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OBJECTIVES: The current study investigated performance fatigability (PF) and time course of changes in force, electromyographic amplitude (EMG AMP) and frequency (EMG MPF), and neuromuscular efficiency (NME) during a sustained, isometric, handgrip hold to failure (HTF) using the rating of perceived exertion (RPE)-Clamp Model. METHODS: Twelve males performed a handgrip HTF anchored to RPE=5. The time to task failure (Tlim), force (N), EMG AMP and MPF, and NME (normalized force/ normalized EMG AMP) were recorded. Analyses included a paired samples t-test for PF at an alpha of p<0.05, 1-way repeated measures ANOVA across time and post-hoc t-tests (p<0.0025) for force, EMG AMP and MPF, and NME responses. RESULTS: The PF (pre- to post- maximal force % decline) was 38.2±11.5%. There were decreases in responses, relative to 0% Tlim, from 40% to 100% Tlim (force), at 30%, 60%, and 100% Tlim (EMG AMP), from 10% to 100% Tlim(EMP MPF), and from 50% to 65%, and 80% to 100% Tlim (NME) (p<0.0025). CONCLUSIONS: The RPE-Clamp Model in this study demonstrated that pacing strategies may be influenced by the integration of anticipatory, feedforward, and feedback mechanisms, and provided insights into the relationship between neuromuscular and perceptual responses, and actual force generating capacity.
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Eletromiografia , Força da Mão , Fadiga Muscular , Músculo Esquelético , Humanos , Masculino , Força da Mão/fisiologia , Fadiga Muscular/fisiologia , Adulto Jovem , Adulto , Eletromiografia/métodos , Músculo Esquelético/fisiologia , Contração Isométrica/fisiologia , Esforço Físico/fisiologiaRESUMO
BACKGROUND: In general, it has been suggested that females are more fatigue-resistant than males, with the magnitude of difference being most pronounced during low-intensity sustained contractions. However, the mechanisms for the apparent sex difference have not yet been fully elucidated in the literature. This study aimed to examine sex-related differences in fatigability and patterns of neuromuscular responses for surface electromyographic (sEMG) and mechanomyographic (sMMG) amplitude and frequency (MPF) characteristics during a sustained submaximal bilateral, isometric leg extension muscle action. METHODS: A sample of 20 young recreationally active males and females with previous resistance training experience performed a sustained, submaximal, bilateral isometric leg extension until task failure. Time-to-task failure was compared using a nonparametric bootstrap of the 95% confidence interval for the mean difference between males and females. Additionally, patterns of response for sEMG and sMMG amplitude and MPF of the dominant limb were examined using linear mixed effect models. RESULTS: There were no differences in time-to-task failure between males and females. Additionally, neuromuscular responses revealed similar patterns of responses between males and females. Interestingly, sEMG amplitude and sMMG amplitude and MPF all revealed non-linear responses, while sEMG MPF demonstrated linear responses. CONCLUSION: These data revealed that time-to-task failure was not different between males and females during sustained submaximal bilateral, isometric leg extension. Interestingly, the parallel, non-linear, increases in sEMG and sMMG amplitude may indicate fatigue induced increases in motor unit recruitment, while the parallel decreases in sMMG MPF may be explained by the intrinsic properties of later recruited motor units, which may have inherently lower firing rates than those recruited earlier.
