The Effects of Anchoring a Fatiguing Forearm Flexion Task to a High vs. Low Rating of Perceived Exertion on Torque and Neuromuscular Responses.

ABSTRACT: Ortega, DG, Housh, TJ, Smith, RW, Arnett, JE, Neltner, TJ, Schmidt, RJ, and Johnson, GO. The effects of anchoring a fatiguing forearm flexion task to a high versus low rating of perceived exertion on torque and neuromuscular responses. J Strength Cond Res 38(5): e219-e225, 2024-This study examined the torque and neuromuscular responses following sustained, isometric, forearm flexion tasks anchored to 2 ratings of perceived exertion (RPE). Nine men (mean ± SD: age = 21.0 ± 2.4 years; height = 179.5 ± 5.1 cm; body mass = 79.6 ± 11.4 kg) completed maximal voluntary isometric contractions (MVIC) before and after sustained, isometric, forearm flexion tasks to failure anchored to RPE = 2 and RPE = 8. The amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) signal were recorded from the biceps brachii. Normalized torque was divided by normalized EMG AMP to calculate neuromuscular efficiency (NME). A dependent t-test was used to assess the mean difference for time to task failure (TTF). Repeated-measures analysis of variances was used to compare mean differences for MVIC and normalized neuromuscular parameters. There was no significant difference in TTF between RPE = 2 and RPE = 8 (p = 0.713). The MVIC decreased from pretest to posttest at RPE = 2 (p = 0.009) and RPE = 8 (p = 0.003), and posttest MVIC at RPE = 8 was less than that at RPE = 2 (p < 0.001). In addition, NME decreased from pretest to posttest (p = 0.008). There was no change in normalized EMG AMP or EMG MPF (p > 0.05). The current findings indicated that torque responses were intensity specific, but TTF and neuromuscular responses were not. Furthermore, normalized EMG AMP and EMG MPF remained unchanged but NME decreased, likely due to peripheral fatigue and excitation-contraction coupling failure. Thus, this study provides information regarding the neuromuscular responses and mechanisms of fatigue associated with tasks anchored to RPE, which adds to the foundational understanding of the relationship between resistance exercise and the perception of fatigue.

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

BACKGROUND: Ratings of perceived exertion (RPE) can be used to regulate exercise intensity. This study examined the effect of anchor scheme on performance fatigability and neuromuscular responses following fatiguing forearm flexion tasks. METHODS: Twelve men (age 20.9±2.2 years; height 179.8±5.3 cm; body mass 80.2±9.9 kg) performed sustained, isometric forearm flexion tasks to failure anchored to RPE=6 (RPEFT) and the torque (TRQFT) that corresponded to RPE=6. Pre-test and post-test maximal voluntary isometric contractions (MVIC) were performed to quantify changes in the amplitude (AMP) and mean power frequency (MPF) of the electromyographic (EMG) and mechanomyographic (MMG) signals. Neuromuscular efficiency (NME) was calculated by dividing normalized torque by normalized EMG AMP. A dependent t-test was used to assess the mean difference for time to task failure (TTF). Repeated measures ANOVAs were used to compare mean differences for performance fatigability and normalized neuromuscular parameters. RESULTS: The RPEFT had a greater TTF than the TRQFT (P<0.001). MVIC and NME decreased from pre-test to post-test following the RPEFT and TRQFT (P<0.05) with no differences between anchor schemes. Following the TRQFT, normalized EMG MPF decreased from pre-test to post-test (P=0.004). Following the RPEFT, normalized MMG MPF increased from pre-test to post-test (P=0.021). There were no changes in normalized EMG AMP or MMG AMP (P>0.05). CONCLUSIONS: These findings indicated anchor scheme-specific neuromuscular responses and TTF, despite no difference in performance fatigability. Furthermore, performance fatigability was likely due to peripheral fatigue (based on normalized EMG MPF and NME) following the TRQFT, but peripheral and central fatigue (based on normalized MMG MPF and NME) following the RPEFT.

The effects of sustained, low- and high-intensity isometric tasks on performance fatigability and the perceived responses that contributed to task termination.

