Higher Force Levels Research Articles

Relationships between Isometric Force-Time Characteristics and Dynamic Performance.

The purpose of this study was to explore the relationships between isometric mid-thigh pull (IMTP) force-time characteristics (peak force and time-specific force vales (100–250 ms)) and dynamic performance and compare dynamic performance between stronger and weaker athletes. Forty-three athletes from different sports (rowing, soccer, bicycle motocross, and hockey) performed three trials of the squat jump (SJ), countermovement jump (CMJ), and IMTP, and performed a one repetition maximum power clean (PC). Reactive strength index modified (RSImod) was also calculated from the CMJ. Statistically significant large correlations between IMTP force-time characteristics and PC (ρ = 0.569–0.674, p < 0.001), and moderate correlations between IMTP force-time characteristics (excluding force at 100 ms) and RSImod (ρ = 0.389–0.449, p = 0.013–0.050) were observed. Only force at 250 ms demonstrated a statistically significant moderate correlation with CMJ height (ρ = 0.346, p = 0.016) and no statistically significant associations were observed between IMTP force-time characteristics and SJ height. Stronger athletes (top 10) demonstrated statistically significantly greater CMJ heights, RSImods, and PCs (p ≤ 0.004, g = 1.32–1.89) compared to weaker (bottom 10) athletes, but no differences in SJ height were observed (p = 0.871, g = 0.06). These findings highlight that the ability to apply rapidly high levels of force in short time intervals is integral for PC, CMJ height, and reactive strength.

Differences in grip force control between young and late middle-aged adults.

Grip force control is a crucial function for human to guarantee the quality of life. To examine the effects of age on grip force control, 10 young adults and 11 late middle-aged adults participated in visually guided tracking tasks using different target force levels (25, 50, and 75% of the subject's maximal grip force). Multiple measures were used to evaluate the tracking performance during force rising phase and force maintenance phase. The measurements include the rise time, fuzzy entropy, mean force percentage, coefficient of variation, and target deviation ratio. The results show that the maximal grip force was significantly lower in the late middle-aged adults than in the young adults. The time of rising phase was systematically longer among late middle-aged adults. The fuzzy entropy is a useful indicator for quantitating the force variability of the grip force signal at higher force levels. These results suggest that the late middle-aged adults applied a compensatory strategy that allow allows for sufficient time to reach the required grip force and reduce the impact of the early and subtle degenerative changes in hand motor function.

Evaluation of pulse height control for rapid isometric contractions in college sprinters.

The ability of rapid force development is one of the important factors for improving physical performance. It has been known that rapid isometric force is controlled by a central motor program to maintain the rise time relatively constant independent of force amplitude (pulse height control). The advantage of using pulse height control is that it increases the rate of force with force amplitude. However, this strategy is believed to be applicable up to about 50-60% of maximal voluntary contractions (MVC). When the force level increases further, individuals often switch to pulse width control to increase the time to peak force. The aim of this study was to determine the force level (turning point) at which participants switch from pulse height control to pulse width control. This turning point was defined as the maximum force produced by pulse height control. We then attempted to examine whether this turning point is different among participants (control and sprinter groups). Therefore, participants were asked to perform isometric plantar flexions as fast as possible over a wide range of force levels (10-90%MVC). Our results showed that a turning point (%MVC) between two strategies was detected in all participants and the mean values were significantly higher in the sprinter group than that in the control group. Our results suggest that each participant has different limits of force level produced by pulse height control. The sprinter and control groups may use different control strategies for rapid force production at a higher force level.

Impaired corticomuscular coherence during isometric elbow flexion contractions in humans with cervical spinal cord injury

After spinal cord injury (SCI), the reorganization of the neuromuscular system leads to increased antagonist muscles' co-activation-that is, increased antagonist vs. agonist muscles activation ratio-during voluntary contractions. Increased muscle co-activation is supposed to result from reduced cortical influences on spinal mechanisms inhibiting antagonist muscles. The assessment of the residual interactions between cortical and muscles activity with corticomuscular coherence (CMC) in participants with SCI producing different force levels may shed new lights on the regulation of muscle co-activation. To achieve this aim, we compared the net joint torque, the muscle co-activation and the CMC ~10 and ~20Hz with both agonist and antagonist muscles in participants with SCI and healthy participants performing actual isometric elbow flexion contractions at three force levels. For all participants, overall CMC and muscle co-activation decreased with the increase in the net joint torque, but only CMC ~10Hz was correlated with muscle co-activation. Participants with SCI had greater muscle co-activation and lower CMC ~10Hz, at the highest force levels. These results emphasize the importance of CMC as a mechanism that could take part in the modulation of muscle co-activation to maintain a specific force level. Lower CMC ~10Hz in SCI participants may reflect the decreased cortical influence on spinal mechanisms, leading to increased muscle co-activation, although plasticity of the corticomuscular coupling seems to be preserved after SCI to modulate the force level. Clinically, the CMC may efficiently evaluate the residual integrity of the neuromuscular system after SCI and the effects of rehabilitation.