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ABSTRACT: Kwak, M, Succi, PJ, Benitez, B, Mitchinson, C, Samaan, MA, Abel, MG, and Bergstrom, HC. Comparison of force, neuromuscular, and metabolic responses during sustained, isometric handgrip holds to failure anchored to low and high perceptual intensities in men: An exploratory study. J Strength Cond Res 38(8): e405-e416, 2024-This study examined the responses of force alterations, relative to critical force (CF), neuromuscular parameters, and muscle oxygenation (SmO2) for isometric handgrip holds to failure (HTF) anchored to ratings of perceived exertion (RPE) of 3 and 7. Twelve men completed pre-maximal voluntary isometric contractions (pre-MVIC), submaximal HTF at 4 percentages of pre-MVIC, HTF at RPE = 3 and 7, and post-MVIC. Mechanomyograpic (MMG) signals and SmO2 were recorded during the RPE HTF. Analyses included paired-samples t-tests and repeated-measures ANOVAs at an alpha level of p ≤ 0.05. Time to task failure was not different between RPE 3 (478.7 ± 196.6 s) and RPE 7 (495.8 ± 173.8 s). Performance fatigability (PF) and MMG amplitude (AMP) were greater for RPE 7 (PF: 37.9 ± 12.9%; MMG AMP: 15.7 ± 7.4% MVIC) than RPE 3 (PF: 30.0 ± 14.5%; MMG AMP: 10.2 ± 6.5% MVIC), but MMG mean power frequency (MPF) was greater for RPE 3 (146.2 ± 31.1% MVIC) than RPE 7 (128.8 ± 23.0% MVIC). There were RPE-dependent decreases in force (p ≤ 0.01) across 3 discernable phases during the HTF. There were decreases in MMG AMP across time for both RPEs, but there were no significant changes in MMG MPF or SmO2. There were overall similar motor unit control strategies and local metabolic demand between RPEs. The majority of the HTF performed below CF at RPE 3 and 7 indicated CF did not reflect the highest sustainable force. When prescribing isometric exercise anchored to RPE, practitioners should be aware of the magnitude of force loss and relative intensity of the task to be sure desired training loads are met.
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Força da Mão , Contração Isométrica , Músculo Esquelético , Humanos , Masculino , Força da Mão/fisiologia , Contração Isométrica/fisiologia , Adulto Jovem , Músculo Esquelético/fisiologia , Adulto , Esforço Físico/fisiologia , Consumo de Oxigênio/fisiologia , Fadiga Muscular/fisiologia , EletromiografiaRESUMO
PURPOSE: A square-wave verification bout to confirm maximal oxygen uptake ([Formula: see text]O2max) from a graded exercise test (GXT) has been recommended. This study ascertained if a verification bout is necessary to determine [Formula: see text]O2max in moderately trained men. METHODS: Ten men (24 ± 4 years) completed familiarization and two treadmill GXTs, followed by a submaximal verification bout to determine [Formula: see text]O2GXT and [Formula: see text]O2verification (highest [Formula: see text]O2 from each testing method). After completing the GXT, subjects rested for 5 min then performed a verification bout at 90% speed and 50% incline at termination of the GXT. The analyses included a 2-way repeated-measures ANOVA, intra-class correlation coefficients (ICC2,1), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (CoV). RESULTS: There was no test (test 1 vs test 2) × method (GXT vs verification) interaction (p = 0.584), or main effect for test (p = 0.320), but there was a main effect for method (p = 0.011). The [Formula: see text]O2GXT (50.9±3.0 mL·kg-1·min-1) was greater than [Formula: see text]O2verification (46.9 ± mL·kg-1·min-1). The [Formula: see text]O2GXT (ICC = 0.988, SEM = 1.0 mL·kg-1 min-1, MD = 2.9 mL kg-1 min-1, CoV = 2.03%) and [Formula: see text]O2verification (ICC = 0.976, SEM = 1.0 mL·kg-1 min-1, MD = 2.7 mL·kg-1·min-1, CoV = 2.03%) demonstrated "excellent" reliability. No subject exceeded the MD for [Formula: see text]O2GXT test-retest or for [Formula: see text]O2verification test-retest, but 50% of subjects had a [Formula: see text]O2GXT that was greater than the [Formula: see text]O2verification (> MD). CONCLUSION: While [Formula: see text]O2GXT and [Formula: see text]O2verification demonstrated excellent reliability, [Formula: see text]O2GXT from a stand-alone GXT provided higher estimates of [Formula: see text]O2 and, therefore, should be considered [Formula: see text]O2max. The lack of test-retest differences in [Formula: see text]O2GXT above the MD indicated that subjects achieved their highest [Formula: see text]O2 ([Formula: see text]O2max) from a standalone GXT. Therefore, the verification bout may not be required to confirm [Formula: see text]O2max in this population.
