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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.
J Strength Cond Res ; 35(Suppl 1): S31-S37, 2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32796415

RESUMO

ABSTRACT: Moss, AC, Dinyer, TK, Abel, MG, and Bergstrom, HC. Methodological considerations for the determination of the critical load for the deadlift. J Strength Cond Res 35(2S): S31-S37, 2021-This study determined whether performance method during conventional deadlifting affects critical load (CL) estimates derived from the linear work limit (Wlim) vs. repetitions relationship. Eleven subjects completed 1-repetition maximum (1RM) deadlift testing followed by separate visits, to determine the number of repetitions to failure at 50, 60, 70, and 80% 1RM for both reset (RS) and touch-and-go (TG) methods. The CL was the slope of the line of total work completed (load [kg] × repetitions) vs. total repetitions for 4 intensities (50-80% 1RM). The number of repetitions to failure were determined at CLRS and CLTG. The kg values and repetitions to failure at CLRS and CLTG, and total repetitions at each intensity (50-80%) for each method (RS and TG) were compared. There were no significant mean differences (±SD) in kg values (-0.4 ± 7.9 kg, range = -8.8 to 17 kg, p = 0.856), %1RM (-1.2 ± 5.6%, p = 0.510), or total repetitions completed (2.8 ± 15.7 reps, range = -15 to 37 reps, p = 0.565) for CLRS and CLTG. These findings indicated that performance method did not affect mean estimation of CL or number of repetitions completed at submaximal loads. Thus, the estimates of CL from the modeling of total work vs. repetitions were relatively robust to variations in deadlifting methodologies. However, individual variability (range of scores) in kg values and repetition to failure at CLRS and CLTG indicated that deadlifting methods may differ in anatomical region of fatigue. The CL is an individually derived threshold that may be used to examine and describe performance capabilities.


Assuntos
Treinamento de Força , Humanos , Força Muscular
4.
J Strength Cond Res ; 35(1): 97-101, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29489713

RESUMO

ABSTRACT: Byrd, MT, Wallace, BJ, Clasey, JL, and Bergstrom, HC. Contributions of lower-body strength parameters to critical power and anaerobic work capacity. J Strength Cond Res 35(1): 97-101, 2021-This study examined the contribution of lower-body strength and isokinetic peak torque measures to the prediction of critical power (CP) and anaerobic work capacity (AWC). Fourteen recreationally trained males (mean ± SD age: 22.4 ± 2.5 years; height: 177.9 ± 7.7 cm; body mass: 84.2 ± 12.4 kg) with anaerobic training experience participated in this study. The lower-body strength measures included 1 repetition max bilateral back squat (BSq), isokinetic peak torque at 30°·s-1 [PT30], and isokinetic peak torque at 240°·s-1 [PT240] of the dominant leg. The CP and AWC were determined from the 3-minute all-out CP cycle ergometer test (CP3MT), with the resistance set at 4.5% of the total body mass. The CP was defined as the mean power output over the final 30 seconds of the test, and the AWC was calculated using the equation, AWC = 150 seconds (P150 - CP), where P150 equals the mean power output for the first 150 seconds. Stepwise regression analyses indicated that only BSq contributed significantly to the prediction of AWC (AWC = 0.0527 [BSq] + 8.094 [standard error of estimate = 2.151 kJ; p = 0.012]), with a correlation of r2 = 0.423. None of the strength parameters significantly predicted CP. These findings indicated that BSq strength accounted for 42% of the variance in AWC, but lower-body strength was not related to CP. The current results indirectly support the unique metabolic characteristics of both CP and AWC in providing separate measures of an individual's aerobic and anaerobic capabilities, respectively.


Assuntos
Limiar Anaeróbio , Teste de Esforço , Adulto , Anaerobiose , Ergometria , Humanos , Masculino , Força Muscular , Análise de Regressão , Adulto Jovem
5.
J Strength Cond Res ; 34(12): 3346-3355, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33044367

