Dynamic Constant External Resistance Research Articles

Effects of High-Intensity, Eccentric-Only Muscle Actions on Serum Biomarkers of Collagen Degradation and Synthesis.

Neltner, TJ, Sahoo, PK, Smith, RW, Anders, JPV, Arnett, JE, Ortega, DG, Schmidt, RJ, Johnson, GO, Natarajan, SK, and Housh, TJ. Effects of high-intensity, eccentric-only muscle actions on serum biomarkers of collagen degradation and synthesis. J Strength Cond Res 37(9): 1729-1737, 2023-The purpose of this study was to examine the effects of high-intensity, eccentric-only muscle actions of the leg extensors on (a) serum biomarkers of collagen degradation (hydroxyproline [HYP] and C-terminal telopeptide of type I collagen [C1M]) and synthesis (pro-c1α1) and (b) the time course of changes in maximal voluntary isometric contraction (MVIC) and ratings of muscle soreness after the eccentric-only exercise bout. Twenty-five recreationally active men (mean ± SD: age = 21.2 ± 2.0 years) completed 5 sets of 10 bilateral, eccentric-only dynamic constant external resistance muscle actions of the leg extensors at a load of 110% of their concentric leg extension 1 repetition maximum. Analysis of variances (p < 0.05) and a priori planned pairwise comparisons using Bonferroni corrected (p < 0.0167) paired t tests were used to examine mean changes in blood biomarkers from baseline to 48 hours postexercise as well as in MVIC and soreness ratings immediately, 24 hours, and 48 hours postexercise. There were increases in HYP (3.41 ± 2.37 to 12.37 ± 8.11 μg·ml-1; p < 0.001) and C1M (2.50 ± 1.05 to 5.64 ± 4.89 μg·L-1; p = 0.003) from preexercise to 48 hours postexercise, but no change in pro-c1α1. Maximal voluntary isometric contraction declined immediately after the exercise bout (450.44 ± 72.80 to 424.48 ± 66.67 N·m; p = 0.002) but recovered 24 hours later, whereas soreness was elevated immediately (6.56 ± 1.58; p < 0.001), 24 hours (3.52 ± 1.53; p < 0.001), and 48 hours (2.60 ± 1.32; p = 0.001) postexercise. The eccentric-only exercise bout induced increases in collagen degradation but had no effect on collagen synthesis. These findings provide information for clinicians to consider when prescribing exercise after an acute injury or surgery.

Intentionally Slow Concentric Velocity Resistance Exercise and Strength Adaptations: A Meta-Analysis.

Hermes, MJ and Fry, AC. Intentionally slow concentric velocity resistance exercise and strength adaptations: a meta-analysis. J Strength Cond Res 37(8): e470-e484, 2023-Intentionally slow-velocity resistance exercise (ISVRE) is suggested by some to be equally or more effective than fast or traditional velocities for increasing muscular strength. The purpose of this meta-analysis was to assess the effect ISVRE has on strength adaptations compared with faster or traditional velocities, with subgroup analyses exploring age, sex, and training status as confounding factors on the influence of velocity on strength adaptation. Eligible studies (n = 24) were required to be chronic (multiple weeks) randomized or nonrandomized comparative studies using dynamic constant external resistance for training and testing, and pre-post strength assessments. All studies examined healthy individuals (n = 625; fast or traditional n = 306, intentionally slow n = 319). A random-effects meta-analysis indicated a significant (p ≤ 0.05) effect in favor of fast training (effect size [ES] = 0.21, 95% confidence interval [CI] = 0.02-0.41, p = 0.03). Publication bias was noted through trim and fill analysis, with an adjusted effect size estimate of 0.32 (p < 0.001). Subgroup analyses indicated no difference between trained and untrained subjects (QM = 0.01, p = 0.93), and no difference between older and younger subgroups (QM = 0.09, p = 0.77), despite younger favoring faster (ES = 0.23, p = 0.049) and older not favoring either velocity (ES = 0.16, p = 0.46). Subgroup analysis also indicated women favored faster training (ES = 0.95, p < 0.001) in comparison to men (ES = 0.08, p = 0.58). Contrary to some previous reviews, these results indicate that chronic fast or traditional velocity resistance exercise increases muscular strength to a greater degree than ISVRE training. Resistance training velocity must be considered if strength is a desired outcome.

