Size Principle Research Articles

Big Baby, Little Mother: Tsetse Flies Are Exceptions to the Juvenile Small Size Principle.

While across the animal kingdom offspring are born smaller than their parents, notable exceptions exist. Several dipteran species belonging to the Hippoboscoidea superfamily can produce offspring larger than themselves. In this essay, the blood-feeding tsetse is focused on. It is suggested that the extreme reproductive strategy of this fly is enabled by feeding solely on highly nutritious blood, and producing larval offspring that are soft and malleable. This immense reproductive expenditure may have evolved to avoid competition with other biting flies. Tsetse also transmit blood-borne parasites that cause the fatal diseases called African trypanosomiases. It is discussed how tsetse life history and reproductive strategy profoundly influence the type of vector control interventions used to reduce fly populations. In closing, it is argued that the unusual life history of tsetse warrants their preservation in the areas where human and animal health is not threatened.

A modeling study of spinal motoneuron recruitment regulated by ionic channels during fictive locomotion.

During fictive locomotion cat lumbar motoneurons exhibit changes in membrane proprieties including a decrease in voltage threshold (Vth), afterhyperpolarization (AHP) and input resistance (Rin) and an increase in non-linear membrane property. The impact of these changes on the motoneuron recruitment remains unknown. Using modeling approach we investigated the channel mechanism regulating the motoneuron recruitment. Three types of motoneuron pools including slow (S), fatigue-resistant (FR) and fast-fatigable (FF) motoneurons were constructed based on the membrane proprieties of cat lumbar motoneurons. The transient sodium (NaT), persistent sodium (NaP), delayed-rectifier potassium [K(DR)], Ca2+-dependent K+ [K(AHP)] and L-type calcium (CaL) channels were included in the models. Simulation results showed that (1) Strengthening synaptic inputs increased the number of recruitments in all three types of motoneurons following the size principle. (2) Increasing NaT or NaP or decreasing K(DR) or K(AHP) lowered rheobase of spike generation thus increased recruitment of motoneuron pools. (3) Decreasing Rin reduced recruitment in all three types of motoneurons. (4) The FF-type motoneuron pool, followed by FR- and S-type, were the most sensitive to increase of synaptic inputs, reduction of Rin, upregulation of NaT and NaP, and downregulation of K(DR) and K(AHP). (5) Increasing CaL enhanced overall discharge rate of motoneuron pools with little effect on the recruitment. Simulation results suggested that modulation of ionic channels altered the output of motoneuron pools with either modulating the number of recruited motoneurons or regulating the overall discharge rate of motoneuron pools. Multiple channels contributed to the recruitment of motoneurons with interaction of excitatory and inhibitory synaptic inputs during walking.

Myosin heavy chains in extraocular muscle fibres: Distribution, regulation and function.

This review examines kinetic properties and distribution of the 11 isoforms of myosin heavy chain (MyHC) expressed in extraocular muscle (EOM) fibre types and the regulation and function of these MyHCs. Although recruitment and discharge characteristics of ocular motoneurons during fixation and eye movements are well documented, work directly linking these properties with motor unit contractile speed and MyHC composition is lacking. Recruitment of motor units according to Henneman's size principle has some support in EOMs but needs consolidation. Both neurogenic and myogenic mechanisms regulate MyHC expression as in other muscle allotypes. Developmentally, multiply-innervated (MIFs) and singly-innervated fibres (SIFs) are derived presumably from distinct myoblast lineages, ending up expressing MyHCs in the slow and fast ends of the kinetic spectrum respectively. They modulate the synaptic inputs of their motoneurons through different retrogradely transported neurotrophins, thereby specifying their tonic and phasic impulse patterns. Immunohistochemical analyses of EOMs regenerating in situ and in limb muscle beds suggest that the very impulse patterns driving various ocular movements equip effectors with appropriate MyHC compositions and speeds to accomplish their tasks. These experiments also suggest that satellite cells of SIFs and MIFs are distinct lineages expressing different MyHCs during regeneration. MyHC compositions and functional characteristics of orbital fibres show longitudinal variations that facilitate linear ocular rotation during saccades. Palisade endings on global MIFs are postulated to respond to active and passive tensions by triggering axon reflexes that play important roles during fixation, saccades and vergence. How EOMs implement Listings law during ocular rotation is discussed.

