A method for simulating forward falls and controlling impact velocity.

Assessment of protective arm reactions associated with forward falls are typically performed by dropping research participants from a height onto a landing surface. The impact velocity is generally modulated by controlling the total height of the fall. This contrasts with an actual fall where the fall velocity is dependent on several factors in addition to fall height and not likely predictable at the onset of the fall. A counterweight and pulley system can be used to modulate the fall velocity in simulated forward falls in a manner that is not predictable to study participants, enhancing experimental validity. However, predicting the fall velocity based on participant height and weight and counterweight mass is not straightforward. In this article, the design of the FALL simulator For Injury prevention Training and assessment (FALL FIT) system is described. A dynamic model of the FALL FIT and counterweight system is developed and model parameters are fit using nonlinear optimization and experimental data. The fitted model enables prediction of fall velocity as a function of participant height and weight and counterweight load. The method can be used to provide controllable perturbations thereby elucidating the control strategy used when protecting the body from injury in a forward fall, how the control strategy changes because of aging or dysfunction or as a method for progressive protective arm reaction training.•Construction of device to simulate forward falls with controllable impact velocity using material that are commercially available is described•A dynamic model of the FALL FIT is developed to estimate the impact velocity of a simulated forward fall using participant height and counterweight load•The dynamic model is validated using data from 3 previous studies.

Micro-doppler radar to evaluate risk for musculoskeletal injury: Protocol for a case-control study with gold standard comparison.

BACKGROUND: Beyond causing significant morbidity and cost, musculoskeletal injuries (MSKI) are among the most common reasons for primary care visits. A validated injury risk assessment tool for MSKI is conspicuously absent from current care. While motion capture (MC) systems are the current gold standard for assessing human motion, their disadvantages include large size, non-portability, high cost, and limited spatial resolution. As an alternative we introduce the Micro Doppler Radar (MDR); in contrast with MC, it is small, portable, inexpensive, and has superior spatial resolution capabilities. While Phase 1 testing has confirmed that MDR can identify individuals at high risk for MSKI, Phase 2 testing is still needed. Our aims are to 1) Use MDR technology and MC to identify individuals at high-risk for MSKI 2) Evaluate whether MDR has diagnostic accuracy superior to MC 3) Develop MDR algorithms that enhance accuracy and enable automation. METHODS AND FINDINGS: A case control study will compare the movement patterns of 125 ACL reconstruction patients to 125 healthy controls. This study was reviewed and approved by the Pennsylvania State University Human Research Protection Program (HRPP) on May 18, 2022, and the IRB approval number is STUDY00020118. The ACL group is used as a model for a "high risk" population as up to 24% will have a repeat surgery within 2 years. An 8-camera Motion Analysis MC system with Cortex 8 software to collect MC data. Components for the radar technology will be purchased, assembled, and packaged. A micro-doppler signature projection algorithm will determine correct classification of ACL versus healthy control. Our previously tested algorithm for processing the MDR data will be used to identify the two groups. Discrimination, sensitivity and specificity will be calculated to compare the accuracy of MDR to MC in identifying the two groups. CONCLUSIONS: We describe the rationale and methodology of a case-control study using novel MDR technology to detect individuals at high-risk for MSKI. We expect this novel approach to exhibit superior accuracy than the current gold standard. Future translational studies will determine utility in the context of clinical primary care.

The timing and amplitude of the muscular activity of the arms preceding impact in a forward fall is modulated with fall velocity.

