An atomic boson sampler.

A boson sampler implements a restricted model of quantum computing. It is defined by the ability to sample from the distribution resulting from the interference of identical bosons propagating according to programmable, non-interacting dynamics1. An efficient exact classical simulation of boson sampling is not believed to exist, which has motivated ground-breaking boson sampling experiments in photonics with increasingly many photons2-12. However, it is difficult to generate and reliably evolve specific numbers of photons with low loss, and thus probabilistic techniques for postselection7 or marked changes to standard boson sampling10-12 are generally used. Here, we address the above challenges by implementing boson sampling using ultracold atoms13,14 in a two-dimensional, tunnel-coupled optical lattice. This demonstration is enabled by a previously unrealized combination of tools involving high-fidelity optical cooling and imaging of atoms in a lattice, as well as programmable control of those atoms using optical tweezers. When extended to interacting systems, our work demonstrates the core abilities required to directly assemble ground and excited states in simulations of various Hubbard models15,16.

Realizing spin squeezing with Rydberg interactions in an optical clock.

Neutral-atom arrays trapped in optical potentials are a powerful platform for studying quantum physics, combining precise single-particle control and detection with a range of tunable entangling interactions1-3. For example, these capabilities have been leveraged for state-of-the-art frequency metrology4,5 as well as microscopic studies of entangled many-particle states6-11. Here we combine these applications to realize spin squeezing-a widely studied operation for producing metrologically useful entanglement-in an optical atomic clock based on a programmable array of interacting optical qubits. In this demonstration of Rydberg-mediated squeezing with a neutral-atom optical clock, we generate states that have almost four decibels of metrological gain. In addition, we perform a synchronous frequency comparison between independent squeezed states and observe a fractional-frequency stability of 1.087(1) × 10-15 at one-second averaging time, which is 1.94(1) decibels below the standard quantum limit and reaches a fractional precision at the 10-17 level during a half-hour measurement. We further leverage the programmable control afforded by optical tweezer arrays to apply local phase shifts to explore spin squeezing in measurements that operate beyond the relative coherence time with the optical local oscillator. The realization of this spin-squeezing protocol in a programmable atom-array clock will enable a wide range of quantum-information-inspired techniques for optimal phase estimation and Heisenberg-limited optical atomic clocks12-16.

Half-minute-scale atomic coherence and high relative stability in a tweezer clock.

The preparation of large, low-entropy, highly coherent ensembles of identical quantum systems is fundamental for many studies in quantum metrology1, simulation2 and information3. However, the simultaneous realization of these properties remains a central challenge in quantum science across atomic and condensed-matter systems2,4-7. Here we leverage the favourable properties of tweezer-trapped alkaline-earth (strontium-88) atoms8-10, and introduce a hybrid approach to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout and preservation of atomic coherence. With this approach, we achieve trapping and optical-clock excited-state lifetimes exceeding 40 seconds in ensembles of approximately 150 atoms. This leads to half-minute-scale atomic coherence on an optical-clock transition, corresponding to quality factors well in excess of 1016. These coherence times and atom numbers reduce the effect of quantum projection noise to a level that is comparable with that of leading atomic systems, which use optical lattices to interrogate many thousands of atoms in parallel11,12. The result is a relative fractional frequency stability of 5.2(3) × 10-17τ-1/2 (where τ is the averaging time in seconds) for synchronous clock comparisons between sub-ensembles within the tweezer array. When further combined with the microscopic control and readout that are available in this system, these results pave the way towards long-lived engineered entanglement on an optical-clock transition13 in tailored atom arrays.

Linking whole-body angular momentum and step placement during perturbed human walking.

Human locomotion is remarkably robust to environmental disturbances. Previous studies have thoroughly investigated how perturbations influence body dynamics and what recovery strategies are used to regain balance. Fewer studies have attempted to establish formal links between balance and the recovery strategies that are executed to regain stability. We hypothesized that there would be a strong relationship between the magnitude of imbalance and recovery strategy during perturbed walking. To test this hypothesis, we applied transient ground surface translations that varied in magnitude, direction and onset time while 11 healthy participants walked on a treadmill. We measured stability using integrated whole-body angular momentum (iWBAM) and recovery strategy using step placement. We found the strongest relationships between iWBAM and step placement in the frontal plane for earlier perturbation onset times in the perturbed step (R2=0.52, 0.50) and later perturbation onset times in the recovery step (R2=0.18, 0.25), while correlations were very weak in the sagittal plane (all R2≤0.13). These findings suggest that iWBAM influences step placement, particularly in the frontal plane, and that this influence is sensitive to perturbation onset time. Lastly, this investigation is accompanied by an open-source dataset to facilitate research on balance and recovery strategies in response to multifactorial ground surface perturbations, including 96 perturbation conditions spanning all combinations of three magnitudes, eight directions and four gait cycle onset times.