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Teste de Esforço , Consumo de Oxigênio , Masculino , Humanos , Reprodutibilidade dos Testes , Teste de Esforço/métodosRESUMO
PURPOSE: Critical force (CF) provides an estimate of the asymptote of the force-duration curve and the physical working capacity at the rating of perceived exertion (PWCRPE) estimates the highest force that can be sustained without an increase in perceived exertion. Handgrip-related musculoskeletal disorders and injuries derived from sustained or repetitive motion-induced muscle fatigue are prevalent in the industrial workforce. Thus, it is important to understand the physiological mechanisms underlying performance during handgrip specific tasks to describe individual work capacities. This study examined prolonged, isometric, handgrip exercises by comparing the relative force levels, sustainability, and perceptual responses at two fatigue thresholds, CF and PWCRPE. METHODS: Ten women (26.5 ± 3.5 years) performed submaximal, isometric handgrip holds to failure (HTF) with the dominant hand at four, randomly ordered percentages (30, 40, 50, and 60%) of maximal voluntary isometric contraction (MVIC) force to determine CF and PWCRPE. Isometric handgrip HTF were performed at CF and PWCRPE. Time to task failure and RPE responses were recorded. RESULTS: There were no differences in the relative forces (p = 0.381) or sustainability (p = 0.390) between CF (18.9 ± 2.5% MVIC; 10.1 ± 2.7 min) and PWCRPE (19.5 ± 7.9% MVIC; 11.6 ± 8.4 min), and the RPE increased throughout both holds at CF and PWCRPE. CONCLUSION: It is possible that complex physio-psychological factors may have contributed to the fatigue-induced task failure. CF and PWCRPE may overestimate the highest force output that can be maintained for an extended period of time without fatigue or perceptions of fatigue for isometric handgrip holds.
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Força da Mão , Músculo Esquelético , Feminino , Humanos , Eletromiografia , Exercício Físico , Força da Mão/fisiologia , Contração Isométrica/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Adulto Jovem , AdultoRESUMO
PURPOSE: This study examined neuromuscular responses of the biceps brachii (BB) for concentric and eccentric muscle actions during bilateral, dynamic constant external resistance (DCER), reciprocal forearm flexions and extensions to failure at high (80% 1 repetition maximum [1RM]) and low (30% 1RM) relative loads. METHODS: Nine women completed 1RM testing and repetitions to failure (RTF) at 30 and 80% 1RM. Electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) signals were measured from the BB. Analyses included repeated measures ANOVAs (p < 0.05) and post-hoc pairwise comparisons with Bonferroni corrected alpha of p < 0.008 and p < 0.01 for between and within factor pairwise comparisons, respectively. RESULTS: EMG AMP and MPF were significantly greater for concentric than eccentric muscle actions, regardless of load or time. However, time course of change analysis revealed parallel increases in EMG AMP for concentric and eccentric muscle actions during the RTF trials at 30% 1RM, but no change at 80% 1RM. There were significant increases in MMG AMP during concentric muscle actions, but decreases or no change during eccentric muscle actions. EMG and MMG MPF decreased over time, regardless of muscle action type and loading condition. CONCLUSION: The greater EMG AMP and MPF values during concentric compared to eccentric muscle actions may reflect the difference in the efficiency characteristic of these muscle actions. The neuromuscular responses suggested that fatigue may be mediated by recruitment of additional motor units with lower firing rates during concentric muscle actions, and changes in motor unit synchronization during eccentric muscle actions.
