Saied Jalal Aboodarda

Massage and stretching reduce spinal reflex excitability without affecting twitch contractile properties

Both stretching and massage can increase range of motion. Whereas the stretching-induced increases in ROM have been attributed to changes in neural and muscle responses, there is no literature investigating the ROM mechanisms underlying the interaction of stretch and massage. The objective of this paper was to evaluate changes in neural and evoked muscle responses with two types of massage and static stretching. With this repeated measures design, 30s of plantar flexors musculotendinous junction (MTJ) and tapotement (TAP) massage were implemented either with or without 1min of concurrent stretching as well as a control condition. Measures included the soleus maximum H-reflex/M-wave (H/M) ratio, as well as electromechanical delay (EMD), and evoked contractile properties of the triceps surae. With the exception of EMD, massage and stretch did not significantly alter triceps surae evoked contractile properties. Massage with and without stretching decreased the soleus H/M ratio. Both TAP conditions provided greater H/M ratio depression than MTJ massage while the addition of stretch provided the greatest inhibition. Both massage types when combined with stretching increased the duration of the EMD. In conclusion, MTJ and TAP massage as well as stretching decreased spinal reflex excitability, with TAP providing the strongest suppression. While static stretching prolongs EMD, massage did not affect contractile properties.

Knee extension fatigue attenuates repeated force production of the elbow flexors

Abstract Non-local muscle fatigue has been demonstrated with unilateral activities, where fatiguing one limb alters opposite limb forces. Fewer studies have examined if non-local fatigue occurs with unrelated muscles. The purpose of this study was to investigate if knee extensors fatigue alters elbow flexors force and electromyography (EMG) activity. Eighteen males completed a control and fatiguing session (randomised). Blood lactate was initially sampled followed by three maximal voluntary contractions (MVC) with the elbow flexors and two with the knee extensors. Thereafter, subjects either sat (control) or performed five sets of bilateral dynamic knee extensions to exhaustion using a load equal to the dominant limb MVC (1-min rest between sets). Immediately afterwards, subjects were assessed for blood lactate and unilateral knee extensors MVC, and after 1 min performed a single unilateral elbow flexor MVC. Two minutes later, subjects performed 12 unilateral elbow flexor MVCs (5 s contraction/10 s rest) followed by a third blood lactate test. Compared to control, knee extensor force dropped by 35% (p < 0.001; ES = 1.6) and blood lactate increased by 18% (p < 0.001; ES = 2.8). Elbow flexor forces were lower after the fatiguing protocol only during the last five MVCs (p < 0.05; ES = ∼0.58; ∼5%). No changes occurred between conditions in EMG. Elbow flexor forces significantly decreased after knee extensors fatigue. The effect was revealed during the later stages of the repeated MVCs protocol, demonstrating that non-local fatigue may have a stronger effect on repeated rather than on single attempts of maximal force production.

Elbow flexor fatigue modulates central excitability of the knee extensors

The present study investigated the effects of exercise-induced elbow flexor fatigue on voluntary force output, electromyographic (EMG) activity and motoneurone excitability of the nonexercised knee extensor muscles. Eleven participants attended 3 testing sessions: (i) control, (ii) unilateral fatiguing elbow flexion and (iii) bilateral fatiguing elbow flexion (BiFlex). The nonfatigued knee extensor muscles were assessed with thoracic motor evoked potentials (TMEPs), maximal compound muscle action potential (Mmax), knee extensor maximal voluntary contractions (MVCs), and normalized EMG activity before and at 30 s, 3 min, and 5 min postexercise. BiFlex showed significantly lower (Δ = -18%, p = 0.03) vastus lateralis (VL) normalized EMG activity compared with the control session whereas knee extension MVC force did not show any statistical difference between the 3 conditions (p = 0.12). The TMEP·Mmax(-1) ratio measured at the VL showed a significantly higher value (Δ = +46%, p = 0.003) following BiFlex compared with the control condition at 30 s postexercise. The results suggest that the lower VL normalized EMG following BiFlex might have been due to a reduction in supraspinal motor output because spinal motoneuronal responses demonstrated substantially higher value (30 s postexercise) and peripheral excitability (compound muscle action potential) showed no change following BiFelex than control condition.

Electromyographic activity and applied load during high intensity elastic resistance and nautilus machine exercises

Electromyographic Activity and Applied Load During High Intensity Elastic Resistance and Nautilus Machine Exercises This study was designed to quantify and compare Electromyographic activity (EMG) and applied load in quadriceps muscle within performing high intensity knee extension exercises by Elastic Resistance (ER) and Nautilus Machine (NM). Sixteen male and female subjects (22.4 ± 4.7 yrs) completed 8 RM seated knee extension by NM, elastic tubing with original length (E0) and elastic tubing with 30% decrement of original length (E30). The mean value of EMG and external force were calculated and synchronized across various segments of motion for the three modes of training. The results demonstrated that in the early concentric and late eccentric segments of contraction, NM elicited significantly higher muscle activation than both E30 and E0 (p < 0.05). However, in the mid-concentric and mid-eccentric as well as late concentric and early eccentric segments no significant differences were observed between NM and E30. These findings supported the approach that developing external recoil of force in ER device by reducing 30% of initial length of elastic material can offer similar neuromuscular activation compared with NM. On this basis, E30 can be suggested as an affordable and non-gym based exercise device which has the capacity to provide an appropriate high resistance stimulus to meet the training requirement of athletes.

