Muscle Tuning Research Articles

Experiment-guided tuning of muscle–tendon parameters to estimate muscle fiber lengths and passive forces

The workflow to simulate motion with recorded data usually starts with selecting a generic musculoskeletal model and scaling it to represent subject-specific characteristics. Simulating muscle dynamics with muscle–tendon parameters computed from existing scaling methods in literature, however, yields some inconsistencies compared to measurable outcomes. For instance, simulating fiber lengths and muscle excitations during walking with linearly scaled parameters does not resemble established patterns in the literature. This study presents a tool that leverages reported in vivo experimental observations to tune muscle–tendon parameters and evaluates their influence in estimating muscle excitations and metabolic costs during walking. From a scaled generic musculoskeletal model, we tuned optimal fiber length, tendon slack length, and tendon stiffness to match reported fiber lengths from ultrasound imaging and muscle passive force–length relationships to match reported in vivo joint moment–angle relationships. With tuned parameters, muscle contracted more isometrically, and soleus’s operating range was better estimated than with linearly scaled parameters. Also, with tuned parameters, on/off timing of nearly all muscles’ excitations in the model agreed with reported electromyographic signals, and metabolic rate trajectories varied significantly throughout the gait cycle compared to linearly scaled parameters. Our tool, freely available online, can customize muscle–tendon parameters easily and be adapted to incorporate more experimental data.

Whole Body Vibration: A Valid Alternative Strategy to Exercise?

Several studies agree that mechanical vibration can induce physiological changes at different levels, improving neuromuscular function through postural control strategies, muscle tuning mechanisms and tonic vibration reflexes. Whole-body vibration has also been reported to increase bone mineral density and muscle mass and strength, as well as to relieve pain and modulate proprioceptive function in patients with osteoarthritis or lower back pain. Furthermore, vibratory training was found to be an effective strategy for improving the physical performance of healthy athletes in terms of muscle strength, agility, flexibility, and vertical jump height. Notably, several benefits have also been observed at the brain level, proving to be an important factor in protecting and/or preventing the development of age-related cognitive disorders. Although research in this field is still debated, certain molecular mechanisms responsible for the response to whole-body vibration also appear to be involved in physiological adaptations to exercise, suggesting the possibility of using it as an alternative or reinforcing strategy to canonical training. Understanding these mechanisms is crucial for the development of whole body vibration protocols appropriately designed based on individual needs to optimize these effects. Therefore, we performed a narrative review of the literature, consulting the bibliographic databases MEDLINE and Google Scholar, to i) summarize the most recent scientific evidence on the effects of whole-body vibration and the molecular mechanisms proposed so far to provide a useful state of the art and ii) assess the potential of whole-body vibration as a form of passive training in place of or in association with exercise.

Tuned muscle and spring properties increase elastic energy storage.

Elastic recoil drives some of the fastest and most powerful biological movements. For effective use of elastic recoil, the tuning of muscle and spring force capacity is essential. Although studies of invertebrate organisms that use elastic recoil show evidence of increased force capacity in their energy loading muscle, changes in the fundamental properties of such muscles have yet to be documented in vertebrates. Here, we used three species of frogs (Cuban tree frogs, bullfrogs and cane toads) that differ in jumping power to investigate functional shifts in muscle-spring tuning in systems using latch-mediated spring actuation (LaMSA). We hypothesized that variation in jumping performance would result from increased force capacity in muscles and relatively stiffer elastic structures, resulting in greater energy storage. To test this, we characterized the force-length property of the plantaris longus muscle-tendon unit (MTU), and quantified the maximal amount of energy stored in elastic structures for each species. We found that the plantaris longus MTU of Cuban tree frogs produced higher mass-specific energy and mass-specific forces than the other two species. Moreover, we found that the plantaris longus MTU of Cuban tree frogs had higher pennation angles than the other species, suggesting that muscle architecture was modified to increase force capacity through packing of more muscle fibers. Finally, we found that the elastic structures were relatively stiffer in Cuban tree frogs. These results provide a mechanistic link between the tuned properties of LaMSA components, energy storage capacity and whole-system performance.

Response to select comments on the proposed paradigm shifts in running

Background: Six experts in the field of running-related research have critically addressed a proposal to abandon the paradigms of ‘impact force’ and ‘pronation control’ when investigating running shoes, running injury, and running performance. Further, these experts have commented on the suggestion of the new paradigms of ‘muscle tuning’ and the ‘preferred movement path’ that can be used to investigate questions related to running injuries and performance as well running shoe design and comfort. This publication synthesizes and addresses the main criticisms of the experts and describes future directions to further develop the ‘muscle tuning and ‘preferred movement’ paradigms.

