Eccentric Contractions Research Articles

Asynchrony Injures Lung and Diaphragm in Acute Respiratory Distress Syndrome.

Patient-ventilator asynchrony is often observed during mechanical ventilation and is associated with higher mortality. We hypothesized that patient-ventilator asynchrony causes lung and diaphragm injury and dysfunction. Prospective randomized animal study. University research laboratory. Eighteen New Zealand White rabbits. Acute respiratory distress syndrome (ARDS) model was established by depleting surfactants. Each group (assist control, breath stacking, and reverse triggering) was simulated by phrenic nerve stimulation. The effects of each group on lung function, lung injury (wet-to-dry lung weight ratio, total protein, and interleukin-6 in bronchoalveolar lavage), diaphragm function (diaphragm force generation curve), and diaphragm injury (cross-sectional area of diaphragm muscle fibers, histology) were measured. Diaphragm RNA sequencing was performed using breath stacking and assist control (n = 2 each). Inspiratory effort generated by phrenic nerve stimulation was small and similar among groups (esophageal pressure swing ≈ -2.5 cm H2O). Breath stacking resulted in the largest tidal volume (>10 mL/kg) and highest inspiratory transpulmonary pressure, leading to worse oxygenation, worse lung compliance, and lung injury. Reverse triggering did not cause lung injury. No asynchrony events were observed in assist control, whereas eccentric contractions occurred in breath stacking and reverse triggering, but more frequently in breath stacking. Breath stacking and reverse triggering significantly reduced diaphragm force generation. Diaphragmatic histology revealed that the area fraction of abnormal muscle was ×2.5 higher in breath stacking (vs assist control) and ×2.1 higher in reverse triggering (vs assist control). Diaphragm RNA sequencing analysis revealed that genes associated with muscle differentiation and contraction were suppressed, whereas cytokine- and chemokine-mediated proinflammatory responses were activated in breath stacking versus assist control. Breath stacking caused lung and diaphragm injury, whereas reverse triggering caused diaphragm injury. Thus, careful monitoring and management of patient-ventilator asynchrony may be important to minimize lung and diaphragm injury from spontaneous breathing in ARDS.

Functional Activity of Reciprocal Inhibition of α-Motor Neurons of Antagonistic Muscles in Different Types of Muscle Contractions of Submaximal and Maximal Force

INTRODUCTION: Currently, the results of investigation of different types of spinal inhibition in isometric voluntary contraction of muscles have been published. There are separate reports devoted to the role of recurrent and presynaptic inhibition in the regulation of isometric and anisometric voluntary contractions of submaximal and maximal strength.
 AIM: To evaluate the effect of the type and strength of muscle contraction with and without performing Jendrassik maneuver on the manifestation of reciprocal inhibition of -motor neurons of antagonistic muscles of the lower leg.
 MATERIALS AND METHODS: The study involved 8 healthy men aged 2022 years. Reciprocal inhibition was evaluated by suppression of the amplitude of testing H-reflex of m. soleus in conditioning stimulation of n. peroneus profundus, and of testing stimulation of n. tibialis with 3 msec interval between stimuli. Reciprocal inhibition was recorded in concentric, eccentric and isometric contractions with 50% and 100% of maximal voluntary contraction (MVC) with and without Jendrassic maneuver.
 RESULTS: In performing concentric, eccentric and isometric contractions of lower leg muscles with increase in strength from 50% to 100% of MVC, the activity of reciprocal inhibition decreased. Reciprocal inhibition was most evident in concentric contraction with 50% of MVC strength, less evident in eccentric contraction and was lowest in isometric contraction. With the maximal strength, reciprocal inhibition was most expressed in isometric contraction, less expressed in concentric contraction and was weakest in eccentric contraction. With Jendrassik maneuver, reduction of reciprocal inhibition was more expressed in different types of MVCs in comparison with parameters obtained with 50% of MVC. Using Jendrassic maneuver with 50% and 100% of MVC effort, strongest reciprocal inhibition was recorded in isometric contraction, weaker inhibition in concentric contraction and weakest in eccentric contraction. The effect of Jendrassik maneuver was manifested by weakening of reciprocal inhibition in concentric and eccentric contraction of submaximal force, and by its enhancement in isometric contraction.
 CONCLUSION: Variability of manifestation of reciprocal inhibition of -motor neurons of antagonistic muscles of lower leg in different types of muscle contractions of submaximal and maximal strength is associated with the fact that the pool of segmental motor neurons of m. soleus is controlled not only by a wide spectrum of excitatory cortico- and reticulospinal influences, but also by other kinds of inhibition, thus providing coordinated motor actions.

