Eccentric training may affect the longitudinal adaptation of the muscle. Usually the muscle fiber lengthening during eccentric training is measured by the joint kinematics. Due to tendon compliance, this method offers insufficient information about the muscle fiber behavior. The present study investigated the muscle fiber behavior of the Vastus Lateralis muscle (VL) during eccentric knee contractions in humans by measuring the changes of fascicle length in vivo with ultrasonography, at force levels of 65% and 95% of the maximum voluntary isometric contraction force (MVC). Seven young adults were tested by a Biodex. They performed eccentric knee contractions with one leg at 65% and 95% of their MVC (knee angle 25°-100°, angular velocity 90°/s). Potential joint axis deviations were recorded using a Vicon camera system. Exerted knee moments were captured synchronously with the Vicon system at 1000Hz. Fascicle length of the VL muscle visualized by a 10cm Ultrasound prob. The means and standard deviations of fascicle elongation at 65% and 95% of the MVC were 42.71±8.54mm and 39.11±10.64mm respectively, with no statistically significant difference between both conditions. All subjects showed a plateau or slide decrease in fascicle length at the beginning of the movement. This slight decrease in fascicle length, which occurs despite a lengthening of the VL muscle-tendon unite, can be explained by the tendon compliance. The similar fascicle elongation between the two conditions (65% vs. 95% MVC) reveals that the amplitude of the force level during eccentric knee extension contractions does not affect the lengthening of the fascicle.
A high incidence of lower extremity injuries has been reported in runners, with half of the injuries occurring at the knee joint. Sagittal plane trunk posture was shown to influence hip and knee kinetics during landing. This suggests trunk posture may be a risk factor of running injuries. The purpose of this study was aimed to examine the influence of sagittal plane trunk posture on hip and knee kinetics during running. Forty runners were recruited. Three-dimensional kinematics (250Hz, Qualisys) and ground reaction force data (1500Hz, AMTI) were collected while subjects ran with a self-selected trunk posture (speed: 3.4m/s). Mean trunk flexion angle and peak hip and knee extensor moments during the stance phase were calculated. Subjects were dichotomized into High-Flex and Low-Flex groups based on trunk flexion angles. On average, the two groups demonstrate 7.4°difference in trunk flexion. Independent t-tests showed that the Low-Flex group demonstrated significantly higher knee extensor moments and lower hip extensor moments compared to the High-Flex group. Pearson correlations showed that trunk flexion angle was positively correlated with peak hip extensor moment (r=0.44) and inversely correlated with peak knee extensor moment (r=-0.51). The results suggested a small difference in trunk flexion angle has significant influences on hip and knee kinetics. Individuals who run with a more upright trunk posture may be predisposed to a higher risk of patellar tendinopathy and patellofemoral pain. Incorporating a forward lean trunk may be utilized as an intervention strategy to reduce knee loading and risk of knee injuries in runners.
When an active muscle is stretched, the resulting post-eccentric steady-state force is known to be greater than the isometric force at the corresponding muscle length. The aim of our research was to clarify if residual force enhancement (RFE) is relevant for voluntary human muscle action in everyday like scenarios. Therefore 13 healthy subjects participated in our study and had to perform bilateral leg extensions using a motor-driven leg press dynamometer, measuring external reaction forces (Fext) as well as activity of 9 lower extremity muscles. In addition, ankle (Ma) and knee (Mk) joint torque were calculated using inverse dynamics. Subjects performed isometric and isometric-eccentric-isometric contractions (20° stretch, ω=60°/s) at 30% of maximum voluntary activation. Visual feedback of VL muscle activation was given to control submaximal muscle action. We did not find differences in VL activation level between contraction conditions and time points. Mean VL activity ranged between 29.1 ± 2.2% and 29.8±2.5% MVA. We found significantly enhanced Fext (p < 0.002) as well as joint torques in knee (p < 0.002) and ankle joint (p < 0.033) for all instances in time. In summary RFE seems to be relevant in everyday like human motion.
