Emiliano Cè

Effects of Stretching on Maximal Anaerobic Power: The Roles of Active and Passive Warm-ups

The purpose of the study was to provide practical suggestions on the effect of stretching on the maximal anaerobic power preceded by active or passive warm-up. To this aim, 15 relatively fit male subjects (age 23 ± 0.2 years, height 177 ± 2 cm, body mass 74 ± 2 kg; [mean ± SE]) randomly performed a series of squat jumps (SJ) and countermovement jumps (CMJ). Jumps were preceded alternatively by: i) passive stretching of lower limbs muscles; ii) active warm-up (AWU); iii) passive warm up (PWU); and iv) the joining of stretching with either active warm-up (AWU+S) or passive warm-up (PWU+S). In control conditions (C) only jumps were required. For the 2 jumps the flight time (Ft), the peak force (Pf), and the maximal power (&U1E86;pmax) were calculated. It resulted that Ft, Pf, and &U1E86;max values were significantly higher: i) after AWU than after PWU and PWU+S in CMJ; and ii) in AWU as compared to those of other protocols of SJ. Stretching did not negatively affect the maximal anaerobic power, per se, but seems to inhibit the effect of AWU. The results suggested that AWU seemed to increase vertical jump performance when compared to PWU, presumably due to an increase in metabolic activity as a consequence of AWU, which did not occur in PWU, despite the same skin temperature. Passive stretching alone seemed not to negatively influence vertical jump performance, whereas, if added after AWU, could reduce the power output.

Effects of temperature and fatigue on the electromechanical delay components

Introduction: Neuromuscular activation can be influenced by both muscle temperature (Tm) and fatigue. Methods: To assess the effects of Tm and fatigue on the electromechanical delay (EMD), 15 participants performed voluntary isometric contractions of different intensities under neutral (TmN), low (TmL), and high (TmH) Tm, before and after a fatiguing exercise. During contraction, electromyogram (EMG), mechanomyogram (MMG), and force (F) were recorded from the biceps brachii muscle. The EMD and the latencies between EMG and MMG (Δt EMG‐MMG, which includes the electrochemical processes of EMD) and between MMG and F (Δt MMG‐F, which includes the mechanical processes of EMD) were calculated. Results: TmL increased only Δt EMG‐MMG, both before and after fatigue. Fatigue lengthened EMD, Δt EMG‐MMG, and Δt MMG‐F under all Tm to a similar extent. Conclusions: While fatigue increased all EMD components, muscle cooling affected only the electrochemical but not the mechanical processes of EMD. Muscle Nerve, 2013

Acute passive stretching in a previously fatigued muscle: Electrical and mechanical response during tetanic stimulation

Abstract The aim of this study was to assess the effects of acute passive stretching on the electrical and mechanical response of a previously fatigued muscle. Eleven participants underwent maximal tetanic stimulations (50 Hz) of the medial gastrocnemius, before and after a fatiguing protocol and after a bout of passive stretching of the fatigued muscle. During contraction, surface electromyography (EMG), mechanomyography (MMG), and force were recorded. The following parameters were calculated: (1) the EMG root mean square (RMS), mean frequency, and fibre conduction velocity; (2) MMG peak-to-peak and RMS; (3) the peak force, contraction time, half-relaxation time, peak rate of force development (dF/dt) and its acceleration (d2 F/dt 2). Fatigue reduced peak force by 18% (P < 0.05) and affected the other force, EMG, and MMG parameters. After stretching: (1) all EMG parameters recovered to pre-fatigue values; (2) MMG peak-to-peak remained depressed, while RMS recovered to pre-fatigue values; (3) the peak force, peak rate of force development and its acceleration were further reduced by 22, 18, and 51%, respectively, and half-relaxation time by 40% (P < 0.05). In conclusion, acute passive stretching, when applied to a previously fatigued muscle, further depresses the maximum force-generating capacity. Although stretching does not alter the electrical parameters of the fatigued muscle, it does affect the mechanical behaviour of the muscle–tendon unit.

ACUTE EFFECTS OF STATIC STRETCHING ON SQUAT JUMP PERFORMANCE AT DIFFERENT KNEE STARTING ANGLES

La Torre, A, Castagna, C, Gervasoni, E, Cè, E, Rampichini, S, Ferrarin, M, and Merati, G. Acute effects of static stretching on squat jump performance at different knee starting angles. J Strength Cond Res 24(3): 687-694, 2010-The purpose of this study was to examine the effects of static stretching on leg extensor muscles during squat jump (SJ) at different knee starting angles. Seventeen male subjects (23 ± 3 years, 179 ± 5 cm, and 74 ± 6 kg) performed on a force platform 2 series (preceded or not [control condition] by 10-minute static stretching of quadriceps and triceps surae muscles) of SJs at different knee starting angles: 50°, 70°, 90°, and 110°. Squat jump height, peak force, maximal acceleration, velocity, and power were calculated for each jump. The angle that maximized power development was obtained from the power-angle relationship. The SJ height, peak force, and maximal velocity increased according to angle amplitude in both control and stretching conditions (p < 0.01), performance being significantly lower in the stretching condition (p < 0.01). Peak power was obtained at 90° in both control and stretching conditions, but was significantly lower (p < 0.01) after stretching. These results suggest that an acute bout of static stretching reduces power and force development during SJ, decrements being significantly higher at lower knee starting angles. Therefore, the use of static stretching may be questionable in those power activities requiring maximal power output at knee angles near full extension.