Vitamin D deficiency contributes to overtraining syndrome in excessive trained C57BL/6 mice.

Overtraining syndrome is a condition resulting from excessive training load associated with inadequate recovery and poor sleep quality, leading to performance decrements and fatigue. Here we hypothesized that vitamin D (VitD) deficiency is a lead factor in the development of the overtraining syndrome. To test this hypothesis, two groups of 60-week-old C57BL/6 mice followed a 16-week excessive eccentric-based overtraining by excessive downhill running with or without dietary VitD depletion (EX and EX-D- groups). Two control groups were trained by uphill running at the same load with or without VitD depletion (CX and CX-D- groups). Handgrip strength decreased throughout the protocol for all groups but the decrease was sharper in EX-D- group (VitD × training, p = 0.0427). At the end of the protocol, the mass of Triceps brachii muscle, which is heavily stressed by eccentric contractions, was reduced in eccentric-trained groups (training effect, p = 0.0107). This atrophy was associated with a lower concentration of the anabolic myokine IL-15 (training effect, p = 0.0314) and a tendency to a higher expression of the atrogene cathepsin-L (training effect, p = 0.0628). VitD depletion led to a 50% decrease of the fractional protein synthesis rate in this muscle (VitD effect, p = 0.0004) as well as decreased FGF21 (VitD effect, p = 0.0351) and increased osteocrin (VitD effect, p = 0.038) concentrations that would lead to metabolic defects. Moreover, the proportion of anti-inflammatory Th2 lymphocytes was significantly decreased by the combination of eccentric training with VitD depletion (vitD × training, p = 0.0249) suggesting a systemic inflammation. Finally, exploratory behavior time of mice was decreased by VitD depletion (VitD effect, p = 0.0146) suggesting a cognitive dysfunction. Our results suggest that VitD deficiency exacerbates the effects of overtraining.

Eccentric Contractions of the Diaphragm During Mechanical Ventilation.

Diaphragm dysfunction is a highly prevalent phenomenon in patients receiving mechanical ventilation, mainly due to ventilatory over-assistance and the development of diaphragm disuse atrophy. Promoting diaphragm activation whenever possible and facilitating an adequate interaction between the patient and the ventilator is encouraged at the bedside to avoid myotrauma and further lung injury. Eccentric contractions of the diaphragm are defined as muscle activation while muscle fibers are lengthening within the exhalation phase. There is recent evidence that suggests that eccentric activation of the diaphragm is very frequent and may occur during post-inspiratory activity or under different types of patient-ventilator asynchronies, which include ineffective efforts, premature cycling, and reverse triggering. The consequences of this eccentric contraction of the diaphragm may have opposite effects, depending on the level of breathing effort. For instance, during high or excessive effort, eccentric contractions can result in diaphragm dysfunction and injured muscle fibers. Conversely, when eccentric contractions of the diaphragm occur along with low breathing effort, a preserved diaphragm function, better oxygenation, and more aerated lung tissue are observed. Despite this controversial evidence, evaluating the level of breathing effort at the bedside seems crucial and is highly recommended to optimize ventilatory therapy. The impact of eccentric contractions of the diaphragm on the patient's outcome remains to be elucidated.