Protective arm reactions have been shown to be an important injury avoidance mechanism in unavoidable falls. Protective arm reactions have been shown to be modulated with fall height, however it is not clear if they are modulated with impact velocity. The aim of this study was to determine if protective arm reactions are modulated in response to a forward fall with an initially unpredictable impact velocity. Forward falls were evoked via sudden release of a standing pendulum support frame with adjustable counterweight to control fall acceleration and impact velocity. Thirteen younger adults (1 female) participated in this study. Counterweight load explained more than 89% of the variation of impact velocity. Angular velocity at impact decreased (p < 0.001), drop duration increased from 601 ms to 816 ms (p < 0.001), and the maximum vertical ground reaction force decreased from 64%BW to 46%BW (p < 0.001) between the small and large counterweight. Elbow angle at impact (129 degrees extension), triceps (119 ms) and biceps (98 ms) pre-impact time, and co-activation (57%) were not significantly affected by counterweight load (p-values > 0.08). Average triceps and biceps EMG amplitude decreased from 0.26 V/V to 0.19 V/V (p = 0.004) and 0.24 V/V to 0.11 V/V (p = 0.002) with increasing counterweight respectively. Protective arm reactions were modulated with fall velocity by reducing EMG amplitude with decreasing impact velocity. This demonstrates a neuromotor control strategy for managing evolving fall conditions. Future work is needed to further understand how the CNS deals with additional unpredictability (e.g., fall direction, perturbation magnitude, etc.) when deploying protective arm reactions.

Effect of Multicomponent Home-Based Training on Gait and Muscle Strength in Older Adults After Hip Fracture Surgery: A Single Site Randomized Trial.

OBJECTIVE: To investigate the effect of 16-week home-based physical therapy interventions on gait and muscle strength. DESIGN: A single-blinded randomized controlled trial. SETTING: General community. PARTICIPANTS: Thirty-four older adults (N=34) post hip fracture were randomly assigned to either experimental group (a specific multi-component intervention group [PUSH], n=17, 10 women, age=78.6±7.3 years, 112.1±39.8 days post-fracture) or active control (a non-specific multi-component intervention group [PULSE], n=17, 11 women, age=77.8±7.8 years, 118.2±37.5 days post-fracture). INTERVENTION: PUSH and PULSE groups received 32-40 sessions of specific or non-specific multi-component home-based physical therapy, respectively. Training in the PUSH group focused on lower extremity strength, endurance, balance, and function for community ambulation, while the PULSE group received active movement and transcutaneous electrical nerve stimulation on extremities. MAIN OUTCOME MEASURES: Gait characteristics, and ankle and knee muscle strength were measured at baseline and 16 weeks. Cognitive testing of Trail Making Test (Part A: TMT-A; Part-B: TMT-B) was measured at baseline. RESULTS: At 16 weeks, both groups demonstrated significant increases in usual (P<.05) and fast (P<.05) walking speed, while there was no significant difference in increases between the groups. There was only 1 significant change in lower limb muscle strength over time (non-fractured side) between the groups, such that PUSH did better (mean: 4.33%, 95% confidence interval:1.43%-7.23%). The increase in usual and fast walking speed correlated with the baseline Trail-making Test-B score (r=-0.371, P=.037) and improved muscle strength in the fractured limb (r=0.446, P=.001), respectively. CONCLUSION: Gait speed improved in both home-based multicomponent physical therapy programs in older adults after hip fracture surgery. Muscle strength of the non-fractured limb improved in the group receiving specific physical therapy training. Specific interventions targeting modifiable factors such as muscle strength and cognitive performance may assist gait recovery after hip fracture surgery.

The Effect of an Overnight Summer Camp on the Quality of Life for Individuals Who Require Ventilatory Support.

PURPOSE: Summer camps are a modality that addresses barriers to social interaction. Although there is a growing amount of evidence supporting camps for individuals with chronic illness, there is no known research on camp experiences for those who require ventilatory support. The purpose of this study was to examine the perceptions of attending camp on self-esteem, social functioning, emotional functioning, and physical functioning for individuals who require ventilatory support. METHODS: Eleven participants completed the Pediatric Camp Outcome Measure via an online survey. RESULTS: This study found positive correlations between the number of years an individual attended the camp and his or her overall Pediatric Camp Outcome Measure score, as well as social functioning and physical functioning subscales. This study found positive correlations with questions in all subscales with the number of years attending camp. CONCLUSION: Findings suggest that attending summer camp may positively impact the quality of life for individuals who require ventilatory support.

Test-retest reliability of the FALL FIT system for assessing and training protective arm reactions in response to a forward fall.

