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1.
J Strength Cond Res ; 2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34474433

RESUMO

ABSTRACT: Succi, PJ, Dinyer, TK, Byrd, MT, Voskuil, CC, and Bergstrom, HC. Application of V[Combining Dot Above]O2 to the critical power model to derive the critical V[Combining Dot Above]O2. J Strength Cond Res XX(X): 000-000, 2021-The purposes of this study were to (a) determine whether the critical power (CP) model could be applied to V[Combining Dot Above]O2 to estimate the critical V[Combining Dot Above]O2 (CV[Combining Dot Above]O2) and (b) to compare the CV[Combining Dot Above]O2 with the V[Combining Dot Above]O2 at CP (V[Combining Dot Above]O2CP), the ventilatory threshold (VT), respiratory compensation point (RCP), and the CV[Combining Dot Above]O2 without the V[Combining Dot Above]O2 slow component (CV[Combining Dot Above]O2slow). Nine subjects performed a graded exercise test to exhaustion to determine V[Combining Dot Above]O2peak, VT, and RCP. The subjects performed 4 randomized, constant power output work bouts to exhaustion. The time to exhaustion (TLim), the total work (WLim), and the total volume of oxygen consumed with (TV[Combining Dot Above]O2) and without the slow component (TV[Combining Dot Above]O2slow) were recorded during each trial. The linear regressions of the TV[Combining Dot Above]O2 vs. TLim, TV[Combining Dot Above]O2slow vs. TLim, and WLim vs. TLim relationship were performed to derive the CV[Combining Dot Above]O2, CV[Combining Dot Above]O2slow, and CP, respectively. A 1-way repeated-measures analysis of variance (p ≤ 0.05) with follow-up Sidak-Bonferroni corrected pairwise comparisons indicated that CV[Combining Dot Above]O2 (42.49 ± 3.22 ml·kg-1·min-1) was greater than VT (30.80 ± 4.66 ml·kg-1·min-1; p < 0.001), RCP (36.74 ± 4.49 ml·kg-1·min-1; p = 0.001), V[Combining Dot Above]O2CP (36.76 ± 4.31 ml·kg-1·min-1; p < 0.001), and CV[Combining Dot Above]O2slow (38.26 ± 2.43 ml·kg-1·min-1; p < 0.001). However, CV[Combining Dot Above]O2slow was not different than V[Combining Dot Above]O2CP (p = 0.140) or RCP (p = 0.235). Thus, the CP model can be applied to V[Combining Dot Above]O2 to derive the CV[Combining Dot Above]O2 and theoretically is the highest metabolic steady state that can be maintained for an extended period without fatigue. Furthermore, the ability of the CV[Combining Dot Above]O2 to quantify the metabolic cost of exercise and the inefficiency associated with the V[Combining Dot Above]O2 slow component may provide a valuable tool for researchers and coaches to examine endurance exercise.

2.
Sports (Basel) ; 9(2)2021 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-33494200

RESUMO

The study and application of the critical power (CP) concept has spanned many decades. The CP test provides estimates of two distinct parameters, CP and W', that describe aerobic and anaerobic metabolic capacities, respectively. Various mathematical models have been used to estimate the CP and W' parameters across exercise modalities. Recently, the CP model has been applied to dynamic constant external resistance (DCER) exercises. The same hyperbolic relationship that has been established across various continuous, whole-body, dynamic movements has also been demonstrated for upper-, lower-, and whole-body DCER exercises. The asymptote of the load versus repetition relationship is defined as the critical load (CL) and the curvature constant is L'. The CL and L' can be estimated from the same linear and non-linear mathematical models used to derive the CP. The aims of this review are to (1) provide an overview of the CP concept across continuous, dynamic exercise modalities; (2) describe the recent applications of the model to DCER exercise; (3) demonstrate how the mathematical modeling of DCER exercise can be applied to further our understanding of fatigue and individual performance capabilities; and (4) make initial recommendations regarding the methodology for estimating the parameters of the CL test.

3.
Motor Control ; 25(1): 59-74, 2020 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-33059330

RESUMO

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.


Assuntos
Exercício Físico/fisiologia , Perna (Membro)/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Adulto , Feminino , Humanos , Masculino , Adulto Jovem
4.
Int J Exerc Sci ; 13(2): 455-469, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32509109