Recovery kinetics following eccentric exercise is volume-dependent

ABSTRACT The present study compared the effect of 75 vs 150 vs 300 intensity-matched eccentric contractions on muscle damage and performance recovery kinetics. Ten healthy males participated in a randomized, cross-over study consisted of 4 experimental trials (ECC75, ECC150, ECC300 and Control – no exercise) with a 4-week washout period in-between. Performance and muscle damage, inflammatory and oxidative stress markers were evaluated at baseline, post-exercise, 24, 48 and 192 hours following each exercise protocol. Concentric and eccentric peak torque decreased similarly in ECC150 and ECC300 during the first 48 h of recovery (p < 0.05) but remained unaffected in ECC75. Countermovement jump indices decreased post-exercise and at 24 h in ECC150 and ECC300, with ECC300 inducing a more pronounced reduction (p < 0.05). Creatine kinase increased until 48 h of recovery in all trials and remained elevated up to 192 h only in ECC300 (p < 0.05). Delayed onset of muscle soreness increased, and knee-joint range of motion decreased in a volume-dependent manner during the first 48 h (p < 0.05). Likewise, a volume-dependent decline of glutathione and a rise of protein carbonyls was observed during the first 48 h of recovery (p < 0.05). Collectively, our results indicate that muscle damage and performance recovery following eccentric exercise is volume dependent, at least in lower limbs.

The Agonist-Antagonist Myoneural Interface in a Transtibial Amputation.

The agonist-antagonist myoneural interface (AMI) technique at the time of transtibial amputation involves the use of agonist-antagonist muscle pairs to restore natural contraction-stretch relationships and to improve proprioceptive feedback when utilizing a prosthetic limb1. Utilizing the standard incision for a long posterior myofasciocutaneous flap, the lateral and medial aspects of the limb are dissected, identifying and preserving the superficial peroneal and saphenous nerve, respectively. The tendons of the tibialis anterior and peroneus longus are transected distally to allow adequate length for the AMI constructs. After ligation of the anterior tibial vessels, the deep peroneal nerve is identified and tagged to create a regenerative peripheral nerve interface (RPNI). The tibia and fibula are cut approximately 15 cm from the medial joint line, facilitating dissection of the deep posterior compartment and ligation of the peroneal and posterior tibial vessels. The tendons of the lateral gastrocnemius and tibialis posterior are transected distally, and the amputation is completed. The extensor retinaculum is harvested from the residual limb along with multiple 2 × 3-cm free muscle grafts, which will be used for the RPNI constructs. The retinaculum is secured to the tibia with suture anchors, and AMI pairs of the lateral gastrocnemius and tibialis anterior as well as the tibialis posterior and peroneus longus are constructed. Separate RPNIs of the major lower-extremity nerves are performed, and the wound is closed in a standard layered fashion. An isometric myodesis of the gastrocnemius without coaptation of agonist-antagonist muscle pairs can be performed at the time of transtibial amputation. The AMI technique restores natural agonist-antagonist relationships at the time of transtibial amputation to increase proprioceptive feedback and improve prosthetic control. These outcomes contrast with those of a traditional isometric myodesis, which prevents proprioceptive communication from the residual limb musculature to the central nervous system. Additionally, the AMI technique allows for concentric and eccentric muscular contractions, which may contribute to the maintenance of limb volume and aid with prosthetic fitting, as opposed to the typical limb atrophy observed following standard transtibial amputation1,2. With the development and availability of more advanced prostheses, the AMI technique offers more precise control and increases the functionality of these innovative devices. Early clinical outcomes of the AMI technique at the time of transtibial amputation have been promising. In a case series of the first 3 patients who underwent the procedure, complications were minor and consisted of 2 episodes of cellulitis and 1 case of delayed wound healing1. Muscle activation measured through electromyography demonstrated an improved ability to limit unintended muscular co-contraction with attempted movement of the phantom limb, as compared with patients who underwent a standard transtibial amputation1. Additionally, residual limb volume was maintained postoperatively without the need for substantial prosthetic modifications. The tendons of the tibialis anterior, peroneus longus, tibialis posterior, and lateral gastrocnemius should be transected as distal as possible to allow adequate length for creation of the AMI constructs.Approximately 2 × 3-cm free muscle grafts are harvested from the amputated extremity for RPNI3.Smooth tendon-gliding through the synovial tunnels should be confirmed before closure. If necessary, muscle debulking can improve gliding and decrease the size of the residual limb.Harvesting the extensor retinaculum for synovial tunnels has been our preferred method, although we acknowledge that other grafts options such as the tarsal tunnel are available1. RPNI = regenerative peripheral nerve interfaceAMI = agonist-antagonist myoneural interfaceEMG = electromyographic.