Resultant muscle torque and electromyographic activity during high intensity elastic resistance and free weight exercises

Abstract The purpose of this study was to quantify and compare Resultant Muscle Torque (RMT) and muscle activation (EMG) pattern, during resistance exercise comprising eight repetitions maximum (8 RM) biceps curl with elastic resistance and free weight exercise. Sixteen male and female recreationally active subjects completed 8 RM biceps curl by each of three modalities of resistance exercise: (i) dumbbell (DB), (ii) elastic tubing with original un-stretched length at the commencement of contraction (E0), and (iii) elastic tubing with 30% decrement of original length (E30) at the commencement of contraction. The magnitude of muscle activation, external force, acceleration as well as range of motion (ROM) were quantified and synchronised by specific software. The data were collected from all eight repetitions but the first (initial), the fifth (middle) and the eighth (last) repetitions were selected for further data analysis. Each selected repetition was partitioned into a concentric and eccentric phase and then each phase was further divided into three equal segments (3 concentric and 3 eccentric = 6 segments per repetition). The EMG and RMT data demonstrated a bell-shaped muscle activation and muscle torque production pattern for the three modes of exercise. The E30 resulted in 15.40% and 14.89% higher total EMG (µV) as well as 36.85% and 17.71% higher RMT (N · m) than E0 and DB, respectively (all P <0.05). These findings support the contention that an elastic resistance device (E30) has the capacity to provide an appropriate high resistance stimulus to meet the training requirement of elite athletes.

Muscle activation comparisons between elastic and isoinertial resistance: A meta-analysis

BACKGROUND Elastic resistance has been commonly used in the therapeutic and fitness setting; however, the ability of elastic resistance to overload and activate muscles has been questioned because of linear increase in elastic resistance as the device is elongated. The purpose of this meta-analysis was to examine the available literature on muscle activation associated with isoinertial and elastic resistance exercises, and to provide a quantitative summary comparing the two resistance training modes. METHODS In a random-effects model, the Hedges g effect size was used to calculate the biased corrected standardized mean difference between the elastic and isoinertial resistance activation of prime movers (agonist), antagonists, assistant movers and stabilizer muscles. FINDINGS There was a lack of significant difference with the prime movers (effect size=-0.037, confidence interval: -0.202 to 0.128, p=0.660), antagonists (effect size=0.089, confidence interval: -0.112 to 0.290, p=0.385), synergists (effect size=-0.133, confidence interval: -0.342 to 0.076, p=0.213) and stabilizer (effect size=0.142, confidence interval: -0.006 to 0.289, p=0.060) muscle electromyography activity recorded during similar exercises using elastic and isoinertial resistance. INTERPRETATION Elastic resistance provides similar prime mover, antagonist, assistant movers and stabilizer muscle activation as isoinertial resistance; contradicting the traditional criticism that the elastic band would not elicit comparable levels of muscle activation as isoinertial resistance exercise. Since development of muscle strength is closely related to the duration of muscle tension, relatively equal muscle adaptations could be expected following the two modes of training provided that equal external resistance is employed between the two exercises. LEVEL OF EVIDENCE 2a.

Bilateral Knee Extensor Fatigue Modulates Force and Responsiveness of the Corticospinal Pathway in the Non-fatigued, Dominant Elbow Flexors.

Exercise-induced fatigue affects muscle performance and modulates corticospinal excitability in non-exercised muscles. The purpose of this study was to investigate the effect of bilateral knee extensor fatigue on dominant elbow flexor (EF) maximal voluntary force production and corticospinal excitability. Transcranial magnetic, transmastoid electrical and brachial plexus electrical stimulation (BPES) were used to investigate corticospinal, spinal, and muscle excitability of the dominant EF before and after a bilateral knee extensor fatiguing protocol or time matched rest period (control). For both sessions three stimuli were delivered every 1.5 s during the three pre-test time points and during the 1st, 3rd, 6th, 9th and 12th post-test 5 s EF isometric maximal voluntary contractions (MVC). In both conditions, overall, EF MVC force (p < 0.001) decreased progressively from repetition #1 to #12 during the post-test MVC protocol. EF MVC force (p < 0.001, ES = 0.9, Δ10.3%) decrements were more pronounced in the knee extensor fatigue intervention condition. In addition, there were no significant differences between conditions for biceps brachii electromyographic (EMG) activity (p = 0.43), motor evoked potentials (MEPs) amplitude (p = 0.908) or MEP silent period (SP; p = 0.776). However, the fatigue condition exhibited a lower MEP/cervicomedullary MEP (CMEP) ratio (p = 0.042, ES = 2.5, Δ25%) and a trend toward higher CMEP values (p = 0.08, ES = 0.5, Δ20.4%). These findings suggest that bilateral knee extensor fatigue can impair performance and modulate corticospinal excitability of the EF.