The use of the hands and arms is an important protective mechanism in avoiding fall-related injury. The aim of this study was to evaluate the test-retest reliability of fall dynamics and evokd protective arm response kinematics and kinetics in forward falls simulated using the FALL simulator For Injury prevention Training and assessment system (FALL FIT). Fall FIT allows experimental control of the fall height and acceleration of the body during a forward fall. Two falls were simulated starting from 4 initial lean angles in Experiment 1 and with 4 different fall accelerations in Experiment 2. Fourteen younger adults (25.1±3.5 years) and 13 older adults (71.3±3.7 years) participated in Experiment 1 and 13 younger adults (31.8±5.7 years) participated in Experiment 2. Intraclass correlation coefficients (ICC) were used to the evaluate absolute agreement of single measures at each condition and averages across conditions. Average measures of fall dynamics and evoked kinematics and kinetics exhibited excellent reliability (ICC(A,4)>0.86). The reliability of single measures (ICC(A,1) > 0.59) was good to excellent, although 18% of single measures had a reliability (ICC(A,1)) between 0.00 and 0.57. The FALL FIT was shown to have good to excellent reliability for most measures. FALL FIT can produce a wide range of fall dynamics through modulation of initial lean angle and body acceleration. Additionally, the range of fall velocities and evoked kinematics and kinetics are consistent with previous fall research.•The FALL FIT can be used to gain further insight into the control of protective arm reactions and may provide a therapeutic tool to assess and train protective arm reactions.

Age-related changes in protective arm reaction kinematics, kinetics, and neuromuscular activation during evoked forward falls.

Fall related injuries in older adults are a major healthcare concern. During a fall, the hands and arms play an important role in minimizing trauma from ground impact. Although older adults are able to orient the hands and arms into a protective orientation after falling and prior to ground impact, an inability to avoid increased body impact occurs with age. Previous investigations have generally studied rapid arm movements in the pre-impact phase or absorbing energy in the post-impact phase. There are no known studies that have directly examined both the pre-impact and post-impact phase in sequence in a forward fall. The aim of this study was to identify age-related biomechanical and neuromuscular changes in evoked arm reactions in response to forward falls that may increase fall injury risk. Fourteen younger and 15 older adults participated. Falls were simulated while standing with torso and legs restrained via a moving pendulum system from 4 different initial lean angles. While there was not a significant age-related difference in the amount of energy absorbed post-impact (p = 0.68), older adults exhibited an 11% smaller maximum vertical ground reaction force when normalized to body weight (p = 0.031), and 8 degrees less elbow extension at impact (p = 0.045). A significant interaction between age and initial lean angle (p = 0.024), indicated that older adults required 54%, 54%, 41%, and 57% greater elbow angular displacement after impact at the low, medium, medium-high, and high initial lean angles compared to younger adults. These results suggested older adults may be at greater risk of increased body impact due to increased elbow flexion angular displacement after impact when the hands and arms are able to contact the ground first. Both groups exhibited robust modulation to the initial lean angle with no observed age-related differences in the initial onset timing or amplitude of muscle activation levels. There were no significant age-related differences in the EMG timing, amplitude or co-activation of muscle activation preceding impact or following impact indicating comparable neuromotor response patterns between older and younger adults. These results suggest that aging changes in muscular elements may be more implicated in the observed differences than changes in neuromuscular capacity. Future work is needed to test the efficacy of different modalities (e.g. instruction, strength, power, perturbation training, fall landing techniques) aimed at reducing fall injury risk.

Examining the influence of mental stress on balance perturbation responses in older adults.