PURPOSE: The present study examined the effects of sustained, isometric low- versus high-intensity tasks on time to task failure (TTF), performance fatigability (PF), ratings of perceived exertion (RPE), and the perceived causes of task termination from a post-test questionnaire (PTQ). METHODS: Ten men (mean ± SD: age = 21.1 ± 2.3 years; height = 180.2 ± 5.7 cm; body mass = 79.5 ± 8.8 kg) performed maximal voluntary isometric contractions (MVICs) before and after fatiguing, isometric forearm flexion tasks anchored to the torque corresponding to RPE values of 2 (TRQ2FT = 23.8 ± 7.1 N·m) and 8 (TRQ8FT = 60.9 ± 11.4 N·m). In addition, the subjects completed a PTQ which surveyed whether the perceived sensations of fatigue or pain, and/or the psychological factors of loss of focus and motivation contributed to the decision to terminate the task. Repeated measures ANOVAs, Wilcoxon-Signed Rank tests, and Spearman's Rank-Order Correlations were used to analyze the data. RESULTS: Across the fatiguing tasks, there were similar decreases in MVIC torque (95.2 ± 20.3 vs. 68.9 ± 15.6 N·m; p < 0.001) and RPE values (p = 0.122) at task failure for TRQ2FT (7.4 ± 2.7) and TRQ8FT (8.9 ± 1.0), but a longer (p = 0.005) TTF for the TRQ2FT (245.0 ± 177.0 s) than TRQ8FT (36.8 ± 11.1 s). CONCLUSIONS: Despite reaching task failure, the subjects were able to perform MVICs that were 100-300% greater than the target torque values within seconds of terminating the tasks. Thus, we hypothesized that task failure was not caused by an inability to produce sufficient torque to sustain the tasks, but rather an unwillingness to continue the task.

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

ABSTRACT: 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.

Performance Fatigability and Neuromuscular Responses Are Not Joint Angle Specific Following a Sustained Isometric Forearm Flexion Task Anchored to a High Perceptual Intensity in Women.

OBJECTIVES: To examine the effects of joint angle (JA) on maximal voluntary isometric contractions (MVIC) and neuromuscular responses following a sustained, isometric forearm flexion task anchored to a rating of perceived exertion (RPE) of 8 (RPE=8). METHODS: Nine women (age: 20.7±2.9 yrs; height: 168.8±7.2 cm; body mass: 66.3±6.8 kg) performed 2,3s forearm flexion MVICs at JAs of 75°, 100°, and 125° prior to and following a sustained, isometric forearm flexion task anchored to RPE=8 to task failure (torque reduced to zero) at JA100. Electromyographic (EMG) and mechanomyographic (MMG) signals were recorded from the biceps brachii. RESULTS: The MVIC at JA100 (collapsed across Time) was significantly greater (p<0.05) than JA75 and JA125. The pre-test MVIC was significantly greater (p<0.001) than the post-test. For EMG amplitude (AMP) and EMG mean power frequency (MPF), pre-test values were significantly greater (p<0.05) than the post-test values, with no differences between JAs. For MMG AMP and MMG MPF, there were no significant (p>0.05) differences between Time or JAs. Pre-test neuromuscular efficiency (normalized MVIC/normalized EMG AMP) was significantly greater (p=0.005) than post-test. CONCLUSION: Following a sustained, isometric forearm flexion task anchored to RPE=8 at JA100, the fatigue-induced MVIC and neuromuscular responses were not affected by JA.

Fatiguing Joint Angle Does Not Influence Torque and Neuromuscular Responses Following Sustained, Isometric Forearm Flexion Tasks Anchored to Perceptual Intensity in Men.

