Oxidative Stress is a shared characteristic of ME/CFS and Long COVID.

More than 65 million individuals worldwide are estimated to have Long COVID (LC), a complex multisystemic condition, wherein patients of all ages report fatigue, post-exertional malaise, and other symptoms resembling myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS). With no current treatments or reliable diagnostic markers, there is an urgent need to define the molecular underpinnings of these conditions. By studying bioenergetic characteristics of peripheral blood lymphocytes in over 16 healthy controls, 15 ME/CFS, and 15 LC, we find both ME/CFS and LC donors exhibit signs of elevated oxidative stress, relative to healthy controls, especially in the memory subset. Using a combination of flow cytometry, bulk RNA-seq analysis, mass spectrometry, and systems chemistry analysis, we also observed aberrations in ROS clearance pathways including elevated glutathione levels, decreases in mitochondrial superoxide dismutase levels, and glutathione peroxidase 4 mediated lipid oxidative damage. Critically, these changes in redox pathways show striking sex-specific trends. While females diagnosed with ME/CFS exhibit higher total ROS and mitochondrial calcium levels, males with an ME/CFS diagnosis have normal ROS levels, but larger changes in lipid oxidative damage. Further analyses show that higher ROS levels correlates with hyperproliferation of T cells in females, consistent with the known role of elevated ROS levels in the initiation of proliferation. This hyperproliferation of T cells can be attenuated by metformin, suggesting this FDA-approved drug as a possible treatment, as also suggested by a recent clinical study of LC patients. Thus, we report that both ME/CFS and LC are mechanistically related and could be diagnosed with quantitative blood cell measurements. We also suggest that effective, patient tailored drugs might be discovered using standard lymphocyte stimulation assays.

Longitudinal cytokine and multi-modal health data of an extremely severe ME/CFS patient with HSD reveals insights into immunopathology, and disease severity.

Introduction: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) presents substantial challenges in patient care due to its intricate multisystem nature, comorbidities, and global prevalence. The heterogeneity among patient populations, coupled with the absence of FDA-approved diagnostics and therapeutics, further complicates research into disease etiology and patient managment. Integrating longitudinal multi-omics data with clinical, health,textual, pharmaceutical, and nutraceutical data offers a promising avenue to address these complexities, aiding in the identification of underlying causes and providing insights into effective therapeutics and diagnostic strategies. Methods: This study focused on an exceptionally severe ME/CFS patient with hypermobility spectrum disorder (HSD) during a period of marginal symptom improvements. Longitudinal cytokine profiling was conducted alongside the collection of extensive multi-modal health data to explore the dynamic nature of symptoms, severity, triggers, and modifying factors. Additionally, an updated severity assessment platform and two applications, ME-CFSTrackerApp and LexiTime, were introduced to facilitate real-time symptom tracking and enhance patient-physician/researcher communication, and evaluate response to medical intervention. Results: Longitudinal cytokine profiling revealed the significance of Th2-type cytokines and highlighted synergistic activities between mast cells and eosinophils, skewing Th1 toward Th2 immune responses in ME/CFS pathogenesis, particularly in cognitive impairment and sensorial intolerance. This suggests a potentially shared underlying mechanism with major ME/CFS comorbidities such as HSD, Mast cell activation syndrome, postural orthostatic tachycardia syndrome (POTS), and small fiber neuropathy. Additionally, the data identified potential roles of BCL6 and TP53 pathways in ME/CFS etiology and emphasized the importance of investigating adverse reactions to medication and supplements and drug interactions in ME/CFS severity and progression. Discussion: Our study advocates for the integration of longitudinal multi-omics with multi-modal health data and artificial intelligence (AI) techniques to better understand ME/CFS and its major comorbidities. These findings highlight the significance of dysregulated Th2-type cytokines in patient stratification and precision medicine strategies. Additionally, our results suggest exploring the use of low-dose drugs with partial agonist activity as a potential avenue for ME/CFS treatment. This comprehensive approach emphasizes the importance of adopting a patient-centered care approach to improve ME/CFS healthcare management, disease severity assessment, and personalized medicine. Overall, these findings contribute to our understanding of ME/CFS and offer avenues for future research and clinical practice.

Spectral tweezers: Single sample spectroscopy using optoelectronic tweezers.

A scheme that combines optoelectronic tweezers (OET) with spectroscopic analysis is presented. Referred to as spectral tweezers, the approach uses a single focused light beam that acts both as the trapping beam for OET and the probe beam for spectroscopy. Having simultaneous manipulation and spectral characterization ability, the method is used to isolate single micro-samples from clusters and perform spectral measurements. Experimental results show that a characteristic spectral signature can be obtained for a given sample. The proposed approach can be easily integrated into the optical setups used for conventional OETs with only a few additional optical components, making it a convenient tool for bio-analytical applications.

Resolution improvement of optoelectronic tweezers using patterned electrodes.