Neuromuscular Electrical Stimulation At Long Pulse Duration Is Associated With Higher Muscle Oxygen Utilization

Conventionally Neuromuscular Electrical Stimulation (NMES), delivered on the muscle belly at low frequency and short pulse duration, is used in rehabilitation protocols to prevent muscle atrophy. However, conventional NMES causes rapid on-set of fatigue and possibly activates muscle fibers in a synchronous, spatially fixed order (i.e. reverse of the size principle). To overcome these limitations, in the past years, a novel approach that utilizes both high frequency (100Hz) and long pulse duration (1000μs) (Wide Pulse High Frequency Stimulation, WPHF) was proposed. During WPHF NMES muscle contraction is achieved via afferent nerve fibers, allowing the reflexive discharge of motor units, with the contribution of spinal circuitries, and mimic the recruitment order of a voluntary effort (i.e. first type I fibers). PURPOSE: Evaluating muscle oxygen consumption via Near-Infrared Spectroscopy (NIRS) technique during two NMES bouts at fixed frequency (100Hz), applying Short (200μs) and Long (1000μs) Pulse duration, while concurrently matching the external force output. METHODS: Two 5 minutes intermittent (1 sec on - 3 sec off) NMES bouts at Short and Long pulse duration were delivered on the right quadricep muscle of 14 healthy subjects while sitting on an isometric chair. NIRS recorded oxygen extraction (i.e. Deoxygenated Hemoglobin - Myoglobin) from the vastus lateralis of the stimulated limb. Equal muscle force between protocols was achieved by carefully selecting the individual stimulation intensity. RESULTS: We selected 10 consecutive contractions for Short and Long Pulse NMES in order to have equal muscle output and evaluate the corresponding oxygen consumption. In the selected contractions, Peak Force was 15.3 ± 5.7 and 15.4 ± 5.6 % (p: ns) of the Maximal Voluntary Contraction while Force Time Integral was 1522.6 ± 593.4 and 1539.4 ± 597.3 Nm∗s (p: ns) for Short and Long Pulse respectively. At the same force output, Long Pulse NMES exhibited higher oxygen consumption, in percentage of the physiological calibration, than Short Pulse NMES (36.71 ± 11.82 % vs 28.79 ± 17.07 %, p:0.041). CONCLUSION: Applying Long Pulse NMES can elicit higher muscle oxygen utilization compared to Short Pulse duration, suggesting preferential recruitment of oxidative, type I muscle fibers, likewise to a voluntary contraction.

A size principle for recruitment of Drosophila leg motor neurons.

To move the body, the brain must precisely coordinate patterns of activity among diverse populations of motor neurons. Here, we use in vivo calcium imaging, electrophysiology, and behavior to understand how genetically-identified motor neurons control flexion of the fruit fly tibia. We find that leg motor neurons exhibit a coordinated gradient of anatomical, physiological, and functional properties. Large, fast motor neurons control high force, ballistic movements while small, slow motor neurons control low force, postural movements. Intermediate neurons fall between these two extremes. This hierarchical organization resembles the size principle, first proposed as a mechanism for establishing recruitment order among vertebrate motor neurons. Recordings in behaving flies confirmed that motor neurons are typically recruited in order from slow to fast. However, we also find that fast, intermediate, and slow motor neurons receive distinct proprioceptive feedback signals, suggesting that the size principle is not the only mechanism that dictates motor neuron recruitment. Overall, this work reveals the functional organization of the fly leg motor system and establishes Drosophila as a tractable system for investigating neural mechanisms of limb motor control.

Consonantal Structures in Phonetics and Phonology

The purpose of this study is to present and compare two different approaches (a phonetic approach and a phonological one) for the speech sound systems of natural languages. To this end, this study investigates natural speech sound systems with the consonantal systems of four Slavic languages, Russian, Polish, Czech and Serbian and Croatian, on the basis of phonetic and phonological approaches. In the phonetic approach, the consonant inventories of the four Slavic languages are analyzed with the theory of maximal and sufficient dispersion and the size principle, together with a frequency-based statistical approach. Segmental universals are discussed regarding sound types such as obstruents and sonorants. From the phonetic approach, it is shown that Slavic consonant systems are very unusual in terms of natural languages. Palatalized sounds in Russian and affricates and fricatives in Russian and Polish support that the Slavic consonantal system is far removed from the general aspect of human languages. On the other hand, with the phonological approach, four of the five feature-based principles proposed by Clements are employed to reveal the universals of the languages. They are Feature Economy, Marked Feature Avoidance, Robustness and Phonological enhancement. What we have seen is that some unsolved problems from the phonetic approach are explained by phonological accounts. The fact that Russian has plenty of segments represented by [+palatal] may not be unusual with respect to a feature-based approach. In addition, while the phonetic approach claims that Slavic languages (in particular, Russian and Polish) have different consonantal systems from the general aspect of natural languages because of the marked segments, the phonological approach accounts for the universals of these languages in the light of Robustness and Feature Economy. In short, what we get from phonetic accounts are language universals, found by frequency-based statistical approach while what we get from phonological accounts, using a feature-based approach, are linguistic universals.

