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Electrical and mechanical response of skeletal muscle to electrical stimulation after acute passive stretching in humans : an EMG and mechanomyographic (MMG) combined approach
No full textTwo mechanisms have been suggested to explain stretching-induced maximum force
depression: a mechanical alteration in the stretched muscle and an impairment of
neural activation. Electrical stimulation allows standardization of the level of
muscle activation without being limited by neural control. The aim of this study
was to evaluate the stretching-induced changes in the electrical and mechanical
properties of muscle during electrically elicited contractions. Twelve
participants (age 22 +/- 1 years; body mass 75 +/- 2 kg; stature 1.79 +/- 0.02 m;
mean +/- standard error) underwent six electrical stimulations of the medial
gastrocnemius muscle before and after stretching. During the contractions,
surface electromyogram (EMG) and mechanomyogram (MMG) were recorded
simultaneously together with force. After stretching we found: (i) no differences
in EMG parameters; (ii) MMG amplitude decreased by 4 +/- 1% (P < 0.05); and (iii)
the peak force, the peak rate of force development, and the acceleration peak of
force development decreased by 12 +/- 3%, 14 +/- 1%, and 24 +/- 5%, respectively
(P < 0.05). In conclusion, acute passive stretching did not change EMG properties
but altered the mechanical characteristics of the contracting muscle. Indeed,
muscle force-generating capacity and stiffness of the muscle-tendon unit were
significantly impaired
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 ventilatory pattern during prolonged cycle exercise
No full textPassive stretching, by inducing mechanical and chemical stimuli that activate receptors on the terminal end of group III and IV nerve fibres located within joints and muscle, may increase ventilation (VE) during exercise. The aim of the study was to assess the effects of an acute bout of passive stretching on the ventilatory pattern. Maximum oxygen uptake was determined in nine participants who then performed a sustained cycle exercise of high intensity (constant workload of 85% of the minimum power to elicit maximum oxygen uptake,W 85) with and without previous stretching. During the tests metabolic and respiratory parameters were recorded breath-by-breath. Time to exhaustion in the W 85 test was significantly shorter (-29%) with stretching. During the first 12 min of exercise the following parameters were significantly higher with stretching than without: oxygen uptake (+4%), ventilation (+9%), respiratory muscle power (+16%) and respiratory muscle oxygen uptake (+13%; P < 0.05). The increase in ventilation was accompanied mainly by an increase in respiratory frequency rather than in tidal volume. However, after stretching the metabolic rate also increased. Thus, the higher ventilation might have been a consequence of both higher muscle afferent activation and higher metabolic rate. Stretching alters the respiratory and metabolic response to exercise, but its effects on ventilation need further investigation
ACUTE MORPHOLOGICAL AND FUNCTIONAL MODIFICATIONS OF THE GASTROCNEMIUS MUSCLE-TENDON UNIT INDUCED BY PASSIVE STRETCHING
No full textAim. The aim of this study was to evaluate the changes in the gastrocnemius medialis (GM) muscle-tendon unit (MTU) stiffness induced by passive static stretching and to correlate them with electromyogram (EMG) and mechanomyogram (MMG) signals.
Methods. Maximum voluntary isometric force (MVC) of the triceps surae complex was measured at 0° (corresponding to right angle at the ankle joint); the myo-tendinous junction (MTJ) displacement and passive torque (T) of the GM were measured at different dorsiflexion angles (0°, 10° and 20°) and supramaximal tetanic stimulation was applied (50Hz for 2s) at each angle. EMG and MMG were recorded during MVC and stimulation at each angle. All the measurements were repeated after a bout of passive stretching (6 elongations of 45s each, 15s rest in between). Stiffness was calculated for MTU, muscle and tendon components. From EMG signal, root mean square (RMS) and mean frequency (MF) were calculated. From MMG signal, peak-to-peak (p-p) and RMS were identified. Peak torque (pT) was assessed during tetanic evoked contraction.
Results. After stretching, MVC, pT and T significantly decreased (P<0.05), as well as MTU and tendon stiffness (P<0.05). EMG parameters significantly decreased during MVC (P<0.05); MMG p-p and RMS were reduced and increased, respectively, in both MVC and tetanic contractions (P<0.05). Strong inverse correlations (R ranging from -0.55 to -0.81) were found between MTU and tendon stiffness and MMG RMS and MMG RMS, before and after stretching in both voluntary and tetanic contractions (P<0.001).
Conclusion. Passive stretching decreased MVC under voluntary and electrically-evoked conditions, decreasing the global MTU stiffness, with a main effect on tendon. MMG amplitude reflected the stiffness at MTU and tendon level, and could be used as an indirect index to monitor its changes under different physiological conditions (fatigue, training, muscle temperature manipulation).
References.
Esposito F, Limonta E, Cè E (2011). Time course of stretching-induced changes in mechanomyogram and force characteristics. Journal of Electromyography and Kinesiology, Oct;21(5):795-802.
Morse C. I., Degens H., Seynnes O. R., Maganaris C. N., Jones D. A. (2008).The acute effect of stretching on the passive stiffness of the human gastrocnemius muscle tendon unit. Journal of Physiology 586.1: 97–106.
