CHANGES IN THE GRADIENT OF FORCE-VELOCITY PROFILES IN SIMULATIONS OF LOADED SQUAT JUMPS CAN BE INDUCED BY INCREASES IN MAXIMUM TORQUE AND RATE OF TORQUE DEVELOPMENT

In multi-segment movements the relationship between the external applied force and the velocity of the whole body or limbs has often been shown to be quasi-linear. It has been proposed that there is an optimal force-velocity profile for an athlete and that deviations from this profile, termed either a ‘force-deficit’ or a ‘velocity-deficit’, can be corrected by training. The aim of this study was to test the hypothesis that alterations in the maximum torque and rate of activation of the torque generator in a two-segment computer model actuated solely by a knee torque generator can explain changes in the gradient of the force-velocity profile during simulations of loaded squat jumps. It was found that an increase in the rate of activation of the torque generator led to a reduction in the gradient of the force-velocity relationship, addressing a velocity-deficit, and an increase in the maximum torque resulted in an increase in the gradient of the force-velocity relationship, addressing a force-deficit. These results provide potential mechanisms by which force-velocity profiles obtained from loaded squat jumps can be altered by training

Living in Rural Nebraska: Quality of Life and Financial Well-Being

Nebraska’s economy growth has slowed this past year, and recent reports show that some of Nebraska’s counties are the poorest in the nation. How have these changes affected rural Nebraskans? How do rural Nebraskans perceive their quality of life? Do their perceptions differ by community size, the region in which they live, or their occupation? How have they responded to the higher cost of living? Are they able to meet their financial goals? This report details 3,199 responses to the 2001 Nebraska Rural Poll, the sixth annual effort to understand rural Nebraskans’ perceptions. Respondents were asked a series of questions regarding their general well-being, their satisfaction with specific aspects of well-being, and how they are responding to the higher cost of living. Trends for the well-being questions are examined by comparing data from the five previous polls to this year’s results. For all questions, comparisons are made among different respondent subgroups, i.e., comparisons by age, occupation, region, etc. Based on these analyses, some key findings emerged: • Rural Nebraskans are more negative about their current situation than they were last year. This year, 32 percent state they are better off than they were five years ago; however, this compares to 40 percent in 2000. This is the lowest percentage reported during a six-year period. Nineteen percent of the respondents say they are worse off than five years ago, while 16 percent felt this way last year. The percent responding that their situation remained about the same increased from 44 percent last year to 49 percent in 2001. • When asked about the future, fewer respondents assert they will be better off ten years from now, as compared to last year’s results. This year, 34 percent state they will be better off ten years from now, compared to 38 percent last year. The proportion responding they will be worse off increased from 18 percent to 21 percent. The proportion saying they will be about the same in ten years remained steady at 45 percent. • Farmers and ranchers are less optimistic than persons with other occupations about their current situation. Only 24 percent of the farmers and ranchers state they are better off compared to five years ago. In comparison, 50 percent of those with professional occupations say they are better off. • Manual laborers are more likely to believe that people are powerless to control their own lives. Just over one-half (51%) of the manual laborers either strongly agree or agree with the statement that “...people are powerless to control their own lives.” In contrast, only 21 percent of persons with professional occupations agree with the statement. • Respondents report being most satisfied with their family, their marriage, and their religion/spirituality. The items receiving the highest proportion of “very dissatisfied” responses include financial security during retirement, current income level and job opportunities. • Manual laborers are more likely than those with other occupations to express dissatisfaction with their job opportunities. Sixty percent of the manual laborers are dissatisfied with their job opportunities, compared to only 32 percent of the farmers and ranchers. • At least one-third of rural Nebraskans have experienced the following economic hardships during the past year: using savings to meet household expenses, delaying a family vacation because of a lack of money, and being unable to contribute any money toward retirement because the money was needed for everyday household expenses. Twenty percent of rural Nebraskans have taken another job to help meet household expenses during the past year. Seventeen percent couldn’t pay the full amount of their utility bills, 15 percent were unable to afford needed medical care, and seven percent were unable to purchase needed food. • The groups most likely to have experienced many of the hardships listed include: younger respondents, persons living in the North Central region of the state, respondents with lower income levels, females, persons with lower educational levels, the divorced or separated respondents, and the laborers. • Sixty-two percent of rural Nebraskans believe their household income has not kept up with the increased cost of living. Eighteen percent believe it has increased at the same rate as the cost of living, eight percent feel their income has increased faster than the cost of living, and 12 percent are not sure. • Just over one-half of rural Nebraskans say they have just enough to make ends meet at the end of each month. Fifty-two percent say they have just enough to make ends meet, 35 percent end up with money left over at the end of the month, and 13 percent say there is not enough money to make ends meet. • The vast majority of rural Nebraskans say they always had enough food to eat during the past year. Ninety-two percent said they always had enough food, seven percent said there were a few times when they didn’t have enough to eat, and one percent said there were many times when they didn’t have enough to eat. • Younger respondents were more likely than older respondents to say there were a few times when they didn’t have enough to eat last year. Twenty percent of the persons between the ages of 19 and 29 said there were a few times when they didn’t have enough to eat, compared to only three percent of the persons age 65 and older