Valproic acid reduces muscle susceptibility to contraction-induced functional loss but increases weakness in two murine models of Duchenne muscular dystrophy.

Skeletal muscles in animal models of Duchenne muscular dystrophy (DMD) are more susceptible to contraction-induced functional loss, which is not related to fatigue. Valproic acid (VPA) reportedly improves serological and histological markers of damage in dystrophin-deficient murine muscle. Here, we tested whether VPA would reduce the susceptibility to contraction-induced functional loss in two murine DMD models. Adult female mdx (mild) and D2-mdx (severe) DMD murine models were administered VPA (240 mg/kg) or saline for 7 days. Some VPA-treated mdx mice also performed voluntary running in a wheel, which is known to reduce the susceptibility to contraction-induced functional loss; that is, isometric force drop following eccentric contractions. In situ muscle function was assessed before, during and after eccentric contractions. Muscle utrophin and desmin expression were also evaluated using immunoblotting. Interestingly, VPA reduced the isometric force drop following eccentric contractions in both murine models, without change in the relative eccentric maximal force and in the expression of utrophin and desmin. VPA for 7 days combined with voluntary running had no additive effect compared to VPA alone. Furthermore, VPA reduced the absolute isometric maximal force before eccentric contractions in both murine models. The results of our study indicated that VPA in both murine DMD models reduced the susceptibility to contraction-induced functional loss but increased muscle weakness.

Effects of submaximal and supramaximal accentuated eccentric loading on mass and function.

Introduction: Eccentric-overload (EO) resistance training emerges as an alternative to more optimally prescribe intensity relative to the force generation capabilities of the eccentric muscle contraction. Given the difficulties to individually prescribe absolute eccentric loads relative to each person's eccentric ability, setting the load relative to the concentric one-repetition maximum (1-RM) is the most used EO training approach. Therefore, we investigated the effects of submaximal and supramaximal (i.e., eccentric loads above 100% of 1-RM) accentuated eccentric training on changes in lean mass, anabolic hormonal responses and muscle function. Methods: Physically active university students (n = 27) were randomly assigned to two training groups. Participants in the training groups performed dominant leg isotonic training twice a week for 10weeks (four sets of eight repetitions). Isotonic resistance was generated by an electric-motor device at two different percentages of 1-RM for the eccentric phase; 90% submaximal load, SUB group) and 120% (supramaximal load, SUPRA group). Concentric load was the same for both groups (30% of 1-RM). Changes in total thigh lean mass (TTLM), anabolic hormonal responses (growth hormone, IGF-1, IL-6, and total testosterone), unilateral leg-press 1-RM, maximal voluntary isometric contractions (MVIC), local muscle endurance (XRM), muscle power at 40 (PP40), 60 (PP60) and 80% (PP80) of the 1-RM, and unilateral vertical jump height before and after training were compared between groups. Results: After training, both SUB and SUPRA groups showed similar increases (p < 0.05) in MVIC (19.2% and 19.6%), XRM (53.8% and 23.8%), PP40 (16.2% and 15.7%), TTLM (2.5% and 4.2%), IGF-1 (10.0% and 14.1%) and IL-6 (58.6% and 28.6%). However, increases in 1-RM strength (16.3%) and unilateral vertical jump height (10.0%-13.4%) were observed for SUPRA only. Indeed, SUPRA was shown to be more favorable than SUB training for increasing 1-RM [ES = 0.77 (1.49-0.05)]. Unilateral muscle power at medium and high intensity (10.2% and 10.5%) also increased in SUB but without significant differences between groups. Discussion: Similar functional and structural effects were demonstrated after 10weeks EO training with submaximal and supramaximal eccentric loads. Although supramaximal loading might be superior for increasing 1-RM, the use of this approach does not appear to be necessary in healthy, active individuals.