A comprehensive characterization of small-scale fluid-sediment interactions will improve understanding of large-scale ocean engineering phenomena, resulting in more accurate wave forecasting and improved ocean circulation models. The critical shear stress is typically used to determine the initiation of sediment motion in coastal applications. However, this shear stress criterion was primarily developed for steady flows and has been inconclusive in some wave environments where sediment motion may be induced by horizontal pressure gradients. Evidence suggests that the incipient motion formulation should account for the combined effects of the horizontal pressure gradients and bed shear stresses. Other researchers have made one-dimensional and two-dimensional measurements of near-bed velocities. However, previously available technologies could not resolve the three-dimensional velocities at the bed or directly measure sediment motion.
Accurate investigation of the hydrodynamic forces that initiate coastal sediment transport requires high resolution measurements at the fluid-sediment interface. We have made previously unavailable high spatial and temporal resolution laboratory measurements at the sediment bed with state-of-the-art instruments. Additionally, we have performed one of the first direct measurements of sediment motion in response to waves with newly-developed electronic grains. The MEMs sensors are 2.5 x 1.5 x 1.4 cm and measure three-dimensional accelerations, store the data onboard, and transmit them wirelessly after retrieval. The Smart Sediment Grains (SSGs) were developed by embedding MEMs sensors in gravel-sized Delrin plastic spheres. These spheres allow uninhibited movement in any direction, similar to a smooth sand grain. The SSGs are the first freely moving electronic grains that measure sediment dynamics which previous technologies could not, giving insight into the underlying wave forces driving sediment transport. The SSGs enhance our ability to measure the motion, transport, and settling of sediments in the nearshore by capturing translation and rotation of the sediment. This will improve our predictive capabilities of sediment transport phenomena such as beach erosion and seabed evolution in response to wave forces; as well as improve parameterizations of the bottom friction for ocean circulation and wave energy dissipation models.
The SSGs have been successfully deployed in small and field-scale wave flumes to measure the response of coarse gravel sediments to wave forcing. High resolution profiling Acoustic Doppler Velocimeters and a Particle Image Velocimetry system, comprising a laser and four high speed cameras, measured the three-dimensional fluid velocities at the bed. These measurements provide resolution high enough to fully examine the small-scale fluid forces exerted on each individual sediment grain. The SSGs accurately captured the sediment response to the waves at the onset of sediment transport. Additionally, broader incipient motion experiments were conducted with a variety of sediment grain diameters and densities for comparison. The results suggest evidence of pressure gradient influenced incipient motion; in contrast with the more commonly used threshold for sediment motion based on the bed shear stress. Calculated values of the Sleath parameter, used to quantify the effects of the pressure gradients, were comparable with field observations of pressure
gradient induced sediment transport. The data also suggest that vortex shedding could be a factor in triggering sediment transport.
We have directly measured incipient motion in waves by resolving the near-bed fluid velocities and collecting direct measurements of sediment motion with state-of-the-art instruments. The data are being used to validate theoretical and numerical models of the wave bottom boundary layer and bottom friction estimates. These results will be synthesized to propose a comprehensive incipient motion criterion comprising the effects of the shear stress and the pressure gradients, also taking into account a variety of flow and sediment characteristics.
The current configuration of the SSGs helps to identify the characteristics of incipient motion and determine orientation. These mobile nodes make a significant step towards resolving the Lagrangian dynamics of individual coarse gravel-sized particles within the mobile bed layer in the nearshore. On a larger scale, they will reduce the effects of beach erosion by improving beach nourishment design. With technological advancements, these SSGs can be minimized and made field-deployable with enclosures configured to other applications to provide transformative measurements in geotechnical engineering, hydrology, oceanography and human health monitoring.