This study examined the effects of joint angle (JA) on maximal voluntary isometric contraction (MVIC) and neuromuscular responses following fatiguing tasks anchored to RPE. Nine men (mean ± SD: age = 20.7 ± 1.2 yrs) performed forearm flexion MVICs at elbow JAs of 75° and 125° before and after sustained, isometric forearm flexion tasks to failure at fatiguing joint angles (FJA) of 75° and 125° anchored to RPE = 8. The amplitude and frequency of the electromyographic and mechanomyographic signals were recorded. Neuromuscular efficiency was calculated by dividing normalized torque by normalized electromyographic amplitude. A dependent t-test was used to assess the mean difference for time to task failure (TTF) between FJA. Repeated measure ANOVAs were used to assess mean differences for pre-test to post-test MVIC and neuromuscular responses. There was no significant difference between FJA for TTF (p = 0.223). The MVIC (collapsed across FJA and MVIC JA) decreased from pre-test to post-test (51.1 ± 5.0 vs. 45.3 ± 5.6 Nm, p < 0.001). Normalized neuromuscular parameters remained unchanged (p > 0.05). The FJA resulted in similar torque and neuromuscular responses, and the decreases in MVIC were not tracked by changes in the neuromuscular parameters. Thus, the neuromuscular parameters were not sensitive to fatigue, and pre-test to post-test measures may be compared between different FJA.

Effects of High-Intensity, Eccentric-Only Muscle Actions on Serum Biomarkers of Collagen Degradation and Synthesis.

ABSTRACT: Neltner, TJ, Sahoo, PK, Smith, RW, Anders, JPV, Arnett, JE, Ortega, DG, Schmidt, RJ, Johnson, GO, Natarajan, SK, and Housh, TJ. Effects of high-intensity, eccentric-only muscle actions on serum biomarkers of collagen degradation and synthesis. J Strength Cond Res 37(9): 1729-1737, 2023-The purpose of this study was to examine the effects of high-intensity, eccentric-only muscle actions of the leg extensors on (a) serum biomarkers of collagen degradation (hydroxyproline [HYP] and C-terminal telopeptide of type I collagen [C1M]) and synthesis (pro-c1α1) and (b) the time course of changes in maximal voluntary isometric contraction (MVIC) and ratings of muscle soreness after the eccentric-only exercise bout. Twenty-five recreationally active men (mean ± SD: age = 21.2 ± 2.0 years) completed 5 sets of 10 bilateral, eccentric-only dynamic constant external resistance muscle actions of the leg extensors at a load of 110% of their concentric leg extension 1 repetition maximum. Analysis of variances (p < 0.05) and a priori planned pairwise comparisons using Bonferroni corrected (p < 0.0167) paired t tests were used to examine mean changes in blood biomarkers from baseline to 48 hours postexercise as well as in MVIC and soreness ratings immediately, 24 hours, and 48 hours postexercise. There were increases in HYP (3.41 ± 2.37 to 12.37 ± 8.11 µg·ml-1; p < 0.001) and C1M (2.50 ± 1.05 to 5.64 ± 4.89 µg·L-1; p = 0.003) from preexercise to 48 hours postexercise, but no change in pro-c1α1. Maximal voluntary isometric contraction declined immediately after the exercise bout (450.44 ± 72.80 to 424.48 ± 66.67 N·m; p = 0.002) but recovered 24 hours later, whereas soreness was elevated immediately (6.56 ± 1.58; p < 0.001), 24 hours (3.52 ± 1.53; p < 0.001), and 48 hours (2.60 ± 1.32; p = 0.001) postexercise. The eccentric-only exercise bout induced increases in collagen degradation but had no effect on collagen synthesis. These findings provide information for clinicians to consider when prescribing exercise after an acute injury or surgery.

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

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.

Utilizing the RPE-Clamp model to examine interactions among factors associated with perceived fatigability and performance fatigability in women and men.