Biomechanical Evaluation of Stair Ambulation Using Impedance Control on an Active Prosthesis.

Active prostheses can provide net positive work to individuals with amputation, offering more versatility across locomotion tasks than passive prostheses. However, the effect of powered joints on bilateral biomechanics has not been widely explored for ambulation modes different than level ground and treadmill walking. In this study, we present the bilateral biomechanics of stair ascent and descent with a powered knee-ankle prosthesis compared to the biomechanical profiles of able-bodied subjects at different configurations of stair height between 102 mm and 178 mm. In addition, we include reference profiles from users with passive prostheses for the nominal stair height of 152 mm to place our findings in relation to the typical solution for individuals with transfemoral amputation (TFA). We report the biomechanical profiles of kinematics, kinetics, and power, together with temporal and waveform symmetry and distribution of mechanical energy across the joints. We found that an active prosthesis provides a substantial contribution to mechanical power during stair ascent and power absorption during stair descent and gait patterns like able-bodied subjects. The active prosthesis enables step-over-step gait in stair ascent. This translates into a lower mechanical energy requirement on the intact side, with a 57% reduction of energy at the knee and 26% at the hip with respect to the passive prosthesis. For stair descent, we found a 28% reduction in the negative work done by the intact ankle. These results reflect the benefit of active prostheses, allowing the users to complete tasks more efficiently than passive legs. However, in comparison to able-bodied biomechanics, the results still differ from the ideal patterns. We discuss the limitations that explain this difference and suggest future directions for the design of impedance controllers by taking inspiration from the biological modulation of the knee moment as a function of the stair height.

A Review of Current State-of-the-Art Control Methods for Lower-Limb Powered Prostheses.

Lower-limb prostheses aim to restore ambulatory function for individuals with lower-limb amputations. While the design of lower-limb prostheses is important, this paper focuses on the complementary challenge - the control of lower-limb prostheses. Specifically, we focus on powered prostheses, a subset of lower-limb prostheses, which utilize actuators to inject mechanical power into the walking gait of a human user. In this paper, we present a review of existing control strategies for lower-limb powered prostheses, including the control objectives, sensing capabilities, and control methodologies. We separate the various control methods into three main tiers of prosthesis control: high-level control for task and gait phase estimation, mid-level control for desired torque computation (both with and without the use of reference trajectories), and low-level control for enforcing the computed torque commands on the prosthesis. In particular, we focus on the high- and mid-level control approaches in this review. Additionally, we outline existing methods for customizing the prosthetic behavior for individual human users. Finally, we conclude with a discussion on future research directions for powered lower-limb prostheses based on the potential of current control methods and open problems in the field.

Expanding Our Reach: Development of a Civilian Helicopter Air Ambulance K9 Response Program.

This short communication highlights the development and implementation of the first civilian helicopter air ambulance canine response program in the United States.

Demographic Trends From 2005 to 2015 Among Physicians With Accreditation Council for Graduate Medical Education-Accredited Anesthesiology Training and Active Medical Licenses.