Does Performing Drop Jumps With Additional Eccentric Loading Improve Jump Performance

Abstract Aboodarda, SJ, Byrne, JM, Samson, M, Wilson, BD, Mokhtar, AH, and Behm, DG. Does performing drop jumps with additional eccentric loading improve jump performance? J Strength Cond Res 28(8): 2314–2323, 2014—Previous investigators have speculated that applying additional external load throughout the eccentric phase of the jumping movement could amplify the stretch-shortening cycle mechanism and modulate jumping performance and jump exercise intensity. The aims of this study, therefore, were to determine the effect of increased eccentric phase loading, as delivered using an elastic device, on drop jumps (DJs) performed from different drop heights. Of specific interest were changes in (a) the kinetics; eccentric and concentric impulse, rate of force development (RFD), concentric velocity and (b) the electromyographic (EMG) activity of leg muscles. In a randomized repeated-measure study, 15 highly resistance trained male subjects performed DJs from 3 heights (20, 35, and 50 cm) under 3 different conditions: body weight only (free DJ) and with elastic bands providing downward force equivalent to 20% (+20% DJ) and 30% (+30% DJ) of body mass. All DJs were recorded using video and force plate data that were synchronized with EMG data. Results demonstrated that using additional tensile load during the airborne and eccentric phases of the DJ could enhance eccentric impulse (p = 0.042) and RFD (p < 0.001) and resulted in small to moderate effect size (ES) increases in quadriceps intergrated EMG across the eccentric phase (0.23 > ES > 0.51). The observed greater eccentric loading, however, did not immediately alter concentric kinetics and jump height nor did it alter muscle activation levels during this phase. The findings indicated that, in addition to the conventional technique of increasing drop height, using a tensile load during the airborne and eccentric phases of the DJ could further improve eccentric loading of DJs. As it has been suggested that eccentric impulse and RFD are indicators of DJ exercise intensity, these findings suggest that the loaded DJs, using additional elastic load, may be an effective technique for improving DJ exercise intensity without acute effects on the jumping performance and neuromuscular activation level in highly trained athletes.

Unilateral elbow flexion fatigue modulates corticospinal responsiveness in non-fatigued contralateral biceps brachii.

Exercise‐induced fatigue can change motor performance in non‐exercised muscles. The objective was to investigate unilateral elbow flexion (EF) fatigue effects on the maximal voluntary force (MVC) and corticospinal excitability of contralateral non‐exercised biceps brachii (BB). Transcranial magnetic, transmastoid electrical, and brachial plexus electrical stimulation were used to elicit motor evoked potentials (MEP), cervicomedullary motor evoked potentials (CMEP), and compound muscle action potentials in the contralateral non‐exercised BB of 12 participants before and after (i) two bouts of 100‐s unilateral EF (fatigue) or (ii) control. Three stimuli were evoked every 1.5 s during a series of 6‐s isometric EF at 100%, 50%, and 5% of MVC. The non‐exercised EF MVC force, electromyographic activity, and voluntary activation were not significantly different between fatigue and control. Non‐exercised BB MEP and CMEP amplitudes during 100% MVCs demonstrated significantly higher (P = 0.03) and lower values (P = 0.01), respectively, after fatigue compared with control. There was no difference between the two conditions for MEP and CMEP amplitudes during 50% and 5% MVCs. Unilateral exercise‐induced EF fatigue did not lead to cross‐over central fatigue to the contralateral homologous muscle but enhanced the supraspinal responsiveness (MEP/CMEP) of the neural circuitries supplying central commands to non‐exercised muscles at higher contraction intensity.

Changes in supraspinal and spinal excitability of the biceps brachii following brief, non-fatiguing submaximal contractions of the elbow flexors in resistance-trained males.

The purpose of the current study was to assess the effects of 5 brief (2s), intermittent, submaximal elbow flexors voluntary contractions at 50% of maximal voluntary contraction (MVC) on measures of central (i.e. supraspinal and spinal) excitability. Supraspinal and spinal excitability of the biceps brachii were assessed via transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of the corticospinal tract, respectively. TMS-induced motor-evoked potentials (MEPs), TMES-induced cervicomedullary-evoked potentials (CMEPs), Erbs point peripheral nerve stimulation and MVC were assessed prior to and following submaximal voluntary contractions at 50% of MVC. The MEP to CMEP ratio increased (584±77.2%; p=0.011) and CMEP amplitudes decreased (62±3.0%; p=0.02) immediately post-exercise. MVC force output did not change immediately post-exercise. The results suggest that brief, non-fatiguing intermittent submaximal voluntary contractions transiently enhance supraspinal excitability while decreasing spinal excitability. The impact of these changes on ones ability to generate or maintain force production remains unknown.