TRPM8-mediated cutaneous stimulation modulates motor neuron activity during treadmill stepping in mice

Motor units are generally recruited from the smallest to the largest following the size principle, while cutaneous stimulation has the potential to affect spinal motor control. We aimed to examine the effects of stimulating transient receptor potential channel sub-family M8 (TRPM8) combined with exercise on the modulation of spinal motor neuron (MN) excitability. Mice were topically administrated 1.5% icilin on the hindlimbs, followed by treadmill stepping. Spinal cord sections were immunostained with antibodies against c-fos and choline acetyltransferase. Icilin stimulation did not change the number of c-fos+ MNs, but increased the average soma size of the c-fos+ MNs during low-speed treadmill stepping. Furthermore, icilin stimulation combined with stepping increased c-fos+ cholinergic interneurons near the central canal, which are thought to modulate MN excitability. These findings suggest that TRPM8-mediated cutaneous stimulation with low-load exercise promotes preferential recruitment of large MNs and is potentially useful as a new training method for rehabilitation.

Glutamatergic input varies with phrenic motor neuron size.

Like all skeletal muscles, the diaphragm muscle accomplishes a range of motor behaviors by recruiting different motor unit types in an orderly fashion. Recruitment of phrenic motor neurons (PhMNs) is generally assumed to be based primarily on the intrinsic properties of PhMNs with an equal distribution of descending excitatory inputs to all PhMNs. However, differences in presynaptic excitatory input across PhMNs of varying sizes could also contribute to the orderly recruitment pattern. In the spinal cord of Sprague-Dawley rats, we retrogradely labeled PhMNs using cholera toxin B (CTB) and validated a robust confocal imaging-based technique that utilizes semiautomated processing to identify presynaptic glutamatergic (Glu) terminals within a defined distance around the somal membrane of PhMNs of varying size. Our results revealed an ~10% higher density of Glu terminals at PhMNs in the lower tertile of somal surface area. These smaller PhMNs are likely recruited first to accomplish lower force ventilatory behaviors of the diaphragm as compared with larger PhMNs in the upper tertile that are recruited to accomplish higher force expulsive behaviors. These results suggest that differences in excitatory synaptic input to PhMNs may also contribute to the orderly recruitment of diaphragm motor units.NEW & NOTEWORTHY The distribution of excitatory glutamatergic synaptic input to phrenic motor neurons differs across motor neurons of varying size. These findings support the size principle of motor unit recruitment that underlies graded force generation in a muscle, which is based on intrinsic electrophysiological properties of motor neurons resulting from differences in somal surface area. A higher density of glutamatergic inputs at smaller, more excitable motor neurons substantiates the earlier and more frequent recruitment of these units.

Tick‐defense grooming patterns of two sympatric Tibetan ungulates

AbstractGrooming is an important behavioral defense against tick infestation for ungulates. The ‘programmed grooming model' explains the endogenous regulation of tick‐defense grooming and predicts different inter‐ and intra‐specific grooming patterns owing to the body size principle. Here, we studied the summer grooming behaviors of two sympatric Tibetan ungulates, to explore whether or not body size principle works inter‐ and intra‐specifically. The ungulates were sexually and body‐size dimorphic Tibetan antelopes (Pantholops hodgsonii) with body weight of c. 33 kg and sexually dimorphic but body‐size monomorphic Tibetan gazelle (Procapra picticaudata) with body weight of c. 14 kg. Group size was also included in our negative binominal regression model to determine whether or not the ungulates groomed more or less with the increasing group size. Results showed that large Tibetan antelopes groomed much less than small Tibetan gazelles inter‐specifically. Intra‐specifically, sex–age significantly affects the grooming rate of Tibetan antelopes. The largest adult males groomed the least, whereas the smallest fawns groomed the most. However, this sex–age effect is not found in Tibetan gazelle: males and females groomed similarly. These findings indicate that body size principle is fully supported inter‐ and intra‐specifically. Positive group size effect on grooming is observed in Tibetan gazelle, suggesting that released vigilance time from group size effect is probably transferred to grooming. From a conservation point of view, we suggest further studies on the testosterone effect on grooming patterns during the rut as well as on tick biology on the plateau.