PURPOSE: The purpose of the present study was to examine the interactions between perceived fatigability and performance fatigability in women and men by utilizing the RPE-Clamp model to assess the fatigue-induced effects of a sustained, isometric forearm flexion task anchored to RPE = 8 on time to task failure (TTF), torque, and neuromuscular responses. METHODS: Twenty adults (10 men and 10 women) performed two, 3 s forearm flexion maximal voluntary isometric contractions (MVICs) followed by a sustained, isometric forearm flexion task anchored to RPE = 8 using the OMNI-RES (0-10) scale at an elbow joint angle of 100°. Electromyographic amplitude (EMG AMP) was recorded from the biceps brachii. Torque and EMG AMP values resulting from the sustained task were normalized to the pretest MVIC. Neuromuscular efficiency was defined as NME = normalized torque/normalized EMG AMP. Mixed factorial ANOVAs and Bonferroni corrected dependent t tests and independent t tests were used to examine differences across time and between sex for torque and neuromuscular parameters. RESULTS: There were no differences between the women and men for the fatigue-induced decreases in torque, EMG AMP, or NME, and the mean decreases (collapsed across sex) were 50.3 ± 8.6 to 2.8 ± 2.9% MVIC, 54.7 ± 12.0 to 19.6 ± 5.3% MVIC, and 0.94 ± 0.19 to 0.34 ± 0.16, respectively. Furthermore, there were no differences between the women and men for TTF (251.8 ± 74.1 vs. 258.7 ± 77.9 s). CONCLUSION: The results suggested that the voluntary reductions in torque to maintain RPE and the decreases in NME were likely due to group III/IV afferent feedback from peripheral fatigue that resulted in excitation-contraction coupling failure.

Changes in Neuromuscular Response Patterns After 4 Weeks of Leg Press Training During Isokinetic Leg Extensions.

ABSTRACT: Salmon, OF, Housh, TJ, Hill, EC, Keller, JL, Anders, JPV, Johnson, GO, Schmidt, RJ, and Smith, CM. Changes in neuromuscular response patterns after 4 weeks of leg press training during isokinetic leg extensions. J Strength Cond Res 37(7): e405-e412, 2023-The purpose of this study was to identify velocity-specific changes in electromyographic root mean square (EMG RMS), EMG frequency (EMG MPF), mechanomyographic RMS (MMG RMS), and MMG MPF during maximal unilateral isokinetic muscle actions performed at 60° and 240°·s -1 velocities within the right and left vastus lateralis (VL) after 4 weeks of dynamic constant external resistance (DCER) bilateral leg press training. Twelve resistance-trained men (age: mean ± SD = 21.4 ± 3.6 years) visited the laboratory 3d·wk -1 to perform resistance training consisting of 3 sets of 10 DCER leg presses. Four, three-way analysis of variance were performed to evaluate changes in neuromuscular responses (EMG RMS, EMG MPF, MMG RMS, and MMG MPF) from the right and left VL during 1 single-leg maximal isokinetic leg extension performed at 60° and 240°·s -1 before and after 4 weeks of DCER leg press training ( p < 0.05). The results indicated a 36% increase in EMG RMS for the right leg, as well as a 23% increase in MMG RMS and 10% decrease in MMG MPF after training, collapsed across velocity and leg. In addition, EMG RMS was 65% greater in the right leg than the left leg following training, whereas EMG MPF was 11% greater for the left leg than the right leg throughout training. Thus, 4 weeks of DCER leg press training provides sufficient stimuli to alter the neuromuscular activation process of the VL but not velocity-specific neuromuscular adaptations in trained males.

Time course of changes in torque and neuromuscular parameters during a sustained isometric forearm flexion task to fatigue anchored to a constant rating of perceived exertion.

OBJECTIVE: This study examined the time course of changes in torque and electromyographic (EMG) and mechanomyographic (MMG) responses during a sustained isometric task anchored to a constant perception of exertion (RPE). METHODS: Twelve college-aged men performed an isometric forearm flexion task to failure anchored to RPE=7 (OMNI-RES scale). The amplitude (AMP) and frequency (MPF) of the EMG and MMG signals from the biceps brachii were recorded. Repeated measures ANOVAs were used to examine differences for the normalized (%MVIC) torque and neuromuscular parameters. RESULTS: The time to task failure (TTF) was 678.0±468.1s. Torque decreased significantly (p<0.001, ηp2=0.774) across time and all subjects reduced torque to zero. Post-hoc comparisons indicated that the torque values from 20-100% TTF were less than the value at 10% TTF. There were no significant (p>0.05) changes from 10-100% TTF for the EMG and MMG parameters. CONCLUSION: We hypothesize that RPE was maintained by various mechanisms throughout the task: group III/IV afferent neurons, adequate blood flow, and a combination of reduced contractile efficiency, collective afferent feedback (group III/IV afferents) from muscles involved with forearm flexion, and motivation that resulted in an initial decrease, plateau, and final decline in torque to zero, respectively.