In the past we have shown that exposure to increasing amplitudes of Galvanic vestibular stimulation (GVS) induces a corresponding increasing deficit in postural control, cognition and autonomic function. Previous studies have suggested that suprathreshold GVS induces a similar pattern of postural instability as the one observed on bilateral vestibular loss. The aim of the present study was to determine whether different current intensities would affect somatosensory, visual, and vestibular sensory system similarly to patient affected by vestibular deficits. We assessed postural control in unilateral (right and left) and bilateral vestibular loss patients, an aged matched healthy control group, and during pseudorandom binaural bipolar GVS in healthy subjects at one of three current amplitudes (1 mA, 3.5 mA, 5 mA). Balance was assessed with sensory organization test (SOT) that quantifies the effectiveness of vestibular, visual and somatosensory input to postural control. Results showed that GVS significantly affects vestibular control of posture compared to baseline at all current amplitudes, whereas somatosensory and visual performance was unaffected. Vestibular patients showed a significant decrease in vestibular and visual response compared to control. Suprathreshold GVS 5 mA showed a similar large effect size to unilateral and bilateral vestibular loss patients relative to their aged matched control. NASA NCC 9-58 and NNX09AL14G
Our previous study showed that exposure to Galvanic Vestibular Stimulation (GVS) induces temporary postural deficits similar to the ones experienced by astronauts after microgravity exposure. Preliminary evidence suggests that repeated exposures to GVS might induce adaptation of sway response. We studied whether repeated exposure to pseudorandom GVS over a 3 month period facilitates the adaptation response. Twenty healthy subjects were randomly assigned into 2 groups: suprathreshold (5mA) GVS, and subthreshold (1mA). The test battery included: Romberg, sensory organization test (posturography), dynamic visual acuity, and torsional eye movement. Each test was performed with no GVS, and then with 10 min of GVS per session for 12 consecutive weeks. Sensorimotor adaptation was also measured during two follow up sessions at weeks 18 and 36. Results showed that subthreshold GVS did not affect vestibular scores. Suprathreshold GVS significantly decreased vestibular scores during the first few weeks, with postural performance returning to baseline around the 6th week of exposure. This improvement was maintained during the follow up sessions. Our results suggest that 60 min of subthreshold GVS are sufficient to elicit adaptation to the stimulus. No significant changes were shown in low-level vestibulo-ocular reflexes during torsional eye movement, or vestibulo-spinal reflexes during Romberg; confirming that adaptation only occurs at the level of the CNS. NASA NCC 9-58; NNX09AL14G
Functional demands placed on the human knee’s anterior cruciate ligament (ACL) vary with activity but remain impossible to measure directly in-vivo. Our lab is characterizing these demands in the sheep model by recording in vivo knee kinematics and ACL transducer voltages during activities of daily living (ADLs), reproducing these motions using the instrumented limb, and measuring the 3D forces in the ligament. However, up to 13% of patients sustaining ACL injuries will also sustain dual medial meniscus (MM) injuries and up to 10% will sustain dual medial collateral ligament (MCL) injuries. These structures are frequently left unrepaired, which may alter the ACL’s functional demands, resulting in inadequate ACL reconstruction outcomes for patients with dual injuries. Although these structures have been shown to alter ACL loading in cadaveric studies, the extent to which they impact ACL functionality during in vivo ADLs remains unknown. Moreover, changes in ACL functionality over time due to joint healing and remodeling have yet to be investigated. In this study, we aimed to track stifle joint remodeling in response to surgically imposed MCL transections and medial meniscectomies through monitoring vertical ground reaction forces (VGRFs) for three ADLs over 12 weeks. Results of this study may then be used in conjunction with future robotic studies as a tool to estimate in vivo load requirements for ACL reconstructions in patients with dual injuries.