Metabolic cost underlies task-dependent variations in motor unit recruitment.

Mammalian skeletal muscles are comprised of many motor units, each containing a group of muscle fibres that have common contractile properties: these can be broadly categorized as slow and fast twitch muscle fibres. Motor units are typically recruited in an orderly fashion following the 'size principle', in which slower motor units would be recruited for low intensity contraction; a metabolically cheap and fatigue-resistant strategy. However, this recruitment strategy poses a mechanical paradox for fast, low intensity contractions, in which the recruitment of slower fibres, as predicted by the size principle, would be metabolically more costly than the recruitment of faster fibres that are more efficient at higher contraction speeds. Hence, it would be mechanically and metabolically more effective for recruitment strategies to vary in response to contraction speed so that the intrinsic efficiencies and contraction speeds of the recruited muscle fibres are matched to the mechanical demands of the task. In this study, we evaluated the effectiveness of a novel, mixed cost function within a musculoskeletal simulation, which includes the metabolic cost of contraction, to predict the recruitment of different muscle fibre types across a range of loads and speeds. Our results show that a metabolically informed cost function predicts favoured recruitment of slower muscle fibres for slower and isometric tasks versus recruitment that favours faster muscles fibres for higher velocity contractions. This cost function predicts a change in recruitment patterns consistent with experimental observations, and also predicts a less expensive metabolic cost for these muscle contractions regardless of speed of the movement. Hence, our findings support the premise that varying motor recruitment strategies to match the mechanical demands of a movement task results in a mechanically and metabolically sensible way to deploy the different types of motor unit.

S165. Henneman’s size principle for the motor neurons recruitment of human spinal reflex: Evidences from a study of H reflexes during acute compression/ischemia

Introduction In H reflex studies, H waves are recruited from the reflex-elicited depolarization of the Alpha motor neurons, which follows the Henneman’s size principle that the small motor neurons are responsible for the early portion of the recruitment of the H-reflex. However, there has not been a successful experiment in human with EMG techniques to demonstrate this principle. The goal of this study is to demonstrate that small motor fibers are responsible for the elicitation of the H-reflex in the soleus and flexor carpi radialis (FCR) muscles by blocking the conduction of large motor nerve fibers of the tibial and median nerve using partial ischemia via blood pressure cuff. Methods This prospective study recruited 8 health resident physicians (4 m, 4 F). Electrical stimulation to the tibial nerve at the popliteal fossa, with recording from the soleus and to median nerve at above the elbow with recording from FCR was titrated to elicit both M and H waves, with ratios of amplitudes at 1:1. Compression by a blood pressure cuff was placed at the proximal tibia during tibial nerve stimulations, and at the forearm just distal to the elbow for median nerve stimulation. Stimulations with pulse duration of 1 ms at intervals of 2 s were delivered to the two nerves before, during, and post compression/ischemia. Results In all the subjects tested, during blood pressure cuff inflation, the M-waves of the two muscles consistently demonstrated significant loss of amplitude (or disappeared) with mild increase of latency, while the H-reflex showed no, or very mild amplitude reductions without changes in latency. After blood pressure cuff deflation, the M-waves immediately returned to their previous amplitude and latency patterns. There was a significant dissociation between the changes of M and H waves during acute partial compression/ischemia. Conclusion Acute compression/ischemia instantly causes nerve conduction block of the tibial and median nerves motor fibers and reduces the amplitude of the M waves, but not the H-reflexes. M waves elicited by electrical stimulation recruit large motor fibers first, and are more susceptible to the ischemic blockade applied. By contrast, the H reflex first recruits small motor neurons, with their smaller motor nerve fibers less susceptible to partial acute compression/ischemia. This experiment demonstrates the Henneman’s size principle that the smallest motor units are recruited first during spinal reflexes and volitional muscle contraction. It is also of important significance in the application of motor rehabilitation with therapeutic and functional electrical stimulation of nerves and muscles.