Detailed characterization of physiological EMG activations and directional tuning of upper-limb and trunk muscles in point-to-point reaching movements.

In recent years, several studies have investigated upper-limb motion in a variety of scenarios including motor control, physiology, rehabilitation and industry. Such applications assess people’s kinematics and muscular performances, focusing on typical movements that simulate daily-life tasks. However, often only a limited interpretation of the EMG patterns is provided. In fact, rarely the assessments separate phasic (movement-related) and tonic (postural) EMG components, as well as the EMG in the acceleration and deceleration phases. With this paper, we provide a comprehensive and detailed characterization of the activity of upper-limb and trunk muscles in healthy people point-to-point upper limb movements. Our analysis includes in-depth muscle activation magnitude assessment, separation of phasic (movement-related) and tonic (postural) EMG activations, directional tuning, distinction between activations in the acceleration and deceleration phases. Results from our study highlight a predominant postural activity with respect to movement related muscular activity. The analysis based on the acceleration phase sheds light on finer motor control strategies, highlighting the role of each muscle in the acceleration and deceleration phase. The results of this study are applicable to several research fields, including physiology, rehabilitation, design of robots and assistive solutions, exoskeletons.

High vibration frequency of soft tissue occurs during gait in power-trained athletes

ABSTRACT Muscles serve as a critical regulator of locomotion and damping, resulting in changes of soft tissue vibration. However, whether muscle fibre compositions of different individuals will cause different extents of soft tissue vibration during gait is unclear. Therefore, this study investigated the differences in lower extremity vibration frequencies among power-trained and non-power-trained athletes during walking and running. Twelve weightlifting athletes were assigned to the power-trained group and twelve recreational runners were assigned to the non-power-trained group. Accelerometers were used to detect soft tissue compartment vibration frequencies of the rectus femoris (RF) and gastrocnemius medialis (GMS) during walking and running. Results indicated that power-trained athletes, as compared to the non-power-trained, induced significantly (p < 0.05) higher vibration frequencies in their soft tissue compartments during walking and running. This suggests that power-trained athletes, who have higher ratios of fatigable fast-twitch muscle fibres, may have induced higher soft tissue compartment vibration frequencies. As a result, there is a likelihood that power-trained athletes may recruit more fatigable fast-twitch muscle fibres during muscle tuning, causing dysfunctions during prolonged exercises.

Activation patterns of pelvic floor muscles in women with incontinence while running: a randomized controlled trial.

Running is known to cause urinary leakage in women with stress urinary incontinence (SUI). Task-specific fiber-type recruitment while running can be estimated using wavelets. The aim of this study was to compare the effect of a new physiotherapy program including involuntary, reflexive training with a standard physiotherapy program on pelvic floor muscle (PFM) activation patterns and fiber-type recruitment behavior while running. In this triple-blinded randomized controlled trial, women with SUI were randomly allocated to the control group (CON), which performed a standard physiotherapy program, or the experimental group (EXP), which received additional involuntary, reflexive training. PFM electromyography (EMG) was recorded during 10s at three running speeds and analyzed using Morse wavelets. The relative distribution of power (%) over the frequencies from 20 to 200Hz was extracted and analyzed within six-time intervals of 30ms. Statistical nonparametric mapping was performed to identify power spectra differences. Thirty-nine (CON) and 38 (EXP) women were included. The power spectra showed no statistically significant group differences. The time intervals from 30ms before to 30ms after initial contact showed significantly lower intensities than the intervals from 30 to 150ms after initial contact in the lowest and higher intensities in the highest frequencies for all running speeds and both groups. Power spectra shifts toward higher frequency bands in the pre-initial contact phase could indicate a feed-forward anticipation and a muscle tuning for the expected impact of initial contact event in order to maintain continence.

Tinospora cordifolia protects from skeletal muscle atrophy by alleviating oxidative stress and inflammation induced by sciatic denervation

