Resistance exercise training and the motor unit

Herda, Trent J.

doi:10.1007/s00421-022-04983-7

Cited by 16 publications

(11 citation statements)

References 73 publications

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“…Such findings of non-uniform changes in firing rates following resistance training have been documented (Watanabe et al, 2018(Watanabe et al, , 2020 and suggest that earlier recruited motor units are more susceptible to increasing their firing rates after resistance training interventions. However, general changes in motor unit firing rates after resistance training remain mixed due to the variability of training interventions and muscle contraction types used to record motor units (Herda, 2022). Given the specific scope of the training intervention, low-RIR training in the exercises included in this study may influence the firing rates of earlier recruited motor units.…”

Section: Discussionmentioning

confidence: 99%

The effects of resistance training to near failure on strength, hypertrophy, and motor unit adaptations in previously trained adults

Ruple

Plotkin

Smith

et al. 2023

Physiological Reports

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Limited research exists examining how resistance training to failure affects applied outcomes and single motor unit characteristics in previously trained individuals. Herein, resistance‐trained adults (24 ± 3 years old, self‐reported resistance training experience was 6 ± 4 years, 11 men and 8 women) were randomly assigned to either a low‐repetitions‐in‐reserve (RIR; i.e., training near failure, n = 10) or high‐RIR (i.e., not training near failure, n = 9) group. All participants implemented progressive overload during 5 weeks where low‐RIR performed squat, bench press, and deadlift twice weekly and were instructed to end each training set with 0–1 RIR. high‐RIR performed identical training except for being instructed to maintain 4–6 RIR after each set. During week 6, participants performed a reduced volume‐load. The following were assessed prior to and following the intervention: (i) vastus lateralis (VL) muscle cross‐sectional area (mCSA) at multiple sites; (ii) squat, bench press, and deadlift one‐repetition maximums (1RMs); and (iii) maximal isometric knee extensor torque and VL motor unit firing rates during an 80% maximal voluntary contraction. Although RIR was lower in the low‐ versus high‐RIR group during the intervention (p < 0.001), total training volume did not significantly differ between groups (p = 0.222). There were main effects of time for squat, bench press, and deadlift 1RMs (all p‐values < 0.05), but no significant condition × time interactions existed for these or proximal/middle/distal VL mCSA data. There were significant interactions for the slope and y‐intercept of the motor unit mean firing rate versus recruitment threshold relationship. Post hoc analyses indicated low‐RIR group slope values decreased and y‐intercept values increased after training suggesting low‐RIR training increased lower‐threshold motor unit firing rates. This study provides insight into how resistance training in proximity to failure affects strength, hypertrophy, and single motor unit characteristics, and may inform those who aim to program for resistance‐trained individuals.

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Section: Discussionmentioning

confidence: 99%

The effects of resistance training to near failure on strength, hypertrophy, and motor unit adaptations in previously trained adults

Ruple

Plotkin

Smith

et al. 2023

Physiological Reports

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“…Individuals who have scapular dyskinesis from the raising phase may require treatment strategies that bring the MU behavior closer to that of the Normal group as the recruitment size of MU of the lower trapezius and serratus anterior and the ring rate to the serratus anterior may be reduced. High-intensity resistance training may be recommended for MU size [59,60], but it is unclear if it can be applied to the lower trapezius and serratus anterior. Treatment to improve the ring rate has not been reported to date.…”

Section: Discussionmentioning

confidence: 99%

Motor unit behavior of the lower trapezius and serratus anterior in individuals with scapular dyskinesis

Kuniki

Iwamoto

Konishi

et al. 2023

Preprint

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Scapular dyskinesis results from weakness of the lower trapezius and serratus anterior, but no studies have investigated the motor unit (MU) behavior required for muscle exertion. This study aimed to classify scapular dyskinesis into raising (SDR) and lowering (SDL) phases and investigated the MU behaviors of the lower trapezius and serratus anterior. Fifty healthy young subjects underwent a scapular dyskinesis test and were divided into Normal, SDR, and SDL groups. The subjects performed submaximal voluntary contractions of the lower trapezius and serratus anterior, and surface electromyography signals were decomposed into the MU action potential amplitude (MUAPAMP), mean firing rate (MFR), and recruitment threshold (RT). The average MUAPAMP and MFR and the slopes and y-intercepts of the linear MUAPAMP-RT and MFR-RT were compared. The MUAPAMP-RT slopes in the lower trapezius (p = 0.049, r = 0.420) and serratus anterior were smaller (p = 0.010, r = 0.490) and the MFR-RT y-intercept in the serratus anterior was lower (p = 0.004, r = 0.540) in the SDR group than in the Normal group. Differences in other parameters between the SDL and Normal groups were not significant. Lower trapezius and serratus anterior MU behavioral changes may cause scapular dyskinesis in the raising phase.