BACKGROUND: A temporary decrease in anesthesiology residency graduates that occurred around the turn of the millennium may have workforce implications. The aims of this study are to describe, between 2005 and 2015, (1) demographic changes in the workforce of physicians trained as anesthesiologists; (2) national and state densities of these physicians, as well as temporal changes in the densities; and (3) retention of medical licenses by mid- and later-career anesthesiologists. METHODS: Using records from the American Board of Anesthesiology and state medical and osteopathic boards, the numbers of licensed physicians aged 30-59 years who had completed Accreditation Council for Graduate Medical Education-accredited anesthesiology residency training were calculated cross-sectionally for 2005, 2010, and 2015. Demographic trends were then described. Census data were used to calculate national and state densities of licensed physicians. Individual longitudinal data were used to describe retention of medical licenses among older physicians. RESULTS: The number of licensed physicians trained as anesthesiologists aged 30-59 years increased from 32,644 in 2005 to 36,543 in 2010 and 36,624 in 2015, representing a national density of 1.10, 1.18, and 1.14 per 10,000 population in those years, respectively. The density of anesthesiologists among states ranged from 0.37 to 3.10 per 10,000 population. The age distribution differed across the years. For example, anesthesiologists aged 40-49 years predominated in 2005 (47%), but by 2015, only 31% of anesthesiologists were aged 40-49 years. The proportion of female anesthesiologists grew from 22% in 2005, to 24% in 2010, and to 28% in 2015, particularly among early-career anesthesiologists. For anesthesiologists with licenses in 2005, the number who still had active licenses in 2015 decreased by 9.6% for those aged 45-49 years, by 14.1% for those aged 50-54 years, and by 19.7% for those aged 55-59 years. CONCLUSIONS: The temporary decrease in anesthesiology residency graduates around the turn of the 21st century decreased the proportion of anesthesiologists who were midcareer as of 2015. This may affect the future availability of senior leaders as well as the future overall workforce in the specialty as older anesthesiologists retire. National efforts to plan for workforce needs should recognize the geographical variability in the distribution of anesthesiologists.

The exoskeleton expansion: improving walking and running economy.

Since the early 2000s, researchers have been trying to develop lower-limb exoskeletons that augment human mobility by reducing the metabolic cost of walking and running versus without a device. In 2013, researchers finally broke this 'metabolic cost barrier'. We analyzed the literature through December 2019, and identified 23 studies that demonstrate exoskeleton designs that improved human walking and running economy beyond capable without a device. Here, we reviewed these studies and highlighted key innovations and techniques that enabled these devices to surpass the metabolic cost barrier and steadily improve user walking and running economy from 2013 to nearly 2020. These studies include, physiologically-informed targeting of lower-limb joints; use of off-board actuators to rapidly prototype exoskeleton controllers; mechatronic designs of both active and passive systems; and a renewed focus on human-exoskeleton interface design. Lastly, we highlight emerging trends that we anticipate will further augment wearable-device performance and pose the next grand challenges facing exoskeleton technology for augmenting human mobility.

Physician Burnout and Barriers to Care on Professional Applications.

We surveyed New York physicians to study their perceptions of reporting requirements related to their own mental health care on professional applications, including whether they were experiencing symptoms of burnout. Over half of the responding physicians reported experiencing symptoms of burnout and these physicians were at increased odds of perceiving a barrier to seeking mental health care if they had to report such care on professional applications and renewals for medical licensure, malpractice, and hospital privileges and credentialing compared to physicians not experiencing symptoms of burnout. As state medical boards, hospitals, and insurers seek information to help assess risks posed by physicians, it is essential to strike an appropriate balance between their duty to protect the public and the physician's right to confidentiality. This balance can be assessed based on the questions that are asked on various professional applications and how information gleaned through physician responses is used. Overly intrusive questions, though well intentioned to protect the public, may run counter to current interpretations of federal law and may inhibit care-seeking among physicians, which is critical to both patient safety and physician health.

Effectiveness of Written and Oral Specialty Certification Examinations to Predict Actions against the Medical Licenses of Anesthesiologists.

BACKGROUND: The American Board of Anesthesiology administers written and oral examinations for its primary certification. This retrospective cohort study tested the hypothesis that the risk of a disciplinary action against a physician's medical license is lower in those who pass both examinations than those who pass only the written examination. METHODS: Physicians who entered anesthesiology training from 1971 to 2011 were followed up to 2014. License actions were ascertained via the Disciplinary Action Notification Service of the Federation of State Medical Boards. RESULTS: The incidence rate of license actions was relatively stable over the study period, with approximately 2 to 3 new cases per 1,000 person-years. In multivariable models, the risk of license actions was higher in men (hazard ratio = 1.88 [95% CI, 1.66 to 2.13]) and lower in international medical graduates (hazard ratio = 0.73 [95% CI, 0.66 to 0.81]). Compared with those passing both examinations on the first attempt, those passing neither examination (hazard ratio = 3.60 [95% CI, 3.14 to 4.13]) and those passing only the written examination (hazard ratio = 3.51 [95% CI, 2.87 to 4.29]) had an increased risk of receiving an action from a state medical board. The risk was no different between the latter two groups (P = 0.81), showing that passing the oral but not the written primary certification examination is associated with a decreased risk of subsequent license actions. For those with residency performance information available, having at least one unsatisfactory training record independently increased the risk of license actions. CONCLUSIONS: These findings support the concept that an oral examination assesses domains important to physician performance that are not fully captured in a written examination.