Ethanopharmacological relevanceTinospora cordifolia (TC) is widely being used as immunomodulatory and re-juvenile drug and well described in Indian Ayurveda system of medicine. Rejuvenation also means the fine tuning of the skeletal muscles. Skeletal muscle related disorder, i.e. atrophy is major problem which arise due to cachexia, sarcopenia and immobilization. However, despite of the great efforts, there is scarcity of FDA approved drugs in the market to treat skeletal muscle atrophy. Aim of the studyThe current study was aimed to explore the in-vitro and in-vivo efficacy and mechanism of TC in myogenic differentiation and skeletal muscle atrophy to establish the possibility of its usage to counteract skeletal muscle atrophy. Materials and methodsC2C12 cell lines were used to determine myogenic potential and anti-atrophic effects of T. cordifolia water extract (TCE). Its in-vitro efficacy was re-validated in vivo by supplementation of TCE at a dose of 200 mg/kg/p.o. for 30 days in denervated mice model of skeletal muscle atrophy. Effects of TCE administration on levels of oxidative stress, inflammatory markers and proteolysis were determined. ResultsTCE supplementation displayed increased lymphocyte proliferation and induced myogenic differentiation of C2C12 myoblasts by significantly increasing myocytes length and thickness, in comparison to control (p < 0.05). TCE supplementation decreased oxidative stress and inflammatory response by significantly modulating activities of catalase, glutathione peroxidase, lipid peroxidase, superoxide dismutase and β-glucuronidase (p < 0.05). It increased MF-20c expression and ameliorated degradation of muscle protein by down-regulating MuRF-1 and calpain activity. ConclusionTCE supplementation promotes myogenic differentiation in C2C12 cell lines and prevents denervation induced skeletal muscle atrophy by antagonizing the proteolytic systems (calpain and UPS) and maintaining the oxidative defense mechanism of the cell. Hence, TCE can be used as a protective agent against muscle atrophy.

Vibration settling time of the gastrocnemius remains constant during an exhaustive run in rear foot strike runners

In this study, vibrations of human gastrocnemius during an exhaustive run protocol are considered for analysis. Previous studies have shown increased vibration intensity and damping coefficient within the soft tissue with fatigue. The question of this study was to investigate if the vibration settling time remains constant during a prolonged running. Eleven semi-professional middle/long distance runners ran to exhaustion on a treadmill with their preferred constant speed (4.29 ± 0.33 m/s) for 3873 ± 1147 m. Vibration of the gastrocnemius lateralis, electrical activity of the tibialis anterior and the gastrocnemius medialis along with ground reaction force (GRF) were recorded. The results demonstrated significant increase in impact peak and loading rate, and the frequency content of the impact, with no significant change in active peak of the vertical GRF. Fatigue resulted in increased vibration intensity, damping coefficient, and energy dissipation of vibration with no change in vibration settling time. Furthermore, peak acceleration significantly linearly (R = 0.59) increased as a function of running time. The mean frequency of muscle activity of the gastrocnemius medialis and the intensity of muscle activity in TA significantly decreased. The results suggest that constant vibration settling time might either be an objective for muscle tuning which is more pronounced in fatigued state or a passive by-product of muscle function in running. Further studies are needed to address this point.

New paradigms in running injury prevention - Benno M. Nigg on target

In this target article (TA; CISS_2017_007), Benno M. Nigg, Maurice M. Mohr, and Sandro R. Nigg explain and criticize the two main paradigms (‘impact’ and ‘pronation’) in running injury prevention research of the last 40 years and present new paradigms on ‘muscle tuning’, ‘preferred movement path’, and ‘functional groups’. The main article (CISS2017_007) is then discussed by six peer commentaries (CISS2018_102 – CISS2018_107), authored by sport scientists that are experts in the field. Finally, critiques, suggestions, and extensions brought forward by the commentators are acknowledged by Nigg and co-authors in their closing response (CISS2019_001).

Neuroanatomical Basis of Individuality in Muscle Tuning Function: Neural Correlates of Muscle Tuning.

In a conventional view of motor control, the human brain might employ an optimization principle that leads a stereotypical motor behavior which we observe as an averaged behavioral data over subjects. In this scenario, the inter-individual motor variability is considered as an observation noise. Here, we challenged this view. We considered a motor control task where the human participants manipulated arm force by coordinating shoulder and elbow torques and investigated the muscle-tuning function that represents how the brain distributed the ideal joint torques to multiple muscles. In the experimental data, we observed large inter-individual variability in the profile of a muscle-tuning function. This contradicts with a well-established optimization theory that is based on minimization of muscle energy consumption and minimization of motor variability. We then hypothesized the inter-subject differences in the structure of the motor cortical areas might be the source of the across-subjects variability of the motor behavior. This was supported by a voxel-based morphometry analysis of magnetic resonance imaging; The inter-individual variability of the muscle tuning profile was correlated with that of the gray matter volume in the premotor cortex which is ipsilateral to the used arm (i.e., right hemisphere for the right arm). This study suggests that motor individuality may originate from inter-individual variation in the cortical structure.

Soft tissue vibration dynamics after an unexpected impact.