RESUMO

Herrick, LP, Goh, J, Menke, W, Campbell, MS, Fleenor, BS, Abel, MG, and Bergstrom, HC. Effects of curcumin and fenugreek soluble fiber on the physical working capacity at the fatigue threshold, peak oxygen consumption, and time to exhaustion. J Strength Cond Res 34(12): 3346-3355, 2020-The purpose of this study was to examine the effects of curcumin in combination with fenugreek soluble fiber (CUR + FEN) or fenugreek soluble fiber alone (FEN) on the neuromuscular fatigue threshold (PWCFT), peak oxygen consumption (V˙o2peak), and time to exhaustion (Tlim) on a graded exercise test (GXT), in untrained subjects. The PWCFT estimates the highest power output that can be maintained without evidence of neuromuscular fatigue. Forty-seven untrained, college-aged subjects were randomly assigned to one of 3 supplementation groups; placebo (PLA, n = 15), CUR + FEN (500 mg·d, n = 18), or FEN (300 mg·d, n = 14). The subjects completed a maximal GXT on a cycle ergometer to determine the PWCFT, V˙o2peak, and Tlim before (PRE) and after (POST) 28 days of daily supplementation. Surface electromyographic signals were recorded from a bipolar electrode arrangement on the vastus lateralis of the right leg during each test. Separate one-way analysis of covariances were used to determine if there were between-group differences for adjusted POST-PWCFT, POST-V˙o2peak, and POST-Tlim values, covaried for the respective PRE-test scores. The adjusted POST-PWCFT for the CUR + FEN group (mean ± SD: 196 ± 58 W) was greater (p = 0.016) than the PLA group (168 ± 49 W) but the FEN group (185 ± 32 W) was not different from the CUR + FEN or PLA groups (p > 0.05). There were no differences for adjusted POST-V˙o2peak (p = 0.612) or POST-Tlim (p = 0.508) among the groups. These findings suggested curcumin combined with fenugreek soluble fiber might delay neuromuscular fatigue.


Assuntos
Curcumina , Trigonella , Curcumina/farmacologia , Eletromiografia , Teste de Esforço , Humanos , Consumo de Oxigênio , Adulto Jovem
6.
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
7.
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.

8.
Physiol Rep ; 8(9): e14426, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32378353

RESUMO

The purpose of this study was to assess the maturity-related differences in the aerobic and anaerobic adaptations to sprint interval training (SIT) among youth male athletes. Twenty-seven youth male athletes were assessed for years from peak height velocity (PHV) and classified into prepubescent (PRE, n = 7, years from PHV = -2.21 ± 0.47 years), peripubescent (PERI, n = 10, years from PHV = 0.25 ± 0.88 years), and postpubescent (POST, n = 10, years from PHV = 2.81 ± 0.50 years) groups based on their years from estimated peak height velocity. Participants completed a ramp exercise protocol on a cycle ergometer to determine maximal aerobic power, maximal oxygen consumption (VO2peak ), and fatigue thresholds. Following baseline, all participants completed a 4-week SIT program that consisted of eight total training sessions. During each session, participants completed repeated 20-s sprints on a cycle ergometer against a resistance of 7.5% of body mass. The number of sprints per sessions increased from four in session 1 to seven in session 7, with four sprints in session 8. Peak and mean power from sessions 1 and 8 were recorded. All participants completed a post-testing ramp exercise protocol that mirrored baseline. Maximal aerobic power increased (p < .001) across all groups from baseline (212.61 ± 57.45 W) to post-testing (223.24 ± 58.90 W); however, VO2peak only increased in POST (3.31 ± 0.43 to 3.54 ± 0.43 L min-1 , p = .003). Similarly, GET, VT, and RCP increased in POST, with no changes in PRE or PERI. In terms of anaerobic performance, PERI and POST had significant increases in peak and mean power. POST improved aerobic and anaerobic performance following SIT, while PERI only experienced improvements in anaerobic performance. Conversely, PRE had no changes in aerobic or anaerobic performance. The adaptations to SIT appear to be influenced by the somatic maturity status.


Assuntos
Adaptação Fisiológica/fisiologia , Atletas , Desempenho Atlético/fisiologia , Exercício Físico/fisiologia , Treinamento Intervalado de Alta Intensidade/métodos , Adolescente , Anaerobiose , Criança , Humanos , Masculino , Consumo de Oxigênio/fisiologia , Puberdade/fisiologia , Corrida/fisiologia
9.
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
10.
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.

