Development of a ground-based sensorimotor disorientation analog to replicate astronaut postflight experience.

The perceptual and motor coordination problems experienced following return from spaceflight reflect the sensory adaptation to altered gravity. The purpose of this study was to develop a ground-based analog that replicates similar sensorimotor impairment using a standard measures test battery and subjective feedback from experienced crewmembers. This Sensorimotor Disorientation Analog (SDA) included varying levels of sensorimotor disorientation through combined vestibular, visual, and proprioceptive disruptions. The SDA was evaluated on five previously flown astronauts to compare with their postflight experience and functional motor performance immediately (Return (R)+0 days) and +24 h (R+1) after landing. The SDA consisted of galvanic vestibular stimulation (GVS), visual disruption goggles, and a weighted suit to alter proprioceptive feedback and replicate perceived heaviness postflight. Astronauts reported that GVS alone replicated ∼50-90% of their postflight performance with the weighted suit fine-tuning the experience to replicate an additional 10%-40% of their experience. Astronauts did not report feeling that the disruption goggles represented either the visual disruptions or illusory sensations that they experienced, nor did they impact motor performance in postflight tasks similarly. Based on these results, we recommend an SDA including the GVS and the weighted suit. These results provide a more realistic and portable SDA framework to provide transient spaceflight-relevant sensorimotor disruptions for use in countermeasure testing and as a pre-flight training tool.

Back to the future-revisiting Skylab data on ocular counter-rolling and motion sickness.

In the early 1970s, nine astronauts participated in missions to the Skylab space station. During two preflight testing sessions at the Naval Aerospace Medical Research Laboratory in Pensacola, the amplitudes of their ocular counter-rolling (OCR) during body tilts were assessed to determine if their vestibular functions were within normal ranges. We recently re-evaluated this data to determine asymmetry of each astronaut's OCR response and their OCR slope from sigmoid fits during static leftward and rightward body tilts, which we then compared with their Coriolis sickness susceptibility index (CSSI) on the ground, their motion sickness symptom scores during 0 g maneuvers in parabolic flight, and the severity of the symptoms of space motion sickness (SMS) they reported during their spaceflights. We arranged the astronauts in rank order for SMS severity based on the SMS symptoms they reported during spaceflight and the amount of anti-motion sickness medication they used. As previously reported, the OCR amplitudes of these astronauts were within the normal range. We determined that the OCR amplitudes were not correlated with SMS severity ranking, CSSI, or motion sickness symptoms experienced during parabolic flight. Indices of asymmetry in the OCR reflex were generally small and poorly correlated with SMS scores; however, the only subject with a high index of asymmetry also ranked highly for SMS. Although OCR slope, CSSI, and motion sickness symptoms induced during parabolic flight were each only moderately correlated with SMS severity ranking (rho = 0.41-0.44), a combined index that included all three parameters with equal weighting was significantly correlated with SMS severity ranking (rho = 0.71, p = 0.015). These results demonstrate the challenge of predicting an individual's susceptibility to SMS by measuring a single test parameter in a terrestrial environment and from a limited sample size.

A pilot case series for concurrent validation of inertial measurement units to motion capture in individuals who use unilateral lower-limb prostheses.

Introduction: Inertial measurement units (IMUs) may be viable options to collect gait data in clinics. This study compared IMU to motion capture data in individuals who use unilateral lower-limb prostheses. Methods: Participants walked with lower-body IMUs and reflective markers in a motion analysis space. Sagittal plane hip, knee, and ankle waveforms were extracted for the entire gait cycle. Discrete points of peak flexion, peak extension, and range of motion were extracted from the waveforms. Stance times were also extracted to assess the IMU software's accuracy at detecting gait events. IMU and motion capture-derived data were compared using absolute differences and root mean square error (RMSE). Results: Five individuals (n = 3 transtibial; n = 2 transfemoral) participated. IMU prosthetic limb data was similar to motion capture (RMSE: waveform ≤4.65°; discrete point ≤9.04°; stance ≤0.03s). However, one transfemoral participant had larger differences at the microprocessor knee joint (RMSE: waveform ≤15.64°; discrete ≤29.21°) from IMU magnetometer interference. Intact limbs tended to have minimal differences between IMU and motion capture data (RMSE: waveform ≤6.33°; discrete ≤9.87°; stance ≤0.04s). Conclusion: Findings from this pilot study suggest IMUs have the potential to collect data similar to motion capture systems in sagittal plane kinematics and stance time.

