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 36(3): 608-614, 2022-Critical resistance (CR) is the highest sustainable resistance that can be completed for an extended number of repetitions. Exercise performed below (CR 215% ) 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 215% 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 215% 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 215% 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 215% 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 215% . 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.

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.

Succi, PJ, Dinyer-McNeely, TK, Voskuil, CC, Abel, MG, Clasey, JL, and Bergstrom, HC. Responses to exercise at the critical heart rate vs. the power output associated with the critical heart rate. J Strength Cond Res 37(12): 2362-2372, 2023-This study examined the physiological (volume of oxygen consumption [V Ȯ2 ], heart rate [HR], power output [PO], respiration rate [RR], muscle oxygen saturation [%SmO 2 ]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP and MMG AMP] and mean power frequency [EMG MPF and MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise anchored at the critical heart rate (CHR) vs. the PO associated with CHR (PCHR). Nine subjects (mean 6 SD; age 5 26 6 3 years) performed a graded exercise test and 4 constant PO trials to exhaustion at 85-100% of peak PO (PP) to derive CHR and PCHR on a cycle ergometer. Responses were recorded during trials at CHR (173 6 9 b•min 21 , time to exhaustion [T Lim ] 5 45.5 6 20.2 minutes) and PCHR (198 6 58 W, T Lim 5 21.0 6 17.8 minutes) and normalized to their respective values at PP in 10% intervals. There were significant (p # 0.05) mode (CHR vs. PCHR) 3 time (10%-100% T Lim ) interactions for all variables (p , 0.001-0.036) except MMG AMP (p . 0.05). Post hoc analyses indicated differences across time for CHR V Ȯ2 (%change 5 222 6 16%), PCHR

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.

Succi, PJ, Dinyer, TK, Byrd, MT, Voskuil, CC, and Bergstrom, HC. Application of V Ȯ2 to the critical power model to derive the critical V Ȯ2 . J Strength Cond Res 36(12): 3374-3380, 2022-The purposes of this study were to (a) determine whether the critical power (CP) model could be applied to V Ȯ2 to estimate the critical V Ȯ2 (CV Ȯ2 ) and (b) to compare the CV Ȯ2 with the V Ȯ2 at CP (V Ȯ2 CP), the ventilatory threshold (VT), respiratory compensation point (RCP), and the CV Ȯ2 without the V Ȯ2 slow component (CV Ȯ2 slow). Nine subjects performed a graded exercise test to exhaustion to determine V Ȯ2 peak, VT, and RCP. The subjects performed 4 randomized, constant power output work bouts to exhaustion. The time to exhaustion (T Lim ), the total work (W Lim ), and the total volume of oxygen consumed with (TV Ȯ2 ) and without the slow component (TV Ȯ2 slow) were recorded during each trial. The linear regressions of the TV Ȯ2 vs. T Lim , TV Ȯ2 slow vs. T Lim , and W Lim vs. T Lim relationship were performed to derive the CV Ȯ2 , CV Ȯ2 slow, 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 Ȯ2 (42.49 6 3.22 ml•kg 21 •min 21 ) was greater than VT (30.80 6 4.66 ml•kg 21 •min 21 ; p , 0.001), RCP (36.74 6 4.49 ml•kg 21 •min 21 ; p 5 0.001), V Ȯ2 CP (36.76 6 4.31 ml•kg 21 •min 21 ; p , 0.001), and CV Ȯ2 slow (38.26 6 2.43 ml•kg 21 •min 21 ; p , 0.001). However, CV Ȯ2 slow was not different than V Ȯ2 CP (p 5 0.140) or RCP (p 5 0.235). Thus, the CP model can be applied to V Ȯ2 to derive the CV Ȯ2 and theoretically is the highest metabolic steady state that can be maintained for an extended period without fatigue. Furthermore, the ability of the CV Ȯ2 to quantify the metabolic cost of exercise and the inefficiency associated with the V Ȯ2 slow component may provide a valuable tool for researchers and coaches to examine endurance exercise.