Electromyographic and mechanomyographic responses of the biceps brachii during concentric and eccentric muscle actions to failure at high and low relative loads.

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. 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. 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. 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.

Myoelectric activity during electromagnetic resistance alone and in combination with variable resistance or eccentric overload

The purpose of this study was to compare the effects of electromagnetic resistance alone, as well as in combination with variable resistance or accentuated eccentric methods, with traditional dynamic constant external resistance exercise on myoelectric activity during elbow flexion. The study employed a within-participant randomized, cross-over design whereby 16 young, resistance-trained male and female volunteers performed elbow flexion exercise under each of the following conditions: using a dumbbell (DB); using a commercial electromagnetic resistance device (ELECTRO); variable resistance (VR) using a setting on the device that attempts to match the level of resistance to the human strength curve, and; eccentric overload (EO) using a setting on the device that increases the load by 50% on the eccentric portion of each repetition. Surface electromyography (sEMG) was obtained for the biceps brachii, brachioradialis and anterior deltoid on each of the conditions. Participants performed the conditions at their predetermined 10 repetition maximum. " The order of performance for the conditions was counterbalanced, with trials separated by a 10-min recovery period. The sEMG was synced to a motion capture system to assess sEMG amplitude at elbow joint angles of 30°, 50°, 70°, 90°, 110°, with amplitude normalized to the maximal activation. The anterior deltoid showed the largest differences in amplitude between conditions, where median estimates indicated greater concentric sEMG amplitude (~ 7–10%) with EO, ELECTRO and VR compared with DB. Concentric biceps brachii sEMG amplitude was similar between conditions. In contrast, results indicated a greater eccentric amplitude with DB compared to ELECTRO and VR, but unlikely to exceed a 5% difference. Data indicated a greater concentric and eccentric brachioradialis sEMG amplitude with DB compared to all other conditions, but differences were unlikely to exceed 5%. The electromagnetic device tended to produce greater amplitudes in the anterior deltoid, while DB tended to produce greater amplitudes in the brachioradialis; amplitude for the biceps brachii was relatively similar between conditions. Overall, any observed differences were relatively modest, equating to magnitudes of ~ 5% and not likely greater than 10%. These differences would seem to be of minimal practical significance.

Changes in Neuromuscular Response Patterns After 4 Weeks of Leg Press Training During Isokinetic Leg Extensions.

Salmon, OF, Housh, TJ, Hill, EC, Keller, JL, Anders, JPV, Johnson, GO, Schmidt, RJ, and Smith, CM. Changes in neuromuscular response patterns after 4 weeks of leg press training during isokinetic leg extensions. J Strength Cond Res 37(7): e405-e412, 2023-The purpose of this study was to identify velocity-specific changes in electromyographic root mean square (EMG RMS), EMG frequency (EMG MPF), mechanomyographic RMS (MMG RMS), and MMG MPF during maximal unilateral isokinetic muscle actions performed at 60° and 240°·s -1 velocities within the right and left vastus lateralis (VL) after 4 weeks of dynamic constant external resistance (DCER) bilateral leg press training. Twelve resistance-trained men (age: mean ± SD = 21.4 ± 3.6 years) visited the laboratory 3d·wk -1 to perform resistance training consisting of 3 sets of 10 DCER leg presses. Four, three-way analysis of variance were performed to evaluate changes in neuromuscular responses (EMG RMS, EMG MPF, MMG RMS, and MMG MPF) from the right and left VL during 1 single-leg maximal isokinetic leg extension performed at 60° and 240°·s -1 before and after 4 weeks of DCER leg press training ( p < 0.05). The results indicated a 36% increase in EMG RMS for the right leg, as well as a 23% increase in MMG RMS and 10% decrease in MMG MPF after training, collapsed across velocity and leg. In addition, EMG RMS was 65% greater in the right leg than the left leg following training, whereas EMG MPF was 11% greater for the left leg than the right leg throughout training. Thus, 4 weeks of DCER leg press training provides sufficient stimuli to alter the neuromuscular activation process of the VL but not velocity-specific neuromuscular adaptations in trained males.