Nonspatial sequence coding in CA1 neurons

The hippocampus is critical to the memory for sequences of events, a defining feature of episodic memory. However, the fundamental neuronal mechanisms underlying this capacity remain elusive. While considerable research indicates hippocampal neurons can represent sequences of locations, direct evidence of coding for the memory of sequential relationships among nonspatial events remains lacking. To address this important issue, we recorded neural activity in CA1 as rats performed a hippocampus-dependent sequencememory task. Briefly, the task involves the presentation of repeated sequences of odors at a single port and requires rats to identify each item as “in sequence” or “out of sequence”. We report that, while the animals’ location and behavior remained constant, hippocampal activity differed depending on the temporal context of items—in this case, whether they were presented in or out of sequence. Some neurons showed this effect across items or sequence positions (general sequence cells), while others exhibited selectivity for specific conjunctions of item and sequence position information (conjunctive sequence cells) or for specific probe types (probe-specific sequence cells). We also found that the temporal context of individual trials could be accurately decoded from the activity of neuronal ensembles, that sequence coding at the single-cell and ensemble level was linked to sequence memory performance, and that slow-gamma oscillations (20–40 Hz) were more strongly modulated by temporal context and performance than theta oscillations (4–12 Hz). These findings provide compelling evidence that sequence coding extends beyond the domain of spatial trajectories and is thus a fundamental function of the hippocampus

MODELLING TRANSTIBIAL PROSTHESES FOR SIMULATION

Investigating the effect of a prosthetics size, shape, and stiffness on sports performance requires a theoretical approach, however this requires a more complex representation of the prosthetic beyond those previously adopted. A chain model was used to investigate the level of complexity (n-segments; n=2,3,4) required to reproduce the kinematics and kinetics of a prosthetic during six different movements performed by a unilateral transtibial amputee athlete. The optimal solution was evaluated using an angle-driven simulation model and close agreement (3% RMS difference) was observed between the simulation and recorded performances suggesting the complexity was sufficient. This approach could be employed within theoretical approaches to investigate the cause and effect of prostheses on sporting movements or to custom fit appropriate prostheses for individual athletes

A biomechanical evaluation of the combined elevation test

Objectives: To biomechanically evaluate the relationships between the outcome of the Combined Elevation Test, its component joint motions, and thoracic spine angles. Design: Cross-sectional study. Setting: Laboratory. Participants: 18 elite swimmers and triathletes (11 males and 7 females). Main outcome measures: Combined Elevation Test outcome in forehead and chin positions. Individual joint contributions to test outcome. Results: No sex differences were found in test components, or between head positions. Test outcome was greater in the forehead position than the chin position (34.3 cm vs 30.2 cm; p0.05). Conclusions: The Combined Elevation Test is an effective screening tool to measure upper limb mobility into shoulder flexion and scapula retraction in both sexes, and thoracic extension in women. It is recommended that the test be performed in the forehead position. If a subject performs poorly on the test, follow up assessments are required to identify the impairment location

