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  • Author: Haley C. Bergstrom x
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Taylor K. Dinyer, M. Travis Byrd, Ashley N. Vesotsky, Pasquale J. Succi and Haley C. Bergstrom

Purpose: To determine if the mathematical model used to derive critical power could be used to identify the critical resistance (CR) for the deadlift; compare predicted and actual repetitions to failure at 50%, 60%, 70%, and 80% 1-repetition maximum (1RM); and compare the CR with the estimated sustainable resistance for 30 repetitions (ESR30). Methods: Twelve subjects completed 1RM testing for the deadlift followed by 4 visits to determine the number of repetitions to failure at 50%, 60%, 70%, and 80% 1RM. The CR was calculated as the slope of the line of the total work completed (repetitions × weight [in kilograms] × distance [in meters]) vs the total distance (in meters) the barbell traveled. The actual and predicted repetitions to failure were determined from the CR model and compared using paired-samples t tests and simple linear regression. The ESR30 was determined from the power-curve analysis and compared with the CR using paired-samples t tests and simple linear regression. Results: The weight and repetitions completed at CR were 56 (11) kg and 49 (14) repetitions. The actual repetitions to failure were less than predicted at 50% 1RM (P < .001) and 80% 1RM (P < .001) and greater at 60% 1RM (P = .004), but there was no difference at 70% 1RM (P = .084). The ESR30 (75 [14] kg) was greater (P < .001) than the CR. Conclusions: The total work-vs-distance relationship can be used to identify the CR for the deadlift, which reflected a sustainable resistance that may be useful in the design of resistance-based exercise programs.

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Taylor K. Dinyer, Pasquale J. Succi, M. Travis Byrd, Caleb C. Voskuil, Evangeline P. Soucie and Haley C. Bergstrom

This study determined the load- and limb-dependent neuromuscular responses to fatiguing, bilateral, leg extension exercise performed at a moderate (50% one-repetition maximum [1RM]) and high load (80% 1RM). Twelve subjects completed 1RM testing for the bilateral leg extension, followed by repetitions to failure at 50% and 80% 1RM, on separate days. During all visits, the electromyographic (EMG) and mechanomyographic (MMG), amplitude (AMP) and mean power frequency (MPF) signals were recorded from the vastus lateralis of both limbs. There were no limb-dependent responses for any of the neuromuscular signals and no load-dependent responses for EMG AMP, MMG AMP, or MMG MPF (p = .301–.757), but there were main effects for time that indicated increases in EMG and MMG AMP and decreases in MMG MPF. There was a load-dependent decrease in EMG MPF over time (p = .032) that suggested variability in the mechanism responsible for metabolite accumulation at moderate versus high loads. These findings suggested that common drive from the central nervous system was used to modulate force during bilateral leg extension performed at moderate and high loads.

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Clayton L. Camic, Terry J. Housh, Jorge M. Zuniga, Haley C. Bergstrom, Richard J. Schmidt and Glen O. Johnson

The purpose of the current study was to examine the patterns of responses for torque, mechanomyographic (MMG) amplitude, MMG frequency, electromyographic (EMG) amplitude, and EMG frequency across 30 repeated maximal eccentric muscle actions of the leg extensors. Eleven moderately trained females performed an eccentric fatigue protocol at 30°/s with MMG and EMG signals recorded from the vastus lateralis. The results indicated there were significant (P < .05) decreases in MMG frequency (linear, r 2 = .395), EMG frequency (linear, r 2 = .177), and torque (linear, r 2 = .570; % decline = 9.8 ± 13.3%); increases in MMG amplitude (linear, r 2 = .783); and no change in EMG amplitude (r 2 = .003). These findings suggested that the neural strategies used to modulate torque during fatiguing eccentric muscle actions involved de-recruitment of motor units, reduced firing rates, and synchronization. In addition, the decreases in eccentric torque were more closely associated with changes in MMG frequency than EMG frequency. Thus, these findings indicated that MMG frequency, compared with EMG frequency, more accurately tracks fatigue during repeated maximal eccentric muscle actions.

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M. Travis Byrd, Jonathan Robert Switalla, Joel E. Eastman, Brian J. Wallace, Jody L. Clasey and Haley C. Bergstrom

Critical power (CP) and anaerobic work capacity (AWC) from the CP test represent distinct parameters related to metabolic characteristics of the whole body and active muscle tissue, respectively. Purpose: To examine the contribution of whole-body composition characteristics and local lean mass to further elucidate the differences in metabolic characteristics between CP and AWC as they relate to whole body and local factors. Methods: Fifteen anaerobically trained men were assessed for whole-body (% body fat and mineral-free lean mass [LBM]) and local mineral-free thigh lean mass (TLM) composition characteristics. CP and AWC were determined from the 3-min all-out CP test. Statistical analyses included Pearson product–moment correlations and stepwise multiple-regression analyses (P ≤ .05). Results: Only LBM contributed significantly to the prediction of CP (CP = 2.3 [LBM] + 56.7 [r 2 = .346, standard error of the estimate (SEE) = 31.4 W, P = .021]), and only TLM to AWC (AWC = 0.8 [TLM] + 3.7 [r 2 = .479, SEE = 2.2 kJ, P = .004]). Conclusions: The aerobic component (CP) of the CP test was most closely related to LBM, and the anaerobic component (AWC) was more closely related to the TLM. These findings support the theory that CP and AWC are separate measures of whole-body metabolic capabilities and the energy stores in the activated local muscle groups, respectively. Thus, training programs to improve CP and AWC should be designed to include resistance-training exercises to increase whole-body LBM and local TLM.

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Kyle S. Beyer, Jeffrey R. Stout, Michael J. Redd, Kayla M. Baker, Haley C. Bergstrom, Jay R. Hoffman and David H. Fukuda

Purpose: To examine the reliability and the maturity-related differences of fatigue thresholds (FTs) among youth males. Methods: Twenty-nine youth males (11–17 y) completed 2 ramp exercise tests on a cycle ergometer. Systemic FTs were calculated from gas exchange and ventilation variables. Localized FTs were calculated from electromyography and near-infrared spectroscopy of the vastus lateralis. All FTs were determined using the maximal distance method and expressed relative to maximal oxygen consumption. All participants were grouped according to the number of years from peak height velocity into PRE- (< −1.5 y), PERI- (−1.5 to +1.5 y) and POST- (> +1.5 y) peak height velocity. Reliability was assessed with intraclass correlation coefficients, and differences between groups were assessed with analysis of variance and Cohen’s d coefficients. Results: Analysis of variance revealed significant group differences with PRE having significantly greater systemic pulmonary FTs than POST, while localized muscular FTs were significantly greater in PRE when compared with PERI and POST. All FTs exhibited excellent reliability (intraclass correlation coefficient > .75) in all maturity groups. Conclusion: Maturity status appears to influence the onset of FTs among youth male athletes, with FTs occurring later in younger athletes. Furthermore, all FTs were reliable measures regardless of maturity.