11.
J Strength Cond Res ; 34(8): 2165-2172, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31714455

RESUMO

Lesniak, AY, Bergstrom, HC, Clasey, JL, Stromberg, AJ, and Abel, MG. The effect of personal protective equipment on firefighter occupational performance. J Strength Cond Res 34(8): 2165-2172, 2020-The purpose of this study was to evaluate the effects of load carriage (LC) and LC plus respirator use (LC + self-contained breathing apparatus [SCBA]) on firefighters' work capacity to enhance our understanding of occupational demands. Twenty-one male structural firefighter recruits (age: 28.6 ± 4.3 years; height: 178.6 ± 7.2 cm; body mass: 94.1 ± 15.4 kg; body fat: 22.9 ± 6.1%) participated. Occupational performance was assessed by time to complete a simulated fire ground test (SFGT). After 2 familiarization trials, recruits performed the following SFGT conditions in a randomized order: PT (physical training clothes), LC only, and LC + SCBA. To describe within-group differences between SFGT conditions, relative difference scores were calculated as follows: % difference = ([experimental trial outcome - PT trial outcome]/PT trial outcome) × 100. Statistical differences between conditions were assessed with repeated-measures analysis of variance. The level of significance was set p < 0.01. Time to complete the LC + SCBA trial (345.9 ± 43.7 seconds; p < 0.001) and LC-only trial (331.2 ± 39.3 seconds; p < 0.001) were significantly greater than the PT trial (241.0 ± 33.3 seconds). Post-SFGT rating of perceived exertion was higher in the LC + SCBA trial (6.7 ± 1.7) and LC trial (6.4 ± 1.5) compared with the PT trial (4.7 ± 1.8; p < 0.001). Heart rate and lactate measures were similar across conditions (p = 0.488; p = 0.287). Personal protective equipment (PPE) significantly decreases the work capacity and increases the perceived effort of occupational tasks. Thus, these findings describe the additional physical demands produced by PPE and indicate that performance of firefighting tasks in an unloaded condition does not reflect work capacity in a bona fide condition.


Assuntos
Bombeiros , Saúde do Trabalhador , Dispositivos de Proteção Respiratória , Suporte de Carga/fisiologia , Adulto , Frequência Cardíaca/fisiologia , Humanos , Ácido Láctico/sangue , Masculino , Percepção , Esforço Físico/fisiologia , Adulto Jovem
12.
J Funct Morphol Kinesiol ; 5(2)2020 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-33467250

RESUMO

This study examined the effects of curcumin and fenugreek soluble fiber supplementation on the ventilatory threshold (VT) and peak oxygen consumption ( V ˙ O2 peak). METHODS: Forty-five untrained men and women were randomly assigned to one of three supplementation groups: placebo (PLA, n = 13), 500 mg·day-1 CurQfen® (CUR, n = 14), or 300 mg·day-1 fenugreek soluble fiber (FEN, n = 18). Participants completed a maximal graded exercise test on a cycle ergometer to determine the VT and V ˙ O2 peak before (PRE) and after (POST) 28 days of daily supplementation. Separate, one-way analyses of covariance (ANCOVAs) were used to examine the between-group differences for adjusted POST VT and V ˙ O2 peak values, covaried for the respective PRE-test values. RESULTS: The adjusted POST VT V ˙ O2 values for the CUR (mean ± SD = 1.593 ± 0.157 L·min-1) and FEN (1.597 ± 0.157 L·min-1) groups were greater than (p = 0.039 and p = 0.025, respectively) the PLA (1.465 ± 0.155 L·min-1) group, but the FEN and CUR groups were not different (p = 0.943). There were no differences in the adjusted V ˙ O2 peak values (F = 0.613, p = 0.547) among groups. CONCLUSION: These findings indicated that fenugreek soluble fiber was responsible for the improvements in the submaximal performance index for both CUR and FEN groups.

13.
J Strength Cond Res ; 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31800481

RESUMO

Keeler, JM, Pohl, MB, Bergstrom, HC, Thomas, JM, and Abel, MG. The effect of tactical tasks and gear on muscle activation of SWAT officers. J Strength Cond Res XX(X): 000-000, 2019-Special Weapons and Tactics (SWAT) officers perform a variety of tactical operations while wearing tactical gear. Load carriage has been shown to alter muscle activation in the torso and is also associated with lower back pain, which is a prevalent musculoskeletal injury suffered by SWAT Officers. The purpose of this study was to quantify the effect of tactical gear on muscle activation of torso musculature while performing occupational tasks. Twenty male SWAT Officers (age: 34.7 ± 4.5 years; height: 1.79 ± 0.1 m; body mass: 91.5 ± 17.3 kg) performed 4 tasks (standing, rifle walk, sitting, and shield walk) with and without gear (mass of gear: 13.8 ± 1.9 kg). Mean electromyographic amplitude was evaluated bilaterally for the erector spinae, rectus abdominis, and external oblique muscles during the trials and expressed relative to maximal voluntary isometric contraction (MVIC). Addition of gear significantly increased erector spinae mean muscle activation during the rifle walk task (mean delta: +0.16%). However, no differences in muscle activation were identified for any other muscles between gear conditions (effect size ≤ 0.15). The shield walk produced the highest mean activation for each muscle during different tasks. The dynamic tasks yielded (0.24-4.18% MVIC) greater muscle activation levels than sitting and standing tasks. Despite minimal increases in muscle activation levels with the addition of gear, load carriage is known to increase the risk of acute and chronic injury. Collectively, these findings indicate that SWAT Officers should perform most skills without gear during tactical training to simulate task-specific movement patterns but reduce the risk of musculoskeletal injury.