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Contração Muscular , Músculo Esquelético , Humanos , Feminino , Eletromiografia , Músculo Esquelético/fisiologia , Contração Muscular/fisiologia , Braço/fisiologia , AntebraçoRESUMO
ABSTRACT: Benitez, B, Dinyer-McNeeley, TK, McCallum, L, Kwak, M, Succi, PJ, and Bergstrom, HC. Load-specific performance fatigability, coactivation, and neuromuscular responses to fatiguing forearm flexion muscle actions in women. J Strength Cond Res 37(4): 769-779, 2023-This study examined the effects of fatiguing, bilateral, dynamic constant external resistance (DCER) forearm flexion on performance fatigability, coactivation, and neuromuscular responses of the biceps brachii (BB) and triceps brachii (TB) at high (80% 1 repetition maximum [1RM]) and low (30% 1RM) relative loads in women. Ten women completed 1RM testing and repetitions to failure (RTF) at 30 and 80% 1RM. Maximal voluntary isometric force was measured before and after RTF. Electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) signals were measured from the BB and TB. Performance fatigability was greater (p < 0.05) after RTF at 30% (%∆ = 41.56 ± 18.61%) than 80% (%∆ = 19.65 ± 8.47%) 1RM. There was an increase in the coactivation ratio (less coactivation) between the initial and final repetitions at 30%, which may reflect greater increases in agonist muscle excitation (EMG AMP) relative to the antagonist for RTF at 30% than 80% 1RM. The initial repetitions EMG AMP was greater for 80% than 30% 1RM, but there was no difference between loads for the final repetitions. For both loads, there were increases in EMG MPF and MMG AMP and decreases in MMG MPF that may suggest fatigue-dependent recruitment of higher-threshold motor units. Thus, RTF at 30 and 80% 1RM during DCER forearm flexion may not necessitate additional muscle excitation to the antagonist muscle despite greater fatigability after RTF at 30% 1RM. These specific acute performance and neuromuscular responses may provide insight into the unique mechanism underlying adaptations to training performed at varying relative loads.
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Antebraço , Fadiga Muscular , Humanos , Feminino , Fadiga Muscular/fisiologia , Eletromiografia , Músculo Esquelético/fisiologia , FadigaRESUMO
Maternal hypothalamic-pituitary-adrenal axis activity may prenatally program sex-specific stress-response pathways. We investigated associations between maternal cortisol during pregnancy and infant parasympathetic responsivity to stress among 204 mother-infant pairs. Cortisol indices included 3rd trimester hair cortisol, as well as diurnal slope and area under the curve, derived from saliva samples collected during pregnancy. Mother-infant dyads participated in the Repeated Still-Face Paradigm (SFP-R) at age 6 months. We calculated respiration-adjusted respiratory sinus arrhythmia (RSAc ), an indicator of parasympathetic activation, from infant respiration and cardiac activity measured during the SFP-R. We used multivariable linear mixed models to examine each cortisol index in relation to infant RSAc and investigated sex differences using cross-product terms. Diurnal cortisol indices were not associated with RSAc . There was no association between hair cortisol and baseline RSAc . However, hair cortisol was associated with sex-specific changes in RSAc over the SFP-R such that, among girls, parasympathetic withdrawal was reduced with increasing prenatal exposure to cortisol. Consistently higher levels of prenatal cortisol exposure may lead to dampened parasympathetic responsivity to stress during infancy, particularly among girls. Maternal hair cortisol may be particularly valuable for studying the effects of prenatal cortisol exposure on infant autonomic reactivity.
