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Initial Arm Muscle Activation in a Planar Ballistic Arm Movement with Varying External Force Directions: A Simulation Study

Tom G. Welter and Maarten F. Bobbert

It has been shown in previous research that the initial phase of EMG for a punching movement remained almost unchanged regardless of whether an external force was applied to the arm. The purpose of the present study was to explain this finding with the help of simulations. A two-dimensional model of me arm actuated by 6 Hill-type muscles was used to simulate a punching movement in the horizontal plane from a prescribed starting position with 90° elbow flexion. Input to the model was the stimulation of me muscles, and output were, among others, muscle forces and segmental accelerations. A genetic algorithm was used to determine the muscle onset times mat minimized movement duration and targeting error. In a subsequent forward simulation, the optimized muscle onset times for an unloaded punching movement were superimposed on the isometric stimulation necessary to hold me arm in the starting position while an external force was applied to the arm. The resulting movement was only slightly different from the unloaded movement. It appeared that because of the low level of isometric muscle force prior to the movement, and the high level of stimulation during the movement, muscle force was increased at a rate mat was almost independent of the prior force level. These results confirmed the suggestion that the initial phase of EMG in ballistic movements is more related to the rate of change of force than to the absolute force level. It is hypothesized mat this may simplify the task of the nervous system in the choice of initial muscle activity in ballistic arm movements because no adjustments to varying external forces are required.

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The Force–Velocity Profiling Concept for Sprint Running Is a Dead End

Gertjan Ettema

Purpose: In this commentary, I present arguments against the use of the force–velocity profiling concept in design and adaptations of training programs targeting sprinting. The purpose of this commentary is to make sports practitioners more aware of the rationale behind the concept and explain why it does not work. Rationale: Force–velocity profiling is a mathematical way to present the velocity development during sprint behavior. Some details of this behavior may be accentuated by transforming it to other variables, but it does not add any new information about sprint performance. Thus, contrary to what is often claimed, the force–velocity profile does not represent maximal capacities (ability of force and velocity generation) of the athlete. It is claimed that through force–velocity profiling one may identify the optimal ratio of force and velocity capacities. Furthermore, proponents of the force–velocity profiling concept suggest that through directed training force and velocity capacities can be altered (inversely dependent) to obtain this optimal ratio, without changing the capacity to express power. Fundamentally, this idea is unfounded and implausible. Conclusion: At best, force–velocity profiling may be able to identify between-athletes differences. However, these can be more easily deduced directly from performance time traces.

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Are Injuries More Common With CrossFit Training Than Other Forms of Exercise?

Chelsey Klimek, Christopher Ashbeck, Alexander J. Brook, and Chris Durall

CrossFit gym using successive and rapid ballistic movements with minimal to no recovery time between movements. A wide variety of high-intensity exercises that include running, rowing, Olympic lifting, powerlifting, and gymnastic exercises were included in the CrossFit training. A physical fitness training

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Submovements Grow Larger, Fewer, and More Blended during Stroke Recovery

Brandon Rohrer, Susan Fasoli, Hermano Igo Krebs, Bruce Volpe, Walter R Frontera, Joel Stein, and Neville Hogan

Submovements are hypothesized building blocks of human movement, discrete ballistic movements of which more complex movements are composed. Using a novel algorithm, submovements were extracted from the point-to-point movements of 41 persons recovering from stroke. Analysis of the extracted submovements showed that, over the course of therapy, patients' submovements tended to increase in peak speed and duration. The number of submovements employed to produce a given movement decreased. The time between the peaks of adjacent submovements decreased for inpatients (those less than 1 month post-stroke), but not for outpatients (those greater than 12 months post-stroke) as a group. Submovements became more overlapped for all patients, but more markedly for inpatients. The strength and consistency with which it quantified patients' recovery indicates that analysis of submovement overlap might be a useful tool for measuring learning or other changes in motor behavior in future human movement studies.