BACKGROUND: Reach-to-grasp responses following balance perturbations are important to fall prevention but are often ineffective in older adults. The ability to shift attention from an ongoing cognitive task to balance related processes has been shown to influence reach-to-grasp effectiveness in older adults. However, the added influence of stress and anxiety - known to negatively affect attention shifting ability - has not yet been explored in relation to recovery from balance perturbations. Given that fear and anxiety over falling is a key fall risk factor, an understanding of how such a negative mental state may affect postural reactions is important. This study aimed to investigate the effect of varied induced emotional states on reach-to-grasp balance responses in older adults. METHODS: Healthy older adults (mean age 70.5 ± 5.38 years) stood laterally between 2 handrails with contact sensors. A safety harness with an integrated loadcell was worn to prevent falls and measure the amount of harness assistance (expressed as percent body weight). With instructions to grasp one rail to restore balance, participants' balance was laterally disturbed using surface translations under three randomized conditions: no cognitive task, neutral (verb generation) task, and mental stress task with negative prompts (paced auditory serial addition). The primary outcome was frequency of protective grasps. Secondary outcomes included frequency of harness assistance during trials with grasp errors as well as wrist movement time, trajectory distance, and peak velocity. RESULTS: Perceived level of distress was highest for the mental stress task compared to no task (p < 0.001) and neutral task conditions (p = 0.008). The mental stress task resulted in the lowest percentage of protective grasps (p < 0.001) in response to balance perturbations. Closer examination of trials that resulted in grasp errors (i.e., collisions or overshoots), revealed increased harness assistance and reduced peak velocity of wrist movement (p < 0.001) under the mental stress condition compared to grasp errors that occurred under the no task or neutral task condition. DISCUSSION AND CONCLUSION: Distressing mental thoughts immediately prior to a balance perturbation lead to reduced effectiveness in reach-to-grasp balance responses compared to no or neutral cognitive tasks and should be considered as a possible fall risk factor.

Neuromuscular mechanisms that contribute to gross motor performance in survivors of childhood acute lymphoblastic leukemia.

PURPOSE: This study explored neuromuscular mechanisms and clinical measures that contribute to countermovement jump performance in survivors of childhood acute lymphoblastic leukemia (ALL CCS) compared to age- and sex-matched peers. METHODS: This exploratory cross-sectional observational study examined 12 participants, six ALL CCS and six age- and sex-matched peers (7-16 years). During a countermovement jump, rates of muscle activation of lower leg muscles were measured with electromyography, and joint torques and peak jump height with force plates and a motion capture system. Clinical measures included muscle extensibility, balance, and mobility measured by active ankle dorsiflexion, Bruininks-Oseretsky Motor Proficiency (BOT-2), and Timed Up and Go (TUG) tests. RESULTS: Compared to peers, ALL CCS demonstrated reduced gastrocnemius muscle extensibility and tibialis anterior rate of muscle activation, decreased jump height, and poorer performance on the BOT-2 and TUG. Jump height was significantly correlated with clinical measures of the BOT-2 and TUG. CONCLUSION: These ALL CCS demonstrated neuromuscular impairments that may impact jump performance, an essential childhood physical activity. Further research is needed to explore intervention strategies to improve the neuromuscular mechanisms that contribute to high-level gross motor skills in ALL CCS.

Effects of transcranial direct current stimulation (tDCS) on posture, movement planning, and execution during standing voluntary reach following stroke.

BACKGROUND: Impaired movement preparation of both anticipatory postural adjustments and goal directed movement as shown by a marked reduction in the incidence of StartReact responses during a standing reaching task was reported in individuals with stroke. We tested how transcranial direct current stimulation (tDCS) applied over the region of premotor areas (PMAs) and primary motor area (M1) affect movement planning and preparation of a standing reaching task in individuals with stroke. METHODS: Each subject performed two sessions of tDCS over the lesioned hemisphere on two different days: cathodal tDCS over PMAs and anodal tDCS over M1. Movement planning and preparation of anticipatory postural adjustment-reach sequence was examined by startReact responses elicited by a loud acoustic stimulus of 123 dB. Kinetic, kinematic, and electromyography data were recorded to characterize anticipatory postural adjustment-reach movement response. RESULTS: Anodal tDCS over M1 led to significant increase of startReact responses incidence at loud acoustic stimulus time point - 500 ms. Increased trunk involvement during movement execution was found after anodal M1 stimulation compared to PMAs stimulation. CONCLUSIONS: The findings provide novel evidence that impairments in movement planning and preparation as measured by startReact responses for a standing reaching task can be mitigated in individuals with stroke by the application of anodal tDCS over lesioned M1 but not cathodal tDCS over PMAs. This is the first study to show that stroke-related deficits in movement planning and preparation can be improved by application of anodal tDCS over lesioned M1. Trial registration ClinicalTrial.gov, NCT04308629, Registered 16 March 2020-Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/NCT04308629.

Comparison of Lateral Perturbation-Induced Step Training and Hip Muscle Strengthening Exercise on Balance and Falls in Community-Dwelling Older Adults: A Blinded Randomized Controlled Trial.