Clinical evaluation of fall risk in older adults who use lower-limb prostheses: A scoping review.

BACKGROUND: No reviews or evidence-based clinical protocols exist to evaluate fall risk in older adults who use lower-limb prostheses, despite falls being prevalent and costly in this population. This scoping review sought to determine assessments, defined as clinical outcome measures and gait parameters, associated with fall risk in this population to determine if a systematic review is warranted and help inform an evidence-based clinical protocol. METHODS: Google Scholar, PubMed, and Scopus were searched on April 19th, 2022 to include peer-reviewed original research. Included articles reported relationships between falls and clinical outcome measures or gait parameters in older adults who use transtibial or transfemoral prostheses. Clinical outcome measures included self-reported questionnaires and functional mobility tests. Gait parameters included spatiotemporal, kinematic, and kinetic data during walking and stair negotiation. RESULTS: Nineteen articles were included. Clinical outcome measure scores, gait parameter data, and cutoff scores by fall status (nonfallers, single fallers, recurrent fallers) were summarized. Six articles determined clinical outcome measures that had statistically significant associations with falls, and two articles determined gait parameters that had statistically significant associations with falls. CONCLUSIONS: The majority of articles found no clinical outcome measure or gait parameter alone was effective at identifying fall risks in this population. Future research should evaluate a combination of assessments and collect prospective fall data to move towards establishing an evidence-based protocol to evaluate fall risk in older adults using lower-limb prostheses.

Mission-critical tasks for assessing risks from vestibular and sensorimotor adaptation during space exploration.

To properly assess the risk induced by vestibular and sensorimotor adaptation during exploration missions, we examined how long-duration stays on the International Space Station affect functional performance after gravity transitions. Mission-critical tasks that challenge the balance and the locomotion control systems were assessed: i.e., sit-to-stand, recovery-from-fall, tandem-walk, and walk-and-turn. We assessed 19 astronauts, including 7 first-time flyers and 12 experienced flyers, before their flight, a few hours after landing, and then 1 day and 6-11 days later. Results show that adaptation to long-term weightlessness causes deficits in functional performance immediately after landing that can last for up to 1 week. No differences were observed between first-time and experienced astronaut groups. These data suggest that additional sensorimotor-based countermeasures may be necessary to maintain functional performance at preflight levels when landing on planetary surfaces after a long period in weightlessness.

Altered mechanics and increased loading on intact limbs of individuals with a unilateral transtibial amputation in comparison with non-amputees during a start-stop task.

Individuals with a unilateral transtibial amputation (ITTA) often experience greater loading on the intact limb during running and stepping tasks compared to individuals without amputation. This study aimed to investigate the mechanics of load absorption in the intact limb of ITTA and determine if increased ground reaction forces (GRF) persist during a start-stop task which (i) controlled touch-down velocity and (ii) removed the requirement for on-going locomotion. Data were collected using a twelve-camera motion capture system with two Kistler force platforms. Variables were extracted during the final loading phase of a 2-step start-stop task. The intact limb of ITTA and the dominant limb of able-bodied controls were compared using independent t-tests and effect size analysis. ITTA showed lower knee flexion angles at touchdown (p = 0.007, g = -1.43), and peak vertical GRF (p = 0.01, g = -1.33) compared to control subjects. ITTA also exhibited less hip (p = 0.14, g = 0.76) and ankle (p = 0.002, g = 1.82) absorptive power at touchdown and at peak vertical GRF (hip: p = 0.01, g = 1.23; ankle: p = 0.05, g = 0.97). ITTA exhibited greater peak vertical GRF (p = 0.01, g = 1.30) and braking GRF (p = 0.05, g = -0.96) on the intact limb compared to the controls. Our results indicate altered joint mechanics through the intact limb of ITTA are independent of the touchdown conditions or the need for ongoing locomotion. These altered joint mechanics increased loading experienced by the intact limb. Further work should be conducted examining a variety of other dynamic movements to fully understand the involved mechanics, so that intervention studies can be developed to reduce the load experienced by ITTA.

Effects of osteopathic manipulative treatment vs. osteopathic cranial manipulative medicine on Parkinsonian gait.

