Forward Jumps Research Articles

Structure, Sex, and Strength and Knee and Hip Kinematics During Landing

Researchers have observed that medial knee collapse is a mechanism of knee injury. Lower extremity alignment, sex, and strength have been cited as contributing to landing mechanics. To determine the relationship among measurements of asymmetry of unilateral hip rotation (AUHR); mobility of the foot, which we described as relative arch deformity (RAD); hip abduction-external rotation strength; sex; and medial collapse of the knee during a single-leg jump landing. We hypothesized that AUHR and RAD would be positively correlated with movements often associated with medial collapse of the knee, including hip adduction and internal rotation excursions and knee abduction and rotation excursions. Descriptive laboratory study. Research laboratory. Thirty women and 15 men (age = 21 ± 2 years, height = 171.7 ± 9.5 cm, mass = 68.4 ± 9.5 kg) who had no history of surgery or recent injury and who participated in regular physical activity volunteered. Participants performed 3 double-leg forward jumps with a single-leg landing. Three-dimensional kinematic data were sampled at 100 Hz using an electromagnetic tracking system. We evaluated AUHR and RAD on the preferred leg and evaluated isometric peak hip abductor-external rotation torque. We assessed AUHR by calculating the difference between internal and external hip rotation in the prone position (AUHR = internal rotation - external rotation). We evaluated RAD using the Arch Height Index Measurement System. Correlations and linear regression analyses were used to assess relationships among AUHR, RAD, sex, peak hip abduction-external rotation torque, and kinematic variables for 3-dimensional motion of the hip and knee. The dependent variables were joint angles at contact and joint excursions between contact and peak knee flexion. We found that AUHR was correlated with hip adduction excursion (R = 0.36, P = .02). Asymmetry of unilateral hip rotation, sex, and peak hip abduction-external rotation torque were predictive of knee abduction excursion (adjusted R(2) = 0.47, P < .001). Asymmetry of unilateral hip rotation and sex were predictive of knee external rotation excursion (adjusted R(2) = 0.23, P = .001). The RAD was correlated with hip adduction at contact (R(2) = 0.10, R = 0.32, P = .04) and knee flexion excursion (R(2) = 0.11, R = -0.34, P = .03). Asymmetry of unilateral hip rotation, sex, and hip strength were associated with kinematic components of medial knee collapse.

Elementary Mechanisms of Force Generation

Elementary mechanisms of force generationAmin L.1, Shahapure R.1, Ercolini E.1,2, & Torre V.1,31International School for Advanced Studies (SISSA-ISAS), Trieste, Italy. 2 Cluster in Biomedicine (CBM), Area Science Park Basovizza, Trieste, Italy. 3Italian Institute of Technology, ISAS Unit, Italy.By using optical tweezers, we have characterized in details the mechanism of force generation in neuronal filopodia and lamellipodia with a nanometer sensitivity and sub-millisecond temporal resolution. Filopodia of dorsal root ganglia (DRG) neurons exert forces up to 2 pN, while those of hippocampal neurons a larger force up to 4-6 pN. When lamellipodia of DRG or hippocampal growth cones grow pushing a trapped bead, the autocorrelation of bead fluctuations decays with multiple time constants, while during Brownian fluctuations a single time constant of approximately 1 msec is observed. During push the power spectrum density of bead fluctuations is not fitted by a Lorentzian distribution and the energy content of low frequencies is higher than during Brownian fluctuations. Bead fluctuations along the three spatial components during push exhibit a higher cross-correlation than during Brownian fluctuations. Thus, during push the underlying dynamics is spatially and temporally correlated. Several algorithms show that during push, forward and backward jumps of 2-20 nm are detected. The net protrusion in a given time window is equal to the sum of all forward and backward jumps in the same window. These forward and backward jumps are identified as bursts of actin polymerization and depolymerization respectively and represent the elementary mechanisms of force generation.