BACKGROUND: This factorial, assessor-blinded, randomized, and controlled study compared the effects of perturbation-induced step training (lateral waist-pulls), hip muscle strengthening, and their combination, on balance performance, muscle strength, and prospective falls among older adults. METHODS: Community-dwelling older adults were randomized to 4 training groups. Induced step training (IST, n = 25) involved 43 progressive perturbations. Hip abduction strengthening (HST, n = 25) utilized progressive resistance exercises. Combined training (CMB, n = 25) included IST and HST, and the control performed seated flexibility/relaxation exercises (SFR, n = 27). The training involved 36 sessions for a period of 12 weeks. The primary outcomes were the number of recovery steps and first step length, and maximum hip abduction torque. Fall frequency during 12 months after training was determined. RESULTS: Overall, the number of recovery steps was reduced by 31% and depended upon the first step type. IST and CMB increased the rate of more stable single lateral steps pre- and post-training than HST and SFR who used more multiple crossover and sequential steps. The improved rate of lateral steps for CMB exceeded the control (CMB/SFR rate ratio 2.68). First step length was unchanged, and HST alone increased hip torque by 25%. Relative to SFR, the fall rate ratios (falls/person/year) [95% confidence interval] were CMB 0.26 [0.07-0.90], IST 0.44 [0.18-1.08], and HST 0.30 (0.10-0.91). CONCLUSIONS: Balance performance through stepping was best improved by combining perturbation and strength training and not strengthening alone. The interventions reduced future falls by 56%-74% over the control. Lateral balance perturbation training may enhance traditional programs for fall prevention.

Neurocognitive measures predict voluntary stepping performance in older adults post-hip fracture.

BACKGROUND: Hip fracture is a debilitating injury, especially in older adults. The purpose of this study was to determine the relationships between Trail-Making test performance and parameters of the choice stepping reaction time test in community-dwelling older adults after hip fracture. METHODS: Twenty-four older adults post-hip fracture repair participated in an ancillary study for physical therapy interventions. Measures included Trail-Making test (Parts A & B) scores, movement time (time from foot liftoff to touchdown), step speed, reaction time (time from cue to foot liftoff), and total response time (time from step cue to touchdown) in the forward and lateral directions. Paired t-tests and multiple linear regressions were used for analysis. FINDINGS: Significant differences were found in movement time, speed and reaction time between limbs in the lateral direction, and in movement and reaction time in the forward direction. Trails A predicted step speed, reaction time and total response time for the fractured limb in the lateral direction, as well as reaction time and total response time in the forward direction. However, Trails A could not predict performance for the non-fractured limb. Trails B predicted stepping performance for both limbs in the forward and lateral directions. INTERPRETATION: Trails A correlated with the fractured limb's ability to perform the choice stepping test, but not in the non-fractured limb. Meanwhile, Trails B correlated with stepping performance in both limbs, suggesting those with poorer executive function have a lower protective stepping capability and may be at a higher risk for future falls and injury.

Acoustic pre-stimulation modulates startle and postural reactions during sudden release of standing support surface in aging.

Falls contribute to injuries and reduced level of physical activity in older adults. During falls, the abrupt sensation of moving downward triggers a startle-like reaction that may interfere with protective response movements necessary to maintain balance. Startle reaction could be dampened by sensory pre-stimulation delivered immediately before a startling stimulus. This study investigated the neuromodulatory effects of pre-stimulation on postural/startle responses to drop perturbations of the standing support surface in relation to age. Ten younger and 10 older adults stood quietly on an elevated computer-controlled moveable platform. At an unpredictable time, participants were dropped vertically to elicit a startle-like response. Reactive drop perturbation trials without a pre-stimulus (control) were alternated with trials with acoustic pre-stimulus tone (PSI). A two-way mixed design analysis of variance comparing condition (control vs. PSI) X group (younger vs. older) was performed to analyze changes in muscle activation patterns, ground reaction force, and joint angular displacements. Compared to younger adults, older adults showed lower neck muscle electromyography amplitude reduction rate and incidence of response. Peak muscle activation in neck, upper arm, and hamstring muscles were reduced during PSI trials compared to control trials in both groups (p < 0.05). In addition, knee and hip joint flexion prior to ground contact was reduced in PSI trials compared to control (p < 0.05). During post-landing balance recovery, increased knee and hip flexion displacement and time to peak impact force were observed in PSI trials compared to control condition (p < 0.05). PSI reduced startle-induced muscle activation at proximal body segments and likely decreased joint flexion during abrupt downward vertical displacement perturbations of the body. Older adults retained the ability to modulate startle and postural responses but their neuromodulatory capacity was reduced compared with younger adults. Further research on the potential of applying PSI as a possible therapeutic tool to reduce the risk of fall-related injury is needed.

