: Introductionmentioning

confidence: 99%

“…Neuromuscular efficiency (NME) describes how a muscle responds to neural excitation (10) and is estimated by using the ratio of normalized MVIC torque to normalized EMG AMP (20,39). Although there are differences of opinion regarding the applicability of NME (13), decreases in NME have been associated with excitation-contraction coupling failure (10,31) due to peripheral fatigue (39). Furthermore, under some conditions, MMG AMP is related to motor unit recruitment, whereas MMG MPF qualitatively describes changes in the global firing rate of the activated, unfused motor units (6,33).…”

Section: Introductionmentioning

confidence: 99%

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Effects of a Sustained, Isometric Forearm Flexion Task to Failure on Torque and Neuromuscular Responses at 3 Elbow Joint Angles

Ortega,

Housh,

Smith

et al. 2024

Journal of Strength and Conditioning Research

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Ortega, DG, Housh, TJ, Smith, RW, Arnett, JE, Neltner, TJ, Anders, JPV, Schmidt, RJ, and Johnson, GO. The effects of a sustained, isometric forearm flexion task to failure on torque and neuromuscular responses at 3 elbow joint angles. J Strength Cond Res 38(1): e25–e33, 2024—This study examined the effects of a sustained, isometric forearm flexion task anchored to torque to task failure on maximal voluntary isometric contraction (MVIC) and neuromuscular responses at 3 elbow joint angles. Eleven women (mean ± SD: age = 20.8 ± 2.7 years, height = 169.3 ± 7.4 cm, body mass = 67.7 ± 6.9 kg) performed two 3s forearm flexion MVICs at elbow joint angles (JAs) of 75°, 100°, and 125° before and after a sustained, isometric forearm flexion task to failure at a fatiguing joint angle of 100° anchored to a torque value that corresponded to a rating of perceived exertion of 8 (RPE = 8). The amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii. Repeated-measures ANOVAs were used to compare mean differences for MVIC and neuromuscular parameters. Collapsed across JAs, MVIC (p < 0.001) and EMG MPF (p = 0.006) pretest values were greater than posttest values. Collapsed across time, EMG MPF at JA75 was greater than JA100 (p < 0.001) and JA125 (p < 0.001), and JA100 was greater (p = 0.007) than JA125. For EMG AMP, there was a fatigue-induced decrease at JA75 (p = 0.003). For neuromuscular efficiency (NME = normalized torque/normalized EMG AMP), there were decreases from pretest to posttest at JA100 (p = 0.002) and JA125 (p = 0.008). There were no significant interactions or main effects for MMG AMP and MMG MPF. From these findings, it was hypothesized that the decline in MVICs at JA75, JA100, and JA125 was due to fatigue-induced metabolic perturbations that resulted in JA-specific neuromuscular responses. Thus, neuromuscular parameters may provide insight into the JA-specific mechanisms of fatigue.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of a Sustained, Isometric Forearm Flexion Task to Failure on Torque and Neuromuscular Responses at 3 Elbow Joint Angles

Ortega,

Housh,

Smith

et al. 2024

Journal of Strength and Conditioning Research

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show abstract

“…It has been suggested [14,15] that EMG AMP represents muscle excitation attributed to motor unit recruitment, firing rate, and/or synchronization. For example, previous studies have utilized EMG AMP to make inferences regarding fatigue-induced adjustments in motor unit activation strategies during and after sustained, isometric forearm flexion [7][8][9][10] and leg extension [11,16,17] tasks, with torque or force anchored to a constant RPE using the OMNI-RES (0-10) scale [18][19][20]. In addition, previous studies [21][22][23] have examined the ratio between normalized torque (or force) and normalized EMG AMP to estimate neuromuscular efficiency (NME: a measure of the level of excitation required to generate a given amount of torque).…”

Section: Introductionmentioning

confidence: 99%

“…Given the unique nature of the RPE-Clamp model, recent studies have examined the interactions among factors associated with performance fatigability and perceived fatigability, during [ 7 , 8 , 9 ] and following [ 10 , 11 ] sustained, isometric tasks that are anchored to a high perceptual intensity. For example, Arnett et al [ 10 ] reported mean decreases in the torque and amplitude of the electromyographic signal (EMG AMP) following a sustained, isometric forearm flexion task anchored to RPE = 8.…”

Section: Introductionmentioning

confidence: 99%

The Effects of Anchor Schemes on Performance Fatigability, Neuromuscular Responses and the Perceived Sensations That Contributed to Task Termination

Smith

Housh

Arnett

et al. 2023

JFMK

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The present study examined the effect of anchor schemes on the time to task failure (TTF), performance fatigability, neuromuscular responses, and the perceived sensations that contributed to task termination following the sustained, isometric forearm flexion tasks. Eight women completed sustained, isometric forearm flexion tasks anchored to RPE = 8 (RPEFT) and the torque (TRQFT) that corresponded to RPE = 8. The subjects performed pre-test and post-test maximal isometric contractions to quantify performance fatigability and changes in electromyographic amplitude (EMG AMP) and neuromuscular efficiency (NME). In addition, the subjects completed a post-test questionnaire (PTQ) to quantify the contributions of perceived sensations to task termination. Repeated measure ANOVAs were used to assess the mean differences for TTF, performance fatigability, and neuromuscular responses. Wilcoxon Signed Rank Tests were used to assess the differences between anchor schemes for the average values from the PTQ item scores. For TTF, the RPEFT was longer than the TRQFT (174.9 ± 85.6 vs. 65.6 ± 68.0 s; p = 0.006). Collapsed across the anchor scheme, there were decreases in torque (23.7 ± 5.5 Nm vs. 19.6 ± 4.9 Nm; p < 0.001) and NME (1.00 ± 0.00 vs. 0.76 ± 0.15; p = 0.003). There were no significant (p > 0.577) changes for EMG AMP. For the PTQ, there were no differences (p > 0.05) between anchor schemes. There were, however, inter-individual differences in the response scores. The current findings indicated that performance fatigability was likely due to peripheral fatigue (based on NME), not central fatigue (based on EMG AMP). Furthermore, the use of a PTQ may serve as a simple tool to assess the contributions of perceived sensations to task termination.

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Are performance and perceived fatigability dependent on the anchor scheme of fatiguing isometric tasks in men?

ORTEGA,

SMITH,

ARNETT

et al. 2024

J Sports Med Phys Fitness

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Torque and Neuromuscular Responses are not Joint Angle Dependent During a Sustained, Isometric Task Anchored to a High Perceptual Intensity

Cited by 4 publications

References 0 publications

Effects of a Sustained, Isometric Forearm Flexion Task to Failure on Torque and Neuromuscular Responses at 3 Elbow Joint Angles

Effects of a Sustained, Isometric Forearm Flexion Task to Failure on Torque and Neuromuscular Responses at 3 Elbow Joint Angles

The Effects of Anchor Schemes on Performance Fatigability, Neuromuscular Responses and the Perceived Sensations That Contributed to Task Termination

Are performance and perceived fatigability dependent on the anchor scheme of fatiguing isometric tasks in men?

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