Robotic leg control with EMG decoding in an amputee with nerve transfers.

The clinical application of robotic technology to powered prosthetic knees and ankles is limited by the lack of a robust control strategy. We found that the use of electromyographic (EMG) signals from natively innervated and surgically reinnervated residual thigh muscles in a patient who had undergone knee amputation improved control of a robotic leg prosthesis. EMG signals were decoded with a pattern-recognition algorithm and combined with data from sensors on the prosthesis to interpret the patient's intended movements. This provided robust and intuitive control of ambulation--with seamless transitions between walking on level ground, stairs, and ramps--and of the ability to reposition the leg while the patient was seated.

Running With an Elastic Lower Limb Exoskeleton.

Although there have been many lower limb robotic exoskeletons that have been tested for human walking, few devices have been tested for assisting running. It is possible that a pseudo-passive elastic exoskeleton could benefit human running without the addition of electrical motors due to the spring-like behavior of the human leg. We developed an elastic lower limb exoskeleton that added stiffness in parallel with the entire lower limb. Six healthy, young subjects ran on a treadmill at 2.3 m/s with and without the exoskeleton. Although the exoskeleton was designed to provide ~50% of normal leg stiffness during running, it only provided 24% of leg stiffness during testing. The difference in added leg stiffness was primarily due to soft tissue compression and harness compliance decreasing exoskeleton displacement during stance. As a result, the exoskeleton only supported about 7% of the peak vertical ground reaction force. There was a significant increase in metabolic cost when running with the exoskeleton compared with running without the exoskeleton (ANOVA, P < .01). We conclude that 2 major roadblocks to designing successful lower limb robotic exoskeletons for human running are human-machine interface compliance and the extra lower limb inertia from the exoskeleton.

Intuitive control of a powered prosthetic leg during ambulation: a randomized clinical trial.

IMPORTANCE: Some patients with lower leg amputations may be candidates for motorized prosthetic limbs. Optimal control of such devices requires accurate classification of the patient's ambulation mode (eg, on level ground or ascending stairs) and natural transitions between different ambulation modes. OBJECTIVE: To determine the effect of including electromyographic (EMG) data and historical information from prior gait strides in a real-time control system for a powered prosthetic leg capable of level-ground walking, stair ascent and descent, ramp ascent and descent, and natural transitions between these ambulation modes. DESIGN, SETTING, AND PARTICIPANTS: Blinded, randomized crossover clinical trial conducted between August 2012 and November 2013 in a research laboratory at the Rehabilitation Institute of Chicago. Participants were 7 patients with unilateral above-knee (n = 6) or knee-disarticulation (n = 1) amputations. All patients were capable of ambulation within their home and community using a passive prosthesis (ie, one that does not provide external power). INTERVENTIONS: Electrodes were placed over 9 residual limb muscles and EMG signals were recorded as patients ambulated and completed 20 circuit trials involving level-ground walking, ramp ascent and descent, and stair ascent and descent. Data were acquired simultaneously from 13 mechanical sensors embedded on the prosthesis. Two real-time pattern recognition algorithms, using either (1) mechanical sensor data alone or (2) mechanical sensor data in combination with EMG data and historical information from earlier in the gait cycle, were evaluated. The order in which patients used each configuration was randomized (1:1 blocked randomization) and double-blinded so patients and experimenters did not know which control configuration was being used. MAIN OUTCOMES AND MEASURES: The main outcome of the study was classification error for each real-time control system. Classification error is defined as the percentage of steps incorrectly predicted by the control system. RESULTS: Including EMG signals and historical information in the real-time control system resulted in significantly lower classification error (mean, 7.9% [95% CI, 6.1%-9.7%]) across a mean of 683 steps (range, 640-756 steps) compared with using mechanical sensor data only (mean, 14.1% [95% CI, 9.3%-18.9%]) across a mean of 692 steps (range, 631-775 steps), with a mean difference between groups of 6.2% (95% CI, 2.7%-9.7%] (P = .01). CONCLUSIONS AND RELEVANCE: In this study of 7 patients with lower limb amputations, inclusion of EMG signals and temporal gait information reduced classification error across ambulation modes and during transitions between ambulation modes. These preliminary findings, if confirmed, have the potential to improve the control of powered leg prostheses.