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Hidrocortisona , Efeitos Tardios da Exposição Pré-Natal , Feminino , Humanos , Sistema Hipotálamo-Hipofisário , Lactente , Masculino , Mães , Sistema Hipófise-Suprarrenal , Gravidez , Saliva , Estresse PsicológicoRESUMO
PURPOSE: This study quantified the metabolic demands (oxygen uptake (VÌO 2 )), power output adjustments, changes in the VÌO 2 /power output ratio, and perceptual responses (rating of perceived exertion (RPE)) during constant heart rate (HR) exercise performed within the vigorous intensity range (77%-95% HR peak ). METHODS: Twelve women (mean ± SD age, 22 ± 4 yr) performed a graded exercise test to exhaustion to determine peak parameters, and three randomly ordered, constant HR trials to exhaustion or for 60 min at the lower (HR L = 77% HR peak ), middle (HR M = 86% HR peak ), and higher (HR H = 95% HR peak ) end of the vigorous intensity range. Time course of changes and patterns of responses were examined for VÌO 2 , power output, VÌO 2 /power output, and RPE for the composite and for each subject. RESULTS: Across the HR L (time to exhaustion ( Tlim ) = 56.3 ± 9.9 min), HR M (51.8 ± 13.5 min), and HR H (27.2 ± 17.7 min) trials, VÌO 2 and power output decreased quadratically ( P < 0.05) relative to the initial value from 10% to 100% of Tlim , whereas the VÌO 2 /power output increased quadratically from 20% to 100% Tlim , and RPE increased linearly from 50% to 100% Tlim . The VÌO 2 and RPE, collapsed across time, for HR L (54.3% ± 3.3% VÌO 2peak , 11 ± 1.5 RPE) were lower than HR M (64.9% ± 4.5% VÌO 2peak , 14 ± 1.7 RPE), and both were lower than HR H (80.1% ± 4.1% VÌO 2peak , 17 ± 1.4 RPE). None of the 12 subjects at HR L , 6 at HR M , and 7 at HR H were within the vigorous VÌO 2 range. CONCLUSIONS: The HR L was not sufficient to meet the desired metabolic intensity for vigorous exercise, whereas the middle to higher end of the range elicited a VÌO 2 within the prescribed range of only ~50%-60% of the subjects. This study indicated that exercise held constant at a percentage of HR peak cannot consistently be used to prescribe a desired metabolic stimulus.
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Exercício Físico , Consumo de Oxigênio , Humanos , Feminino , Adolescente , Adulto Jovem , Adulto , Frequência Cardíaca/fisiologia , Consumo de Oxigênio/fisiologia , Exercício Físico/fisiologia , Teste de Esforço , Esforço Físico/fisiologiaRESUMO
PURPOSE: A square-wave verification bout to confirm maximal oxygen uptake (VÌO 2max ) from a graded exercise test (GXT) has been recommended based on mean responses. This study used the test-retest reliability, mean, and individual differences between the highest VÌO 2 from the GXT (VÌO 2GXT ) and verification bout (VÌO 2verification ) to examine the efficacy of a verification bout in the determination of O 2max in healthy, recreationally trained, well-motivated men. METHODS: Ten men (24 ± 4 yr) completed a GXT on a cycle ergometer followed by a submaximal verification bout to determine VÌO 2GXT and VÌO 2verification . After completion of the initial GXT, subjects rested for 5 min then performed the verification bout at 90% of the peak power output from the initial GXT. Analyses included a two-way repeated-measures ANOVA, intraclass correlation coefficients (ICC 2,1 ), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (COV). RESULTS: There was no test (test 1 vs test 2)-method (GXT vs verification) interaction ( P = 0.300) and no main effect for test ( P = 0.690), but there was a main effect for method ( P = 0.003). The VÌO 2GXT (46.0 mLâ kg -1 â min -1 ) was significantly greater than VÌO 2verification (43.9 mLâ kg -1 â min -1 ), collapsed across test. The VÌO 2GXT (ICC = 0.970, SEM = 1.63 mLâ kg -1 â min -1 , MD = 4.51 mLâ kg -1 â min -1 , COV = 3.54%) and the VÌO 2verification (ICC = 0.953, SEM = 1.87 mLâ kg -1 â min -1 , MD = 5.17 mLâ kg -1 â min -1 , COV = 4.25%) demonstrated "excellent" reliability. No subject exceeded the MD test-retest for VÌO 2GXT or VÌO 2verification . No subject had a VÌO 2verification that exceeded VÌO 2GXT by more than the MD, but two subjects had a VÌO 2GXT , which exceeded VÌO 2verification by more than the MD. CONCLUSIONS: The excellent reliability of VÌO 2GXT in addition to the examination of the individual differences between VÌO 2GXT and VÌO 2verification using the MD indicated that a standalone GXT was sufficient to determine VÌO 2max .