Numerical and experimental study on loaded suspendome subjected to sudden cable failure

Cables are key components of suspendome structures and usually bear a high level of tension force. Thus, their sudden failure may cause a dramatic vibratory response and disproportionate internal force redistributions. This study investigated the cable failure effect of a 10.8m scaled-down suspendome model during in-service state through numerical simulations and failure tests. The deforming behaviors, internal force redistribution pattern, and oscillatory responses were studied and compared. Results showed that cable failure causes evident oscillations to the rest of the members. However, the suspendome exhibited strong structural stiffness, and no obvious collapse or failure behaviors were observed. Cable sliding occurred at rolling joints, which could influence the internal force redistribution patterns and dynamic effects at cables or strut members around the break region. Cable sliding behaviors reduced tension recovering ability and the dynamic effect at cable segments. Dynamic amplification factor and dynamic coefficient methods were both employed to evaluate the dynamic effect from the cable rupture because of different oscillatory patterns between cable segments and the rest of the members. Dynamic amplification factor was more applicable for shell and strut members, and the safety of cable segments can be evaluated and ensured with the dynamic coefficient method. The suggested values for the two indexes were also derived based on the test data, which could easily be used in the structural design process.

Sports Medicine International Open – recently published

During rugby scrummaging, front row forwards encounter high levels of force that has been suggested to cause transient fatigue and is likely to reduce subsequent performance. However, little is known about the effect of repetitive scrummaging on force output and onset of fatigue.

The Effect of Repetitive Rugby Scrummaging on Force Output and Muscle Activity

During rugby scrummaging, front row forwards encounter high levels of force that has been suggested to cause transient fatigue and is likely to reduce subsequent performance. However, little is known about the effect of repetitive scrummaging on force output and onset of fatigue. Twelve male front row forwards (21.5±2.3 yr; height 185.7±4.4 cm; body mass 108.5±7.1 kg) each performed three sets of five maximal-effort isometric scrums for 10 s, with 40 s rest separating each repetition; 2 min recovery was provided between each set. Force output and electromyography (EMG) of the right medial gastrocnemius (MG), biceps femoris (BF), gluteus maximus (GM), erector spinae (ES), rectus abdominis (RA), external oblique (EO), internal oblique (IO), and rectus femoris (RF) were assessed. There was no significant force decrement from performing 15 scrums and no fatigue was detected from EMG median frequency and mean amplitude. For training and practice purposes, coaches and trainers can be confident that 15 individual repetitive static scrums against a machine are unlikely to cause a reduction in force production and promote fatigue. However, the effect of rugby-related activities in conjunction with scrummaging requires further research to determine if transient fatigue is causal to scrummaging for subsequent performance.

Effect of Pre-Procedural Chair-Side Finger Stretches on Pinch Strength amongst Dental Cohort- A Biomechanical Study.

Ergonomics is the essential principle behind the health and successful practice for a dentist and dental hygienist. During the procedure of dental Scaling and Root Planing (SRP), a high level of pinch force is exerted by the finger muscles resulting in early muscle fatigue. This pilot study comparatively evaluated the Pinch Strength (PS) of the finger muscles, prior to and after SRP, amongst dental cohort performing chair-side hand and finger stretches to those not performing the same. Forty dental professionals were recruited by purposive sampling for the study and allocated into a test and control group. PS was recorded for both groups following which the test group performed finger stretches comprising of rubber band stretch, tendon glide, finger flexion and extension, thumb flexion and finger webbing. The subjects of both the groups carried out SRP for 30 minutes after which PS was again recorded. Inter-group difference was analysed for variability at baseline and 30 minutes after SRP using independent samples/unpaired t-test. Within group comparison of PS measurement was done using paired t-test. The PS for the test group declined from 14.425±2.577 pounds (lbs) to 13.725±2.557 lbs, while for the control group, a decline in PS from 13.65±2.636 lbs to 10.675±2.478 lbs after SRP was noted. On comparing the difference of means of both groups, a statistically significant result was obtained. Work-related musculoskeletal disorders can be reduced by performing a few simple chair-side stretches. These stretches can help prevent the finger muscle fatigue during SRP and thus, increase its efficacy.