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Influence of Isoinertial-Pneumatic Mixed Resistances on Force–Velocity Relationship

Simon Avrillon, Boris Jidovtseff, François Hug, and Gaël Guilhem


Muscle strengthening is commonly based on the use of isoinertial loading, whereas variable resistances such as pneumatic loading may be implemented to optimize training stimulus. The purpose of the current study was to determine the effect of the ratio between pneumatic and isoinertial resistance on the force–velocity relationship during ballistic movements.


A total of 15 participants performed 2 concentric repetitions of ballistic bench-press movements with intention to throw the bar at 30%, 45%, 60%, 75%, and 90% of the maximal concentric repetition with 5 resistance ratios including 100%, 75%, 50%, 25%, or 0% of pneumatic resistance, the additional load being isoinertial. Force-, velocity-, and power-time patterns were assessed and averaged over the concentric phase to determine the force–velocity and power–velocity relationships for each resistance ratio.


Each 25% increase in the pneumatic part in the resistance ratio elicited higher movement velocity (+0.11 ± 0.03 m/s from 0% to 80% of the concentric phase) associated with lower force levels (–43.6 ± 15.2 N). Increased isoinertial part in the resistance ratio resulted in higher velocity toward the end of the movement (+0.23 ± 0.01 m/s from 90% to 100%).


The findings show that the resistance ratio could be modulated to develop the acceleration phase and force toward the end of the concentric phase (pneumatic-oriented resistance). Inversely, isoinertial-oriented resistance should be used to develop maximal force and maximal power. Resistance modality could, therefore, be considered an innovative variable to modulate the training stimulus according to athletic purposes.

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Nihil Novum Sub Sole

Daniel Boullosa

, Morin JB . Optimal force–velocity profile in ballistic movements—altius: citius or fortius? Med Sci Sports Exerc . 2012 ; 44 ( 2 ): 313 – 322 . PubMed ID: 21775909 doi:10.1249/MSS.0b013e31822d757a 21775909 10.1249/MSS.0b013e31822d757a 6. Paavolainen LM , Nummela AT , Rusko HK

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The Advantages of Normalizing Electromyography to Ballistic Rather than Isometric or Isokinetic Tasks

Stephen M. Suydam, Kurt Manal, and Thomas S. Buchanan

the underlying motor units to change, which imposes signal variability. 24 Ballistic movements also require a different recruitment pattern than those of MVIC. 25 The possibility of changing recruitment patterns during motion may result in unreliable signals. Ballistic movements require rapid

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Effects of Postactivation Potentiation on Tennis Serve Velocity and Accuracy

Manuel Terraza-Rebollo and Ernest Baiget

accuracy. Although it has been shown that CT improves SSC explosive movements, such as sprint, countermovement jump, throws, and upper body ballistic movements, 6 – 9 , 12 , 16 , 23 our findings did not show any improvement in tennis serve velocity or any decrease in accuracy. However, we found a slight

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Effect of Different Shooting Techniques in Floorball on Accuracy and Velocity in Experienced Male Floorball Players

Roland van den Tillaar

and are perhaps not suitable for ballistic movements (involve several joint movements with maximal effort) that often are used like a shooting task in stick sports (hockey, ice hockey, and floorball). In other ballistic movements, such as throwing ( Indermill & Husak, 1984 ; van den Tillaar & Ettema

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Should We Base Training Prescription on the Force–Velocity Profile? Exploratory Study of Its Between-Day Reliability and Differences Between Methods

Pedro L. Valenzuela, Guillermo Sánchez-Martínez, Elaia Torrontegi, Javier Vázquez-Carrión, Zigor Montalvo, and G. Gregory Haff

Optimum levels of lower-limb muscle power constitute a major determinant of performance in a variety of sports—especially those that require the execution of explosive or ballistic movements such as sprinting or jumping. 1 The assessment and improvement of muscle power are therefore relevant. 1