The influence of direct motor–motor interaction in models for cargo transport by a single team of motors

We analyze theoretically the effects of excluded-volume interactions between motors on the dynamics of a cargo driven by multiple motors. The model considered shares much in common with others recently proposed in the literature, with the addition of direct interaction between motors and motor back steps. The cargo is assumed to follow a continuum Langevin dynamics, while individual motors evolve following a Monte Carlo algorithm based on experimentally accessible probabilities for discrete forward and backward jumps, and attachment and detachment rates. The links between cargo and motors are considered as nonlinear springs. By means of numerical simulations we compute the relevant quantities characterizing the dynamical properties of the system, and we compare the results to those for noninteracting motors. We find that interactions lead to quite relevant changes in the force-velocity relation for cargo, with a considerable reduction of the stall force, and also cause a notable decrease of the run length. These effects are mainly due to traffic-like phenomena in the microtubule. The consideration of several parallel tracks for motors reduces such effects. However, we find that for realistic values of the number of motors and the number of tracks, the influence of interactions on the global parameters of transport of cargo are far from being negligible. Our studies also provide an analysis of the relevance of motor back steps on the modeling, and of the influence of different assumptions for the detachment rates. In particular, we discuss these two aspects in connection with the possibility of observing processive back motion of cargo at large load forces.

Force Generation in Lamellipodia is a Discontinuous Process with Nanometer Discrete Forward and Backward Jumps

The progressive addition of actin monomers to the existing network of actin filaments underlies force generation in lamellipodia. By using optical tweezers, we have characterized the dynamics by which lamellipodia of Dorsal Root Ganglia neurons exerted force on encountered obstacles such as silica beads. Because of the presence of adhesion forces, beads in close contact with a lamellipodium could seal on its membrane so that the standard deviation of Brownian fluctuations could be reduced by 10 times. In several experiments, the bead remained within 300 nm from the center of the optical trap where voltage sensitivity of the detector and trap stiffness is constant. Under these conditions, if the lamellipodium pushed the bead, we could detect discrete jumps possibly constituting the elementary events underlying force generation. Jumps were detected by using algorithms based on nonlinear diffusion methods and on numerical differentiation. These jumps occurred within 1 ms and had an amplitude varying from 5 to 20 nm. When the lamellipodium retracted, pulling the beads with it, no discrete events were observed. These discrete events were not observed in the presence of Latrunculin A, a blocker of actin polymerization or when neurons were fixed with paraformaldehyde. The amplitude of these jumps increased by 20-40% when cholesterol in cellular membrane was depleted by treatment with cyclodextrin. These jumps show that force generation in lamellipodia is not a smooth process but is a discontinuous process in which bursts of actin polymerization and depolymerization alternate continuously.

Neuromuscular Adaptations to Training, Injury and Passive Interventions

Performance in endurance sports such as running, cycling and triathlon has long been investigated from a physiological perspective. A strong relationship between running economy and distance running performance is well established in the literature. From this established base, improvements in running economy have traditionally been achieved through endurance training. More recently, research has demonstrated short-term resistance and plyometric training has resulted in enhanced running economy. This improvement in running economy has been hypothesized to be a result of enhanced neuromuscular characteristics such as improved muscle power development and more efficient use of stored elastic energy during running. Changes in indirect measures of neuromuscular control (i.e. stance phase contact times, maximal forward jumps) have been used to support this hypothesis. These results suggest that neuromuscular adaptations in response to training (i.e. neuromuscular learning effects) are an important contributor to enhancements in running economy. However, there is no direct evidence to suggest that these adaptations translate into more efficient muscle recruitment patterns during running. Optimization of training and run performance may be facilitated through direct investigation of muscle recruitment patterns before and after training interventions. There is emerging evidence that demonstrates neuromuscular adaptations during running and cycling vary with training status. Highly trained runners and cyclists display more refined patterns of muscle recruitment than their novice counterparts. In contrast, interference with motor learning and neuromuscular adaptation may occur as a result of ongoing multidiscipline training (e.g. triathlon). In the sport of triathlon, impairments in running economy are frequently observed after cycling. This impairment is related mainly to physiological stress, but an alteration in lower limb muscle coordination during running after cycling has also been observed. Muscle activity during running after cycling has yet to be fully investigated, and to date, the effect of alterations in muscle coordination on running economy is largely unknown. Stretching, which is another mode of training, may induce acute neuromuscular effects but does not appear to alter running economy. There are also factors other than training structure that may influence running economy and neuromuscular adaptations. For example, passive interventions such as shoes and in-shoe orthoses, as well as the presence of musculoskeletal injury, may be considered important modulators of neuromuscular control and run performance. Alterations in muscle activity and running economy have been reported with different shoes and in-shoe orthoses; however, these changes appear to be subject-specific and non-systematic. Musculoskeletal injury has been associated with modifications in lower limb neuromuscular control, which may persist well after an athlete has returned to activity. The influence of changes in neuromuscular control as a result of injury on running economy has yet to be examined thoroughly, and should be considered in future experimental design and training analysis.