CONTEXT: Sixty thousand people are diagnosed with Parkinson's disease (PD) each year, making it the second most common neurodegenerative disorder. PD results in a variety of gait disturbances, including muscular rigidity and decreased range of motion (ROM), that increase the fall risk of those afflicted. Osteopathic manipulative treatment (OMT) emphasizes the central role of the musculoskeletal system, which could be ideal for addressing the somatic dysfunction associated with neurodegeneration in PD. The close anatomical relationship of structures implicated in PD within the skull and the increased frequency of strain patterns raise the question of whether osteopathic cranial manipulative medicine (OCMM) can improve gait performance by improving circulation to the affected nervous tissue. However, there have been few studies in recent years that explore the effects of a standardized OMT protocol on Parkinsonian gait characteristics, and there have been few studies that include OCMM techniques. OBJECTIVES: This study aims to determine whether a single session of OMT or OMT + OCMM can improve the gait of individuals with PD by addressing joint restrictions in the sagittal plane and by increasing ROM in the lower limb. METHODS: The following study is a two-group, randomized controlled trial in which individuals with PD (n=45) and age-matched healthy control participants (n=45) were recruited from the community. PD participants were included if they were otherwise healthy, able to stand and walk independently, had not received OMT or physical therapy (PT) within 30 days of data collection, and had idiopathic PD in Hoehn and Yahr stages 1.0-3.0. PD participants were randomly assigned to one of three experimental treatment protocols: a 'whole-body' OMT protocol (OMT-WB), which included OMT and OCMM techniques; a 'neck-down' OMT protocol (OMT-ND), including only OMT techniques; and a sham treatment protocol. Control participants were age-matched to a PD participant and were provided the same OMT experimental protocol. An 18-camera motion analysis system was utilized to capture 3-dimensional (3D) position data in a treadmill walking trial before and after the assigned treatment protocol. Pretreatment and posttreatment hip, knee, and ankle ROM were compared with paired t-tests, and joint angle waveforms during the gait cycle were analyzed with statistical parametric mapping (SPM), which is a type of waveform analysis. RESULTS: Individuals with PD had significantly reduced hip and knee extension in the stance phase compared to controls (32.9-71.2% and 32.4-56.0% of the gait cycle, respectively). Individuals with PD experienced a significant increase in total sagittal hip ROM (p=0.038) following a single session of the standardized OMT-WB treatment protocol. However, waveform analysis found no significant differences in sagittal hip, knee, or ankle angles at individual points of the gait cycle following OMT-WB, OMT-ND, or sham treatment protocols. CONCLUSIONS: The increase in hip ROM observed following a single session of OMT-WB suggests that OCMM in conjunction with OMT may be useful for improving gait kinematics in individuals with PD. Longitudinal studies over multiple visits are needed to determine the long-term effect of regular OMT and OMT+OCMM treatments on Parkinsonian gait characteristics.

The associations between asymmetries in quadriceps strength and gait in individuals with unilateral transtibial amputation.

BACKGROUND: Individuals with unilateral transtibial amputations (ITTAs) are asymmetrical in quadriceps strength. It is unknown if this is associated with gait performance characteristics such as walking speed and limb symmetry. RESEARCH QUESTION: Are quadriceps strength asymmetries related to walking speed and/ or gait asymmetries in ITTAs? METHODS: Knee-extensor isometric maximum voluntary torque (MVT) and rate of torque development (RTD) were measured in eight ITTAs. Gait data were captured as the ITTAs walked at self-selected habitual and fast speeds. Step length and single support time, peak knee extension moments and their impulse and peak vertical ground reaction force (vGRF) in the braking and propulsive phases of stance were extracted. Bilateral Asymmetry Index (BAI) and, for gait variables only, difference in BAI between walking speeds (ΔBAI) were calculated. Correlation analyses assessed the relationships between MVT and RTD asymmetry and (1) walking speed; (2) gait asymmetries. RESULTS: Associations between strength and gait BAIs generally became more apparent at faster walking speeds, and when the difference in BAI between fast and habitual walking speed was considered. BAI RTD was strongly negatively correlated with habitual and fast walking speeds (r=∼0.83). Larger BAI RTD was strongly correlated with propulsive vGRF BAI in fast walking, and larger ΔBAIs in vGRF during both the braking and propulsion phases of gait (r = 0.74-0.92). ITTAs who exhibited greater BAI MVT showed greater ΔBAI in single support time (r = 0.83). SIGNIFICANCE: While MVT and RTD BAI appear to be associated with gait asymmetries in ITTAs, the magnitude of the asymmetry in RTD appears to be a more sensitive marker of walking speed. Based on these results, it's possible that strengthening the knee-extensors of the amputated limb to improve both MVT and RTD symmetry may benefit walking speed, and reduce asymmetrical loading in gait.