14.
J Musculoskelet Neuronal Interact ; 19(3): 266-275, 2019 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-31475933

RESUMO

OBJECTIVES: To examine the time course of changes in electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) responses during cycle ergometry to exhaustion performed above (CP+10%) and below (CP-10%) critical power (CP) to infer motor unit activation strategies used to maintain power output. METHODS: Participants performed a 3-min all out test to determine CP, and 2 randomly ordered, continuous rides to exhaustion at CP+10% and CP-10%·V̇O2, EMG AMP, EMG MPF, MMG AMP, MMG MPF, and time to exhaustion (Tlim) were recorded. Responses at CP-10% and CP+10% were analyzed separately. RESULTS: At CP-10%, EMG and MMG AMP were significantly greater than the initial 5% timepoint at 100% Tlim. EMG MPF and MMG MPF reflected a downward trend that resulted in no significant difference between timepoints. At CP+10%, EMG AMP was significantly greater than the initial 5% timepoint from 60% to 100% Tlim. MMG AMP was less than the initial 5% timepoint at only 50% Tlim. EMG and MMG MPF were significantly less than the initial 5% timepoint at 20% Tlim and 100% Tlim, respectively. CONCLUSIONS: The timecourse of changes in EMG and MMG signals were different at CP-10% and CP+10%, but responses observed indicated cycle ergometry to exhaustion relies on similar motor unit activation strategies.


Assuntos
Tolerância ao Exercício/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Eletrofisiologia/métodos , Teste de Esforço , Feminino , Humanos , Masculino , Contração Muscular/fisiologia , Adulto Jovem
15.
J Strength Cond Res ; 33(7): 1737-1744, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31136545

RESUMO

Dinyer, TK, Byrd, MT, Garver, MJ, Rickard, AJ, Miller, WM, Burns, S, Clasey, JL, and Bergstrom, HC. Low-load vs. high-load resistance training to failure on one repetition maximum strength and body composition in untrained women. J Strength Cond Res 33(7): 1737-1744, 2019-This study examined the effects of resistance training (RT) to failure at low and high loads on one repetition maximum (1RM) strength and body composition (bone- and fat-free mass [BFFM] and percent body fat [%BF]) in untrained women. Twenty-three untrained women (age: 21.2 ± 2.2 years; height: 167.1 ± 5.7 cm; body mass: 62.3 ± 16.2 kg) completed a 12-week RT to failure intervention at a low (30% 1RM) (n = 11) or high (80% 1RM) (n = 12) load. On weeks 1, 5, and 12, subjects completed 1RM testing for 4 different exercises (leg extension [LE], seated military press [SMP], leg curl [LC], and lat pull down [LPD]) and a dual-energy x-ray absorptiometry scan to assess body composition. During weeks 2-4 and 6-7, the subjects completed 2 sets to failure for each exercise. During weeks 8-11, the subjects completed 3 sets to failure for each exercise. The 1RM strength increased from week 1 to week 5 (LE: 18 ± 16%; SMP: 9 ± 11%; LC: 12 ± 22%; LPD: 13 ± 9%), week 1 to week 12 (LE: 32 ± 24%; SMP: 17 ± 14%; LC: 23 ± 26%; LPD: 25 ± 13%), and week 5 to week 12 (LE: 11 ± 9%; SMP: 7 ± 9%; LC: 10 ± 7%; LPD: 11 ± 11%) in each exercise, with no significant differences between groups. There were no significant changes in BFFM (p = 0.241) or %BF (p = 0.740) for either group. Resistance training to failure at 30% 1RM and 80% 1RM resulted in similar increases in 1RM strength, but no change in BFFM or %BF. Untrained women can increase 1RM strength during RT at low and high loads, if repetitions are taken to failure.


Assuntos
Composição Corporal/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Treinamento de Força/métodos , Absorciometria de Fóton , Feminino , Humanos , Adulto Jovem
16.
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.

17.
Pediatr Exerc Sci ; 31(1): 99-106, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30251936

RESUMO

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.


