1,721,102 research outputs found
Novel insights into skeletal muscle function by mechanomyography: from the laboratory to the field
No full textPurpose: The review aimed to provide a wider overview on the new application fields of MMG signal. A particular emphasis on measurements reliability and sensitivity was also given.Methods: Five electronic databases were searched for eligible studies published between 2000 and 2014. Two authors assessed selected articles. Several domains (sensor types, participants’ characteristics, experimental protocols, investigated muscle/s, measured parameters, and main results) were extracted for analysis. From a total of 1326 citations, 170 were selected for evaluation and 111 studies were identified.Results: From the analysis of the literature it resulted that MMG signal (a) has a high level of reliability, especially for the parameters calculated during isometric contractions; (b) can be used to examine muscle mechanical activation and motor unit recruitment strategies under several types of exercise paradigms; (c) is influenced by the mechanical characteristics of cross-bridges and series elastic components, and may provide deeper insights into their behaviour under several physiological models; (d) could be a useful biomarker for triggering orthosis or multifunction access devices, and for the evaluation of patients presenting alterations in muscle function.Conclusions: The MMG approach has been proficiently applied in several fields ascribable to both exercise physiology and clinical settings. This approach can provide deeper insights into muscle mechanical behaviour under several physiological models and for the evaluation of patients with altered muscle function
Effects of acute passive stretching on mean response time during an incremental ramp test
No full textThe effects of stretching administration on aerobic performance have not been yet extensively investigated. This study aims to assess the acute effects of pre-exercise passive stretching on the mean response time (MRT), i. e., the temporal interval between the increase in work rate and the rise in pulmonary oxygen uptake (V̇O2), during an incremental ramp test. Eight physically active males (age 23 ± 4 years; stature 1. 74 ± 0. 13 m; body mass 71 ± 7 kg; mean ± standard deviation) performed two incremental ramp tests (25 W/min) of 5 min, with and without pre-exercise stretching. During tests, we measured V̇O2 and other metabolic and cardiorespiratory parameters. Before and after stretching the joint mobility and maximum voluntary contraction (MVC) of the knee extensor muscles were evaluated. Stretching reduced MVC by 9 % (P < 0. 05) and lengthened MRT by 34 % (P < 0. 05). These results are compatible with an altered motor unit activation pattern due to mechanical and neuromuscular changes of the muscle-tendon unit induced by stretching, which lead to an altered aerobic response to ramp exercise
The influence of mouth guard usage on neuromuscular activation and performance
Full text linkAim: The aim of this study was to investigate the effects of a commercially-available mouth guard (BRUX Mod. Sport) on neuromuscular activation and force capacity. Mouth guards, indeed, are commonly used in different sports to prevent injuries, but it is not yet clear whether they can influence the force expression and some athletes remain wary of the perceived potential performance detriments using them.
Method: Ten participants completed a balanced randomized study with (S-MG) and without (Con) a sport mouth guard. Each participant performed two tests, with elbow flexors and knee extensors muscles: 1-min contraction at 100% of maximum voluntary contraction (MVC) and an 80% MVC contraction until exhaustion. During 80% MVC, the time of force within the target (t-target) and the coefficient of variation (CV) of the force signal were calculated. During 100% MVC, force decay (F%) and the root mean square (RMS) of the electromyogram (EMG) were calculated.
Results: MVC values in S-MG were significantly higher than in Con in the elbow flexors (P<0.05). No differences was found in knee extensors muscles.
At 80% MVC, no differences in t-target values were observed between Con and S-MG for both muscles group. Conversely, in knee extensors muscles, CV was significantly lower in S-MG compared to Con. During 1-min at 100% MVC contraction, F% was significantly lower in S-MG than in Con in the elbow-flexors (P<0.05) .
Conclusion: Overall, these findings indicate that despite neuromuscular activation was not affected, S-MG usage increased maximum force production, endurance time and force stability, especially in the upper limb muscles.
References
- Dunn-Lewis, C, Luk, H-Y, Comstock, BA, Szivak, TK, Hooper, DR, Kupchak, BR, Watts, AM, Putney, BJ, Hydren, JR, Volek, JS, Denegar, CR, and Kraemer, WJ. The effects of a customized over-the-counter mouth guard on neuromuscular force and power production in trained men and women. J Strength Cond Res 26(4): 1085–1093, 2012.
- Cetin, C, Kececi, AD, Erdogan, A, and Baydar, ML. Influence of custom-made mouth guards on strength, speed and anaerobic performance of taekwondo athletes. Dent Traumatol 25: 272–276, 2009.