An optoelectronic tweezer (OET) device is presented that exhibits improved trapping resolution for a given optical spot size. The scheme utilizes a pair of patterned physical electrodes to produce an asymmetric electric field gradient. This, in turn, generates an azimuthal force component in addition to the conventional radial gradient force. Stable force equilibrium is achieved along a pair of antipodal points around the optical beam. Unlike conventional OETs where trapping can occur at any point around the beam perimeter, the proposed scheme improves the resolution by limiting trapping to two points. The working principle is analyzed by performing numerical analysis of the electromagnetic fields and corresponding forces. Experimental results are presented that show the trapping and manipulation of micro-particles using the proposed device.

Controlled Transport of Individual Microparticles Using Dielectrophoresis.

A dielectrophoretic device employing a planar array of microelectrodes is designed for controlled transport of individual microparticles. By exciting the electrodes in sequence, a moving dielectrophoretic force is created that can drag a particle across the electrodes in a straight line. The electrode shapes are designed to counter any lateral drift of the trapped particle during transport. This facilitates single particle transport by creating a narrow two-dimensional corridor for the moving dielectrophoretic force to operate on. The design and analysis processes are discussed in detail. Numerical simulations are performed to calculate the electromagnetic field distribution and the generated dielectrophoretic force near the electrodes. The Langevin equation is used for analyzing the trajectory of a microparticle under the influence of the external forces. The simulations show how the designed electrode geometry produces the necessary lateral confinement required for successful particle transport. Finally, experimental results are presented showing controlled bidirectional linear transport of single polystyrene beads of radius 10 and 5 µm for a distances 840 and 1100 µm, respectively. The capabilities of the proposed platform make it suitable for micro total analysis systems (µTAS) and lab-on-a-chip (LOC) applications.

Phenotypic characteristics of peripheral immune cells of Myalgic encephalomyelitis/chronic fatigue syndrome via transmission electron microscopy: A pilot study.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex chronic multi-systemic disease characterized by extreme fatigue that is not improved by rest, and worsens after exertion, whether physical or mental. Previous studies have shown ME/CFS-associated alterations in the immune system and mitochondria. We used transmission electron microscopy (TEM) to investigate the morphology and ultrastructure of unstimulated and stimulated ME/CFS immune cells and their intracellular organelles, including mitochondria. PBMCs from four participants were studied: a pair of identical twins discordant for moderate ME/CFS, as well as two age- and gender- matched unrelated subjects-one with an extremely severe form of ME/CFS and the other healthy. TEM analysis of CD3/CD28-stimulated T cells suggested a significant increase in the levels of apoptotic and necrotic cell death in T cells from ME/CFS patients (over 2-fold). Stimulated Tcells of ME/CFS patients also had higher numbers of swollen mitochondria. We also found a large increase in intracellular giant lipid droplet-like organelles in the stimulated PBMCs from the extremely severe ME/CFS patient potentially indicative of a lipid storage disorder. Lastly, we observed a slight increase in platelet aggregation in stimulated cells, suggestive of a possible role of platelet activity in ME/CFS pathophysiology and disease severity. These results indicate extensive morphological alterations in the cellular and mitochondrial phenotypes of ME/CFS patients' immune cells and suggest new insights into ME/CFS biology.

A touch-based multimodal and cryptographic bio-human-machine interface.

The awareness of individuals' biological status is critical for creating interactive and adaptive environments that can actively assist the users to achieve optimal outcomes. Accordingly, specialized human­machine interfaces­equipped with bioperception and interpretation capabilities­are required. To this end, we devised a multimodal cryptographic bio-human­machine interface (CB-HMI), which seamlessly translates the user's touch-based entries into encrypted biochemical, biophysical, and biometric indices. As its central component, the CB-HMI features thin hydrogel-coated chemical sensors and inference algorithms to noninvasively and inconspicuously acquire biochemical indices such as circulating molecules that partition onto the skin (here, ethanol and acetaminophen). Additionally, the CB-HMI hosts physical sensors and associated algorithms to simultaneously acquire the user's heart rate, blood oxygen level, and fingerprint minutiae pattern. Supported by human subject studies, we demonstrated the CB-HMI's capability in terms of acquiring physiologically relevant readouts of target bioindices, as well as user-identifying and biometrically encrypting/decrypting these indices in situ (leveraging the fingerprint feature). By upgrading the common surrounding objects with the CB-HMI, we created interactive solutions for driving safety and medication use. Specifically, we demonstrated a vehicle-activation system and a medication-dispensing system, where the integrated CB-HMI uniquely enabled user bioauthentication (on the basis of the user's biological state and identity) prior to rendering the intended services. Harnessing the levels of bioperception achieved by the CB-HMI and other intelligent HMIs, we can equip our surroundings with a comprehensive and deep awareness of individuals' psychophysiological state and needs.

A Comprehensive Examination of Severely Ill ME/CFS Patients.