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Teste de Esforço , Consumo de Oxigênio , Masculino , Humanos , Reprodutibilidade dos Testes , Consumo de Oxigênio/fisiologia , Teste de Esforço/métodosRESUMO
This study aimed to investigate the test-retest reliability, mean, and individual responses in the measurement of maximal oxygen consumption (VËO2max) during a cardiopulmonary exercise test (CPET) and the verification phase during cycle ergometry in women. Nine women (22 ± 2 yrs, 166.0 ± 4.5 cm, 58.6 ± 7.7 kg) completed a CPET, passively rested for 5 min, and then completed a verification phase at 90% of peak power output to determine the highest VËO2 from the CPET (VËO2CPET) and verification phase (VËO2verification) on 2 separate days. Analyses included a two-way repeated measures ANOVA, intraclass correlation coefficients (ICC2,1), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (CoV). There was no test (test 1 versus test 2) × method (CPET vs. verification phase) interaction (p = 0.896) and no main effect for method (p = 0.459). However, test 1 (39.2 mL·kg-1·min-1) was significantly higher than test 2 (38.3 mL·kg-1·min-1) (p = 0.043). The VËO2CPET (ICC = 0.984; CoV = 1.98%; SEM = 0.77 mL·kg-1·min-1; MD = 2.14 mL·kg-1·min-1) and VËO2verification (ICC = 0.964; CoV = 3.30%; SEM = 1.27 mL·kg-1·min-1; MD = 3.52 mL·kg-1·min-1) demonstrated "excellent" reliability. Two subjects demonstrated a test 1 VËO2CPET that exceeded the test 2 VËO2CPET, and one subject demonstrated a test 1 VËO2verification that exceeded the test 2 VËO2verification by more than the respective CPET and verification phase MD. One subject demonstrated a VËO2CPET that exceeded the VËO2verification, and one subject demonstrated a VËO2verification that exceeded the VËO2CPET by more than the MD. These results demonstrate the importance of examining the individual responses in the measurement of the VËO2max and suggest that the MD may be a useful threshold to quantify real individual changes in VËO2.
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This study investigated the effects of fatiguing unilateral exercise on the ipsilateral, exercised, and contralateral, non-exercised limb's post-exercise performance in males and females. Ten males and ten females performed a fatiguing, unilateral isometric leg extension at 50% maximal voluntary isometric contraction (MVIC) force. Prior to and immediately after the fatiguing tasks, MVICs were performed for the exercised and non-exercised limb, with surface electromyographic (sEMG) and mechanomyography (sMMG) amplitude (AMP) and mean power frequency (MPF) recorded from each limb's vastus lateralis. There were no fatigue-induced, sex-dependent, differences in time to task failure (p = 0.265) or ipsilateral performance fatigability (p = 0.437). However, there was a limb by time interaction (p < 0.001) which indicated decreases in MVIC force of the ipsilateral, exercised (p < 0.001), but not the contralateral, non-exercised limb (p = 0.962). There were no sex-dependent, fatigue-induced differences in neurophysiological outcomes between the limbs (p > 0.05), but there was a fatigue-induced difference in sEMG MPF (p = 0.005). To summarize, there were no differences in fatigability between males and females. Moreover, there was insufficient evidence to support the presence of a general crossover effect following submaximal unilateral isometric exercise. However, independent of sex, the neurophysiological outcomes suggested that competing inputs from the nervous system may influence the performance of both limbs following unilateral fatigue.