Online professionalism investigations by state medical boards: first, do no harm.

Despite recent guidelines promoting online professionalism, consequences for specific violations by physicians have not been explored. In this article, the authors gauged consensus among state medical boards in the United States (response rate, 71%) about the likelihood of investigations for violations of online professionalism by using 10 hypothetical vignettes. High consensus was defined as more than 75% of respondents indicating that investigation was "likely" or "very likely," moderate consensus as 50% to 75% indicating this, and low consensus as fewer than 50% indicating this. Four online vignettes demonstrated high consensus: Citing misleading information about clinical outcomes (81%; 39/48), using patient images without consent (79%; 38/48), misrepresenting credentials (77%; 37/48), and inappropriately contacting patients (77%; 37/48). Three demonstrated moderate consensus for investigation: depicting alcohol intoxication (73%; 35/48), violating patient confidentiality (65%; 31/48), and using discriminatory speech (60%; 29/48). Three demonstrated low consensus: using derogatory speech toward patients (46%; 22/48), showing alcohol use without intoxication (40%; 19/48), and providing clinical narratives without violation of confidentiality (16%; 7/48). Areas of high consensus suggest "online behaviors" that physicians should never engage in, whereas moderate- and low-consensus areas provide useful contextual information about "gray areas." Increased awareness of these specific behaviors may reduce investigations and improve online professionalism for physicians.

A comparison of the real-time controllability of pattern recognition to conventional myoelectric control for discrete and simultaneous movements.

Myoelectric control has been used for decades to control powered upper limb prostheses. Conventional, amplitude-based control has been employed to control a single prosthesis degree of freedom (DOF) such as closing and opening of the hand. Within the last decade, new and advanced arm and hand prostheses have been constructed that are capable of actuating numerous DOFs. Pattern recognition control has been proposed to control a greater number of DOFs than conventional control, but has traditionally been limited to sequentially controlling DOFs one at a time. However, able-bodied individuals use multiple DOFs simultaneously, and it may be beneficial to provide amputees the ability to perform simultaneous movements. In this study, four amputees who had undergone targeted motor reinnervation (TMR) surgery with previous training using myoelectric prostheses were configured to use three control strategies: 1) conventional amplitude-based myoelectric control, 2) sequential (one-DOF) pattern recognition control, 3) simultaneous pattern recognition control. Simultaneous pattern recognition was enabled by having amputees train each simultaneous movement as a separate motion class. For tasks that required control over just one DOF, sequential pattern recognition based control performed the best with the lowest average completion times, completion rates and length error. For tasks that required control over 2 DOFs, the simultaneous pattern recognition controller performed the best with the lowest average completion times, completion rates and length error compared to the other control strategies. In the two strategies in which users could employ simultaneous movements (conventional and simultaneous pattern recognition), amputees chose to use simultaneous movements 78% of the time with simultaneous pattern recognition and 64% of the time with conventional control for tasks that required two DOF motions to reach the target. These results suggest that when amputees are given the ability to control multiple DOFs simultaneously, they choose to perform tasks that utilize multiple DOFs with simultaneous movements. Additionally, they were able to perform these tasks with higher performance (faster speed, lower length error and higher completion rates) without losing substantial performance in 1 DOF tasks.

Asymmetric dimethylarginine in chronic obstructive pulmonary disease (ADMA in COPD).

L-arginine metabolism including the nitric oxide (NO) synthase and arginase pathways is important in the maintenance of airways function. We have previously reported that accumulation of asymmetric dimethylarginine (ADMA) in airways, resulting in changes in L-arginine metabolism, contributes to airways obstruction in asthma and cystic fibrosis. Herein, we assessed L-arginine metabolism in airways of patients with chronic obstructive pulmonary disease (COPD). Lung function testing, measurement of fractional exhaled NO (FeNO) and sputum NO metabolites, as well as quantification of L-arginine metabolites (L-arginine, L-ornithine, L-citrulline, ADMA and symmetric dimethylarginine) using liquid chromatography-mass spectrometry (LC-MS) were performed. Concentrations of L-ornithine, the product of arginase activity, correlated directly with L-arginine and ADMA sputum concentrations. FeNO correlated directly with pre- and post-bronchodilator forced expiratory volume in one second (FEV1). Sputum arginase activity correlated inversely with total NO metabolite (NOx) and nitrite concentrations in sputum, and with pre- and post-bronchodilator FEV1. These findings suggest that ADMA in COPD airways results in a functionally relevant shift of L-arginine breakdown by the NO synthases towards the arginase pathway, which contributes to airway obstruction in these patients.