Kinetic Monte Carlo theory of sliding friction

The sliding friction as a function of scanning velocity at the nanometer scale was simulated based on a modified one-dimensional Tomlinson model. Monte Carlo theory was exploited to describe the thermally activated hopping of the contact atoms, where both backward and forward jumps were allowed to occur. By comparing with the Monte Carlo results, improvements to current semiempirical solutions [E. Riedo et al., Phys. Rev. Lett. 91, 084502 (2003)] were made. Finally, experimental results of sliding friction on a NaCl(100) as a function of normal load and scanning velocity [E. Gnecco et al., Phys. Rev. Lett. 84, 1172 (2000)] where successfully simulated.

Current fluctuations in the exclusion process and Bethe ansatz

We use the Bethe ansatz to derive analytical expressions for the current statistics in the asymmetric exclusion process with both forward and backward jumps. The Bethe equations are highly coupled and this fact has impeded their use in deriving exact results for finite systems. We overcome this technical difficulty by reformulating Bethe equations into a one-variable polynomial problem, akin to the functional Bethe ansatz. The perturbative solution of this equation leads to the cumulants of the current. We calculate here the first two orders and derive exact formulae for the mean value of the current and its fluctuations.

Detection of fractional steps in cargo movement by the collective operation of kinesin-1 motors

The stepping behavior of single kinesin-1 motor proteins has been studied in great detail. However, in cells, these motors often do not work alone but rather function in small groups when they transport cellular cargo. Until now, the cooperative interactions between motors in such groups were poorly understood. A fundamental question is whether two or more motors that move the same cargo step in synchrony, producing the same step size as a single motor, or whether the step size of the cargo movement varies. To answer this question, we performed in vitro gliding motility assays, where microtubules coated with quantum dots were driven over a glass surface by a known number of kinesin-1 motors. The motion of individual microtubules was then tracked with nanometer precision. In the case of transport by two kinesin-1 motors, we found successive 4-nm steps, corresponding to half the step size of a single motor. Dwell-time analysis did not reveal any coordination, in the sense of alternate stepping, between the motors. When three motors interacted in collective transport, we identified distinct forward and backward jumps on the order of 10 nm. The existence of the fractional steps as well as the distinct jumps illustrate a lack of synchronization and has implications for the analysis of motor-driven organelle movement investigated in vivo.

Lower extremity control and dynamics during backward angular impulse generation in forward translating tasks

Observation of complex whole body movements suggests that the nervous system coordinates multiple operational subsystems using some type of hierarchical control. When comparing two forward translating tasks performed with and without backward angular impulse, we have learned that both trunk-leg coordination and reaction force-time characteristics are significantly different between tasks. This led us to hypothesize that differences in trunk-leg coordination and reaction force generation would induce between-task differences in the control of the lower extremity joints during impulse generation phase of the tasks. Eight highly skilled performers executed a series of forward jumps with and without backward rotation (reverse somersault and reverse timer, respectively). Sagittal plane kinematics, reaction forces, and electromyograms of lower extremity muscles were acquired during the take-off phase of both tasks. Lower extremity joint kinetics were calculated using inverse dynamics. The results demonstrated between-task differences in the relative angles between the lower extremity segments and the net joint forces/reaction force and the joint angular velocity profiles. Significantly less knee extensor net joint moments and net joint moment work and greater hip extensor net joint moments and net joint moment work were observed during the push interval of the reverse somersault as compared to the reverse timer. Between-task differences in lower extremity joint kinetics were regulated by selectively activating the bi-articular muscles crossing the knee and hip. These results indicate that between-task differences in the control of the center of mass relative to the reaction force alters control and dynamics of the multijoint lower extremity subsystem.