Time course of stretching-induced changes in mechanomyogram and force characteristics

To evaluate the time-course of stretching-induced changes in mechanical properties of the muscle-tendon 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 2h) 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.

Novel insights into skeletal muscle function by mechanomyography: from the laboratory to the field

PurposeThe 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.MethodsFive 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.ResultsFrom 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.ConclusionsThe 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.

Electrical and mechanical response of skeletal muscle to electrical stimulation after acute passive stretching in humans: A combined electromyographic and mechanomyographic approach

Abstract Two 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.

Torque and mechanomyogram correlations during muscle relaxation : effects of fatigue and time-course of recovery

To assess the validity and reliability of the mechanomyogram (MMG) as a tool to investigate the fatigue-induced changes in the muscle during relaxation, the torque and MMG signals from the gastrocnemius medialis muscle of 23 participants were recorded during tetanic electrically-elicited contractions before and immediately after fatigue, as well as at min 2 and 7 of recovery. The peak torque (pT), contraction time (CT) and relaxation time (RT), and the acceleration of force development (d2RFD) and relaxation (d2RFR) were calculated. The slope and τ of force relaxation were also determined. MMG peak-to-peak was assessed during contraction (MMG p-p) and relaxation (R-MMG p-p). After fatigue, pT, d2RFD, d2RFR, slope, MMG p-p and R-MMG p-p decreased significantly, while CT, RT and τ increased (P < 0.05 for all comparisons), remaining altered throughout the entire recovery period. R-MMG p-p correlated with pT, MMG p-p, slope, τ and d2RFR both before and after fatigue. Reliability measurements always ranged from high to very high. In conclusion, MMG may represent a valid and reliable index to monitor the fatigue-induced changes in muscle mechanical behavior, and could be therefore considered an effective alternative to the force signal, also during relaxation.

Effects of passive stretching on post-activation potentiation and fibre conduction velocity of biceps brachii muscle

Stretching is usually part of warm-up routines in many sports, but it affects the subsequent muscle force; therefore, it could negatively influence post-activation potentiation (PAP), one of the warm-up’s main effects. The aim of this study was to evaluate the acute effects of passive stretching on PAP and fibre conduction velocity (CV). Seven subjects underwent 2 experimental sessions, control (C) and stretching (S), each consisting of 2 series (7 min resting) of 3 maximal voluntary contractions (MVC) of biceps brachii (5 s isometric contraction, 10 s recovery). During the resting phase of the S session, the biceps brachii was passively stretched (5×45 s stretches, 15 s recovery). Root mean square (RMS), mean frequency (MF) and CV were calculated from electromyography. Peak torque (pT) and half-contraction time (1/2CT) were measured and normalised by the arm muscular area (pTn). After C, pTn increased and 1/2CT decreased (p<0.05); moreover, MF and CV increased (p<0.05). After S, 1/2CT increased (p<0.05) and RMS decreased (p<0.05). Passive stretching could blunt the effects of PAP, presumably due to mechanical and neuromuscular changes. The observed changes in CV suggest a possible decrease in Ca2+ sensitivity in contractile proteins. Therefore, the use of passive stretching in warm-up routines remains questionable.

Stretching and deep and superficial massage do not influence blood lactate levels after heavy-intensity cycle exercise.

Abstract The study aimed to assess the role of deep and superficial massage and passive stretching recovery on blood lactate concentration ([La−]) kinetics after a fatiguing exercise compared to active and passive recovery. Nine participants (age 23 ± 1 years; stature 1.76 ± 0.02 m; body mass 74 ± 4 kg) performed on five occasions an 8-min fatiguing exercise at 90% of maximum oxygen uptake, followed by five different 10-min interventions in random order: passive and active recovery, deep and superficial massage and stretching. Interventions were followed by 1 hour of recovery. Throughout each session, maximum voluntary contraction (MVC) of the knee extensor muscles, [La−], cardiorespiratory and metabolic variables were determined. Electromyographic signal (EMG) from the quadriceps muscles was also recorded. At the end of the fatiguing exercise, [La−], MVC, EMG amplitude, and metabolic and cardiorespiratory parameters were similar among conditions. During intervention administration, [La−] was lower and metabolic and cardiorespiratory parameters were higher in active recovery compared to the other modalities (P < 0.05). Stretching and deep and superficial massage did not alter [La−] kinetics compared to passive recovery. These findings indicate that the pressure exerted during massage administration and stretching manoeuvres did not play a significant role on post-exercise blood La− levels.