Protective arm movements are modulated with fall height.

Protective arm reactions were evoked in 14 younger adults to determine the effect of fall height on protective arm reaction biomechanics. Participants were supported in a forward-leaning position on top of an inverted pendulum that isolated arm reaction by preventing any fall arresting contribution that may come from the ankle, knees, or hip. At an unpredictable time, the pendulum was released requiring participants to rapidly orient their arms to protect the head and body. Vertical ground reaction force (vGRF), arm kinematics, and electromyographic (EMG) measures of the biceps and triceps were compared at four initial lean angles. The time following perturbation onset and prior to impact consisted of two phases: rapid extension of the elbows and co-activation of the biceps and triceps in preparation for impact. The rapid orientation phase was modulated with fall height while the co-activation of the biceps and triceps in preparation for landing was minimally affected. Larger lean angles resulted in increased vGRF, increased elbow extension at impact, decreased elbow angular extension velocity at impact, and increased neck velocity at impact while hand velocity at impact was not significantly affected. The neuromuscular control strategy appears to optimize elbow extension angle/angular velocity prior to co-activation of the biceps and triceps that occurs about 100 ms prior to impact. Future work should investigate how the neuromuscular control strategy handles delayed deployment of protective arm reactions.

Aging effects of motor prediction on protective balance and startle responses to sudden drop perturbations.

This pilot study investigated the effect of age on the ability of motor prediction during self-triggered drop perturbations (SLF) to modulate startle-like first trial response (FTR) magnitude during externally-triggered (EXT) drop perturbations. Ten healthy older (71.4 ±â€¯1.44 years) and younger adults (26.2 ±â€¯1.63 years) stood atop a moveable platform and received blocks of twelve consecutive EXT and SLF drop perturbations. Following the last SLF trial, participants received an additional EXT trial spaced 20 min apart to assess retention (EXT RTN) of any modulation effects. Electromyographic (EMG) activity was recorded bilaterally over the sternocleidomastoid (SCM), vastus lateralis (VL), biceps femoris (BF), medial gastrocnemius (MG), and tibialis anterior (TA). Whole-body kinematics and kinetic data were recorded. Stability in the antero-posterior direction was quantified using the margin of stability (MoS). Compared with EXT trials, both groups reduced SCM peak amplitude responses during SLF and EXT RTN trials. VL/BF and TA/MG coactivation were reduced during SLF FTR compared to EXT FTR (p < 0.05) with reduced peak vertical ground reaction forces (vGRF) in both younger and older adults (p < 0.05). Older adults increased their MoS during SLF FTR compared to EXT FTR (p < 0.05). Both groups performed more eccentric work during SLF trials compared to EXT (p < 0.05). These findings indicate that abnormal startle effects with aging may interfere with balance recovery and increase risk of injury with external balance perturbations. Motor prediction may be used to acutely mitigate abnormal startle/postural responses with aging.

Aging changes in protective balance and startle responses to sudden drop perturbations.

