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13. Perceived Factors That Contributed to Task Termination during Fatiguing Tasks Anchored to Perceptual Intensities.

Author

Ortega, Dolores G., Smith, Robert W., Arnett, Jocelyn E., Neltner, Tyler J., Roberts, Trevor D., Schmidt, Richard J., and Housh, Terry J.

Subjects
REGRESSION analysis, RATE of perceived exertion, MUSCLE contraction, STIMULUS & response (Psychology), TORQUE
Abstract

This study examined the effects of sustained, isometric forearm flexion tasks anchored to ratings of perceived exertion of 2 (RPE2FT) and 8 (RPE8FT) on the patterns of fatigue-induced changes in torque and neuromuscular responses, time to task failure (TTF), performance fatigability (% decline in maximal voluntary isometric contraction [MVIC]), and perceived factors that contributed to task termination. Twelve men (mean ± SD: age = 20.9 ± 2.2 yrs) performed MVICs before and after the tasks and completed post-test questionnaires (PTQ). Data were analyzed using polynomial regression analyses, dependent t-tests, Spearman's rank order correlations, and Wilcoxon signed rank tests. The RPE8FT had greater (p < 0.001) performance fatigability than the RPE2FT, despite no difference (p > 0.05) in TTF. During both tasks, there were significant (p ≤ 0.05) composite linear decreases for torque, electromyographic amplitude, and neuromuscular efficiency, and substantial individual variability in the neuromuscular responses. There were no significant (p > 0.05) associations among the perceived factors and TTF or performance fatigability. Thus, there were RPE-specific differences in performance fatigability, but not TTF or the composite patterns of changes in torque and neuromuscular responses. In addition, in most cases, the individual neuromuscular, but not torque, patterns of responses were RPE-specific. Furthermore, the perceived factors assessed by the PTQ were not related to TTF or performance fatigability. [ABSTRACT FROM AUTHOR]

Published
2024
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26. The Effects of Anchoring a Fatiguing Forearm Flexion Task to a High vs. Low Rating of Perceived Exertion on Torque and Neuromuscular Responses.

Author

Ortega, Dolores G., Housh, Terry J., Smith, Robert W., Arnett, Jocelyn E., Neltner, Tyler J., Schmidt, Richard J., and Johnson, Glen O.

Subjects
MUSCLE fatigue, EXERCISE physiology, EXERCISE, TASK performance, T-test (Statistics), NEUROPHYSIOLOGY, TORQUE, NEUROMUSCULAR system, DESCRIPTIVE statistics, KINESIOLOGY, ELECTROMYOGRAPHY, PRE-tests & post-tests, ANALYSIS of variance, FOREARM, RANGE of motion of joints, MUSCLE contraction, BICEPS brachii
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2024
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44. Unilateral and Bilateral Isokinetic Leg Extensions Exhibit No Differences in Neuromuscular Excitation Under Maximal and Fatiguing Conditions

Author

Anders, John Paul V., Neltner, Tyler J., Smith, Robert W., Arnett, Jocelyn E., Housh, Terry J., Schmidt, Richard J., and Johnson, Glen O.