It has been proposed that during walking and running the body has strategies to minimize the soft tissue vibrations. The concept of muscle tuning suggests that muscle activity changes in response to the input signal to modify the frequency and damping of such vibrations. Although it has been demonstrated for continuous vibrations and single impacts, the adaptations dynamics are still unclear. The purpose of this study was to determine (1) if the neuromuscular adaptation to repeated single impacts is immediate, (2) what are the adaptation mechanisms, and (3) if there are functional groups defined by different adaptation strategies. Twenty‐one subjects performed two sets of knee curl on a dynamometer with a custom‐made appliance that supported the foot and heel. The first set was for familiarization with a 90° range of movement and 400°/sec velocity. The second set had 15 repetitions with a 55° range and the same angular velocity. The subjects were not notified of the change; therefore the first impact was unexpected. A pair of electrodes and a three‐dimensional accelerometer were placed on the gastrocnemius medialis. Damping coefficient, natural frequency, and EMG characteristics were measured. All the participants adapted to the vibrations and showed changes in the damping coefficient and or the natural frequency. Apart from the immediate adaptation, a subgroup showed a progressive adaptation after the first immediate change. Three functional groups were identified using support vector machine, correlations with anthropometric values suggest that muscle mass could affect the adaptation strategy used.

Muscle tuning and preferred movement path: do we need a paradigm shift or should we redefine the old? – comment on Nigg et al.

In the feature paper “Muscle tuning and preferred movement path – a paradigm shift“, Benno Nigg and colleagues discuss that the impact and pronation paradigm should be abandoned as there is not enough biomechanical and epidemiological evidence supporting these paradigms. We agree that the paradigms, as defined in the paper, are currently not supported by strong scientific evidence however we argue that the lack of evidence originates from shortcomings in the methodological approach to these paradigms. In our commentary, we argue for a redefinition of the paradigms rather than defining two ‘new’ paradigms. A better methodological approach and definitions of the paradigms based on the current evidence are needed rather than to abandon them.

A discussion of the Muscle Tuning and the Preferred Movement Path concepts – comment on Nigg et al.

Nigg and colleagues propose two new paradigms, the Muscle Tuning and the Preferred Movement Path concepts. The purpose of this commentary is to discuss plausibility and challenges of these two concepts. Both concepts are highly plausible from a mechanical point of view and they also go in line with every-day observations. The main challenges for the muscle tuning paradigm are that (a) this mechanism is only one of several mechanisms in how the body adapts to impacts, and (b) it is very difficult to develop testable predictions from this paradigm since the mechanical (vibrational) properties of the leg are highly subject-specific and complex. The main open questions regarding the preferred movement path paradigm relate to (a) its integration with the concepts for movement variability, and (b) to the circumstances under which the preferred movement path might change.

A paradigm shift is necessary to relate running injury risk and footwear design – comment on Nigg et al.

In this commentary, we respond to suggestions that new paradigms are needed to relate running-related injury risk and footwear design. We concur with the authors of this paper that the previous paradigms on which footwear were designed are faulty. We also concur with the authors that new paradigms are indeed needed and that research must take into consideration more epidemiological studies and more prospective biomechanical studies. The authors suggest new paradigms including muscle tuning, the preferred movement path and functional groups. However, we do raise questions about each of these suggestions regarding how these paradigms can be developed in future research designs.

Running impact forces: from half a leg to holistic understanding – comment on Nigg et al.

Running impact forces have immediate relevance for the muscle tuning paradigm proposed here and broader relevance for overuse injuries, shoe design and running performance. Here, we consider their mechanical basis. Several studies demonstrate that the vertical ground reaction force-time (vGRFT) impulse, from touchdown to toe-off, corresponds to the instantaneous accelerations of the body’s entire mass (Mb) divided into two or more portions. The simplest, a two-mass partitioning of the body (lower-limb, M1=0.08•Mb; remaining mass, M2=0.92•Mb) can account for the full vGRFT waveform under virtually all constant-speed, level-running conditions. Model validation data indicate that: 1) the non-contacting mass, M2, often accounts for one-third or more of the early “impact” portion of the vGRFT, and 2) extracting a valid impact impulse from measured force waveforms requires only lower-limb motion data and the fixed body mass fraction of 0.08 for M1.