No effect of coactivation on fatigue-induced decreases in isokinetic and isometric torque in healthy young male adults.

BACKGROUND: Antagonist activation may contribute to fatigue-induced decreases in torque while assisting in the maintenance of joint stability. This study utilized a reciprocal, slow velocity (60°·s-1) forearm flexion and extension fatiguing task to examine the contributions of coactivation to torque production at slow and moderate (180°·s-1) velocities, as well as during a maximal voluntary isometric contraction (MVIC). METHODS: Twelve recreationally active men (mean ± SD: age = 21.7 ± 1.6 years; body mass = 83.5 ± 8.8 kg; height = 179.4 ± 5.2 cm) completed isokinetic (60 and 180°·s-1) and isometric pre-testing of forearm flexion and extension, followed by 50 maximal, reciprocal, isokinetic muscle actions at 60°·s-1, followed by post-testing. The amplitude (AMP) of the electromyographic (EMG) signals from the biceps and triceps brachii were simultaneously recorded. Torque and EMG AMP were normalized to the corresponding values from the pre-testing peak torque movements. Repeated measures ANOVAs and pairwise comparisons were used to identify mean changes in torque, EMG AMP, and coactivation ratios. RESULTS: The torque analyses indicated greater (p < 0.03) decreases for 180°·s-1 (24%) and MVIC (23%) than 60°·s-1 (14%) for forearm flexion. For forearm extension, there were no differences (p > 0.05) in fatigability between velocities. For EMG AMP there were no changes (p > 0.05) from pre- to post-testing for any velocity or movement. There were no changes (p > 0.05) in the coactivation ratio for forearm flexion, but significant increases (13.6 ± 6.6 to 16.9 ± 6.0; p = 0.003) for forearm extension, collapsed across Velocity. CONCLUSIONS: There was velocity- and movement-specific fatigability for forearm flexion and extension. The parallel, fatigue-induced EMG AMP responses indicated that coactivation did not contribute to the decreases in torque and would not affect elbow joint stability.

Are There Sex-Specific Neuromuscular or Force Responses to Fatiguing Isometric Muscle Actions Anchored to a High Perceptual Intensity?

ABSTRACT: Keller, JL, Housh, TJ, Hill, EC, Smith, CM, Schmidt, RJ, and Johnson, GO. Are there sex-specific neuromuscular or force responses to fatiguing isometric muscle actions anchored to a high perceptual intensity? J Strength Cond Res 36(1): 156-161, 2022-The purpose of this study was to use the ratings of perceived exertion (RPE) clamp model to examine sex-specific changes in neuromuscular responses and force after a sustained isometric leg extension muscle action anchored to RPE = 8. Twenty adults (10 men and 10 women) performed sustained, isometric leg extension muscle actions at RPE = 8. Electromyographic (EMG) and mechanomyographic signals were recorded from the dominant leg. Neuromuscular and force values resulting from the sustained muscle action were normalized to pretest maximal voluntary isometric contractions (MVICs). The level of significance set for the study was p ≤ 0.05. The pretest MVIC was significantly (p < 0.001) greater (averaged across sex) than posttest MVIC force (55.5 ± 10.0 vs. 47.6 ± 11.1 kg). There was a significant (p < 0.01) decrease from pretest (95.4 ± 7.7 Hz) to posttest (76.2 ± 5.9 Hz) in EMG mean power frequency (MPF) for the men. The normalized force (averaged across sex) decreased significantly (p < 0.001) from the initial timepoint (57.1 ± 16.4%) to the final timepoint (44.3 ± 15.7%) of the sustained muscle action. Normalized EMG MPF (averaged across sex) decreased significantly (p = 0.001) from the initial timepoint (96.4 ± 17.5%) to final timepoint (87.8 ± 18.1%). The men and women exhibited similar fatigue-induced changes in force and neuromuscular parameters; therefore, these findings did not indicate different sex-specific responses after the fatiguing task anchored to a high perception of exertion. The force corresponding to RPE = 8 did not match the anticipated value; so, RPE and percentages of MVIC cannot be used interchangeably, and sustained isometric muscle actions anchored to RPE may elicit unique neuromuscular adaptations.

