*J Strength Cond Res ; 2021 Sep 01.*

##### 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.

*J Strength Cond Res ; 35(1): 97-101, 2021 Jan 01.*

##### 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*Motor Control ; 25(1): 59-74, 2020 Oct 14.*

##### 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*Int J Exerc Sci ; 13(2): 455-469, 2020.*

##### RESUMO

PURPOSE: This study compared the VÌO 2 corresponding to the critical heart rate (CHRVÌO 2 ) and the physical working capacity at the heart rate fatigue threshold (PWChrt VÌO 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 VÌO 2 peak, GET, VT, and RCP. The CHRVÌO 2 and PWChrt VÌO 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% VÌO 2 peak), VT (37.36 mL×kg-1×min-1, 76% VÌO 2 peak), and PWChrt VÌO 2 (38.26 mL×kg-1×min-1, 77% VÌO 2 peak) were not different, but were lower than the RCP (44.70 mL×kg-1×min-1, 90% VÌO 2 peak; p = 0.010, p < 0.001, p = 0.001, respectively). The CHRVÌO 2 (40.09 mL×kg-1×min-1, 81% VÌO 2 peak) was not different from the GET (p = 1.000), VT (p = 0.647), PWChrt VÌO 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.

*J Strength Cond Res ; 2020 Feb 20.*

##### 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.

*J Musculoskelet Neuronal Interact ; 19(3): 266-275, 2019 09 01.*

##### 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%·VÌO2, 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*J Strength Cond Res ; 33(7): 1737-1744, 2019 Jul.*

##### 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*Int J Sports Physiol Perform ; : 1-7, 2019 Oct 10.*

##### 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.

*Int J Exerc Sci ; 11(1): 867-874, 2018.*

##### 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.

*J Strength Cond Res ; 32(6): 1479-1490, 2018 Jun.*

##### RESUMO

Bergstrom, HC, Byrd, MT, Wallace, BJ, and Clasey, JL. Examination of a multi-ingredient preworkout supplement on total volume of resistance exercise and subsequent strength and power performance. J Strength Cond Res 32(6): 1479-1490, 2018-This study examined the acute effects of a multi-ingredient preworkout supplement on (a) total-, lower-, and upper-body volume of resistance exercise and (b) the subsequent lower-body strength (isokinetic leg extension and flexion), lower-body power (vertical jump [VJ] height), upper-body power (bench throw velocity [BTv]), and cycle ergometry performance (critical power and anaerobic work capacity). Twelve men completed baseline strength and power measures before 2 experimental visits, supplement (SUP) and placebo (PL). The experimental visits involved a fatiguing cycling protocol 30 minutes after ingestion of the SUP or PL and 15 minutes before the beginning of the resistance exercise protocol, which consisted of 4 upper-body and 4 lower-body resistance exercises performed for 4 sets to failure at 75% 1 repetition maximum. The exercise volume for the total, lower, and upper body was assessed. The VJ height and BTv were measured immediately after the resistance exercise. Postexercise isokinetic leg extension and flexion strength was measured 15 minutes after the completion of a second cycling protocol. There was a 9% increase in the total-body volume of exercise and a 14% increase in lower-body volume of exercise for the SUP compared with the PL, with no effect on exercise volume for the upper body between the SUP and PL. The increased lower-body volume for the SUP did not result in greater lower-body strength and power performance decrements after exhaustive exercise, compared with the PL. These findings suggested the potential for the SUP to increase resistance exercise volume, primarily related to an increased lower-body volume of exercise.

##### Assuntos

Suplementos Nutricionais , Tolerância ao Exercício , Força Muscular , Treinamento de Força , Adulto , Composição Corporal , Estudos Cross-Over , Método Duplo-Cego , Exercício Físico , Teste de Esforço , Humanos , Extremidade Inferior/fisiologia , Masculino , Extremidade Superior/fisiologia , Adulto Jovem*Int J Sports Physiol Perform ; 13(2): 189-193, 2018 Feb 01.*

##### RESUMO

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 [r2 = .346, standard error of the estimate (SEE) = 31.4 W, P = .021]), and only TLM to AWC (AWC = 0.8 [TLM] + 3.7 [r2 = .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.