Lead limb loading during a single-step descent in persons with and without a transtibial amputation in the trailing limb.

BACKGROUND: Decreased mechanical work done by the trailing limb when descending a single-step could affect load development and increase injury risk on the leading limb. This study assessed the effect of trailing limb mechanics on the development of lead limb load during a step descent by examining individuals with unilateral transtibial amputations who are known to exhibit reduced work in the prosthetic limb. METHODS: Eight amputees and 10 able-bodied controls walked 5 m along the length of a raised platform, descended a single-step of 14 cm height, and continued walking. The intact limb of amputees led during descent. Kinematic and kinetic data were recorded using integrated motion capture and force platform system. Lead limb loading was assessed through vertical ground reaction force, and knee moments and joint reaction forces. Sagittal-plane joint work was calculated for the ankle, knee, and hip in both limbs. FINDINGS: No differences were found in lead limb loading despite differences in trail limb mechanics evidenced by amputees performing 58% less total work by the trailing (prosthetic) limb to lower the centre of mass (P = 0.004) and 111% less for propulsion (P < 0.001). Amputees descended the step significantly slower (P = 0.003) and performed significantly greater lead limb ankle work (P = 0.017). After accounting for speed differences, initial loading at the knee was significantly higher in the lead limb of amputees versus controls. INTERPRETATION: Increasing lead limb work and reducing forward velocity may be effective compensatory strategies to limit lead limb loading during a step descent, in response to reduced trailing limb work.

A sensitive data analysis approach for detecting changes in dynamic postural stability.

Understanding the mechanisms of instability can aid in reducing fall risk. As a sensitive measure of fall risk, the distance between the center of pressure (COP) and center of mass (COM) is currently assessed through discrete points assumed to represent physiological important fall mechanisms. However, it is unclear if these discrete points are appropriate measures of fall risk. Statistical parametric mapping (SPM) is a waveform analysis technique that removes this possibly biased a priori approach. Sixteen healthy young adults (8 males, 8 females; Age: 29 ± 3.6 years, Height: 1.7 ± 0.9 m, Mass: 75 ± 16 kg) performed two tasks that disturbed dynamic stability: voluntary stepping at different step lengths, and forward perturbations at different accelerations. COP-COM distance magnitudes were extracted during the first step in both tasks at discrete points typically assessed in previous research. Discrete point analysis (DPA) was performed on these discrete points and SPM analysis was completed on the COP-COM distance waveform. The results from the study found that SPM analysis identified equivalent significant differences to DPA and identified additional significant differences elsewhere in the COP-COM distance waveform that were not able to be detected by DPA. Two key advantages from using SPM: (1) reduction of possibly biased a priori selection, and (2) increased efficiency and reduced time-cost in data post-processing as inherent variability can limit the detection of discrete points resulting in identifying physiologically different discrete points across trials. This study suggests the use of SPM as a sensitive data analysis approach in detecting fall risk as an alternative to DPA.

Foot strike alters ground reaction force and knee load when stepping down during ongoing walking.