Dealing with forward and backward jumps in workflow management systems

Workflow management systems (WfMS) offer a promising technology for the realization of process-centered application systems. A deficiency of existing WfMS is their inadequate support for dealing with exceptional deviations from the standard procedure. In the ADEPT project, therefore, we have developed advanced concepts for workflow modeling and execution, which aim at the increase of flexibility in WfMS. On the one hand we allow workflow designers to model exceptional execution paths already at buildtime provided that these deviations are known in advance. On the other hand authorized users may dynamically deviate from the pre-modeled workflow at runtime as well in order to deal with unforeseen events. In this paper, we focus on forward and backward jumps needed in this context. We describe sophisticated modeling concepts for capturing deviations in workflow models already at buildtime, and we show how forward and backward jumps (of different semantics) can be correctly applied in an ad-hoc manner during runtime as well. We work out basic requirements, facilities, and limitations arising in this context. Our experiences with applications from different domains have shown that the developed concepts will form a key part of process flexibility in process-centered information systems.

One-dimensional models of thermal activation under shear stress

The analysis of thermal activation under shear stress in three- and even two-dimensional models presents unresolved problems. The analysis of one-dimensional models presented here may illuminate the study of more realistic models. For the model in which as many dislocations are poised for backward jumps as for forward jumps, the experimental activation volume V †e(σa) under applied stresses close to σa is different from the true activation volume V(σ) evaluated at σ = σa. The relations between the two are developed. A model is then discussed in which fewer dislocations are available for backward than for forward jumps. Finally, the appropriateness of the hyperbolic sine approximation for moderately low stresses is defined and shown to be very limited.

Dealing with forward and backward jumps in workflow management systems

Workflow management systems (WfMS) offer a promising technology for the realization of process-centered application systems. A deficiency of existing WfMS is their inadequate support for dealing with exceptional deviations from the standard procedure. In the ADEPT project, therefore, we have developed advanced concepts for workflow modeling and execution, which aim at the increase of flexibility in WfMS. On the one hand we allow workflow designers to model exceptional execution paths already at buildtime provided that these deviations are known in advance. On the other hand authorized users may dynamically deviate from the pre-modeled workflow at runtime as well in order to deal with unforeseen events. In this paper, we focus on forward and backward jumps needed in this context. We describe sophisticated modeling concepts for capturing deviations in workflow models already at buildtime, and we show how forward and backward jumps (of different semantics) can be correctly applied in an ad-hoc manner during runtime as well. We work out basic requirements, facilities, and limitations arising in this context. Our experiences with applications from different domains have shown that the developed concepts will form a key part of process flexibility in process-centered information systems.

Jumping in a winged stick insect.

The Thailand winged stick insect (Sipyloidea sp.) flees rapidly from a disturbance by jumping forwards when stimulated on the abdomen and backwards when stimulated on the head. The mechanisms underlying these fast movements were analysed by measuring movements of the body and legs from images captured at 250 Hz. A forward jump of both adults and nymphs involves movements of the abdomen and the middle and hind pairs of legs. The abdomen is raised and swung forwards by flexion at the joint with the metathorax and at the joint between the meso- and metathorax. At the same time, the tibiae of the hind and middle legs are extended and their femora depressed. The femoro-tibial joints of the legs are not fully flexed before a jump, and no structures in these joints appear to store muscular energy. The whole jumping sequence takes approximately 100 ms and results in take-off angles of 10-35 degrees at velocities of 0.6-0.8 m s(-1) and with an acceleration of 10 m s(-2). The abdominal angular velocity was 2000 degrees s(-1) and the tip of the abdomen moved at linear velocities of some 1 m s(-1), while the maximum rate of tibial extension was 4000 degrees s(-1). Rapid backward movements result either in the collapse of the body onto the ground, with a displacement away from the stimulus of approximately half a body length, or in the propulsion of the insect off its perch. Neither movement involves curling of the abdomen. From a horizontal posture, the forward jumps result in a displacement of a few body lengths. More lift can be generated in adults by elevating the hind wings as the abdomen is swung forwards and depressing them as the legs lose contact with the ground. In this way, jumps can lead directly to flapping flight. Take-off into flight can, however, be achieved without the abdominal movements seen during jumping. From a vertical posture, a forward jump propels the insect upwards and backwards before it falls to the ground horizontally displaced from its perch. Backward movements result in the insect falling with little horizontal displacement from its perch.

