Older adults' neuromuscular adaptations to resistence training and effects on challenging gait tasks

Community locomotion is threatened when older individuals are required to negotiate obstacles, which place considerable stress on the musculoskeletal system. The vulnerability of older adults during challenging locomotor tasks is further compromised by age-related strength decline and muscle atrophy. The first study in this investigation determined the relationship between the major muscle groups of the lower body and challenging locomotor tasks commonly found in the community environment of older adults. Twenty-nine females and sixteen males aged between 62 and 88 years old (68.2 ±6.5) were tested for the maximal voluntary contraction (MVC) strength of the knee extensors and 1-RM for the hip extensors, flexors, adductors, abductors, knee extensors and flexors and ankle plantar flexors. Temporal measurements of an obstacle course comprising four gait tasks set at three challenging levels were taken. The relationship between strength and the obstacle course dependent measures was explored using linear regression models. Significant associations (p≤0.05) between all the strength measures and the gait performances were found. The correlation values between strength and obstructed gait (r = 0.356-0.554) and the percentage of the variance explained by strength (R2 = 13%-31%), increased as a function of the challenging levels, especially for the stepping over and on and off conditions. While the difficulty of community older adults to negotiate obstacles cannot be attributed to a single causal pathway, the findings of the first study showed that strength is a critical requirement. That the magnitude of the association increased as a function of the challenging levels, suggests that interventions aimed at improving strength would potentially be effective in helping community older adults to negotiate environmental gait challenges. In view of the findings of the first study, a second investigation determined the effectiveness of a progressive resistance-training program on obstructed gait tasks measured under specific laboratory conditions and on an obstacle course mimicking a number of environmental challenges. The time courses of strength gains and neuromuscular mechanisms underpinning the exercise-induced strength improvements in community-dwelling older adults were also investigated. The obstructed gait conditions included stepping over an obstacle, on and off a raised surface, across an obstacle and foot targeting. Forty-three community-living adults with a mean age of 68 years (control =14 and experimental=29) completed a 24-week progressive resistance training program designed to improve strength and induce hypertrophy in the major muscles of the lower body. Specific laboratory gait kinetics and kinematics and temporal measures taken on the obstacle course were measured. Lean tissue mass and muscle activation of the lower body muscle groups were assessed. The MVC strength of the knee extensors and 1-RM of the hip extension, hip flexion, knee extension, knee flexion and ankle plantar flexion were measured. A 25% increase on the MVC of the knee extensors (p≤0.05) was reported in the training group. Gains ranging between 197% and 285% were recorded for the 1-RM exercises in the trained subjects with significant improvements found throughout the study (p≤0.05). The exercise-induced strength gains were mediated by hypertrophic and neural factors as shown by 8.7% and 27.7% increases (p≤0.05) in lean tissue mass and integrated electromyographic activity, respectively. Strength gains were accompanied by increases in crossing velocity, stride length and reductions in stride duration, stance and swing time for all gait tasks except for the foot targeting condition. Specific kinematic variables associated with safe obstacle traverse such as vertical obstacle heel clearance, limb flexion, horizontal foot placements prior to and at post obstacle crossing and landing velocities resulted in an improved crossing strategy in the experimental subjects. Significant increases in the vertical and anterior-posterior ground reaction forces accompanied the changes in the gait variables. While further long-term prospective studies of falls rates would be needed to confirm the benefits of lower limb enhanced strength, the findings of the present study provide conclusive evidence of significant improvements to gait efficiency associated with a systematic resistance-training program. It appears, however, that enhanced lower body strength has limited effects on gait tasks involving a dynamic balance component. In addition, due to the larger strength-induced increases in voluntary activation of the leg muscle compared to relatively smaller gains in lean tissue mass, neural adaptations appear to play a greater contributing role in explaining strength gains during the current resistance training protocol.

Tracking multiple mobile agents with single frequency continuous wave radar

In this paper, a novel concept to determine the velocity and the location information of multiple mobile agents using Doppler radar has been introduced. Also, an expression for the minimum number of inline sensors needed to guarantee this estimation for n number of mobile agents has been obtained. Current methods use the time derivative of the displacement of adjacent position measurements to find the velocities of agents. This method is error prone, particularly, if the agents are accelerating. In our approach we incorporate direction-of-arrival (DOA) radar which tracks the location and the velocity of each and every agent in each measurement step.