BACKGROUND: When stepping down from a raised surface, either a toe or heel contact strategy is performed. Increased vertical momentum is likely to be experienced during a step descent, yet the extent to which these descent strategies influence the development of load at the ground and knee has not been examined. RESEARCH QUESTION: Does descent strategy influence ground and knee joint loading? Does the contribution from leading and trailing limb joint mechanics differ between descent strategies? METHODS: Twenty-two healthy male participants (age: 34.0 ±â€¯6.5 years, height: 179 ±â€¯6.3 cm, mass: 83.5 ±â€¯13 kg) walked along a raised platform, stepped down from a 14 cm height utilising either a toe (n = 10) or heel (n = 12) initial contact, and continued walking. Vertical ground reaction forces and knee external adduction and flexor moments were extracted for the duration of the braking phase. Joint work was calculated for the ankle, knee, and hip in both the leading and trailing limbs. RESULTS: Waveform analysis of the loading features indicated that a toe-contact strategy resulted in significantly reduced loading rates during early braking (1-32% of the braking phase) and significantly increased magnitude in late braking (55-96% of the braking phase). Individuals performing toe landings completed 33% greater overall work (p = 0.091) in the lead limb and utilised the lead limb ankle joint as the main shock absorber (79% of total lead limb work). Concurrently, the trailing limb performed 29% and 21% less work when lowering the centre of mass and propulsion, respectively, compared to a heel landing. SIGNIFICANCE: A toe-contact strategy results in reduced limb and knee joint loading rates through greater utilisation of the lead limb ankle joint. A heel-contact strategy, however, can reduce loading during late braking by utilising the functionality of the trailing limb.

The effects of long-term muscle disuse on neuromuscular function in unilateral transtibial amputees.

NEW FINDINGS: What is the central question of this study? The effects of long-term muscle disuse on neuromuscular function are unclear because disuse studies are typically short term. In this study, we used a new model (unilateral transtibial amputees) to investigate the effects of long-term disuse on quadriceps neuromuscular function. What is the main finding and its importance? Kinetic analysis (knee-extension moments during gait) indicated habitual disuse of the amputated limb quadriceps, accompanied by lower quadriceps muscle strength (60-76%) and neural activation (32-44%), slower contractile properties and altered muscle architecture in the amputated limb, which could not be predicted from short-term disuse studies. ABSTRACT: The purpose of this study was to determine: (i) whether individuals with unilateral transtibial amputations (ITTAs), who habitually disuse the quadriceps muscles of their amputated limb, provide an effective model for assessing the effects of long-term muscle disuse; and (ii) the effects of such disuse on quadriceps muscle strength and neuromuscular function in this population. Nine ITTAs and nine control subjects performed isometric voluntary knee extensions of both limbs to assess maximal voluntary torque (MVT) and the rate of torque development (RTD). The interpolated twitch technique and EMG normalized to maximal M-wave were used to assess neural activation, involuntary (twitch and octet) contractions to assess intrinsic contractile properties, and ultrasound images of the vastus lateralis to assess muscle architecture. Clinical gait analysis was used to measure knee kinetic data during walking at an habitual speed. The ITTAs displayed 54-60% lower peak knee-extensor moments during walking in the amputated compared with intact/control limbs, but the intact and control limbs were comparable for loading during walking and muscle strength variables, suggesting that the intact limb provides a suitable internal control for comparison with the disused amputated limb. The MVT and RTD were ∼60 and ∼75% lower, respectively, in the amputated than intact/control limbs. The differences in MVT appeared to be associated with ∼40 and ∼43% lower muscle thickness and neural activation, respectively, and the differences in RTD appeared to be associated with the decline in MVT coupled with slowing of the intrinsic contractile properties. These results indicate considerable changes in strength and neuromuscular function with long-term disuse that could not be predicted from short-term disuse studies.

Mechanisms to Attenuate Load in the Intact Limb of Transtibial Amputees When Performing a Unilateral Drop Landing.

Individuals with unilateral transtibial amputations experience greater work demand and loading on the intact limb compared with the prosthetic limb, placing this limb at a greater risk of knee joint degenerative conditions. It is possible that increased loading on the intact side may occur due to strength deficits and joint absorption mechanics. This study investigated the intact limb mechanics utilized to attenuate load, independent of prosthetic limb contributions and requirements for forward progression, which could provide an indication of deficiencies in the intact limb. Amputee and healthy control participants completed 3 unilateral drop landings from a 30-cm drop height. Joint angles at touchdown; range of motion; coupling angles; peak powers; and negative work of the ankle, knee, and hip were extracted together with isometric quadriceps strength measures. No significant differences were found in the load or movement mechanics (P ≥ .31, g ≤ 0.42), despite deficits in isometric maximum (20%) and explosive (25%) strength (P ≤ .13, g ≥ 0.61) in the intact limb. These results demonstrate that, when the influence from the prosthetic limb and task demand are absent, and despite deficits in strength, the intact limb adopts joint mechanics similar to able-bodied controls to attenuate limb loading.