Backward-to-forward jump rates on a tilted periodic substrate

Driven diffusion of a Brownian particle along a one-dimensional lattice is investigated numerically on decreasing its damping constant. The notions of multiple jumps, jump reversal, and backward-to-forward rates are discussed in detail. In particular, we conclude that in the underdamped limit backward jumps are suppressed relative to forward jumps more effectively than previously assumed. The dependence of such a drive-controlled mechanism on the damping constant and the temperature is interpreted analytically.

Flexibility of saccade adaptation in the monkey: different gain states for saccades in the same direction.

Saccadic accuracy, measured as the ratio of the size of a saccade to the size of the target step that elicits it, i.e., saccade gain, can be altered by jumping the target surreptitiously during the targeting saccade. The gain change produced by this paradigm does not generalize or transfer to saccades of all sizes. Instead, the amount of transfer decreases the more the tested saccade differs in amplitude and direction from that adapted. Here, we tested the limits of this saccade-size specificity by attempting to impose quite different gain states on saccades in the same direction. We altered the saccadic gain by intrasaccadic target jumps of 30% of the initial target step, either forward to produce a gain increase or backward to produce a gain decrease. Three different conditions were studied: (1) saccades to target steps of 20 degrees or 7 degrees were adapted in individual sessions with backward and forward jumps, respectively; (2) saccades to target steps of 20 degrees caused backward target jumps during the same session in which saccades to 7 degrees target steps caused forward steps; (3) the target jumps accompanying 20 and 7 degrees saccades were the same as in (2), but in addition, there were intermediate-sized saccades to 13.5 degrees target steps with no intrasaccadic target jumps. Saccadic gain adaptation was quite flexible. In condition 2, we could simultaneously increase the gain of saccades to 7 degrees target steps while decreasing the gain of saccades to 20 degrees steps in the same direction. Intermediate horizontal saccades to 13.5 degrees target steps experienced gain reductions (average: 6.9%), which were not the sum of gain changes expected from separate 20 degrees gain decreases and 7 degrees gain increases alone, as predicted from condition 1. If adaptation at 20 degrees and 7 degrees occurred while an animal also tracked a non-adapting 13.5 degrees target step (paradigm 3), the gain reduction of saccades to the 13.5 degrees step was reduced considerably (3.4%). Thus, the mechanism that adapts saccade size can support a robust gain increase for saccades of one size while simultaneously supporting a robust gain decrease for saccades only 13 degrees larger. Furthermore, the presence during adaptation of a non-adapted target step with a size intermediate to the two adapting steps reestablishes a nearly normal gain within only 6.5 degrees of a robust gain increase and decrease. These data indicate that saccadic gain adaptation can set very different gain states for saccades with rather similar vectors.

Characteristics of saccadic gain adaptation in rhesus macaques.