Effects of exercise induced muscle damage on cardiovascular responses to isometric muscle contractions and post-exercise circulatory occlusion

PurposeThe aim of the present study was to investigate whether exercise-induced muscle damage (EIMD) influences cardiovascular responses to isometric exercise and post-exercise circulatory occlusion (PECO). We hypothesized that EIMD would increase muscle afferent sensitivity and, accordingly, increase blood pressure responses to exercise and PECO.MethodsEleven male and nine female participants performed unilateral isometric knee extension at 30% of maximal voluntary contraction (MVC) for 3-min. A thigh cuff was rapidly inflated to 250 mmHg for two min PECO, followed by 3 min recovery. Heart rate and blood pressure were monitored beat-by-beat, with stroke volume and cardiac output estimated from the Modelflow algorithm. Measurements were taken before and 48 h after completing eccentric knee-extension contractions to induce muscle damage (EIMD).ResultsEIMD caused 21% decrease in MVC (baseline: 634.6 ± 229.3 N, 48 h: 504.0 ± 160 N), and a 17-fold increase in perceived soreness using a visual-analogue scale (0–100 mm; VASSQ) (both p < 0.001). CV responses to exercise and PECO were not different between pre and post EIMD. However, mean arterial pressure (MAP) was higher during the recovery phase after EIMD (p < 0.05). Significant associations were found between increases in MAP during exercise and VASSQ, Rate of Perceived Exertion (RPE) and Pain after EIMD only (all p < 0.05).ConclusionThe MAP correlations with muscle soreness, RPE and Pain during contractions of damaged muscles suggests that higher afferent activity was associated with higher MAP responses to exercise.

Mild to moderate damage in knee extensor muscles accumulates after two bouts of maximal eccentric contractions.

This study aimed to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days. Thirty participants performed an initial bout of maximal eccentric contractions of knee extensors during the first day of the protocol (ECC1). Then, they were separated in two groups. The Experimental (EXP) group repeated the eccentric bout 24h later (ECC2) while the Control (CON) group did not. Indirect markers of muscle damage (i.e., strength loss, muscle soreness, and shear modulus) were measured to quantify the amount of muscle damage and its time course. Two days after the initial eccentric session, participants from EXP had a higher strength deficit (-14.5 ± 10.6%) than CON (-6.6 ± 8.7%) (P = 0.017, d = 0.9). Although both groups exhibited an increase in knee extensors shear modulus after ECC1, we found a significant increase in muscle shear modulus (+ 13.3 ± 22.7%; P < 0.01; d = 0.5) after ECC2 for the EXP group, despite the presence of mild to moderate muscle damage (i.e., strength deficit about 16%). Although the markers of muscle damage used in the current study were indirect, they suggest that the repetition of two bouts of maximal eccentric contractions with 24h apart induces additional muscle damage in the knee extensors in presence of mild to moderate muscle damage.

Eccentric contractions during downhill running induce Osgood‒Schlatter disease in the tibial tuberosity in rats: a focus on histological structures

Osgood–Schlatter disease (OSD), a condition that affects adolescents, causes inflammation, pain, and prominence at the tibial tuberosity. The causes of OSD are not well understood, but eccentric contractions in the quadriceps have been suggested as a possible factor. To investigate this, a study was conducted in which 24 rats were divided into two groups: the downhill treadmill running (DR) group and the control (CO) group. The DR group underwent a preliminary running program for 1 week, followed by a main running program for 3 weeks. The results showed that the deep region of the tibial tuberosity in the DR group was larger than that in the CO group, and inflammatory cytokines involved in gene expression were upregulated in the DR group. The anterior articular cartilage and deep region in the DR group were also immunoreactive to substance P. Additionally, high-activity chondrocytes of small size were observed in the non-calcified matrix. Thus, the DR group exhibited symptoms similar to OSD, including inflammation, pain, and prominence. These findings suggest that eccentric contractions in the quadriceps may play a role in the development of OSD. Further research is needed to better understand the pathophysiology of this condition and develop effective treatment options.