- Bourdin M, Brunet-Patru I, Hager PE, Allard Y, Hager JP, Lacour JR et al. Influence of maxillary mouthguards on physiological parameters. Med Sci Sports Exerc 38:1500–4,2006
Reliability of the Electromechanical Delay Components Assessment during the Relaxation Phase
Full text linkThe study aimed to assess by an electromyographic (EMG), mechanomyographic (MMG), and force-combined approach the electrochemical and mechanical components of the overall electromechanical delay during relaxation (R-EMD). Reliability of the measurements was also assessed. To this purpose, supramaximal tetanic stimulations (50 Hz) were delivered to the gastrocnemius medialis muscle of 17 participants. During stimulations, the EMG, MMG, and force signals were detected, and the time lag between EMG cessation and the beginning of force decay (∆t EMG-F, as temporal indicators of the electrochemical events) and from the initial force decrease to the largest negative peak of MMG signal during relaxation (∆t F-MMG, as temporal indicators of the mechanical events) was calculated, together with overall R-EMD duration (from EMG cessation to the largest MMG negative peak during relaxation). Peak force (pF), half relaxation time (HRT), and MMG peak-to-peak during the relaxation phase (R-MMG p-p) were also calculated. Test-retest reliability was assessed by Intraclass Correlation Coefficient (ICC). With a total R-EMD duration of 96.9 ± 1.9 ms, ∆t EMG-F contributed for about 24% (23.4 ± 2.7 ms) while ∆t F-MMG for about 76% (73.5 ± 3.2 ms). Reliability of the measurements was high for all variables. Our findings show that the main contributor to R-EMD is represented by the mechanical components (series elastic components and muscle fibres behaviour), with a high reliability level for this type of approach
Effects of fatigue on the electromechanical delay components in gastrocnemius medialis muscle
No full textPURPOSE:
Under electrically evoked contractions, the time interval between the onset of the stimulation pulse (Stim) and the beginning of force (F) development can be partitioned (DelayTOT), by an electromyographic (EMG), mechanomyographic (MMG) and F combined approach, into three components each containing different parts of the electrochemical and mechanical processes underlying neuromuscular activation and contraction. The aim of the study was to evaluate inter- and intra-operator reliability of the measurements and to assess the effects of fatigue on the different DelayTOT components.
METHODS:
Sixteen participants underwent two sets of tetanic stimulations of the gastrocnemius medialis muscle, with 10 min of rest in between. After a fatiguing protocol of 120 s, tetanic stimulations were replicated. The same protocol was repeated on a different day. Stim, EMG, MMG and F signals were recorded during contraction. DelayTOT and its three components (between Stim and EMG, Δt Stim-EMG; between EMG and MMG, Δt EMG-MMG and between MMG and F, Δt MMG-F) were calculated.
RESULTS:
Before fatigue, DelayTOT, Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F lasted 27.5 ± 0.9, 1.4 ± 0.1, 9.2 ± 0.5 and 16.8 ± 0.7 ms, respectively. Fatigue lengthened DelayTOT, Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F by 18, 7, 16 and 22 %, respectively. Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F contributed to DelayTOT lengthening by 2, 27 and 71 %, respectively. Reliability was always from high to very high.
CONCLUSIONS:
The combined approach allowed a reliable calculation of the three contributors to DelayTOT. The effects of fatigue on each DelayTOT component could be precisely assessed
DelayTOT and its subcomponents: a new approach for the electromechanical delay partitioning before and after a fatiguing protocol during electrically-evoked contractions
No full textAim: DelayTOT is the time lag between the onset of the electrical stimulation (Stim) and the force (F) development. During this time frame the following several mechanisms take place to transduce the electrical pulse into a mechanical events: i) the propagation of the action potential from the site of excitation throughout the inner branches of the axons and from the pre- to the post-synaptic membrane of the motor endplate; ii) the propagation of the action potential along the sarcolemma, the dihydropyridine and ryanodine interaction and the excitation-contraction (E-C) coupling processes and iii) the tensioning of the muscle-tendon unit (MTU) with the force development. Several factors influence the neuromuscular processes involved in the muscular contraction among which temperature, diseases, joint angle, and fatigue. A combined electromyogram (EMG) and mechanomyogram (MMG) approach during electrically-evoked contractions allows to partition DelayTOT in three latencies, a synaptic, E-C coupling and mechanical component, and to evaluate each component in different conditions. The study aims to assess the DelayTOT and its subcomponents in fresh and fatigued muscles during stimulated contractions of the gastrocnemius medialis muscle.