The correlation of force-velocity-power relationship of a whole-body movement with 20 m and 60 m sprint performance

Sprinting ability is important for successful performance in sports. The aim of this study was to examine the correlation between force-velocity-power relationship of a whole-body movement and sprint performance. Twelve male participants performed maximal squat jumps with additional loads ranging from 0% to 100% body weight to obtain force-velocity profiles. The mean force and velocity were calculated during the push-off phase for each jump, which resulted in a force-velocity curve. The theoretical maximal force (F0), theoretical maximal velocity (V0) and theoretical maximum power (P0) were computed via extrapolation of the force and velocity data. In the second session, participants performed two 60 m sprints and the time to cover 20 m (t20), time to cover 60 m (t60), and maximum sprint velocity (Vmax) were calculated from the best 60 m trial. Correlation analyses revealed strong and significant correlations between V0 and t20 (r = −0.60), V0 and t60 (r = −0.60), P0 and t20 (r = −0.75) and P0 and t60 (r = −0.78). Multiple linear regression indicated that P0 explained 56%, 61% and 60% of the variability in t20, t60 and Vmax, respectively. Our results emphasise the importance of developing power production capabilities to improve sprint performance

Direct torque control for cable conduit mechanisms for the robotic foot for footwear testing

© 2018 Elsevier Ltd As the shoe durability is affected directly by the dynamic force/pressure between the shoe and its working environments (i.e., the contact ground and the human foot), a footwear testing system should replicate correctly this interaction force profile during gait cycles. Thus, in developing a robotic foot for footwear testing, it is important to power multiple foot joints and to control their output torque to produce correct dynamic effects on footwear. The cable conduit mechanism (CCM) offers great advantages for designing this robotic foot. It not only eliminates the cumbersome actuators and significant inertial effects from the fast-moving robotic foot but also allows a large amount of energy/force to be transmitted/propagated to the compact robotic foot. However, CCMs cause nonlinearities and hysteresis effects to the system performance. Recent studies on CCMs and hysteresis systems mostly addressed the position control. This paper introduces a new approach for modelling the torque transmission and controlling the output torque of a pair of CCMs, which are used to actuate the robotic foot for footwear testing. The proximal torque is used as the input signal for the Bouc–Wen hysteresis model to portray the torque transmission profile while a new robust adaptive control scheme is developed to online estimate and compensate for the nonlinearities and hysteresis effects. Both theoretical proof of stability and experimental validation of the new torque controller have been carried out and reported in this paper. Control experiments of other closed-loop control algorithms have been also conducted to compare their performance with the new controller effectiveness. Qualitative and quantitative results show that the new control approach significantly enhances the torque tracking performance for the system preceded by CCMs

Position tracking control in torque mode for a robotic running foot for footwear testing

Available automatic footwear testing systems still lack flexibility and bio-fidelity to represent the human foot and reproduce the wear conditions accurately. The first part of this article introduces a new design of the robotic running foot for footwear testing using cable conduit mechanisms. This robotic running foot is integrated with an upper leg mechanism to form a complete integrated footwear testing system. The cable conduit mechanisms help remove the bulky actuators and transmissions out of the fast-moving robotic foot. Thus, this robotic running foot design not only allows high-power actuators to be installed, but also avoids a significant dynamic mass and inertia effects on the upper leg mechanism. This means that the integrated footwear testing system can have multiple powered degrees of freedom in the robotic running foot and simulate much higher human running speeds than other available systems. However, cable conduit mechanisms cause significant challenges in control approaches, especially in high-speed systems, due to their nonlinear transmission characteristics. Furthermore, the robotic running foot actuators must operate in a torque/force control mode to reproduce the foot–shoe interaction during gaits while it is critical to control the foot joints’ position in the swing phase of gaits. The latter part of this article presents a study on position tracking control in torque mode for the robotic running foot joints using adaptive and proportional–integral–derivative control designs to evaluate the system’s ability to mimic the human foot kinematics in running. Both controllers proved their effectiveness, implying that the proposed control approach can be implemented on the integrated footwear testing system to control the foot joints’ position in the swing phase of running gaits