The effectiveness of active medical rehabilitation technologies among Paralympians engaged in playing sports

The purpose of the study: to study the effectiveness of active medical rehabilitation technologies among Paralympians engaged in playing sports.Materials and methods: examined 48 male patients aged 25.9 ± 2.1 years with traumatic disease of the lumbar spinal cord. All examined were divided into 2 groups: patients of the main group (19 people) against the background of standard therapy received a course of active medical rehabilitation (AMR), including mechanotherapy and electrical stimulation with biofeedback under the control of electromyography (EMG) of the muscles of the lower extremities and back. Patients in the comparison group (29 people) received standard therapy. After the AMR course, a comprehensive examination was performed, including the data of the questionnaires: the ASIA classification (American Spinal Injury Association), the FIM (Functional Independence Measure) scale of functional independence, the modified functional assessment scale of activity and quality of life VFM (Valutazione Funzionale Mielolesi), State-Trait Anxiety Inventory, the Beck depression scale; electroneurophysiological studies on the Neurosoft Neuro-EMG-Micro device, heart rate variability (HRV) on the Neurosoft Poly-Spectrum computer electrocardiograph, indicators of free movement with concentric and eccentric muscle contractions on EN-TreeM.Results: polysympathetic reflex excitability (PRV) significantly decreased in patients of the main group. There was also an improvement in vegetative reactivity (coefficient 30/15 is 1.45; p &lt;0.001) during the orthostatic test, indicating normalization of parasympathetic regulation and heart rate. The assessment on the ASIA scale revealed an improvement in sensory function by 13.4 % and motor function by 17.4 %. On the VFM scale, an increase in indicators was observed by 14.7 % and on the FIM scale by 11.5 %. When assessing the psycho-emotional sphere on the Spielberger-Khanin scale, a significant decrease in the level of reactive anxiety was noted by 10.9 %, and the level of depression by 30.5 %. A significant increase in muscle strength by 18.1 % (p &lt; 0.001) was also observed during concentric contractions, the average power increased by 83.1 % (p &lt; 0.001), the average amplitude increased by 68.7 % (p &lt; 0.001), the average speed by 27.2 % (p=0.002). When analyzing the indicators after the treatment, significant differences were obtained between the main and the comparison group (p &lt; 0.001).Conclusion: the use of biofeedback technologies under the control of electromyography leads to an increase in the effectiveness of medical rehabilitation and improves the quality of life in Paralympians with traumatic spinal cord disease.

The Combined Effect of Taurine and Omega-3 Supplementation on Delayed Onset Muscle Soreness in High-Intensity Eccentric Exercise

Background: Eccentric exercise makes more tensions in active muscle fibers, resulting in muscle damage and delayed pain. Therefore, Delayed-Onset Muscle Soreness (DOMS) is a common result of severe eccentric contractions. This study aimed to clarify the combined effect of taurine and omega-3 supplementation on DOMS and muscle damage after high-intensity eccentric exercise in young untrained men.&#x0D; Methods: Forty-eight young untrained males were assigned to four groups (taurine+omega-3 [combined], taurine, omega-3, and one placebo group) and given 1,500 mg taurine and 1,500 mg omega-3 or 1,500 mg taurine or 1,500 mg omega-3 or placebo twice a day respectively. Each group received its supplements for twenty-eight days. DOMS and muscle damage in the lower body developed using a leg press with a weight equivalent to 70% of 1RM (One-Repetition Maximum). Lactate dehydrogenase (LDH), Creatine kinase (CK) and perceived muscle soreness measures were repeated before, immediately, 24, 48, and 72 hr after eccentric activity. p&lt;0.05 was considered to be statistically significant.&#x0D; Results: In the combined group, there was no increase in CK and LDH in immediate time and 72 hr after the exercise, respectively, compared to the period before the workout. At 24 and 48 hr after the training, there was a significant decrease in muscle pain perception in all groups compared to placebo (p&lt;0.05).&#x0D; Coclusion: A combination of 1500 mg taurine and 1500 mg omega-3, two times a day, for four weeks can reduce the levels of CK and LDH enzymes as some indicators of muscle damage. It also attenuates exercise-induced DOMS and muscle damage.