Minimum reconfiguration for fault tolerant manipulators

When a robotic manipulator is fault tolerant it is beneficial to study the configurations which tolerate non-catastrophic locked joint failures with a minimum relative change for the joint velocities. This problem is addressed using the properties of the condition number of the Jacobian matrix. The relationship between the faults within the joints of the manipulators and the condition number of the Jacobean matrix is used to introduce the optimal configurations for fault recovery. These optimum configurations require a minimum reconfiguration for fault tolerance of robotics manipulators. Then these configurations are studied for a 4-DOF planar manipulator to validate the proposed framework.

Haptic mobility control for teleoperated rovers

Future missions involving human and robotic systems co-resident on the lunar surface may call for rovers to be teleoperated from the safety of pressurized habitats or vehicles. An approach is presented that emphasizes human-level judgment and intuition in the total control of a rover’s mobility actions. This is facilitated through human-robotic haptics interaction. The concept of a haptics cone control surface is presented, which provides a teleoperator with a means to intuitively determine the velocities he/she is commanding to control rover motion. The teleoperator is also provided with real-time, tasks-relevant haptic augmentation indicating suggestive control actions concerning the desired mobility objective. Utility of the approach for teleoperated control of steep terrain traversal is demonstrated in simulation.

Joint velocity redistribution for fault tolerant manipulators

If the end-effector of a robotic manipulator moves on a specified trajectory, then for the fault tolerant operation, it is required that the end-effector continues the trajectory with a minimum velocity jump when a fault occurs within a joint. This problem is addressed in the paper. A way to tolerate the fault is to find new joint velocities for the faulty manipulator in which results into the same end-effector velocity provided by the healthy manipulator. The aim of this study is to find a strategy which optimally redistributes the joint velocities for the remained healthy joints of the manipulators. The optimality is defined by the minimum end-effector velocity jump. A solution of the problem is presented and it is applied to a robotics manipulator. Then through a case study and a simulation study it is validated. The paper shows that if would be possible the joint velocity redistribution results into a zero velocity jump.

Reliability and variability of day-to-day vault training measures in artistic gymnastics

Inter-day training reliability and variability in artistic gymnastics vaulting was determined using a customised infra-red timing gate and contact mat timing system. Thirteen Australian high performance gymnasts (eight males and five females) aged 11-23 years were assessed during two consecutive days of normal training. Each gymnast completed a number of vault repetitions per daily session. Inter-day variability of vault run-up velocities (at -18 to -12 m, -12 to -6 m, -6 to -2 m, and -2 to 0 m from the nearest edge of the beat board), and board contact, pre-flight, and table contact times were determined using mixed modelling statistics to account for random (within-subject variability) and fixed effects (gender, number of subjects, number of trials). The difference in the mean (Mdiff) and Cohen's effect sizes for reliability assessment and intra-class correlation coefficients, and the coefficient of variation percentage (CV%) were calculated for variability assessment. Approach velocity (-18 to -2 m, CV = 2.4-7.8%) and board contact time (CV = 3.5%) were less variable measures when accounting for day-to-day performance differences, than pre-flight time (CV = 17.7%) and table contact time (CV = 20.5%). While pre-flight and table contact times are relevant training measures, approach velocity and board contact time are more reliable when quantifying vaulting performance.

Maximum likelihood approach for tracking multiple mobile agents with a moving doppler radar system

Tracking mobile agents with a Doppler radar system mounted on a moving vehicle is considered in this paper. Dopplers modulated from mobile agents on the single frequency continuous wave signals are analyzed in order to estimate the positions and velocities of multiple mobile agents. The measurement noise is assumed to be Gaussian and the maximum likelihood estimation is utilized to enhance the localization accuracy.