Load-Specific Performance Fatigability, Coactivation, and Neuromuscular Responses to Fatiguing Forearm Flexion Muscle Actions in Women.

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.

Quadriceps electromyography during flywheel-based inertial training (FIT) and dynamic constant external resistance (DCER) squats at similar tempo

ABSTRACT Flywheel-based iso-inertial training (FIT) has been purported to provide enhanced adaptations to muscle overload compared to dynamic constant external resistance (DCER), but previous studies have not controlled for exercise intensity. We compared quadriceps electromyography (EMG) amplitude between FIT- and DCER-squats with similar tempo. Eleven (5 M and 6F) resistance-trained participants completed sets of five maximal velocity FIT (0.025 kg∙m2) and DCER (55 ± 15 %1RM) squats. Sagittal plane knee joint angles and surface EMG activity of the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) were measured. Repetition time and peak knee angles were similar between FIT and DCER squats. Mean knee angular velocity during the concentric (122.2 ± 23.6 vs. 108.9 ± 22.9, p = 0.022, Cohen’s D: 0.820), but not eccentric, phase was significantly greater during FIT. Peak VM (210.4 ± 49.3 vs. 177.5 ± 56.3 %MVIC, p = 0.001; Cohen’s D: 1.416), but not VL or RF, EMG amplitude was significantly greater in FIT compared to DCER. Mean EMG amplitude was significantly (p < 0.001) greater during the concentric than the eccentric phase for the VL and VM but not RF. Mean EMG amplitude was not significantly different between modes during either the concentric or eccentric phase. Quadriceps EMG amplitude is largely similar between FIT and DCER squats when matched for movement velocity.

Acute Effects of Anodal Transcranial Direct Current Stimulation in Resistance and Power Exercises: A Brief Review for Coaches and Practitioners

ABSTRACT The purpose of this brief review is to provide information about the effects of transcranial direct current stimulation (tDCS) on performance in resistance and power exercises commonly used by the strength and conditioning community. The authors aimed to identify all publications investigating the effects of tDCS on performance with dynamic constant external resistance and power exercises. The performance was analyzed based on the training volume, as the number of repetitions performed in an absolute or relative load (1 RM—%). In addition, the peak power output was also analyzed as a secondary outcome. Based on the eligibility criteria, 13 studies were found. The results showed that applying anodal tDCS on the left dorsolateral prefrontal cortex increased the training volume in exercises commonly used by the strength and conditioning community. However, anodal tDCS does not increase peak power output in upper and lower limbs. A discussion integrating tDCS into the resistance training based on the particular stimulated area was provided. Furthermore, this review provided some practical recommendations for the application of tDCS by coaches and practitioners of strength and conditioning.