A Comparison of Muscle Unit Activation during Biceps Curl Exercise at 40, 60, 80 and 100% of 1 Repetition Maximum

The optimal intensity of resistance training exercise is subject to ongoing debate. There is universal agreement that electromyography (EMG) is an excellent index of motor unit (MU) activation or recruitment. The amount of EMG activity can infer the relative intensity of the exercise as compared to a maximal voluntary contraction (MVC) of a specific muscle, performing a specific exercise within one specific individual. PURPOSE: To determine the magnitude of muscle fiber recruitment (activation) of the Bicep Brachii during various loading of the muscle (40, 60, 80, and 100% of 1 RM) during bicep curl (BC) exercise performed to momentary muscular fatigue (MMF), 12 subjects (age 22.5±1.0 yr, ht. 169.4 cm±11.1 cm, body mass 75.3 kg±17.5 kg, 7♀) with resistance training experience, volunteered. METHODS: A familiarization trial on a selectorized BC machine was performed and the 1 RM was titrated for each subject. In addition, a maximal voluntary contraction (MVC) was obtained for the BC exercise against an immovable load on the same selectorized machine. MU recruitment was estimated by EMG. All subjects adhered to a 3-1-3-1 sec repetition duration during all trials. All trials were randomly assigned and terminated at MMF. RESULTS: Statistical analysis by ANOVA (p<.05) with repeated measures was applied to these data. Percent MVC for the concentric portion of the final repetition were 62.5±27.8, 71.7±24.0, 72.8±18.4, and 79.6 ±18.0 at 40, 60, 80, and 100% 1RM, respectively, with NSD among 60, 80 and 100%1RM. With the exception of the 40% trial, all trials revealed similar peak MU recruitment, despite different loading. The recruitment of ~70% of MVC at MMF may, in part, be attributed to the level of resistance training of the subject’s and their ability to activate MU’s. CONCLUSION: The size principle of MU recruitment is supported, in that peak recruitment of motor units can be accomplished at any workload greater than 60% 1 RM, provided MMF is achieved. Intensity is best defined by the final repetition, as opposed to the initial repetition (i.e. % of 1RM).

The effects of model composition design choices on high-fidelity simulations of motoneuron recruitment and firing behaviors

Objective. Computational models often require tradeoffs, such as balancing detail with efficiency; yet optimal balance should incorporate sound design features that do not bias the results of the specific scientific question under investigation. The present study examines how model design choices impact simulation results. Approach. We developed a rigorously-validated high-fidelity computational model of the spinal motoneuron pool to study three long-standing model design practices which have yet to be examined for their impact on motoneuron recruitment, firing rate, and force simulations. The practices examined were the use of: (1) generic cell models to simulate different motoneuron types, (2) discrete property ranges for different motoneuron types, and (3) biological homogeneity of cell properties within motoneuron types. Main results. Our results show that each of these practices accentuates conditions of motoneuron recruitment based on the size principle, and minimizes conditions of mixed and reversed recruitment orders, which have been observed in animal and human recordings. Specifically, strict motoneuron orderly size recruitment occurs, but in a compressed range, after which mixed and reverse motoneuron recruitment occurs due to the overlap in electrical properties of different motoneuron types. Additionally, these practices underestimate the motoneuron firing rates and force data simulated by existing models. Significance. Our results indicate that current modeling practices increase conditions of motoneuron recruitment based on the size principle, and decrease conditions of mixed and reversed recruitment order, which, in turn, impacts the predictions made by existing models on motoneuron recruitment, firing rate, and force. Additionally, mixed and reverse motoneuron recruitment generated higher muscle force than orderly size motoneuron recruitment in these simulations and represents one potential scheme to increase muscle efficiency. The examined model design practices, as well as the present results, are applicable to neuronal modeling throughout the nervous system.

FES-Cycling at Cybathlon 2016: Overview on Teams and Results.