High strain rate tensile properties of rapidly cured woven carbon fibre composites

Tensile tests at high speeds corresponding to automotive crash events were conducted to understand the dynamic properties of rapidly cured woven carbon fiber composites. The High Strain Rate (HSR) experiments were conducted on a servo-hydraulic machine at constant velocities up to a maximum of 25 m/s (82 ft/s). Results from HSR tests were compared with the static results to determine the rate sensitivity of the composite. A high speed camera was used to capture the failure at HSR. The tensile properties of rapidly cured laminate were compared to oven cured laminate to justify its productivity while maintaining the desired properties. The methodology used to achieve constant velocity during HSR tests is discussed in detail. The specimen geometry was specially designed to suit the test rig and to achieve high speeds during tests. All the specimens failed with linear elasticity until sudden brittle fracture. The Scanning Electron Microscopy (SEM) images of the fracture zone were used to identify the failure modes observed at static and high strain rates.

Too close for comfort : a fishway exit and a hydro-power station inlet

A major environmental issue for hydro-electric power generation is passage of fish through turbines, or entrainment onto trash racks. At Yarrawonga Weir, on the upper Murray River in south-eastern Australia, the positioning of a fish lock resulted in the potential for upstream migrating fish to be swept back into the adjacent power station by cross flows. In 2004, a 4.5-m long steel extension flume was attached to the exit to alleviate this problem. To determine the fate of native fish after exiting the extension flume, 72 individuals (305–1015 mm long) were implanted with radio-transmitters and released into the fish lock exit channel. In 2004 (power station inflows 10 300 ML day^–1), the majority of fish exited successfully (44 of 45) and only a single fish (2%) was entrained into the power station. In 2005 (power station inflows 12 000 ML day^–1), fish again exited successfully (26 of 27) but with a higher proportion entrained (5 of 27; 18%). This reduced success appeared to be related to strong transverse flows with high water velocities adjacent to the fish lock exit. The efficiency of fish passage at this site might be improved by altering water management strategies, integrating engineering and fish biology, and through field-testing of proposed solutions

High rate filtration using buoyant medium : experiments and mathematical models

In this study, the high rate filtration system using buoyant medium of polypropylene or polystyrene was introduced with the study on its performance evaluation via: (i) specific surface coverage, (ii) ultimate specific deposit, (iii) blocking effect and (iv) particle detachment. The filter system was arranged in the downflow mode with an in-line flocculation. Experimental results obtained were analyzed using filtration models. This study showed that: (i) the specific surface coverage increased with the increase in the velocity; (ii) the ultimate specific deposit changed slightly at different filtration velocities and different flocculants; (iii) the blocking effect was significant in the transient stage removal of flocs; and (iv) the detachment model parameter was found to decrease with the increase in the adhesive force, Fad that acts on the flocs (above-micron size).

High-speed pollen release in the white mulberry tree, Morus alba L

Anemophilous plants described as catapulting pollen explosively into the air have rarely attracted detailed examination. We investigated floral anthesis in a male mulberry tree with high-speed video and a force probe. The stamen was inflexed within the floral bud. Exposure to dry air initially resulted in a gradual movement of the stamen. This caused fine threads to tear at the stomium, ensuring dehiscence of the anther, and subsequently enabled the anther to slip off a restraining pistillode. The sudden release of stored elastic energy in the spring-like filament drove the stamen to straighten in less than 25 μs, and reflex the petals to velocities in excess of half the speed of sound. This is the fastest motion yet observed in biology, and approaches the theoretical physical limits for movements in plants.

Interfacial energy states of moisture-exposed cracks in mica

Results of crack growth observations on mica in water-containing environments are described. The study focuses on equilibrium crack states for reversed loading cycles, i.e., for initial propagation through virgin solid and subsequent retraction-repropagation through healed or misoriented-healed interfaces. Departures from these equilibrium states are manifest as steady-state forward or backward crack velocities at specific applied loads. The equilibria are thereby interpreted as quiescent, threshold configurations G = W_E, with G the Griffith mechanical-energy-release rate and W_E the Dupré work of adhesion, on crack velocity (v-G) diagrams. Generally, W_E is found to decrease with concentration of water, in accordance with a Gibbs formalism. Hysteresis is observed in the forward-backward-forward crack propagation cycle, signifying a reduction in the adhesion energy on exposure of the open interface to environmental species prior to healing. This hysteresis is especially marked for those interfaces that are misoriented before healing, indicating that the structure of the underlying solid substrate as well as of the intervening fluid is an important consideration in the interface energetics. The equilibrium states for different environments can be represented on a simple energy-level diagram, as differences between thermodynamic end-point states: initial, closed-interface states refer to crystallographic bonding configurations ahead of the crack-tip adhesion zone; final, open interface states refer to configurations behind the crack-tip zone. The significance of this diagram in relation to the fundamental atomic structure of interfaces in fracture and other adhesion geometries, including implications concerning kinetics, is discussed.