The Likelihood That Remedial Continuing Medical Education (CME) Reduces Disciplinary Recidivism Among Physicians.

PURPOSE: State medical boards are charged through their medical practice acts to regulate physician practice and, when necessary, discipline physicians for incompetent or inappropriate behavior. Boards often authorize remedial continuing medical education (CME) as part of a disciplinary action; however, it is unclear how effective remedial CME is in reducing the likelihood of physicians receiving additional discipline. This study examined the relationship between physicians who were required to complete remedial CME as part of their first discipline by state medical boards and the likelihood of additional discipline. METHOD: The national-level sample included 4,061 MD-physicians whose first discipline included license restrictions, probation, or other conditions imposed by state medical boards between 2011 and 2015. A multivariate logistic regression model examined whether physicians required to complete remedial CME as part of their first discipline were less likely to receive additional discipline by boards within 5 years. RESULTS: Of the 4,061 physicians, 36% (n = 1,449) were required to complete remedial CME as part of their first discipline, and 35% (n = 1,426) received additional discipline within 5 years. After accounting for other factors, physicians who were required to complete remedial CME as part of their first discipline by boards were less likely to receive additional discipline (odds ratio = 0.597; 95% confidence interval = 0.513, 0.696; P < .001) within 5 years compared to physicians who were not required to complete remedial CME. CONCLUSIONS: Findings support remedial CME as a means to help reduce physician disciplinary recidivism in certain circumstances. Physicians required to complete remedial CME as part of their first discipline were less likely to receive additional discipline by state medical boards within 5 years.

Estimating human joint moments unifies exoskeleton control, reducing user effort.

Robotic lower-limb exoskeletons can augment human mobility, but current systems require extensive, context-specific considerations, limiting their real-world viability. Here, we present a unified exoskeleton control framework that autonomously adapts assistance on the basis of instantaneous user joint moment estimates from a temporal convolutional network (TCN). When deployed on our hip exoskeleton, the TCN achieved an average root mean square error of 0.142 newton-meters per kilogram across 35 ambulatory conditions without any user-specific calibration. Further, the unified controller significantly reduced user metabolic cost and lower-limb positive work during level-ground and incline walking compared with walking without wearing the exoskeleton. This advancement bridges the gap between in-lab exoskeleton technology and real-world human ambulation, making exoskeleton control technology viable for a broad community.

Comparing the lower limb joint biomechanics of the Power Knee, C-Leg and Rheo Knee during ramp and stair ambulation.

One of the most significant developments in prosthetic knee technology has been the introduction of the Microprocessor-Controlled Prosthetic Knee (MPK). However, there is a lack of consensus over how different types of MPKs affect performance in different ambulation modes. In this study, we investigated the biomechanical differences in ramp and stair maneuvers when an individual with transfemoral amputation wears three commercial MPKs: the Össur Power Knee, the Össur Rheo Knee and the Ottobock C-Leg 4. The primary outcome variable for this study was the lower limb biological joint work, inclusive of the intact leg and prosthetic side hip. We hypothesized that (1) the Power Knee would result in lower biological work during ascent activities than the C-Leg and Rheo, both passive MPKs, and (2) the C-Leg and Rheo would result in lower biological work during descent activities than the Power Knee. During ramp ascent, the C-Leg was associated with lower biological joint work (p < 0.05) than the Power Knee. However, this relationship did not hold during stair ascent, where the Power Knee showed advantages for stair ascent with net reductions in biological joint work of 14.1% and 23.3% compared to the Rheo and C-leg, respectively. There were no significant differences in biological joint work between the knees during ramp and stair descent, indicating that choice of MPK may not be as important for descent activities. Our results demonstrate that differences are present between different types of MPKs during ascent activities which could prove useful in the prescription of these devices.