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Resistance training variables such as volume, load, and frequency are well defined. However, the variable proximity to failure does not have a consistent quantification method, despite being defined as the number of repetitions in reserve (RIR) upon completion of a resistance training set. Further, there is between-study variability in the definition of failure itself. Studies have defined failure as momentary (inability to complete the concentric phase despite maximal effort), volitional (self-termination), or have provided no working definition. Methods to quantify proximity to failure include percentage-based prescription, repetition maximum zone training, velocity loss, and self-reported RIR; each with positives and negatives. Specifically, applying percentage-based prescriptions across a group may lead to a wide range of per-set RIR owing to interindividual differences in repetitions performed at specific percentages of 1 repetition maximum. Velocity loss is an objective method; however, the relationship between velocity loss and RIR varies set-to-set, across loading ranges, and between exercises. Self-reported RIR is inherently individualized; however, its subjectivity can lead to inaccuracy. Further, many studies, regardless of quantification method, do not report RIR. Consequently, it is difficult to make specific recommendations for per-set proximity to failure to maximize hypertrophy and strength. Therefore, this review aims to discuss the strengths and weaknesses of the current proximity to failure quantification methods. Further, we propose future directions for researchers and practitioners to quantify proximity to failure, including implementation of absolute velocity stops using individual average concentric velocity/RIR relationships. Finally, we provide guidance for reporting self-reported RIR regardless of the quantification method.
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Treinamento Resistido , Exercício Físico , Humanos , Hipertrofia , Força Muscular , Músculo Esquelético , Treinamento Resistido/métodosRESUMO
This study examined the accuracy of predicting a free-weight back squat and a bench press one-repetition maximum (1RM) using both 2- and 4-point submaximal average concentric velocity (ACV) methods. Seventeen resistance trained men performed a warm-up and a 1RM test on the squat and bench press with ACV assessed on all repetitions. The ACVs during the warm-up closest to 1.0 and 0.5m.s-1 were used in the 2-point linear regression forecast of the 1RM and the ACVs established at loads closest to 20, 50, 70, and 80% of the 1RM were used in the 4-point 1RM prediction. Repeated measures ANOVA and Bland-Altman and Mountain plots were used to analyze agreement between predicted and actual 1RMs. ANOVA indicated significant differences between the predicted and the actual 1RM for both the 2- and 4-point equations in both exercises (p<0.001). The 2-point squat prediction overestimated the 1RM by 29.12±0.07kg and the 4-point squat prediction overestimated the 1RM by 38.53±5.01kg. The bench press 1RM was overestimated by 9.32±4.68kg with the 2-point method and by 7.15±6.66kg using the 4-point method. Bland-Altman and Mountain plots confirmed the ANOVA findings as data were not tightly conformed to the respective zero difference lines and Bland-Altman plots showed wide limits of agreement. These data demonstrate that both 2- and 4-point velocity methods predicted the bench press 1RM more accurately than the squat 1RM. However, a lack of agreement between the predicted and the actual 1RM was observed for both exercises when volitional velocity was used.
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Delayed auditory feedback (DAF) causes asynchronies between perception and action that disrupt sequence production. Different delay lengths cause differing amounts of disruption that may reflect the phase location of feedback onsets relative to produced inter-response intervals, or the absolute temporal separation between actions and sounds. Two experiments addressed this issue by comparing the effects of traditional DAF, which uses a constant temporal separation, with delays that adjust temporal separation to maintain the phase location of feedback onsets within inter-response intervals. Participants played simple isochronous melodies on a keyboard, or tapped an isochronous beat, at three production rates. Disruption was best predicted by the phase location of feedback onsets, and diminished when feedback onsets formed harmonic phase ratios (phase synchrony). Both delay types led to similar effects. Different movement tasks (melody production versus tapping) led to slightly different patterns of disruption across phase that may relate to differing task demands. In general, these results support the view that perception and action are coordinated in relative rather than absolute time.