Regulation of glycogen synthase and phosphorylase during recovery from high-intensity exercise in the rat

The aim of this study was to determine the role of the phosphorylation state of glycogen synthase and glycogen phosphorylase in the regulation of muscle glycogen repletion in fasted animals recovering from high-intensity exercise. Groups of rats were swum to exhaustion and allowed to recover for up to 120 min without access to food. Swimming to exhaustion caused substantial glycogen breakdown and lactate accumulation in the red, white and mixed gastrocnemius muscles, whereas the glycogen content in the soleus muscle remained stable. During the first 40 min of recovery, significant repletion of glycogen occurred in all muscles examined except the soleus muscle. At the onset of recovery, the activity ratios and fractional velocities of glycogen synthase in the red, white and mixed gastrocnemius muscles were higher than basal, but returned to pre-exercise levels within 20 min after exercise. In contrast, after exercise the activity ratios of glycogen phosphorylase in the same muscles were lower than basal, and increased to pre-exercise levels within 20 min. This pattern of changes in glycogen synthase and phosphorylase activities, never reported before, suggests that the integrated regulation of the phosphorylation state of both glycogen synthase and phosphorylase might be involved in the control of glycogen deposition after high-intensity exercise.

Adaptive mechanically controlled lubrication mechanism found in articular joints

Articular cartilage is a highly efficacious water-based tribological system that is optimized to provide low friction and wear protection at both low and high loads (pressures) and sliding velocities that must last over a lifetime. Although many different lubrication mechanisms have been proposed, it is becoming increasingly apparent that the tribological performance of cartilage cannot be attributed to a single mechanism acting alone but on the synergistic action of multiple "modes" of lubrication that are adapted to provide optimum lubrication as the normal loads, shear stresses, and rates change. Hyaluronic acid (HA) is abundant in cartilage and synovial fluid and widely thought to play a principal role in joint lubrication although this role remains unclear. HA is also known to complex readily with the glycoprotein lubricin (LUB) to form a cross-linked network that has also been shown to be critical to the wear prevention mechanism of joints. Friction experiments on porcine cartilage using the surface forces apparatus, and enzymatic digestion, reveal an "adaptive" role for an HA-LUB complex whereby, under compression, nominally free HA diffusing out of the cartilage becomes mechanically, i.e., physically, trapped at the interface by the increasingly constricted collagen pore network. The mechanically trapped HA-LUB complex now acts as an effective (chemically bound) "boundary lubricant"-reducing the friction force slightly but, more importantly, eliminating wear damage to the rubbing/shearing surfaces. This paper focuses on the contribution of HA in cartilage lubrication; however, the system as a whole requires both HA and LUB to function optimally under all conditions.

Understanding macrographia in children with autism spectrum disorders

It has been consistently reported that children with autism spectrum disorders (ASD) show considerable handwriting difficulties, specifically relating to accurate and consistent letter formation, and maintaining appropriate letter size. The aim of this study was to investigate the underlying factors that contribute to these difficulties, specifically relating to motor control.

We examined the integrity of fundamental handwriting movements and contributions of neuromotor noise in 26 children with ASD aged 8-13 years (IQ. >. 75), and 17 typically developing controls. Children wrote a series of four cursive letter l's using a graphics tablet and stylus.

Children with ASD had significantly larger stroke height and width, more variable movement trajectory, and higher movement velocities. The absolute level of neuromotor noise in the velocity profiles, as measured by power spectral density analysis, was significantly higher in children with ASD; relatively higher neuromotor noise was found in bands >3. Hz.

Our findings suggest that significant instability of fundamental handwriting movements, in combination with atypical biomechanical strategies, contribute to larger and less consistent handwriting in children with ASD.