Comparison of shoulder external rotation fatigue protocols on kinetic determinants and fatigue index in overhead athletes: a cross over study

Abstract The purpose of present study is to compare prone lying and half kneeling external rotator fatigue protocols on the kinetic parameters of external rotators and fatigue index in collegiate overhead athletes. Twenty overhead collegiate male athletes were recruited in this randomised cross-over experimental study design with two different shoulder external rotator fatigue protocols. Subjects were performed with prone lying and half kneeling shoulder external rotation fatigue protocol with a washout period of at least 72 h. Outcome measures like peak force, peak velocity, peak power, average power, and total work were observed in concentric and eccentric contraction and fatigue index was assessed before and after fatigue protocols. Concentric peak force (P=0.001), peak velocity (P&lt;0.001), peak power (P&lt;0.001), average power (P&lt;0.001) and total work (P=0.022) showed significant time difference whereas group difference and time× group interaction was found to be non-significant. Similarly, eccentric peak force (P=0.043), average power (P=0.001) and total work (P=0.032) showed only significant time difference. Prone-lying and half kneeling external rotation fatigue protocols reduces the peak force, peak velocity, peak power and total work in concentric contraction and peak force and total work in eccentric contraction in a similar fashion.

The Effect of Varying Eccentric Velocity on Muscle Hypertrophy

Resistance training is essential to muscle hypertrophy as it fatigues fibres through time-under-tension (TUT). As myocyte energy depletes, metabolites accrete, leading to inflammation to increase cell size, so it is adapted for future stimuli. TUT can be measured by varying eccentric velocities: i.e., the rate at which a muscle lengthens under load. A longer period of lengthening will lead to greater metabolite accretion and inflammation. However, it is unknown whether TUT is a threshold or if it can gradually increase and lead to more muscle growth. Through a literature review and experiment, this project investigates the effect of varying eccentric velocity on muscle hypertrophy. Previous research in the field of muscle physiology and metabolism were explored, with an emphasis on eccentric training. The supplementary experiment measured shoulder growth in response to the medial deltoid exercise called lateral raises, where different eccentric velocities were assigned to groups. Individualistic daily calorie and protein intake were controlled to ensure that sufficient nutrients were available for recovery and performance. Surprisingly, post-experimental research suggested that high-velocity eccentric training was best for hypertrophy due to greater levels of force production. This was consistent with the experiment, which found that the group with a fast-velocity eccentric, a lower TUT, experienced greater growth. They also exhibited greater strength gain due to neuromuscular junction adaptation. These findings related to TUT are significant for designing exercise regimens that are optimal for the prevention and rehabilitation of musculoskeletal injuries and disorders. The review’s findings suggest that fast-velocity eccentric contractions are ideal for increasing muscle size and strength.

Eccentric Cycling to Address Skeletal Muscle Dysfunction After Coronary Artery Bypass Surgery

Inpatient cardiac rehabilitation (CR) aims to address skeletal muscle dysfunction following coronary artery bypass grafting (CABG). Muscle lengthening (eccentric) contractions have a lower metabolic demand than concentric contractions and are advantageous for patients with reduced physiological reserve. This study aimed to assess the feasibility of incremental eccentric cycling during inpatient CR following CABG, utilising a custom-built eccentric cycle ergometer.

The Effect of Diaphragm Muscle Strengthening Exercise Using Incentive Spirometry on Body Balance

Based on data that has been reported by WHO, every year it is estimated that 684,000 people die cause of falls, which means that there is a failure in postural control. Postural control is known to have a relationship with diaphragmatic muscle contraction, with the intra-abdominal pressure produced by each contraction causing eccentric muscle contractions that affect postural stability. This study was conducted to determine the effect of diaphragmatic muscle strengthening exercises on body balance. This study used a pre-experimental design with one group pre and post test types. This study included 21 students. The diaphragmatic muscle strengthening exercises was held 4 weeks online. The pre-test and post-test of balance were held in the Faculty of Medicine and Health Sciences, Bengkulu University. Sampling techique that has been used is non-probability purposive sampling. The impact of two variables was analyzed using Paired T-Test. The results showed that diaphragmatic muscle strengthening exercises had a significant effect on body balance with a significance value of 0.000. The static and dynamic balance of the students of the Faculty of Medicine and Health Sciences, Bengkulu University was normal and increased after being given diaphragmatic muscle strengthening exercises. Diaphragm muscle strengthening exercises have a significant effect on student body balance.

The acute and repeated bout effects of multi-joint eccentric exercise on physical function and balance in older adults.