Purpose: Total Hip Replacements (THR) are a common procedure for older people who suffer from degenerative joint disease. Golf is a very popular leisure sport played by many older Americans including those with THR. Hip torques encountered in a golf swing after THR has not been reported. The purpose of this study is to describe three- dimensional (3D) hip joint torques generated during a golf swinging by those with THR. Methods: Three male amateur golfers who were at least 1 year post THR (ages 59-71 year old and right hand dominant, (2 were left THR) participated. Golf handicap ranged from 16-18. All participants completed the Hip Harris Score. Passive reflective markers were placed on key boney anatomical landmarks. Participants were allowed to warm up prior to testing by performing golf swings. During data collection, participants completed ten swings using a standardized driver. Kinetics and kinematics were captured using a 10 camera Motion Analysis system (Motion Analysis Corp, Santa Rose, CA) and two AMTI (Advanced Medical Technology, Inc., Watertown, MA) forceplates. Inverse dynamics procedure was used to calculate peak hip torques in all three planes. Hip torques were normalized to body weight x height (BW x Ht) and presented as internal torques. Comparisons were made to previously collected similarly aged healthy male golfers (senior group). Results: Average Club head velocity was slower than senior group. Like the senior group, THR golfers exhibited the greatest torque in the sagittal plane .In the frontal plane, all THR golfers demonstrated a lower hip adductor torque on the lead leg compared to the trail leg and compared to senior group. In the transverse plane, those with THR exhibited higher hip external rotation torques compared to the internal rotation torques and compared to the senior group. Conclusion: Three dimensional peak hip torques generated during the golf swing by persons with a THR are greatest in the sagittal plane. THR golfers demonstrated slower club head speed but generated higher hip torques in the transverse plane as compared to those without a THR. Hip external rotation torque was higher in all of the THR compared to the senior group. Clinical Significance: Subjects with a THR may be prone to abnormal forces in the transverse plane during the golf swing. Future studies are needed to determine impact on return to golf decisions following a THR.
Introduction: Stair gait is an activity performed daily. Inherently falls during stair gait continue to be a concern especially for older adults 65 years +. Recently falls have become the most common cause of injury-related deaths in individuals over the age of 75 y.o. Stair descent falls account for 75% of stair falls and also present a greater injury severity. Poor shoes or insoles and lighting condition can contribute to an increased risk of falls during stair locomotion. Stability can be measured using the COM-BOS ‘stability margin’ relationship. Center of pressure (COP), another stability measure,can be calculated from a multi-axis force-plate system. As well, plantar pressure is an important indicator of gait pattern efficiency. Aim: To identify aspects of stair gait that increase the risk of falls. By measuring the COM-BOS ‘stability margin’, the COP and plantar pressure patterns of individuals during stair gait, while modifying insoles and lighting. Methods: Young and older adults will ascend and descend a 4 level staircase, with two imbedded AMTI-force platforms in varying lighting condition (low, normal). Participants will be fitted with standardized footwear with Medi-logic insoles placed under varying hardnesses of insoles. An Optotrak motion capture system will record 12 IRED markers placed on the individual to determine the COM trajectory and BOS of location. Hypothesis: Partipants should demonstrate a greater lateral displacement in the single support phase during dim lighting as opposed to normal lighting. The stability of older adults will be compromised with alteration to the insoles (soft and hard).
Dexterous manipulation relies on modulation of digit forces as a function of digit placement. However, little is known about the sense of position of the finger pads relative to each other. We quantified subjects' ability to match perceived vertical distance between the thumb and index finger pads (dy) of the right hand (“reference” hand, Rhand) using the ipsilateral or contralateral hand (“test” hand, Thand) without vision of the hands. The Rhand digits were passively placed non-collinearly (dy = ±30 mm) or collinearly (dy = 0 mm). Subjects reproduced Rhand dy by using a congruent or inverse Thand posture. We hypothesized that matching error would be greater (a) for collinear than non-collinear digits positions, (b) when Rhand and Thand postures were not congruent, and (c) when subjects reproduced dy using the contralateral hand. Subjects made greater errors when matching collinear than non-collinear dys, when the posture of Thand and Rhand were not congruent, and when Thand was the contralateral hand. Under-estimation errors were produced only for non-collinear digits positions, when the postures of Thand and Rhand were not congruent, and when Thand was the contralateral hand. These findings indicate that perceived finger pad distance is transferred across hands less accurately than when it is reproduced within the hand and reproduced less accurately when a higher-level processing of the somatosensory feedback is required for non-congruent hand postures. We propose that erroneous representation of finger pad distance, if not compensated for between contact and onset of manipulation, might lead to manipulation performance errors.