Method: Sixteen healthy students underwent two sessions (SA and SB) of three tetanic stimulations (50 Hz, 3s), with 5 min of rest in between. Moreover, after a fatiguing protocol (35 Hz, 120s), three tetanic stimulations were administered after 1, 2 and 7 minute, respectively. Stimulation current (Stim), surface electromyogram (EMG), mechanomyogram (MMG) and force signal (F) were acquired. The DelayTOT (the time lag between Stim and F development), the synaptic delay (∆t Stim-EMG, the time interval from Stim onset and the EMG artefact), the E-C coupling latency (∆t EMG-MMG, the time frame between the EMG artefact and the MMG onset) and the mechanical component (∆t MMG-F, the delay from the MMG onset and the F development) were calculated and expressed as mean ± standard error (SE). The statistical analysis were performed using one-way ANOVA for repeated measures and post-hoc multiple comparison.
Results: DelayTOT, Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F were 27.5±0.9 ms, 1.4±0.1 ms, 9.2±0.5 ms and 16.8±0.7 ms, respectively. Fatigue lengthened DelayTOT, Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F by about 18%, 7%, 16% and 22%, respectively (P<0.05). Δt Stim-EMG, Δt EMG-MMG and Δt MMG-F contributed to DelayTOT increase by about 2%, 27% and 71%, respectively. Reliability analysis showed from high to very high values.
Conclusion: The combined approach allowed a reliable calculation of synaptic, E-C coupling and mechanical contribution to DelayTOT. Moreover, the effects of fatigue on each DelayTOT component is differently distributed and could be precisely assessed
Fatigue and cooling alter skeletal muscle electromechanical characteristics during isometric contractions
No full textThe effects of mouth guard usage on neuromuscular activation and muscle performance
No full textTo assess the effects of a commercially-available mouth guard on neuromuscular activation and muscle performance, 8 participants completed a balanced and randomized study with (S-MG) and without (Con) a sport mouth guard. Each participant performed two tests with both elbow flexors and knee extensors muscles: a 1-min contraction at 100% of maximum voluntary contraction (MVC) and an 80% MVC until exhaustion. During 100% MVC, force decay (F%) and the root mean square (RMS) of the electromyogram (EMG) were calculated. During 80% MVC, the time the force target (t-target) and the coefficient of variation (CV) of the force signal were determined. MVC was significantly higher in S-MG than in Con in both muscle groups (P<0.05). F% was significantly lower in S-MG than in Con in the knee-extensors (61.1±1.7% and 68.9±1.3% in S-MG and Con, respectively; P<0.05) but not in the elbow flexors. At 80% MVC, higher t-target values were observed in S-MG compared to Con for the knee-extensors (18.1±2.5 s and 12.9±2.7 s in S-MG and Con, respectively; P<0.05), but not for the elbow flexors. CV was significantly lower in S-MG compared to Con in both muscle groups. These findings indicate that despite neuromuscular activation was not altered, S-MG usage increased maximum force production, endurance time and force stability, especially in the lower limb muscles
Effects of fatigue on the electromechanical delay during the relaxation phase: partitioning the contributors
Full text linkAim. Similarly to the contraction phase, also during the relaxation phase a latency between the cessation of muscle electrical activity and muscle mechanical return to resting condition can be observed (R-DelayTOT). By a combined electromyographic (EMG), mechanomyographic (MMG) and force (F) analysis, R-DelayTOT can be partitioned non-invasively into an electrochemical and two mechanical components. The aim of the study was twofold: (i) to assess the reliability of the measurement of R-DelayTOT components; and (ii) to evaluate the effects of fatigue on R-DelayTOT components.
Method. During tetanic stimulations, EMG, MMG and F signals were recorded from the gastrocnemius medialis muscle, both before and after fatigue. The time lag between EMG and MMG ripple cessations (R-Δt EMG-MMGR, electrochemical component of R-DelayTOT), between MMG ripple cessation and the onset of force decay (R-Δt MMGR-F, first mechanical component of R-DelayTOT), and between the onset of force decay and the maximum MMG negative peak (R-Δt F-MMGp-p, second mechanical component of R-DelayTOT) were calculated. For statistical analysis, a one-way ANOVA for repeated measures was utilised with post-hoc multiple comparisons. Reliability analysis was also performed.
Results. Before fatigue, R-Δt F-MMGp-p was the major contributor (61.9±1.7 ms, about 75%) to R-DelayTOT, while R-Δt EMG-MMGR and R-Δt MMGR-F accounted for 16% (13.3±1.2 ms) and 9% (7.5±1.0 ms), respectively. After fatigue, R-Δt EMG-MMGR and R-Δt MMGR-F increased by about 41% and 67%, respectively (P<0.05), whereas R-Δt F-MMGp-p did not change. The reliability of the measurement was from high to very high (range from 0.705 to 0.959) both before and after fatigue. Conclusion. These findings indicate that the present combined approach can provide reliable measurements of the different R-DelayTOT components during muscle relaxation. Fatigue altered the processes between neuromuscular activation cessation and the beginning of force decay, but had no effects on the second mechanical component, which is determined by cross-bridges detachment rate and series elastic components release
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