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“…5,7,13 Therefore, an inverse relationship exists between firing rates and recruitment thresholds (RTs) when MU behavior is observed separately for each individual and contraction. 6,14 It is theorized that this motor control scheme is not designed to enhance force production, but rather maximize the balance between MU force output and endurance. 15,16 There is evidence that the central nervous system provides a common excitation input to the MU pool, rather than controlling the firing of individual MUs during voluntary contractions.…”

Section: Introductionmentioning

confidence: 99%

“…It is suggested that regressing firing rates across RTs for each subject to account for the inter-individual variability of MU properties should be the preferred analytical approach. 14 However, intramuscular electrodes typically yield ≤4 MUs during a single contraction, which does not allow for the quantification of MU recruitment and firing rate patterns. Furthermore, the lower MU twitch forces resulting from sex-related fiber-type differences may necessitate a greater level of input excitation (normalized electromyographic amplitude [N-EMG RMS ]) to the MU pool for females (p = 0.018-0.031) with the slopes for the MUAP AMP , IFR, and MFR versus RT relationships at 70% MVC (r = −0.599-0.585).…”

Section: Introductionmentioning

confidence: 99%

“…[32][33][34] Examining MU properties in relation to their RTs may account for the variability when comparing recruitment and firing rate patterns on a subject-to-subject basis. 14 In addition, correlations were calculated to examine the relationship of type I %MHC isoform content of the VL and MU properties for the moderate-and highintensity contraction.…”

Section: Introductionmentioning

confidence: 99%

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Sex‐related differences in motor unit behavior are influenced by myosin heavy chain during high‐ but not moderate‐intensity contractions

et al. 2023

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AimsMotor unit recruitment and firing rate patterns of the vastus lateralis (VL) have not been compared between sexes during moderate‐ and high‐intensity contraction intensities. Additionally, the influence of fiber composition on potential sex‐related differences remains unquantified.MethodsEleven males and 11 females performed 40% and 70% maximal voluntary contractions (MVCs). Surface electromyographic (EMG) signals recorded from the VL were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMP), initial firing rates (IFRs), mean firing rates (MFRs), and normalized EMG amplitude (N‐EMGRMS) at steady torque were analyzed. Y‐intercepts and slopes were calculated for MUAPAMP, IFR, and MFR versus RT relationships. Type I myosin heavy chain isoform (MHC) was determined with muscle biopsies.ResultsThere were no sex‐related differences in MU characteristics at 40% MVC. At 70% MVC, males exhibited greater slopes (p = 0.002) for the MUAPAMP, whereas females displayed greater slopes (p = 0.001–0.007) for the IFR and MFR versus RT relationships. N‐EMGRMS at 70% MVC was greater for females (p < 0.001). Type I %MHC was greater for females (p = 0.006), and was correlated (p = 0.018–0.031) with the slopes for the MUAPAMP, IFR, and MFR versus RT relationships at 70% MVC (r = −0.599–0.585).ConclusionBoth sexes exhibited an inverse relationship between MU firing rates and recruitment thresholds. However, the sex‐related differences in MU recruitment and firing rate patterns and N‐EMGRMS at 70% MVC were likely due to greater type I% MHC and smaller twitch forces of the higher threshold MUs for the females. Evidence is provided that muscle fiber composition may explain divergent MU behavior between sexes.

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Resistance exercise training and the motor unit

Cited by 16 publications

References 73 publications

The effects of resistance training to near failure on strength, hypertrophy, and motor unit adaptations in previously trained adults

The effects of resistance training to near failure on strength, hypertrophy, and motor unit adaptations in previously trained adults

Motor unit behavior of the lower trapezius and serratus anterior in individuals with scapular dyskinesis

Sex‐related differences in motor unit behavior are influenced by myosin heavy chain during high‐ but not moderate‐intensity contractions

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