Limb mobilization and movement exercises prevent the effects of immobility and sedentarity after spinal cord injury (SCI) 1-4. Functional electrical stimulation (FES) has been successfully applied to facilitate exercise of paralyzed muscles, and thus to restore movement and function 5-7. FES‐induced cycling in people with SCI has been demonstrated to positively affect the cardiopulmonary system 8, 9, bone mineral density 10, and muscle strength 11, 12. FES‐cycling was achieved by means of a fixed ergocycle in most of these studies. Mobile cycling using tricycles 13 can add a recreational dimension to the exercise and improve the attractiveness of FES‐assisted exercises 14. Mobile FES‐cycling has also become a sport, as demonstrated a few times since the first competition in Cardiff (UK) in 2006. Thereby, “long” distance races, for example, about 1000 m, address a major challenge when applying FES in people with SCI. Indeed, in comparison to healthy muscles, neuromuscular fatigue occurs quite early as motor units are synchronously activated and not according to Henneman's size principle. Besides the problem of limited fatigue resistance, broad applicability of any FES technology is also hampered by limitations in achievable muscle force magnitude, muscle selectivity and movement controllability 15-18. In order to further advance technologies such as FES for their potential acceptability and use by people relying on assistive devices, the Cybathlon event was launched by ETH Zurich 19, 20. In October 2016, the first Cybathlon took place in Kloten, Switzerland. FES‐cycling is one of the six Cybathlon disciplines. This summary introduces the discipline and synthesizes the characteristics and performances of the twelve teams that participated in the 2016 event.

Spinal Cord Injury Paralysis: Synaptic Competitive-Learning and Rewiring Therapy Restores Locomotoricity

At this point in time there are only limited treatment options available for spinal cord injury (SCI) paralysis (e.g. implanted stimulation devices, stem cells). They are in clinical trials, complex, invasive, ill-affordable, and quality of outcome rather unpredictable. This author had presented two alternative treatment procedures based on over five decades of fundamental research on the functioning of the spinal cord motor system in 2009, 2013 and 2015. These are non-invasive, functional, and recovery predictable. The first one uses low-dose Botulinum toxin to select paralyzed limb muscles. The second consists of transient partial denervation of the muscles. They both operate on similar principles of synaptic competitive-learning (SCL) and rewiring. They focus on the spinal motoneuron, its synaptic connectivity, and spinal cord reflexes. They are (i) induce competition among neuromuscular synapses, (ii) modify the motoneurons’ soma sizes (Size principle) and thus their excitability-inhibitability, firing properties, (iii) resize the motor units of the paralyzed muscles, and (iv) reposition the synaptic memory weights impinging on the motoneurons. Animal model treated by the second procedure shows that even in complete cord injury, the residual networks of the isolated distal cord are capable of remarkable motor restoration (see videos). This paper now explains the precise mechanisms behind the restorative rewiring (SCL) therapy.

Análisis crítico de la Ley de Henneman

La Ley de Henneman (también denominada "principio del tamaño") establece que, dado que el tamaño de las motoneuronas determina su umbral de excitación, durante la aplicación de una fuerza muscular las unidades motoras de menor tamaño serán las primeras en reclutarse, y en la medida en que el esfuerzo lo requiera, se irán reclutando más unidades motoras en un patrón estereotipado según su progresivo tamaño. No obstante, durante las actividades propias de la vida diaria o el deporte, este principio adolece de numerosas excepciones. El propósito de este trabajo de revisión es describir, en concordancia con la evidencia científica, en qué condiciones esta Ley no se cumple, o bien se ve significativamente alterada.

Organization of the motor-unit pool for different directions of isometric contraction of the first dorsal interosseous muscle.

Muscle force generation involves recruitment and firing rate modulation of motor units (MUs). The control of MUs in producing multidirectional forces remains unclear. We studied MU recruitment and firing properties, recorded from the first dorsal interosseous muscle, for 3 different directions of contraction: abduction; abduction/flexion combination; and flexion. MUs were recruited systematically at higher threshold force during flexion. Larger MUs were recruited and firing rates of MUs were lower during abduction. There was an orderly recruitment of MUs according to MU size regardless of contraction direction, obeying the "size principle." Firing rates of earlier-recruited MUs were consistently higher than later-recruited MUs, affirming the "onion-skin" property. Our findings suggest that the size principle and onion-skin organization together provide a general description of MU recruitment patterns and firing properties. The directional alternations of MU control properties likely reflect changes in neural drive to the muscle. Muscle Nerve 57: E85-E93, 2018.