The Effects of Short-Term Resistance Training and Subsequent Detraining on Neuromuscular Function, Muscle Cross-Sectional Area, and Lean Mass

PurposeTo examine and compare the effects of three days of dynamic constant external resistance (DCER) and isokinetic (ISOK) training and subsequent detraining on thigh muscle cross-sectional area (TMCSA) and thigh lean mass (TLM), ISOK peak torque (PT), DCER strength, isometric force, muscle activation, and percent voluntary activation (%VA).MethodsThirty-one apparently-healthy untrained men (mean ± SD age = 22.2 ± 4.2 years; body mass = 77.9 ± 12.9 kg; height = 173.9 ± 5.4 cm) were randomly assigned to a DCER training group (n = 11), ISOK training group (n = 10) or control (CONT) group (n = 10). Subjects visited the laboratory eight times. The first visit was a familiarization session, the second visit was a pre-training assessment, the subsequent three visits were for unilateral training of the quadriceps (if assigned to a training group), and the last three visits were the post-training assessments conducted at three days, one week, and two weeks after training ended.ResultsDCER strength increased from pre- to post-training assessment 1 in both limbs for the DCER group only, and remained elevated during post-training assessments 2 and 3 (P < 0.05). In addition, surface EMG for the biceps femoris was higher at post-training assessment 3 than at the pre-training assessment, and post-training assessments 1 and 2 (P < 0.05). No other training-related changes were found.ConclusionThe primary finding of this study was that DCER strength of the trained and untrained limbs can be increased with three days of training. This has important implications for injury rehabilitation, where in the initial period post-injury strength gains on an injured limb can possibly be obtained with short-term contralateral resistance training.

Isolated Joint Block Progression Training Improves Leaping Performance in Dancers.

The purpose of this study was to investigate the effect of a 12-week ankle-specific block progression training program on saut de chat leaping performance [leap height, peak power (PP), joint kinetics and kinematics], maximal voluntary isometric plantar flexion (MVIP) strength, and Achilles tendon (AT) stiffness. Dancers (training group n = 7, control group n = 7) performed MVIP at plantarflexed (10◦) and neutral ankle positions (0◦) followed by ramping isometric contractions equipped with ultrasound to assess strength and AT stiffness, respectively. Dancers also performed saut de chat leaps surrounded by 3-D motion capture atop force platforms to determine center of mass and joint kinematics and kinetics. The training group then followed a 12-week ankle-focused program including isometric, dynamic constant external resistance, accentuated eccentric loading, and plyometric training modalities, while the control group continued dancing normally. We found that the training group's saut de chat ankle PP (59.8%), braking ankle stiffness (69.6%), center of mass PP (11.4%), and leap height (12.1%) significantly increased following training. We further found that the training group's MVIP significantly increased at 10◦ (17.0%) and 0◦ (12.2%) along with AT stiffness (29.6%), while aesthetic leaping measures were unchanged (peak split angle, mean trunk angle, trunk angle range). Ankle-specific block progression training appears to benefit saut de chat leaping performance, PP output, ankle-joint kinetics, maximal strength, and AT stiffness, while not affecting kinematic aesthetic measures. We speculate that the combined training blocks elicited physiological changes and enhanced neuromuscular synchronization for increased saut de chat leaping performance in this cohort of dancers.

Applications of the Critical Power Model to Dynamic Constant External Resistance Exercise: A Brief Review of the Critical Load Test

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.

Neuromuscular responses at acute moderate and severe hypoxic exposure during fatiguing exercise of the biceps brachii.

PurposeThe present study examined acute normobaric hypoxic exposure on the number of repetitions to failure, electromyographic (EMG) repetition duration (Time), EMG root mean square (RMS) and EMG mean power frequency (MPF) during biceps brachii (BB) dynamic constant external resistance (DCER) exercise.MethodsThirteen subjects performed two sets of fatiguing DCER arm curl repetitions to failure at 70% of their one repetition maximum under normoxic (NH), moderate hypoxia FiO2 = 15% (MH) and severe hypoxia FiO2 = 13% (SH). Electromyography of the BB was analyzed for EMG Time, EMG RMS, and EMG MPF. Repetitions were selected as 25%, 50%, 75%, and 100% of total repetitions (%Fail) completed. Pulse oximetry (SpO2) was measured pre-and post-fatigue.ResultsThere was no significant three-way (Condition x Set x %Fail) or two-way (Condition x Set) interaction for any variable. The number of repetitions to failure significantly decreased from (mean ± SEM) 18.2 ± 1.4 to 9.5 ± 1.0 with each Set. In addition, EMG Time increased (25% < 50%<75% < 100%), EMG RMS decreased (50% > 75%>100%), and EMG MPF decreased (75% > 100%) as a result of fatiguing exercise. SpO2 was lower during MH (Δ5.3%) and SH (Δ9.2%) compared to NH and as a result of fatiguing exercise increased only in MH (Δ2.1%) and SH (Δ5.7%).ConclusionThe changes in BB EMG variables indicated exercise caused myoelectric manifestations of fatigue, however, acute moderate or severe hypoxia had no additional influence on the rate of fatigue development or neuromuscular parameters.