Sex differences in muscle excitation and oxygenation, but not in force fluctuations or active hyperemia resulting from a fatiguing, bilateral isometric task.

It remains to be fully elucidated if there are sex-specific physiological adjustments within the human neuromuscular and vascular systems that contribute to symptoms of fatigue during a sustained bilateral task. This, in part, is likely due to various limitations in experimental design such as an inability to independently record force fluctuations from each limb.Objective. Therefore, the purpose of the current study was to examine the fatigue-induced changes in muscle excitation, force fluctuations, skeletal muscle tissue saturation (StO2), and muscle blood flow resulting from a sustained, bilateral task.Approach. Thirty healthy, college-aged adults (15 males, 15 females) performed a bilateral leg task at 25% of maximum voluntary isometric (MVIC). Before and after the task, MVICs were completed. Resting and post-task femoral artery blood flow (FABF) were determined. Muscle excitation was quantified as electromyographic amplitude (EMG AMP) from the right and left vastus lateralis. During the task, force fluctuations were determined independently from each leg. The StO2signal was collected with a near-infrared spectroscopy device attached to the right vastus lateralis. The rate of change in these variables was calculated via simple linear regression. The exercise-induced magnitude of change in MVIC (i.e. performance fatigability) and FABF (i.e. active hyperemia) was determined.Main Results. There was no sex difference in the percent decline in MVIC (20.5 ± 20.1% versus 16.4 ± 3.5%;p> 0.05). There were no inter-leg differences in EMG AMP or force fluctuations. The males exhibited a faster rate of increase in EMG AMP (b= 0.13 versusb= 0.08;p< 0.001), whereas the females exhibited a slower rate of decline in StO2(b= -0.049 versusb= -0.080). There was no sex difference in force fluctuations or change in FABF.Significance. Males and females likely have different neuromuscular strategies and muscle characteristics, but these did not elicit a sex difference in performance fatigability.

The effects of phosphocreatine disodium salts plus blueberry extract supplementation on muscular strength, power, and endurance.

BACKGROUND: Numerous studies have demonstrated the efficacy of creatine supplementation for improvements in exercise performance. Few studies, however, have examined the effects of phosphocreatine supplementation on exercise performance. Furthermore, while polyphenols have antioxidant and anti-inflammatory properties, little is known regarding the influence of polyphenol supplementation on muscular strength, power, and endurance. Thus, the purpose of the present study was to compare the effects of 28 days of supplementation with phosphocreatine disodium salts plus blueberry extract (PCDSB), creatine monohydrate (CM), and placebo on measures of muscular strength, power, and endurance. METHODS: Thirty-three men were randomly assigned to consume either PCDSB, CM, or placebo for 28 days. Peak torque (PT), average power (AP), and percent decline for peak torque (PT%) and average power (AP%) were assessed from a fatigue test consisting of 50 maximal, unilateral, isokinetic leg extensions at 180°·s- 1 before and after the 28 days of supplementation. Individual responses were assessed to examine the proportion of subjects that exceeded a minimal important difference (MID). RESULTS: The results demonstrated significant (p < 0.05) improvements in PT for the PCDSB and CM groups from pre- (99.90 ± 22.47 N·m and 99.95 ± 22.50 N·m, respectively) to post-supplementation (119.22 ± 29.87 N·m and 111.97 ± 24.50 N·m, respectively), but no significant (p = 0.112) change for the placebo group. The PCDSB and CM groups also exhibited significant improvements in AP from pre- (140.18 ± 32.08 W and 143.42 ± 33.84 W, respectively) to post-supplementation (170.12 ± 42.68 W and 159.78 ± 31.20 W, respectively), but no significant (p = 0.279) change for the placebo group. A significantly (p < 0.05) greater proportion of subjects in the PCDSB group exceeded the MID for PT compared to the placebo group, but there were no significant (p > 0.05) differences in the proportion of subjects exceeding the MID between the CM and placebo groups or between the CM and PCDSB groups. CONCLUSIONS: These findings indicated that for the group mean responses, 28 days of supplementation with both PCDSB and CM resulted in increases in PT and AP. The PCDSB, however, may have an advantage over CM when compared to the placebo group for the proportion of individuals that respond favorably to supplementation with meaningful increases in muscular strength.