RESUMO

PURPOSE: This study compared the V̇O 2 corresponding to the critical heart rate (CHRV̇O 2 ) and the physical working capacity at the heart rate fatigue threshold (PWChrt V̇O 2 ) to the gas exchange threshold (GET), ventilatory threshold (VT), and respiratory compensation point (RCP). METHODS: Nine runners (mean ± SD, age 23 ± 3 years) completed an incremental test on a treadmill to determine V̇O 2 peak, GET, VT, and RCP. The CHRV̇O 2 and PWChrt V̇O 2 were determined from 4 separate constant velocity treadmill runs to exhaustion and HR and time to exhaustion were recorded. Differences among the thresholds were examined with a one-way repeated measures ANOVA (p ≤ 0.05). RESULTS: The GET (38.44 mL×kg-1×min-1, 78% V̇O 2 peak), VT (37.36 mL×kg-1×min-1, 76% V̇O 2 peak), and PWChrt V̇O 2 (38.26 mL×kg-1×min-1, 77% V̇O 2 peak) were not different, but were lower than the RCP (44.70 mL×kg-1×min-1, 90% V̇O 2 peak; p = 0.010, p < 0.001, p = 0.001, respectively). The CHRV̇O 2 (40.09 mL×kg-1×min-1, 81% V̇O 2 peak) was not different from the GET (p = 1.000), VT (p = 0.647), PWChrt V̇O 2 (p = 1.000), or RCP (p = 0.116). CONCLUSIONS: These results indicated that the initial metabolic intensities at CHR and PWChrt lie within the heavy and moderate intensity domains, respectively. Therefore, the PWChrt may provide a relative intensity more appropriate for untrained populations, while the CHR may be more appropriate for more trained populations.

5.
J Musculoskelet Neuronal Interact ; 20(1): 77-87, 2020 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-32131371

RESUMO

OBJECTIVES: This study examined the time course of changes and patterns of responses in electromyographic amplitude (EMG AMP) and EMG mean power frequency (MPF) for the superficial quadriceps muscles during exhaustive treadmill runs within the severe exercise intensity zones (SIZ1 and SIZ2). METHODS: The EMG signals for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) as well as times to exhaustion (Tlim) were recorded in ten runners during two exhaustive treadmill runs (SIZ1 and SIZ2). The composite and individual responses were compared among muscles and between intensities. RESULTS: The composite patterns of responses in EMG AMP (linear, quadratic, and cubic increases; r2/R2=0.684-0.848) and EMG MPF (linear, quadratic, and cubic decreases; r2/R2=0.648 - 0.852) for the VL and RF were consistent with neuromuscular fatigue in both zones, but those for the VM were not (quadratic, cubic, and non-significant relationships with responses near baseline). The RF tended to demonstrate greater fatigue (EMG MPF decreased from 80-100% Tlim). There was large inter-individual variability (only 10-60% of responses consistent with composite) in response to fatiguing treadmill running. CONCLUSIONS: The current findings support the examination and characterization of neuromuscular fatigue on an intensity, muscle, and subject-by-subject basis.


Assuntos
Teste de Esforço/métodos , Fadiga Muscular/fisiologia , Junção Neuromuscular/fisiologia , Músculo Quadríceps/fisiologia , Corrida/fisiologia , Adulto , Eletromiografia/métodos , Feminino , Humanos , Masculino , Adulto Jovem
6.
J Strength Cond Res ; 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-32084106

RESUMO

Dinyer, TK, Byrd, MT, Succi, PJ, and Bergstrom, HC. The time course of changes in neuromuscular responses during the performance of leg extension repetitions to failure below and above critical resistance in women. J Strength Cond Res XX(X): 000-000, 2020-Critical resistance (CR) is the highest sustainable resistance that can be completed for an extended number of repetitions. Exercise performed below (CR-15%) and above (CR+15%) CR may represent 2 distinct intensities that demonstrate separate mechanisms of fatigue. Electromyography (EMG) and mechanomyography (MMG) have been used to examine the mechanism of fatigue during resistance exercise. Therefore, the purposes of this study were to (a) compare the patterns of responses and time course of changes in neuromuscular parameters (EMG and MMG amplitude [AMP] and mean power frequency [MPF]) during the performance of repetitions to failure at CR-15% and CR+15% and (b) identify the motor unit activation strategy that best describes the fatigue-induced changes in the EMG and MMG signals at CR-15% and CR+15%. Ten women completed one repetition maximum (1RM) testing and repetitions to failure at 50, 60, 70, and 80% 1RM (to determine CR), and at CR-15% and CR+15% on the leg extension. During all visits, EMG and MMG signals were measured from the vastus lateralis. There were similar patterns of responses in the neuromuscular parameters, and time-dependent changes in EMG AMP and EMG MPF, but not MMG AMP or MMG MPF, during resistance exercise performed at CR-15% and CR+15% (p < 0.05). The onset of fatigue occurred earlier for EMG AMP, but later for EMG MPF, during repetitions performed at CR+15% compared with those performed at CR-15%. Thus, resistance exercise performed below and above CR represented 2 distinct intensities that were defined by different neuromuscular fatigue mechanisms but followed similar motor unit activation strategies.

7.
Int J Sports Physiol Perform ; : 1-7, 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-30958050

RESUMO

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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