When Task Constraints Delimit Movement Strategy: Implications for Isolated Joint Training in Dancers.

Athletic performance is determined by numerous variables that cannot always be controlled or modified. Due to aesthetic requirements during sports such as dance, body alignment constrains possible movement solutions. Increased power transference around the ankle-joint, coupled with lower hip-joint power, has become a preferential strategy in dancers during leaps and may be considered a dance-specific stretch-shortening cycle (SSC) demand. Newell's theoretical model of interacting constraints includes organismic (or individual), environmental, and task constraints describing the different endogenous and exogenous constraints individuals must overcome for movement and athletic performance. The unique task constraints imposed during dance will be used as a model to justify an isolated joint, single-targeted block progression training to improve physical capacity within the context of motor behavior to enhance dance-specific SSC performance. The suggested ankle-specific block progression consists of isometrics, dynamic constant external resistance, accentuated eccentrics, and plyometrics. Such programming tactics intend to collectively induce tendon remodeling, muscle hypertrophy, greater maximal strength, improved rate of force development, increased motor unit firing rates, and enhanced dynamic movement performance. The current perspective provides a dualistic approach and justification (physiological and motor behavioral) for specific strength and conditioning programming strategies. We propose implementation of a single-targeted block progression program, inspired by Newell's theoretical model of interacting constraints, may elicit positive training adaptations in a directed manner in this population. The application of Newell's theoretical model in the context of a strength and conditioning supports development of musculoskeletal properties and control and is conceptually applicable to a range of athletes.

Variable resistance training versus traditional weight training on the reflex pathway following four weeks of leg press training

Purpose: The purpose of this study was to examine the changes in reflex-electromechanical delay (EMD) as a result of 2- and 4-wks of variable resistance training (VRT) or dynamic constant external resistance (DCER) leg press training.Material and Methods: Thirty-six men were randomised into either the Control, DCER, or VRT groups. The DCER and VRT groups performed 3 sets of 10 leg press repetitions 3-d·wk−1 for 4-wks. Reflex-EMD was measured at Baseline, Week-2, and Week-4.Results: The reflex-EMD durations decreased from Baseline at Week-2 and Week-4 for the VRT group, but not the DCER or Control groups. The reflex response < electrochemical process < mechanical process < total reflex-EMD for all groups.Conclusions: VRT elicited greater reflex adaptations compared to DCER training which indicated that VRT may be beneficial to incorporate into training or physical therapy programmes for pilots, soldiers, elderly, athletes, or professions that require quick reflexes and response times.

Sex Comparisons for Very Short-Term Dynamic Constant External Resistance Training.

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.

Effects of Very Short-Term Dynamic Constant External Resistance Exercise on Strength and Barbell Velocity in Untrained Individuals

Effects of Very Short-Term Dynamic Constant External Resistance Exercise on Strength and Barbell Velocity in Untrained Individuals

Changes in electromechanical delay during fatiguing dynamic muscle actions.