Mental Illness, Police Use of Force, and Citizen Injury

Police departments are increasingly becoming the primary entity for managing incidents involving persons with mental illness, thereby leading to calls for additional research. Drawing on a multicity use-of-force research project, the current inquiry examines whether citizens displaying signs of mental illness are subjected to higher levels of police use of force, and whether they are more likely to be injured, controlling for a host of relevant predictors. The findings show that officers use higher levels of force on persons with mental illness, but such citizens are not at an enhanced risk of injury. The policy and research implications of the findings are discussed.

Punching shear tests on compact footings with uniform soil pressure

AbstractPunching shear is usually the governing failure criterion when selecting the depth of reinforced concrete footings. Despite the fact that large experimental programmes aimed at the punching strength of slender flat slabs have been performed in the past, only a few experimental campaigns on full‐scale compact reinforced concrete footings can be found in the literature. This paper presents the results of an experimental programme including eight reinforced concrete footings with a nominal thickness of 550 mm. These experiments investigated the influence of column size, member slenderness and the presence of compression and shear reinforcement. The tests were performed using an innovative test setup to ensure a uniform soil pressure. The experimental results show that slenderness influences the punching shear strength as well as the effectiveness of the shear reinforcement. The experiments also show that an important interaction occurs between bending and shear for high levels of shear force near the column (the typical case of compact footings or members with large amounts of shear reinforcement). Different continuous measurements recorded during the experimental tests allow a complete description of the kinematics and strains at failure. On that basis, experimental evidence is obtained showing that crushing of the concrete struts near the column is the phenomenon that triggers the punching failure of compact footings.

Developing Normal Turns-Amplitude Clouds for Upper and Lower Limbs.

Turns and amplitude analysis (T&A) is a frequently used method for automatic EMG interference pattern analysis. The T&A normal values have only been developed for a limited number of muscles. Our objective was to obtain normal T&A clouds for upper and lower extremity muscles for which no normal values exist in the literature. The T&A normative data using concentric needle electrodes were obtained from 68 men and 56 women aged 20 to 60 years. Normal upper and lower extremity T&A clouds were obtained and presented in this article. The T&A normal values collected in this study maybe used to detect neurogenic and myopathic abnormalities in men and women at low-to-moderate muscle contractions. The effect of turns-amplitude data obtained at high force level of muscle contraction and its potential to falsely show neurogenic abnormalities are discussed.

Theorizing Unidentified Normative Objectss of Global Regulatory Regimes

Much of the contemporary theorizing about the growing and diverging body of global regulatory regimes conspicuously avoids dealing with problems of their legality. However, it would be erroneous to think that the mission of this scholarship will be completed if theorists identify criteria that regulatory instruments must satisfy in order to qualify for the status of ‘law’. If this were the case, a number of the existing regulatory instruments would remain under the radar, destined to be classified as “unidentified normative objects” (UNO). This essay contains two main parts. The first part tackles the problem of normativity. If UNOs are really normative instruments, as they are commonly taken to be, it is necessary to elucidate in what ways they can be said to display normativity and how, if at all, this is any different from the normativity of paradigmatic legal rules. In this part, I will unload the two how questions of normativity. Whereas the first refers to the epistemological problem of how we are to ascertain normative statements (norms) and differentiate them from “is-statements”, the second opens up the perspective of practical rationality, by asking how norms provide us with reasons for action. The first part of the paper concludes that there is nothing special about the normativity of law. It will be demonstrated that law’s normative force competes with the normative force of other normative orders, and that its higher level of efficiency should not be attributed to its special sort of normativity, but to the combined effects of law’s normativity and its other typical features – institutionalization and (coercive) guarantees. The second part will be concerned with applying the findings of the first part to two paradigmatic cases of UNOs – regulatory instruments of the World Health Organization and the Basel Committee on Banking Supervision. This analysis will reveal that although the former qualify for the status of traditional international legal instruments, their degree of normativity – understood as the capacity to give rise to obligations – is very low. On the other hand, although latter instruments do not appear to pass the threshold of ‘legality’, they manage to display a surprisingly high level of normative force. Results of the undertaken analysis will, hopefully, bring more clarity in the burgeoning GAL literature.