Abstract

Anders, JPV, Neltner, TJ, Smith, RW, Arnett, JE, Housh, TJ, Schmidt, RJ, and Johnson, GO. Unilateral and bilateral isokinetic leg extensions exhibit no differences in neuromuscular activation under maximal and fatiguing conditions. J Strength Cond Res38(3): 474–480, 2024—The bilateral deficit is a phenomenon where force production during a bilateral (BL) muscle action is less than the sum of force produced when the muscle action is performed unilaterally (UL) with both limbs. The purpose of this study was to compare peak force, electromyographic (EMG) amplitude (AMP), and mean power frequency (MPF) of the nondominant leg between UL and BL isokinetic leg extensions. Eleven recreationally trained men (mean ± SD; age = 20.8 ± 1.7 years; body mass = 84.0 ± 16.2 kg; height = 179.3 ± 7.2 cm) volunteered to participate in this study. The 2 test visits included UL and BL maximal isokinetic leg extensions at 180°·second−1followed by a fatiguing task of either 50 UL or 25 UL followed immediately by 25 BL (ULBL) maximal, isokinetic leg extensions at 180°·second−1, in random order on separate days. The results demonstrated a significant (p= 0.015, ηp2= 0.460) bilateral deficit in force (UL = 56.29 ± 11.20 kg; BL = 50.32 ± 7.35 kg; d= 0.63; 95% CI [1.42, 10.52]) but no significant bilateral deficit in EMG AMP (p= 0.892, ηp2= 0.002). The peak force during the fatiguing task demonstrated a significant main effect for repetition (p< 0.001, ηp2= 0.943) characterized by a reduced peak force from repetitions 20–50. Similarly, EMG MPF demonstrated a significant main effect for repetition (p< 0.001, ηp2= 0.702) characterized by a reduced EMG MPF from repetitions 35–50. There were no significant effects (p= 0.102–0.387, ηp2= 0.096–0.203) for EMG AMP. These findings suggested that the bilateral deficit was not associated with a neuromuscular deficit and UL muscle actions may be used to potentiate force production of subsequent BL muscle actions.

Published
2024
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49. Effects of 8 Weeks of Shilajit Supplementation on Serum Pro-c1α1, a Biomarker of Type 1 Collagen Synthesis: A Randomized Control Trial.

Author

Neltner, Tyler J., Sahoo, Prakash K., Smith, Robert W., Anders, John Paul V., Arnett, Jocelyn E., Schmidt, Richard J., Johnson, Glen O., Natarajan, Sathish Kumar, and Housh, Terry J.

Subjects
DRUG therapy for asthma, BIOMARKERS, COLLAGEN, COLLEGE students, HYPERTENSION, TENDON injuries, AYURVEDIC medicine, NEUROLOGICAL disorders, ONE-way analysis of variance, HEALTH outcome assessment, RECREATIONAL therapy, EXERCISE physiology, DIETARY supplements, RANDOMIZED controlled trials, GENE expression, T-test (Statistics), COMPARATIVE studies, BRONCHITIS, DOSE-effect relationship in pharmacology, FACTOR analysis, CHI-squared test, DESCRIPTIVE statistics, RESEARCH funding, MINERALS, STATISTICAL sampling, BODY mass index, METABOLISM
Abstract

Type 1 collagen is an abundant structural protein with importance to the skin, eyes, bones, ligaments, tendons, and muscles. Shilajit supplementation has been shown to increase gene expression of collagen synthesis, however, it is unclear if increased gene expression translates to increases in circulating levels. Therefore, the purpose of the present study was to examine the effects of 8 weeks of daily supplementation with 500 mg·d-1 and 1000 mg·d-1 of Shilajit versus placebo on serum pro-c1α1, a biomarker of type 1 collagen synthesis. Thirty-five recreationally trained men (mean ± S D: age = 21.1 ± 1.8 yrs; body mass = 80.7 ± 12.4 kg; height = 180.9 ± 6.7 cm) volunteered to participate in this study. Mixed factorial and one-way ANOVAs were used to analyze mean differences between groups, with follow-up t-tests when necessary. Individual subject responses were assessed using the minimal clinically important difference and Chi-squared tests. There were significant (Low dose: p = 0.008, d = 1.2; High dose: p = 0.007, d = 1.3) increases in serum pro-c1α1 from pre- (Low dose: 42.5 ± 12.4 ng·mL-1; High dose: 42.7 ± 12.7 ng·mL-1) to post-supplementation (Low dose: 82.3 ± 46.5 ng·mL-1; High dose: 113.1 ± 78.7 ng·mL-1) for the low and high dose groups, however, no change (p > 0.05) for the placebo group. A greater proportion (p = 0.03) of subjects exhibited increases in pro-c1α1 that exceeded the minimal clinically important difference in the high dose Shilajit group (75%) compared to the placebo group (30%), but no differences (p = 0.06) between the low dose Shilajit group (69%) and placebo. In conclusion, 8 weeks of Shilajit supplementation with 500 and 1000 mg·d-1 increased type 1 collagen synthesis as indicated by serum levels of pro-c1α1. [ABSTRACT FROM AUTHOR]

Published
2024
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