The onsets of the electromyographic (EMG) signal, mechanomyographic (MMG) signal, and force production were used to identify voluntary electromechanical delay (EMD) during maximal and submaximal leg extensions. Twelve men performed 30% 1-repetition-maximum concentric, dynamic constant external resistance leg extensions to failure. The time periods for the onsets of EMG to MMG (EMDE-M ), MMG to force (EMDM-F ), and EMG to force (EMDE-F ) were assessed before, during, and after testing. Pretest vs. posttest assessments indicated approximately equal contributions from excitation-contraction coupling (EMDE-M ) and series elastic component (EMDM-F ) to the overall EMDE-F . During the workbout, excitation-contraction coupling failure and increases in the compliance of the series elastic component began at 40% and 30% of the repetitions to failure, respectively, and continued to failure. Increases in the series elastic component (EMDM-F ) began to affect EMDE-F before excitation-contraction coupling failure (EMDE-M ), and both contributed to EMDE-F throughout the remainder of the fatiguing workbout. Muscle Nerve 56: 315-320, 2017.

Dynamic versus isometric electromechanical delay in non-fatigued and fatigued muscle: A combined electromyographic, mechanomyographic, and force approach

This study used a combined electromyographic, mechanomyographic, and force approach to identify electromechanical delay (EMD) from the onsets of the electromyographic to force signals (EMDE-F), onsets of the electromyographic to mechanomyogrpahic signals (EMDE-M), and onsets of mechanomyographic to force signals (EMDM-F). The purposes of the current study were to examine: (1) the differences in EMDE-F, EMDE-M, and EMDM-F from the vastus lateralis during maximal, voluntary dynamic (1 repetition maximum [1-RM]) and isometric (maximal voluntary isometric contraction [MVIC]) muscle actions; and (2) the effects of fatigue on EMDE-F, EMDM-F, and EMDE-M. Ten men performed pretest and posttest 1-RM and MVIC leg extension muscle actions. The fatiguing workbout consisted of 70% 1-RM dynamic constant external resistance leg extension muscle actions to failure. The results indicated that there were no significant differences between 1-RM and MVIC EMDE-F, EMDE-M, or EMDM-F. There were, however, significant fatigue-induced increases in EMDE-F (94% and 63%), EMDE-M (107%), and EMDM-F (63%) for both the 1-RM and MVIC measurements. Therefore, these findings demonstrated the effects of fatigue on EMD measures and supported comparisons among studies which examined dynamic or isometric EMD measures from the vastus lateralis using a combined electromyographic, mechanomyographic, and force approach.

Time Course of Changes in Neuromuscular Responses at 30% versus 70% 1 Repetition Maximum during Dynamic Constant External Resistance Leg Extensions to Failure

Time Course of Changes in Neuromuscular Responses at 30% versus 70% 1 Repetition Maximum during Dynamic Constant External Resistance Leg Extensions to Failure

Effects of Short-Term Dynamic Constant External Resistance Training and Subsequent Detraining on Strength of the Trained and Untrained Limbs: A Randomized Trial.

Short-term resistance training has been shown to increase isokinetic muscle strength and performance after only two to nine days of training. The purpose of this study was to examine the effects of three days of unilateral dynamic constant external resistance (DCER) training and detraining on the strength of the trained and untrained legs. Nineteen men were randomly assigned to a DCER training group or a non-training control group. Subjects visited the laboratory eight times, the first visit was a familiarization session, the second visit was a pre-training assessment, the subsequent three visits were for training sessions (if assigned to the training group), and the last three visits were post-training assessments 1, 2, and 3 (i.e., 48 h, 1 week, and 2 weeks after the final training session). Strength increased in both trained and untrained limbs from pre- to post-training assessment 1 for the training group and remained elevated at post-training assessments 2 and 3 (p ≤ 0.05). No changes were observed in the control (p > 0.05). Possible strength gains from short-term resistance training have important implications in clinical rehabilitation settings, sports injury prevention, as well as other allied health fields such as physical therapy, occupational therapy, and athletic training.