Reduction of Iliac Crest Height Difference After Intervention with the Krullaards Perfect Reset Treatment Plate in Patients with Chronic Non- Specific Low Back Pain: A Randomized Controlled Trial

Background: Nonspecific low back pain is the most common disease in the Netherlands and has a prevalence of over 2.500.000 patients. The last decade, vibration plates are evaluated as influencing muscle tuning and soft tissues of the lumbar spine. The Krullaards Perfect Reset (KPR) plate as treatment plate with vibration function has not been investigated yet.Objective: To evaluate if an intervention with the Krullaards Perfect Reset treatment plate (KPR) could decrease iliac crest height difference, as measured using a PALM meter, to a difference smaller than 0.5 centimeters in patients with nonspecific low back pain.Study design: Double-blind randomized controlled trialMethods: 26 participants with a non-specific low back pain history were randomly assigned to intervention or control group. Following pre-treatment measurements of anatomic leg length difference (LLD), clinical LLD, iliac crest height and pelvic torsion, participants had to step onto the KPR or a placebo plate. After treatment measurements on clinical LLD, iliac crest height and pelvic torsion were repeated.Results: Significant results were found for changes in iliac crest height difference after treatment with the KPR vibration plate (0.4 centimetres) and control group comparison (0.7 centimetres), p=0.02. In addition, a large effect size of 0.85 was seen in favour of the intervention group. No significant results were found for changes in clinical LLD and pelvic torsion.Conclusion: This proof of concept study demonstrates a decrease of iliac crest height difference, as measured using a PALM meter, to a difference smaller than 0.5 centimeters in patients with nonspecific low back pain using the KPR treatment plate based on the novel concept of combining vibrations and movement to influence pelvic muscle tuning

Muscle tuning and preferred movement path – a paradigm shift

In the last 40 years, the scientific debate around running injuries and running shoes has been dominated by two paradigms, the ‘impact’ and the ‘pronation’ paradigms. However, the development of running shoe technologies aimed at reducing impact forces and pronation has not led to a decline of running-related injuries. This article recommends to abandon the ‘impact’ and ‘pronation’ paradigms due to a lack of biomechanical and epidemiological evidence and instead suggests a shift to new paradigms: ‘Muscle tuning’ and the ‘preferred movement path’. These paradigms represent new approaches to understanding the biomechanical patterns of each individual runner and how they are controlled by the neuromuscular system. Experimental evidence in support of the ‘muscle tuning’ and ‘preferred movement path’ paradigms are presented and discussed regarding their relevance for running performance, injuries, and footwear. Finally, this paper proposes that the concept of ‘functional groups’ should be used and further developed to overcome the challenge that groups of individuals respond differently to footwear interventions. First, groups of individuals who behave similarly (functional groups) should be identified. Second, running shoes should be selected to match the characteristics of the identified functional groups in order to optimize the beneficial effects of running shoes for improving running performance and reducing the risk of running injuries.

Muscle tuning and preferred movement path – a paradigm shift

Muscle tuning and preferred movement path – a paradigm shift

Multi-facets of Serum Response Factor in the Cardiac Pathophysiology

Heart is a vital organ that pumps blood to all body parts of an organism through synchronous contraction and relaxation movements of the cardiac muscle. Homeostasis of cardiac muscle is thus necessary for normal heart functioning. Fine tuning of the cardiac muscle is maintained by numerous signal transduction pathways which are not only responsible for physiological functions, but pathological lesions as well. Many intrinsic or extrinsic stimuli like physical stress, pressure overload, hypertension, etc. disturbs cardiac homeostasis and affects signal transduction pathways causing disease phenotype such as hypertrophy, cardiomyopathy, and consequent heart failure. The most unique characteristic of cardiomyocytes is that they are terminally differentiated and do not grow in number postnatally, they only grow in size by lateral/longitudinal hypertrophy. Hypertrophy is also induced in cardiomyocytes to overcome acute wall tension caused by various biochemical stresses. At molecular level, several signalling pathways and interacting networks have been implicated with the heart’s molecular response to physiological and/or pathological biomechanical stress, reviewed in detail elsewhere [1‐4]. Calcineurin, a Ca2+-calmodulin activation dependent serine‐threonine phosphatase is one of the key signaling molecules strongly linked to cardiac hypertrophy [5‐8]. Its prohypertrophic effects are well established through series of in vitro and in vivo studies and is highly correlated with human patients of cardiac hypertrophy and cardiomyopathy [6,9]. Moreover, Calcineurin signaling is found to be interconnected with many other important hypertrophic pathways, such as those controlled by glycogen synthase kinase (GSK) 3β and mitogenactivated protein (MAP) kinase signaling [3,10]. Interestingly, Rho family of small GTPase proteins, consisting of Rho, Rac, and Cdc42 subfamilies regulate the sarcomere organization in cardiomyocytes, one of the hallmarks of hypertrophy [11]. These GTPase effectors are also upstream of a very important cardiac signaling molecule, serum response factor (SRF) [12,13].