FMS: Relationship between muscul activity in deep squat ans trunk stability pushup

Aims and Objectives:Motor control is described as the internal control and regulation processes which facilitate movements. Scientists divide motor control into the function of stability and the movement to maintain balance in locomotion. The FMS is used to analyze the motor behavior of muscle slings on the one hand, and to estimate injury risk on the other hand. Yet, the true extent of the FMS’ diagnostic information remains unclear. The low intensity level of the FMS items causes low tension within the motor network. Based on Hennemen’s size principle, this is a clear indicator for the activation of slow-twitch fibers in the muscle. A possible relationship between movement and stability function of muscle slings has yet to be examined. Therefore, the aim of this investigation was to shed light on the motor behavior of dynamic and isometric muscle activity as well as the examination of average muscle activity when performing the items deep squat (DS) and trunk stability pushup (TSPU).Materials and Methods:Data from 16 collegiate athletes (22.1±1.5yrs) with various sports histories was analyzed. The data analysis was based on Kendall’s tau correlation coefficient. The items DS and TSPU were rated via an ordinal ranking system ranging from 0 (pain) to 3 (adequate). Muscle activity was recorded with a new EMG device at a rate of 25 Hz (Myontec Ltd, Kuopio, Finland). In a concurrent pilot study the reliability of this device was examined with a progressive loaded squat protocol (50 up to 125% BW). It indicated almost perfect reliability for the quad/ham balance, quadriceps distribution (r< 0.9, CV:3-5%) and high reliability for the hamstrings (r >0.8, CV:<10%).Results:Strong relationships between the quad/ham balance (r=0.7, p<0.01) and quadriceps distribution (r=0.6, p<0.03) in DS and TSPU were identified. The connection between hamstring muscle activity balance was low (r< 0.2, p>0.5). In both items, the muscle contractions were dominated by the activation of the quadriceps (79% vs. 21% hamstrings). Additionally, the average muscle activity was 4 times higher in a loaded squat (100% BW) than it was in DS. Generally, DS was rated as follows: score 3 (3 times) and score 2 (13 times). For the item TSPU score 3 was given 14 times and score 2 was given 2 times.Conclusion:The relationship between dynamic and static motor behavior of the quadriceps supports the connection between the stabilizing and movement function of muscle slings. The low intensity corresponds with the slow EMG activity in DS, which is an indicator for the activation of mainly slow twitch muscle fibers. This scientific innovation is relevant for practitioners as it establishes the diagnostic value of the FMS. Based on this evidence, the FMS provides information with regards to low tension motor behavior. It is unlikely that this information is specific enough to estimate injury risk or performance because when it comes to return to sport decisions, it is also important to obtain information of motor control associated with fast-twitch fibers.

Rational Learners and Moral Rules

AbstractPeople draw subtle distinctions in the normative domain. But it remains unclear exactly what gives rise to such distinctions. On one prominent approach, emotion systems trigger non‐utilitarian judgments. The main alternative, inspired by Chomskyan linguistics, suggests that moral distinctions derive from an innate moral grammar. In this article, we draw on Bayesian learning theory to develop a rational learning account. We argue that the ‘size principle’, which is implicated in word learning, can also explain how children would use scant and equivocal evidence to interpret candidate rules as applying more narrowly than utilitarian rules.

High- and Low-Load Resistance Training: Interpretation and Practical Application of Current Research Findings.

Our current state of knowledge regarding the load (lighter or heavier) lifted in resistance training programmes that will result in 'optimal' strength and hypertrophic adaptations is unclear. Despite this, position stands and recommendations are made based on, we propose, limited evidence to lift heavier weights. Here we discuss the state of evidence on the impact of load and how it, as a single variable, stimulates adaptations to take place and whether evidence for recommending heavier loads is available, well-defined, currently correctly interpreted or has been overlooked. Areas of discussion include electromyography amplitude, in vivo and in vitro methods of measuring hypertrophy, and motor schema and skill acquisition. The present piece clarifies to trainers and trainees the impact of these variables by discussing interpretation of synchronous and sequential motor unit recruitment and revisiting the size principle, poor agreement between whole-muscle cross-sectional area (CSA) and biopsy-determined changes in myofibril CSA, and neural adaptations around task specificity. Our opinion is that the practical implications of being able to self-select external load include reducing the need for specific facility memberships, motivating older persons or those who might be less confident using heavy loads, and allowing people to undertake home- or field-based resistance training intervention strategies that might ultimately improve exercise adherence.