We adapted the saccadic gain (saccadic amplitude/target step amplitude) by requiring monkeys to track a small spot that stepped to one side by 5, 10, or 15 degrees and then, during the initial targeting saccade, jumped either forward or backward by a fixed percentage of the initial step. Saccadic gain increased or decreased, respectively, as a function of the number of adapting saccades made in that direction. The relation between gain and the number of adapting saccades was fit with an exponential function, yielding an asymptotic gain and a rate constant (the number of saccades to achieve 63% of the total change in gain). Backward intrasaccadic target jumps of 15, 30, and 50% of the initial target step reduced the asymptotic gain by an average of 12.2, 23.1, and 36.4%, respectively, with average rate constants of 163, 368, and 827 saccades, respectively. During 50% backward jumps, some saccades, especially those to larger target steps, became slower and lasted longer. Forward intrasaccadic jumps of 30% increased the asymptotic gain by 23.3% (average rate constant of 1,178 saccades). After we had caused adaptation, we induced recovery of gain toward normal by requiring the animal to track target steps without intrasaccadic jumps. Recovery following forward adaptation required about one third fewer saccades than the preceding gain increase. Recovery following backward adaptation required about the same average number of saccades as the preceding gain decrease. The first saccades of recovery were slightly less adapted than the last saccades of adaptation, suggesting that a small part of adaptation might have been strategic. After 50% backward jumps had reduced saccadic gain, the hypometric primary saccades during recovery were followed by hypometric corrective saccades, suggesting that they too had been adapted. When saccades of only one size underwent gain reduction, saccades to target steps of other amplitudes showed much less adaptation. Also, saccades in the direction opposite to that adapted were not adapted. Gain reductions endured if an adapted animal was placed in complete darkness for 20 h. These data indicate that saccadic gain adaptation is relatively specific to the adapted step and does not produce parametric changes of all saccades. Furthermore, adaptation is not a strategy, but involves enduring neuronal reorganization in the brain. We suggest that this paradigm engages mechanisms that determine saccadic gain in real life and therefore offers a reversible means to study their neuronal substrate.

Reverse Barkhausen jumps

The magnetic parameters, forward and reverse magnetic reversal jumps in iron-core quartzite specimens and in magnetite single crystals, and the effect of thermal treatment on the magnetic and electric parameters of quartzites are studied. Reverse Barkhausen jumps are larger than the forward ones, but they are considerably fewer. The maxima of forward jumps correspond to the coercive force, while those of the reverse ones to fields exceeding the coercive force. Possible causes of the manifestation of reverse Barkhausen jumps are discussed.

The movements of jumping ciliates

Jumping ciliates fall into 3 movement groups. The movements of Halteria, Mesodinium and Uronychia resemble those of typical motile ciliates. The backward jumps of their usual avoidance reactions are due to the high development of the motor organelles. In Askenasia volvox, Cyclidium and Strobilidium gyrans forward jumps and darts take the place of the avoidance reaction's backward movement and rapid forward spiraling, over a wide range, replaces reversal. However, these species can move backward. Urotricha farcta (group 3) also responds with forward jumps and darts to brief repellent stimuli and with rapid forward spiraling to intense, continuous noxious stimuli. But U. farcta is incapable of backward movement. The mechanisms and nature of the movements are described and discussed. The avoidance reaction is re-examined.

The jump of Petrobius (Thysanura, Machilidae)

The jump of the sea‐shore bristletails, Petrobius brevistylis and P. maritimus, has been investigated. A brief study of jumping distance and orientation showed that jumping behaviour was partly random, particularly with regard to the direction of a jump. A high speed cine camera was used to analyse both forward and backward jumps. The jumping action consists of a tail beat which reflects the strong depression of the posterior abdomen. This swings up the anterior part of the body, including the centre of gravity. The model suggested to explain this action proposes two movements spreading from either end of the bristletail: 1. A straightening of the abdomen starting posteriorly, 2. An increasing ventral curvature of the thorax starting anteriorly. Movement 1 will account for the raising of the centre of gravity, and the rapidity of movement 2 will determine the final direction of the jump.The muscular basis of these movements has been discussed using the data of Manton (1972), Barlet (1967) and Bitsch (1973). A catapult system was proposed which depended on the dynamic balance between two abdominal muscular systems. It was suggested that the dorsal longitudinal muscles were antagonised by the deep oblique muscles. A short study of the energetics of jumping was made in order to estimate the times needed for sufficient energy to be stored for particular jumps. These times were then compared with known times spent by Petrobius in the cocked (energy storing) pre‐jump position.