##### Assuntos

Limiar Anaeróbio/fisiologia , Composição Corporal/fisiologia , Índice de Massa Corporal , Resistência Física/fisiologia , Teste de Esforço , Tolerância ao Exercício/fisiologia , Humanos , Masculino , Adulto Jovem*J Funct Morphol Kinesiol ; 3(4)2018 Oct 18.*

##### RESUMO

This study compared sex responses for strength and barbell velocity from very short-term resistance training (VST, consisting of 2-3 training sessions) for an upper body dynamic constant external resistance (DCER) exercise (bench press [BP]). Ten females (mean ± standard deviation (SD) age: 21.3 ± 3 years, height: 166.2 ± 6 cm, body mass: 71.4 ± 10.7 kg) and 10 males (mean ± SD age: 24.6 ± 4 years, height: 179.5 ± 8 cm, body mass: 88.6 ± 11 kg) completed a pre-test visit to determine the BP 1 repetition maximum (1RM) as well as the mean (BPMV) and peak (BPPV) barbell velocities from the BP 1RM. The VST involved three training visits where the participants performed 5 sets of 6 repetitions, at 65% of the 1RM. The post-test followed the same procedures as the pre-test visit. There were significant increases in 1RM strength for both the males (5.1%) and females (5.4%) between pre-test and post-test. There were no significance differences between sex for mean (BPMV) and peak (BPPV); however, overall there was a 32.7% increase in BPMV and a 29.8% increase in BPPV. These findings indicated an increase in strength and barbell velocity for both males and females as a result of VST upper body DCER exercise in untrained subjects.

*J Strength Cond Res ; 31(12): 3260-3265, 2017 Dec.*

##### RESUMO

Bergstrom, HC, Housh, TJ, Cochrane-Snyman, KC, Jenkins, NDM, Byrd, MT, Switalla, JR, Schmidt, RJ, and Johnson, GO. A model for identifying intensity zones above critical velocity. J Strength Cond Res 31(12): 3260-3265, 2017-The purpose of this study was to describe the V[Combining Dot Above]O2 responses relative to V[Combining Dot Above]O2peak at 4 different intensities within the severe domain and, based on the V[Combining Dot Above]O2 responses, identify intensity zones above critical velocity (CV). Twelve runners (mean ± SD age = 23.2 ± 3.0 years) performed an incremental treadmill test (ITT) to exhaustion to determine the V[Combining Dot Above]O2peak and velocity associated with V[Combining Dot Above]O2peak (vV[Combining Dot Above]O2peak). Critical velocity was determined from 4 exhaustive, constant velocity, randomly ordered treadmill runs (V1, V2, V3, and V4; V1 = highest, V4 = lowest). The V[Combining Dot Above]O2 responses were recorded during each of the constant velocity runs. Mean differences among V[Combining Dot Above]O2peak values from the ITT and the highest value recorded during the constant velocity runs were examined. The V[Combining Dot Above]O2 values at exhaustion for V1 (3.32 ± 0.10 L·min, p = 0.15) and V2 (3.27 ± 0.91 L·min, p = 0.13) were not significantly different from V[Combining Dot Above]O2peak (3.39 ± 0.96 L·min) from the ITT. The V[Combining Dot Above]O2 values at exhaustion for V3 (3.18 ± 0.88 L·min; p = 0.007) and V4 (3.09 ± 0.86 L·min; p = 0.003), however, were significantly less than the V[Combining Dot Above]O2peak from the ITT. There were intensity-dependent V[Combining Dot Above]O2 responses above CV. Based on these findings, we have hypothesized 3 intensity zones (first severe intensity zone [SIZ1], second severe intensity zone [SIZ2], and extreme intensity zone [EIZ]) within the severe and extreme domains, which are characterized by specific V[Combining Dot Above]O2 responses and may be used to design programs that maximize aerobic performance adaptations.