Muscle Oxygenation Correlates of Handgrip Fatigue with Obesity

The aims of this study were to determine obesity-related muscle oxygenation correlates of submaximal fatigue, across 20, 40, 60, and 80% of maximum voluntary contractions (MVC). 72 normal weight, overweight and obese adults, matched by gender, performed the four endurance tests on different days. Muscle oxygenation of the flexor and extensor carpi radialis were measured by near infrared spectroscopy and endurance time was recorded for each test. The findings indicated that obesity-related reduction in handgrip endurance was evident at low force contraction levels. Obesity was associated with impaired muscle oxygenation; however, the changes were independent of force contraction levels. Muscle oxygenation did not directly limit the time to failure for endurance tests at higher force levels. Thus, it is likely that factors other than local metabolic and hemodynamic changes impede fatigue resistance at higher force contraction levels.

A new approach to mitigate the effect of force variation on pattern recognition for myoelectric control.

In myoelectric prosthetic control, the motion classification performance would be decayed if an electromyography (EMG) pattern to be recognized differs significantly from the one used for classifier training. Generally, the training signals are acquired when a subject performs motions with a proper force. In practical use of a myoelectric prosthesis, however, the variation of force levels to do a motion would be inevitable, which will cause a change of EMG patterns. In this study, we proposed a Parallel Classification Strategy consisting of three parallel classifiers created at low, medium, and high force levels, respectively, and designed a regulation to categorize the input signals into corresponding classifiers for pattern recognition. The pilot experimental results demonstrated that the proposed method could enhance the classification accuracy at different force levels with an average classification rate of 98.8%, which was higher than the current method (91.9%). Thus, the proposed method might improve the control performance for present myoelectric prostheses.

Virtual Tissue Cutting With Haptic Feedback Using a Hybrid Actuator With DC Servomotor and Magnetorheological Brake

Surgical training is an important and recent application where haptic interfaces are used to enhance the realism of virtual training simulators. Tissue cutting with surgical scissors is a common interaction mode in the simulations. The haptic interface needs to render a wide range of tissue properties and resistance forces accurately. In this research, we developed a hybrid haptic device made of a DC servomotor and a magnetorheological (MR) brake. The motor can provide fast dynamic response and compensate for inertia and friction effects of the device. But alone, it cannot supply high force levels and the sensation of stiff interaction with hard tissues such as tendons. On the other hand, the MR-brake can provide very stiff interaction forces yet cannot reflect fast dynamics that are encountered as the virtual scissors go through the tissue. The hybrid actuator developed in this work combines the two based on a control scheme that decomposes the actuator command signal into two branches considering each actuator's capabilities. It is implemented on a compact single degree-of-freedom (DOF) interface to simulate virtual tissue cutting with three different scissor types (Mayo, Metzenbaum, Iris) and four types of rat tissue (liver, muscle, skin, tendon). Results have shown close tracking of the desired force profile in all cases. Compared to just using a DC motor, the hybrid actuator provided a wider range of forces (up to 18 N) with fast response to render quick force variations without any instability for all simulated tissue and scissor types.

Penetration depth of torpedo anchor in cohesive soil by free fall

Developing deep sea technologies, many marine novel facilities have been introduced; and mooring systems, however, have become more expensive, complex, and hard cooperative in deep-water marine industry. The torpedo anchor is regarded as a modern technology benefits from easy installation, cost efficiency, and high level of anchor force. In this study, the penetration depth of a free falling torpedo anchor into cohesive soil has been laboratory investigated. 128 Sets of tests have been conducted with nine different torpedo anchors not only in shape, but also in size. Three anchor aspect ratios and three different types of muds were tested while mud rheological properties such as the yield stress and flow curves were also measured. Finally, a formula calculating the penetration depth of the anchor, regardless of soil separation has been proposed based on energy conservation principle and experimental measurements. Results indicate that the predicted penetration depth has a good conformity with the measured penetration depths in laboratory and field tests. Static undrained shear strength values should be reduced in formula when the impact velocity exceeds a critical value. Soil separation occurs depending on the anchor nose angle and surface roughness, and also soil properties. Nevertheless, the critical impact velocity resulting into soil separation and its degree require further study in the future.