Eccentric muscle actions generate high levels of force at a low metabolic cost, making them a suitable training modality to combat age-related neuromuscular decline. The temporary muscle soreness associated with high intensity eccentric contractions may explain their limited use in clinical exercise prescription, however any discomfort is often alleviated after the initial bout (repeated bout effect). Therefore, the aims of the present study were to examine the acute and repeated bout effects of eccentric contractions on neuromuscular factors associated with the risk of falling in older adults. Balance, functional ability [timed up-and-go and sit-to-stand], and lower-limb maximal and explosive strength were measured in 13 participants (67.6 ± 4.9 year) pre- and post-eccentric exercise (0, 24, 48, and 72hr) in Bout 1 and 14days later in Bout 2. The eccentric exercise intervention was performed on an isokinetic unilateral stepper ergometer at 50% of maximal eccentric strength at 18 step‧min-1 per limb for 7min (126 steps per limb). Two-way repeated measures ANOVAs were conducted to identify any significant effects (P ≤ 0.05). Eccentric strength significantly decreased (-13%) in Bout 1 at 24hr post-exercise; no significant reduction was observed at any other time-point after Bout 1. No significant reductions occurred in static balance or functional ability at any time-point in either bout. Submaximal multi-joint eccentric exercise results in minimal disruption to neuromuscular function associated with falls in older adults after the initial bout.

Biceps Femoris Fascicle Behavior during Submaximal and Maximal Slow Speed Contractions.

The present study compared the effects of contraction intensity (submaximal vs maximal) and mode (concentric vs eccentric) on biceps femoris long head (BFlh) fascicle lengthening, rotation, and architectural gear ratio at long and short muscle lengths. Data were captured from 18 healthy adults (10 men and 8 women) without history of right hamstring strain injury. BFlh fascicle length ( Lf ), fascicle angle (FA), and muscle thickness (MT) were assessed in real time using two serially aligned ultrasound devices while submaximal and maximal concentric and eccentric isokinetic knee flexions were performed at 30°·s -1 . Ultrasound videos were exported and edited to create a single, synchronized video, and three fascicles were analyzed through the range of motion (10° to 80°). Changes (Δ) in Lf , FA, MT, and muscle gear at long (60° to 80° knee angle; 0° = full knee extension) and short (10° to 30°) muscle lengths and across the full knee flexion range were measured and compared. Greater Δ Lf was observed at long muscle length ( P < 0.001) during both submaximal and maximal eccentric and concentric contractions. When the full length range was analyzed, a slightly greater ΔMT was observed in concentric contractions ( P = 0.03). No significant differences between submaximal and maximal contractions were observed for Δ Lf , ΔFA, or ΔMT. No changes were detected in the calculated muscle gear between muscle lengths, intensities, or conditions ( P > 0.05). Although gear ratio ranged ~1.0 to 1.1 under most conditions, the increased fascicle lengthening observed at long muscle lengths might influence acute myofiber damage risk but also speculatively play a role in chronic hypertrophic responses to training.

Neuromuscular activation of the quadriceps femoris, including the vastus intermedius, during isokinetic knee extensions

The purpose of this study was to compare the neuromuscular activation patterns of the individual muscles of the quadriceps femoris (QF), including the vastus intermedius (VI), during isokinetic concentric (CON) and eccentric (ECC) contractions. Thirteen healthy men performed maximum isokinetic CON and ECC knee extensions at angular velocities of 30, 90, and 120°/sec at knee joint angles from 80 to 180° (180° = full extension). The surface electromyographic (EMG) activities of the four individual muscles of the QF were recorded. The root mean squares of the EMG signals were normalized by the root mean square (nRMS) during CON contraction at 30°/sec. To investigate the nRMS changes, we classified the range of motion into four subcategories for each CON and ECC contraction. The nRMS of the VI was significantly higher in the flexed position during CON and ECC contractions at all velocities, and gradually decreased toward the extended positions regardless of the type of muscle contraction or angular velocity. These results suggest that the QF undergoes neuromuscular activation in a joint angle-dependent manner. In particular, the VI may contribute greatly during flexed contractions, independent of the type of contraction and angular velocity.