This study investigated aging changes in protective balance and startle responses to sudden drop perturbations and their effect on landing impact forces (vertical ground reaction forces, vGRF) and balance stability. Twelve healthy older (6 men; mean age = 72.5 ± 2.32 yr, mean ± SE) and 12 younger adults (7 men; mean age = 28.09 ± 1.03 yr) stood atop a moveable platform and received externally triggered drop perturbations of the support surface. Electromyographic activity was recorded bilaterally over the sternocleidomastoid (SCM), middle deltoid, biceps brachii, vastus lateralis (VL), biceps femoris (BF), medial gastrocnemius (MG), and tibialis anterior (TA). Whole body kinematics were recorded with motion analysis. Stability in the anteroposterior direction was quantified using the margin of stability (MoS). Incidence of early onset of bilateral SCM activation within 120 ms after drop onset was present during the first-trial response (FTR) for all participants. Co-contraction indexes during FTRs between VL and BF as well as TA and MG were significantly greater in the older group (VL/BF by 26%, P < 0.05; TA/MG by 37%, P < 0.05). Reduced shoulder abduction between FTR and last-trial responses, indicative of habituation, was present across both groups. Significant age-related differences in landing strategy were present between groups, because older adults had greater trunk flexion (P < 0.05) and less knee flexion (P < 0.05) that resulted in greater peak vGRFs and decreased MoS compared with younger adults. These findings suggest age-associated abnormalities of delayed, exaggerated, and poorly habituated startle/postural FTRs are linked with greater landing impact force and diminished balance stabilization. NEW & NOTEWORTHY This study investigated the role of startle as a pathophysiological mechanism contributing to balance impairment in aging. We measured neuromotor responses as younger and older adults stood on a platform that dropped unexpectedly. Group differences in landing strategies indicated age-associated abnormalities of delayed, exaggerated, and poorly habituated startle/postural responses linked with a higher magnitude of impact force and decreased balance stabilization. The findings have implications for determining mechanisms contributing to falls and related injuries.

Impaired posture, movement preparation, and execution during both paretic and nonparetic reaching following stroke.

Posture and movement planning, preparation, and execution of a goal-directed reaching movement are impaired in individuals with stroke. No studies have shown whether the deficits are generally impaired or are specific to the lesioned hemisphere/paretic arm. This study utilized StartReact (SR) responses elicited by loud acoustic stimuli (LAS) to investigate the preparation and execution of anticipatory postural adjustments (APAs) and reach movement response during both paretic and nonparetic arm reaching in individuals with stroke and in age-matched healthy controls. Subjects were asked to get ready after receiving a warning cue and to reach at a "go" cue. An LAS was delivered at -500, -200, and 0 ms relative to the go cue. Kinetic, kinematic, and electromyographic data were recorded to characterize APA-reach movement responses. Individuals with stroke demonstrated systemwide deficits in posture and in movement planning, preparation, and execution of APA-reach sequence as shown by significant reduction in the incidence of SR response and impaired APA-reach performance, with greater deficits during paretic arm reaching. Use of trunk compensation strategy as characterized by greater involvement of trunk and pelvic rotation was utilized by individuals with stroke during paretic arm reaching compared with nonparetic arm reaching and healthy controls. Our findings have implications for upper extremity and postural control, suggesting that intervention should include training not only for the paretic arm but also for the nonparetic arm with simultaneous postural control requirements to improve the coordination of the APA-reach performance and subsequently reduce instability while functional tasks are performed during standing. NEW & NOTEWORTHY Our study is the first to show that nonparetic arm reaching also demonstrates impairment in posture and movement planning, preparation, and execution when performed during standing by individuals with stroke. In addition, we found compensatory trunk and pelvic rotations were used during a standing reach task for the paretic arms. The findings have clinical implications for upper extremity and postural rehabilitation, suggesting that training should include the nonparetic arms and incorporate simultaneous postural control demands.

Control of lateral weight transfer is associated with walking speed in individuals post-stroke.

Restoring functional gait speed is an important goal for rehabilitation post-stroke. During walking, transferring of one's body weight between the limbs and maintaining balance stability are necessary for independent functional gait. Although it is documented that individuals post-stroke commonly have difficulties with performing weight transfer onto their paretic limbs, it remains to be determined if these deficits contributed to slower walking speeds. The primary purpose of this study was to compare the weight transfer characteristics between slow and fast post-stroke ambulators. Participants (N=36) with chronic post-stroke hemiparesis walked at their comfortable and maximal walking speeds on a treadmill. Participants were stratified into 2 groups based on their comfortable walking speeds (≥0.8m/s or <0.8m/s). Minimum body center of mass (COM) to center of pressure (COP) distance, weight transfer timing, step width, lateral foot placement relative to the COM, hip moment, peak vertical and anterior ground reaction forces, and changes in walking speed were analyzed. Results showed that slow walkers walked with a delayed and deficient weight transfer to the paretic limb, lower hip abductor moment, and more lateral paretic limb foot placement relative to the COM compared to fast walkers. In addition, propulsive force and walking speed capacity was related to lateral weight transfer ability. These findings demonstrated that deficits in lateral weight transfer and stability could potentially be one of the limiting factors underlying comfortable walking speeds and a determinant of chronic stroke survivors' ability to increase walking speed.