Blast dynamics of beam-columns via analytical approach

Problems involving forced transverse vibrations of beam-columns have many applications in different fields of engineering. This paper presents an analytical procedure allowing the prediction of the blast dynamic response of a beam-column to a combined action of axial and transverse loads. The solution is based on the continuous formulation and the Euler–Bernoulli beam theory. The response of the beam-column in the quasi-static, dynamic and impulsive regimes is analysed using the developed analytical model. The analysis shows that the number of modes of vibration needed to produce an accurate estimate of the beam-column behaviour may vary depending on the loading regime. Various types of spatial load distributions and time histories of transverse loads commonly used in engineering practice for modelling of extreme loads are discussed. The significance of the axial force and the shape of the transverse load time history for the beam-column response is shown using the response spectrum and pressure–impulse diagram methods. The initial imperfections in the beam-column geometry and applied loads are introduced into the analysis and their effects are also examined. The results obtained by the analytical model are compared to the results of a nonlinear finite element analysis performed in ABAQUS. Certain discrepancies between the beam-column response yielded by the analytical solution and the finite element model were observed at high levels of axial force and quasi-static transverse loading conditions.

Force Reproduction Error Depends on Force Level, Whereas the Position Reproduction Error Does Not.

When reproducing a previously perceived force or position humans make systematic errors. This study determined the effect of force level on force and position reproduction, when both target and reproduction force are self-generated with the same hand. Subjects performed force reproduction tasks at different force levels, against a fixed handle, and performed a position reproduction task against a haptic manipulator which applied constant opposing forces. Subjects performed a series of two interchanging trials: matching an onscreen force or position (reference trial), and subsequently reproducing the same force or position without visual feedback (reproduction trial). Subjects generated too high forces for low force levels (<;40 N) and too low forces for high force levels (>130 N). No effect of force level on the position reproduction error was found. Previous studies proposed that reafference feedback, i.e., the sensory prediction from self-generated forces, causes the force reproduction error. However, if the force reproduction error is exclusively caused by the reafference feedback, the force reproduction error should disappear when both target and reproduction force are self-generated. The results of this study show an effect of force level on the force reproduction error, indicating that reafference feedback is not the sole factor in force reproduction tasks.

Age- and gender-related development of stretch shortening cycle during a sub-maximal hopping task.

The aim of this study was to analyse the effects of age and gender (and their interaction) on a stretch shortening cycle solicited during a hopping task. For this aim, 147 girls and 148 boys aged 11 to 20 years, who were enrolled in middle school or secondary school with no experience in sport activity, or training less than three times per week, performed 3×5 hops in place. Leg-stiffness, jump-height and reactive-strength indices were assessed using an accelerometer (Myotest). The participants were selected in order to form five age groups: 11 12, 13-14, 15-16, 17-18 and 19-20 years. Regression analysis between force and centre of mass displacement revealed spring-mass behaviour for all groups (r2=.73-.89), meaning that beginning at the age of 11 years, children are able to perform complex inter-muscular coordination of the lower limbs, revealing efficient neural control early in childhood. Leg stiffness increased from 24.7 ± 10.6 kN · m−1 at 11-12 years to 44.1 ± 14 kN · m−1 in boys, with a small increase until 16 years (+17%) and a large increase between 17 and 20 years (+32.7%). In girls, leg stiffness increased from 26.6 ± 9 kN · m−1 at 11-12 years to 39.4 ± 10.9 kN · m−1 at 19-20 years, with a curious decrease in leg stiffness at 17-18 years, probably due to an increase in the percentage of fat at this age (25%). While no gender effect was found, the reactive-strength index revealed that, from 15-16 years onward, boys were better able to produce high levels of force in a shorter time than girls. The age of 15-16 years is a threshold of maturity and gender differentiation, where the boys investigated are more efficient in the stretch shortening cycle.

Performing Isometric Force Control in Combination with a Cognitive Task: A Multidimensional Assessment.

IntroductionWe used a multidimensional approach to study isometric force control in single and dual-task conditions.MethodsMultiple measures of performance, efficiency, variability, and structural interference were calculated at low and higher force levels under single (force maintenance) and dual-task (force maintenance and reaction time) conditions.ResultsReaction time and signal-to-noise ratio were larger in the dual-task conditions. They were also greater for the higher force condition, while sample entropy was lower. Perturbation analyses revealed smaller relative amplitude of downward perturbations for the higher force level.DiscussionAttentional effort and efficiency are positively related when force level increases, and inversely related to entropy. These relations were presumably mediated by attentional investment. Behavioral perturbations show that attentional resources and structural interference models are not mutually exclusive to account for dual-task situation. Overall, the present study highlights the interest of a multidimensional assessment of force control.