1,721,100 research outputs found
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
Morphological analysis of force/velocity relationship in dynamic exercise at varying loads
No full textThis study examined the force/velocity (F/V) curve morphology among the entire concentric phase of the countermovement squat (CMS). The hypothesis is that F/V curve shape of the lower limb muscles complex is different from F/V isolated muscle curve and
that these analyses could be useful in characterizing athletes’ muscular capacity and training programs. Squat exercise was
performed by 29 subjects (15 men and 14 women, divided into resistance and endurance athletes). The protocol was 6 3 1
CMS at maximal speed with increasing loads: 20, 35, 50, 65, 80, 90% of 1 repetition maximum (1RM). Displacement, speed, and acceleration of the weight bar, joint knee angles, knee angular speed, and total and normalized forces were collected. F/V relation was obtained by force and velocity values of each 10 angular interval of the concentric phase for any load.
Results show that the F/V relationship does not follow a linear shape and an equivalent criterion for all loads. We observed a ‘‘second peak force’’ statistically higher (p , 0.05) than the inversion peak at 80 and 90% 1RM. Resistance trained men showed a ‘‘second peak’’ higher and larger than that shown by endurance trained men. This indicated a higher ability to produce and maintain greater force at higher relative speed. These results may be helpful to identify the muscle characteristics of the athletes at various speeds and joint positions. With a phase division of the specific move, it will be possible to determine an individualized program to monitor the specific phases of technical moves and to evaluate the training effect in long run
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 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 role of anticipatory postural adjustments in interlimb coordination of coupled arm movements in the parasagittal plane : III. Difference in the energy cost of postural actions during cyclic flexion–extension arm movements, ISO- and ANTI-directionally coupled
No full textWhen oscillating the upper limbs together in the parasagittal plane, movements coordination is lower (i.e., variability of the interlimb relative phase is higher) in antidirectional (ANTI) than in isodirectional (ISO) coupling. In contrast, we previously observed that for arm movements in the horizontal plane, the coordination was worse in ISO than ANTI and the energetic cost of postural activities was higher in ISO. Having hypothesised that the higher postural cost was one factor responsible for the coordination deficit in horizontal ISO, we measured the oxygen uptake (VO2) in parasagittal movements, expecting that in this case too, the postural cost is higher in the less-coordinated mode (ANTI). Breath-by-breath metabolic (VO2, VCO2) and cardiorespiratory (HR, VE) parameters were measured in seven participants, who performed cyclic flexions–extensions in the parasagittal plane with either one arm or both arms, in ISO or ANTI coupling and at 1.4, 2.2 and 2.6 Hz. In each condition, the intermittent exercise (12 s movement, 12 s rest) lasted 264 s. A force platform recorded the mechanical actions to the ground. The exercise metabolic cost (ΔVO2) was found to be significantly higher in parasagittal ANTI than ISO. The movement amplitude being equal in the two modes, the ANTI-ISO difference should be ascribed to postural activities. This would confirm that the less-coordinated coupling mode requires the higher postural effort in parasagittal movements too. When rising the movement frequency, ΔVO2 increased and linearly correlated with the coordination loss. Comparison of parasagittal with horizontal movements showed that ΔVO2 was lower in parasagittal ANTI than in horizontal ISO (the less-coordinated modes), while it was not different between parasagittal ISO and horizontal ANTI (the more-coordinated modes)
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
The 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
Fatigue effects on the electromechanical delay components during the relaxation phase after isometric contraction
No full textAIM:
By a combined electromyographic (EMG), mechanomyographic (MMG) and force analysis, the electromechanical delay during muscle relaxation (R-DelayTOT ) was partitioned into electrochemical and mechanical components. The study aimed to evaluate the effects of fatigue on R-DelayTOT components and to assess their inter-session and inter-day reliability.
METHODS:
During tetanic stimulations, EMG, MMG and force were recorded from the human gastrocnemius medialis muscle before and after fatigue. The latency between EMG and MMG ripple cessations (R-Δt EMG-MMGR , electrochemical R-DelayTOT component); between MMG ripple cessation and force decay onset (R-Δt MMGR -F, first R-DelayTOT mechanical component), and between force decay onset and maximum MMG negative peak (R-Δt F-MMGp-p , second R-DelayTOT mechanical component) were calculated.
RESULTS:
Before fatigue, R-Δt F-MMGp-p was the major contributor (61.9±1.7 ms, 75%) to R-DelayTOT (82.7±1.0 ms), 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-DelayTOT , R-Δt EMG-MMGR and R-Δt MMGR -F increased by 11%, 41% and 67%, respectively (P<0.05), whereas R-Δt F-MMGp-p didn't change. Consequently, the relative contribution of R-Δt EMG-MMGR , R-Δt MMGR -F and R-Δt F-MMGp-p , to R-DelayTOT changed to 20±2%, 12±1% and 68±2%, respectively. Measurement reliability was always from high to very high (0.705 to 0.959).
CONCLUSION:
Fatigue altered the processes between neuromuscular activation cessation and force decay onset, but not the second mechanical component (cross-bridges detachment rate and series elastic components release). This combined approach provided reliable measurement of the different R-DelayTOT components and it may represent a valid tool to get more insights on muscle electromechanical behaviour
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