Assuntos
Desempenho Atlético/fisiologia , Exercício Físico/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Adolescente , Atletas/estatística & dados numéricos , Criança , Eletromiografia/métodos , Ergometria/métodos , Humanos , Pulmão/fisiologia , Masculino , Consumo de Oxigênio/fisiologia , Reprodutibilidade dos Testes , Espectroscopia de Luz Próxima ao Infravermelho/métodos
18.
Int J Exerc Sci ; 11(1): 867-874, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29997728

RESUMO

This study examined the effect of an upper body dynamic constant external resistance (DCER) exercise (barbell bench press [BP]), using the very short-term training (VST) model on strength and barbell velocity. Ten (5 females, 5 males) subjects (mean ± SD age: 21.4 ± 2.8 yrs; height: 1.75 ± 0.12 m; body mass: 83 ± 8.8 kg) completed two pre-test visits (pre-test 1 and pretest 2) to serve as the within subjects control, three training visits, and one post-test visit. The subject's 1 repetition maximum (1RM) for the BP as well as the mean (BPMV) and peak (BPPV) barbell velocities were determined during pre-test 1, pre-test 2 and post-test visits. The barbell bench press throw (BT) mean (BTMV) and peak (BTPV) velocities were also measured utilizing 35% of the subject's BP 1RM as resistance. The three training visits consisted of 5 sets of 6 repetitions, at 65% of the subject's 1RM. Statistical analyses included one-way repeated measures ANOVAs and paired samples t-tests (alpha level of p≤0.05). The post-test 1RM, BTMV, and BTPV were all significantly greater than pre-test 1 (p=0.002, p=0.0001, and p=0.002) and pre-test 2 (p=0.008, p=0.034, and p=0.015), with no significant differences seen between pre-test 1 and pre-test 2 for any of the variables. The posttest BPMV and BPPV were significantly greater than pre-test 1 (p=0.024 and p=0.005), but not pre-test 2 (p=0.131 and p=0.069). These findings showed the VST model, utilizing an upper body DCER exercise improved strength and barbell velocity in untrained subjects.

19.
J Electromyogr Kinesiol ; 40: 88-94, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29704787

RESUMO

The selection of epoch lengths affects the time and frequency resolution of electromyographic (EMG) and mechanomyographic (MMG) signals, as well as decisions regarding the signal processing techniques to use for determining the power density spectrum. No previous studies, however, have examined the effects of epoch length on parameters of the MMG signal. The purpose of this study was to examine the differences between epoch lengths for EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF from the VL and VM muscles during MVIC muscle actions as well as at each 10% of the time to exhaustion (TTE) during a continuous isometric muscle action of the leg extensors at 50% of MVIC. During the MVIC trial, there were no significant (p > 0.05) differences between epoch lengths (0.25, 0.50, 1.00, and 2.00-s) for mean absolute values for any of the EMG or MMG parameters. During the submaximal, sustained muscle action, however, absolute MMG amplitude and MMG MPF were affected by the length of epoch. All epoch related differences were eliminated by normalizing the absolute values to MVIC. These findings supported normalizing EMG and MMG parameter values to MVIC and utilizing epoch lengths that ranged from 0.25 to 2.00-s.


Assuntos
Eletromiografia/métodos , Contração Isométrica/fisiologia , Músculo Esquelético/fisiologia , Fenômenos Biomecânicos/fisiologia , Feminino , Humanos , Masculino , Processamento de Sinais Assistido por Computador , Fatores de Tempo , Torque , Adulto Jovem
20.
Int J Exerc Sci ; 11(4): 585-597, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29541334

RESUMO

There are conflicting suggestions regarding the most valid resistance (3-5% of body weight) to use for the critical power (CP) 3-min all-out (CP3min) test to estimate CP and anaerobic work capacity (AWC). The purpose of this study was to determine if the CP and AWC estimates from the CP3min test were affected by the percentage of body weight used to set the resistance on a Monark cycle ergometer. Ten recreationally trained participants (mean ± SD: Age: 22.2 ± 2.2 yrs.) completed the CP3min test at resistances of 4.5% (CP4.5%) and 3% (CP3%) of body weight to determine the CP and AWC. There were no significant differences between the CP4.5% (167 ± 34 W) and CP3% (156 ± 36 W) estimates. The AWC3% (5.6 ± 2.5 kJ) estimates were significantly lower than the AWC4.5% (9.0 ± 4.0 kJ). The CP and AWC estimates from the CP4.5% were consistent with values reported in the literature, however, the AWC estimate from the CP3% was lower than typically reported. These findings suggested that a resistance set at 3% of body weight for the CP3min test may be too low to accurately estimate AWC, but 3% and 4.5% resulted in the same estimation of CP. Thus, the principal finding of this study was that a resistance of 4.5% of body weight for CP3-min in recreationally trained participants resulted in more accurate estimates of AWC, compared to a resistance of 3%, and supports the use of 4.5% body weight resistance to measure both CP and AWC.

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