Effects of 4-weeks of elastic variable resistance training on the electrochemical and mechanical components of voluntary electromechanical delay durations.

PURPOSE: Literature is conflicted on whether electromechanical delay durations decrease following resistance training programs. Therefore, the aim of this study is to examine the contributions and durations of the electrochemical (EMDE-M) and mechanical (EMDM-F) components to the overall electromechanical delay (EMDE-F) during step isometric muscle actions following 4-weeks of structured, multi-joint, lower-body variable resistance training (VRT) program. METHODS: Twelve men performed 4-weeks of VRT leg press training utilizing combination of steel plates (80% total load) and elastic bands (20% total load). Training consisted of 3 sets of 10 repetitions at a 10 repetition maximum load, 3 day week-1 for 4-weeks. EMDE-M, EMDM-F, and EMDE-F was measured at Baseline, Week-2, and Week-4 during voluntary step isometric muscle actions (20, 40, 60, 80, and 100% of maximal voluntary isometric contraction) from the vastus lateralis using electromyographic, mechanomyographic, and force signals. RESULTS: The EMDE-M, EMDM-F, and EMDE-F exhibited decreases in duration following 4-weeks of VRT. In addition, EMDE-M contributed significantly less (42-47%) than EMDM-F (53-58%) to the total duration of EMDE-F across the 4-weeks of VRT. CONCLUSIONS: These findings indicated that a structured, VRT program utilizing multi-joint exercise was sufficient to induce decreases in the electrochemical and mechanical processes associated with step isometric muscle contractions. In addition, the utilization of the electromyographic, mechanomyographic, and force signals were capable of quantifying electrochemical and mechanical component changes associated with voluntary muscle contraction. Thus, EMDE-M, EMDM-F, and EMDE-F can be useful in quantifying physiological changes in athletic, clinical, and applied research interventions.

Acute changes in muscle thickness, edema, and blood flow are not different between low-load blood flow restriction and non-blood flow restriction.

The purpose of the present study was to examine the acute changes in muscle swelling (as assessed by muscle thickness and echo intensity) and muscle blood flow associated with an acute bout of low-load blood flow restriction (LLBFR) and low-load non-blood flow restriction (LL) exercise. Twenty women (mean ± SD; 22 ± 2years) volunteered to perform an acute exercise bout that consisted of 75 (1 × 30, 3 × 15) isokinetic, reciprocal, concentric-only, submaximal (30% of peak torque), forearm flexion and extension muscle actions. Pretest, immediately after (posttest), and 5-min after (recovery) completing the 75 repetitions, muscle thickness and echo intensity were assessed from the biceps brachii and triceps brachii muscles and muscle blood flow was assessed from the brachial artery. There were no between group differences for any of the dependent variables, but there were significant simple and main effects for muscle and time. Biceps and triceps brachii muscle thickness increased from pretest (2.13 ± 0.39 cm and 1.88 ± 0.40 cm, respectively) to posttest (2.58 ± 0.49 cm and 2.17 ± 0.43 cm, respectively) for both muscles and remained elevated for the biceps brachii (2.53 ± 0.43 cm), but partially returned to pretest levels for the triceps brachii (2.06 ± 0.41 cm). Echo intensity and muscle blood flow increased from pretest (98.0 ± 13.6 Au and 94.5 ± 31.6 ml min-1 , respectively) to posttest (109.2 ± 16.9 Au and 312.2 ± 106.5 ml min-1 , respectively) and pretest to recovery (110.1 ± 18.3 Au and 206.7 ± 92.9 ml min-1 , respectively) and remained elevated for echo intensity, but partially returned to pretest levels for muscle blood flow. The findings of the present study indicated that LLBFR and LL elicited comparable acute responses as a result of reciprocal, concentric-only, forearm flexion and extension muscle actions.