Relationship Between Head-Turn Gait Speed and Lateral Balance Function in Community-Dwelling Older Adults.

OBJECTIVE: To determine and compare gait speed during head-forward and side-to-side head-turn walking in individuals with lower versus greater lateral balance. DESIGN: Cross-sectional study. SETTING: University research laboratory. PARTICIPANTS: Older adults (N=93; 42 men, 51 women; mean age ± SD, 73 ± 6.08y) who could walk independently. MAIN OUTCOME MEASURES: (1) Balance tolerance limit (BTL), defined as the lowest perturbation intensity where a multistep balance recovery pattern was first evoked in response to randomized lateral waist-pull perturbations of standing balance to the left and right sides, at 6 different intensities (range from level 2: 4.5-cm displacement at 180cm/s2 acceleration, to level 7: 22.5-cm displacement at 900cm/s2 acceleration); (2) gait speed, determined using an instrumented gait mat; (3) balance, evaluated with the Activities-specific Balance Confidence Scale; and (4) mobility, determined with the Timed Up and Go (TUG). RESULTS: Individuals with low versus high BTL had a slower self-selected head-forward gait speed and head-turn gait speed (P=.002 and P<.001, respectively); the magnitude of difference was greater in head-turn gait speed than head-forward gait speed (Cohen's d=1.0 vs 0.6). Head-turn gait speed best predicted BTL. BTL was moderately and positively related (P=.003) to the ABC Scale and negatively related (P=.017) to TUG. CONCLUSIONS: Head-turn gait speed is affected to a greater extent than head-forward gait speed in older individuals with poorer lateral balance and at greater risk of falls. Moreover, head-turn gait speed can be used to assess the interactions of limitations in lateral balance function and gait speed in relation to fall risk in older adults.

A comparison of initial lactate and initial base deficit as predictors of mortality after severe blunt trauma.

BACKGROUND: After injury, base deficit (BD) and lactate are common measures of shock. Lactate directly measures anaerobic byproducts, whereas BD is calculated and multifactorial. Although recent studies suggest superiority for lactate in predicting mortality, most were small or analyzed populations with heterogeneous injury severity. Our objective was to compare initial BD with lactate as predictors of inhospital mortality in a large cohort of blunt trauma patients all presenting with hemorrhagic shock. MATERIALS AND METHODS: The Glue Grant multicenter prospective cohort database was queried; demographic, injury, and physiologic parameters were compiled. Survivors, early deaths (≤24 h), and late deaths were compared. Profound shock (lactate ≥ 4 mmol/L) and severe traumatic brain injury subgroups were identified a priori. Chi-square, t-test, and analysis of variance were used as appropriate for analysis. Multivariable logistic regression and area under the receiver operating characteristic curve analysis assessed survival predictors. P < 0.05 was significant. RESULTS: A total of 1829 patients met inclusion; 289 (15.8%) died. Both BD and lactate were higher for nonsurvivors (P < 0.00001). After multivariable regression, both lactate (odds ratio [OR] 1.17; 95% confidence interval [CI]: 1.12-1.23; P < 0.00001) and BD (OR 1.04; 95% CI: 1.01-1.07; P < 0.005) predicted overall mortality. However, when excluding early deaths (n = 77), only lactate (OR 1.12 95% CI: 1.06-1.19; P < 0.0001) remained predictive but not BD (OR 1.00 95% CI: 0.97-1.04; P = 0.89). For the shock subgroup, (n = 915), results were similar with lactate, but not BD, predicting both early and late deaths. Findings also appear independent of traumatic brain injury severity. CONCLUSIONS: After severe blunt trauma, initial lactate better predicts inhospital mortality than initial BD. Initial BD does not predict mortality for patients who survive >24 h.