Kato E, Vieillevoye S, Costantino B, Guissard N, Duchateau J (2011). Acute effect of muscle stretching on the steadiness of sustained submaximal contractions of the plantar flexor muscles. Journal of Applied Physiology 110: 407–415
Passive stretching effects on electromechanical delay and time course of recovery in human skeletal muscle : new insights from an electromyographic and mechanomyographic combined approach
No full textAcute passive stretching has been shown to alter muscle-tendon unit (MTU) stiffness and to reduce peak tetanic force (pF). MTU mechanical properties and electro-mechanical delay (EMD) are closely related. Thus, EMD changes would be expected after stretching. The aim of the study was to assess the stretching-induced changes in both contractile and viscoelastic contributors to EMD. The time course of these changes will be also evaluated. Tetanic stimulations were delivered on the medial gastrocnemius muscle of 16 active males, before and after (every 15 min, for 2 h) passive stretching administration. During contractions, electromyographic (EMG), mechanomyographic (MMG) and force signals were recorded. The delays between EMG and force (Delta t EMG-F, which corresponds to EMD), EMG and MMG (Delta t EMG-MMG) and MMG and force (Delta t MMG-F) signals were calculated, together with pF and EMG conduction velocity (CV). After stretching (i) pF decreased by 31% (P < 0.05) and remained depressed for the entire recovery period, while EMG CV did not change; (ii) Delta t EMG-F, Delta t EMG-MMG and Delta t MMG-F increased significantly from 45.4 +/- A 3.0 ms, 2.2 +/- A 0.3 ms and 42.4 +/- A 3.1 ms to 52.7 +/- A 3.4 ms, 2.4 +/- A 0.3 ms and 50.3 +/- A 3.5 ms, respectively; (iii) Delta t EMG-F and Delta t MMG-F remained lengthened for the entire recovery period, while Delta t EMG-MMG recovered to its pre-stretching condition within 15 min. These findings suggest that after stretching, the reduction in pF was accompanied by an elongation of the overall EMD. However, stretching had effects of short duration at the contractile level, but more persisting effects on MTU viscoelastic characteristics
Time course of stretching-induced changes in mechanomyogram and force characteristics
No full textTo evaluate the time-course of stretching-induced changes in mechanical properties of the muscletendon unit (MTU), 11 participants (age 22 +/- 1 yr; body mass 77 +/- 5 kg; stature 1.78 +/- 0.05 m; mean +/- SD) underwent tetanic electrical stimulations of the medial gastrocnemius muscle before and after (up to 2 h) stretching administration. During contractions, surface electromyogram (EMG), mechanomyogram (MMG) and force were recorded simultaneously. From MMG, peak-to-peak (p-p) and root mean square (RMS) were calculated during the on-phase and plateau phase of tetanic contraction, respectively. After stretching: (i) no differences were found in EMG parameters; (ii) MMG p-p and slope decreased (-16% and -10%, respectively; P < 0.05) and remained depressed for the entire recovery period; (iii) MMG RMS increased (+20%; P < 0.05), returning to pre-stretching values within 15 min; and (iv) peak force (pF), with its first (dF/dt) and second (d(2)F/dt(2)) derivative, decreased significantly by 32%, 35% and 54%, respectively, and remained depressed for the entire recovery period. The lack of MMG p-p and pF recovery could be ascribable to a reduced muscle force generating capacity due to persisting changes in viscoelastic characteristics of series elastic components. The early return of MMG RMS to pre-stretching values suggests that changes in viscoelastic parallel components recovered after few minutes
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
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
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
Cycling efficiency and time to exhaustion are reduced after acute passive stretching administration
No full textThe aim of this study was to assess the effects of acute passive stretching on cycling efficiency during an exercise of heavy intensity. After maximum aerobic power (V̇O(2max) ) assessment, nine active males (24 ± 5 years; stature 1.71 ± 0.09 m; body mass 69 ± 7 kg; mean ± standard deviation) performed tests at 85% of V̇O(2max) (Ẇ(85) ) until exhaustion, with and without pre-exercise stretching. During the tests, we determined the gas exchange, metabolic and cardiorespiratory parameters. With stretching, no differences in V̇O(2max) occurred (3.64 ± 0.14 vs 3.66 ± 0.07 L/min for stretching and control, respectively). During Ẇ(85) , pre-exercise stretching (i) decreased time to exhaustion (t(lim) ) by 26% (P<0.05); (ii) increased average V̇O(2) by 4% (3.24 ± 0.07 and 3.12 ± 0.07 L/min in stretching and control, respectively; P<0.05); and (iii) reduced net mechanical efficiency (e(net) ) by 4% (0.185 ± 0.006 and 0.193 ± 0.006 in stretching and control, respectively; P<0.05). Although acute passive stretching did not have an effect on V̇O(2max) , t(lim) and e(net) during heavy constant load exercise were significantly affected. These results are suggestive of an impairment in cycling efficiency due to changes in muscle neural activation and viscoelastic characteristics induced by stretching
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