One in four myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients are estimated to be severely affected by the disease, and these house-bound or bedbound patients are currently understudied. Here, we report a comprehensive examination of the symptoms and clinical laboratory tests of a cohort of severely ill patients and healthy controls. The greatly reduced quality of life of the patients was negatively correlated with clinical depression. The most troublesome symptoms included fatigue (85%), pain (65%), cognitive impairment (50%), orthostatic intolerance (45%), sleep disturbance (35%), post-exertional malaise (30%), and neurosensory disturbance (30%). Sleep profiles and cognitive tests revealed distinctive impairments. Lower morning cortisol level and alterations in its diurnal rhythm were observed in the patients, and antibody and antigen measurements showed no evidence for acute infections by common viral or bacterial pathogens. These results highlight the urgent need of developing molecular diagnostic tests for ME/CFS. In addition, there was a striking similarity in symptoms between long COVID and ME/CFS, suggesting that studies on the mechanism and treatment of ME/CFS may help prevent and treat long COVID and vice versa.

Modeling Brownian Microparticle Trajectories in Lab-on-a-Chip Devices with Time Varying Dielectrophoretic or Optical Forces.

Lab-on-a-chip (LOC) devices capable of manipulating micro/nano-sized samples have spurred advances in biotechnology and chemistry. Designing and analyzing new and more advanced LOCs require accurate modeling and simulation of sample/particle dynamics inside such devices. In this work, we present a generalized computational physics model to simulate particle/sample trajectories under the influence of dielectrophoretic or optical forces inside LOC devices. The model takes into account time varying applied forces, Brownian motion, fluid flow, collision mechanics, and hindered diffusion caused by hydrodynamic interactions. We develop a numerical solver incorporating the aforementioned physics and use it to simulate two example cases: first, an optical trapping experiment, and second, a dielectrophoretic cell sorter device. In both cases, the numerical results are found to be consistent with experimental observations, thus proving the generality of the model. The numerical solver can simulate time evolution of the positions and velocities of an arbitrarily large number of particles simultaneously. This allows us to characterize and optimize a wide range of LOCs. The developed numerical solver is made freely available through a GitHub repository so that researchers can use it to develop and simulate new designs.

Noninvasive wearable electroactive pharmaceutical monitoring for personalized therapeutics.

To achieve the mission of personalized medicine, centering on delivering the right drug to the right patient at the right dose, therapeutic drug monitoring solutions are necessary. In that regard, wearable biosensing technologies, capable of tracking drug pharmacokinetics in noninvasively retrievable biofluids (e.g., sweat), play a critical role, because they can be deployed at a large scale to monitor the individuals' drug transcourse profiles (semi)continuously and longitudinally. To this end, voltammetry-based sensing modalities are suitable, as in principle they can detect and quantify electroactive drugs on the basis of the target's redox signature. However, the target's redox signature in complex biofluid matrices can be confounded by the immediate biofouling effects and distorted/buried by the interfering voltammetric responses of endogenous electroactive species. Here, we devise a wearable voltammetric sensor development strategy-centering on engineering the molecule-surface interactions-to simultaneously mitigate biofouling and create an "undistorted potential window" within which the target drug's voltammetric response is dominant and interference is eliminated. To inform its clinical utility, our strategy was adopted to track the temporal profile of circulating acetaminophen (a widely used analgesic and antipyretic) in saliva and sweat, using a surface-modified boron-doped diamond sensing interface (cross-validated with laboratory-based assays, R2 ∼ 0.94). Through integration of the engineered sensing interface within a custom-developed smartwatch, and augmentation with a dedicated analytical framework (for redox peak extraction), we realized a wearable solution to seamlessly render drug readouts with minute-level temporal resolution. Leveraging this solution, we demonstrated the pharmacokinetic correlation and significance of sweat readings.

Automated Motion Tracking and Data Extraction for Red Blood Cell Biomechanics.

Red blood cell biomechanics can provide us with a deeper understanding of macroscopic physiology and have the potential of being used for diagnostic purposes. In diseases like sickle cell anemia and malaria, reduced red blood cell deformability can be used as a biomarker, leading to further assays and diagnoses. A microfluidic system is useful for studying these biomechanical properties. We can observe detailed red blood cell mechanical behavior as they flow through microcapillaries using high-speed imaging and microscopy. Microfluidic devices are advantageous over traditional methods because they can serve as high-throughput tests. However, to rapidly analyze thousands of cells, there is a need for powerful image processing tools and software automation. We describe a workflow process using Image-Pro to identify and track red blood cells in a video, take measurements, and export the data for use in statistical analysis tools. The information in this protocol can be applied to large-scale blood studies where entire cell populations need to be analyzed from many cohorts of donors. © 2020 The Authors. Basic Protocol 1: Enhancing raw video for motion tracking Basic Protocol 2: Extracting motion tracking data from enhanced video.

Changes in Motor Skill Proficiency After Equine-Assisted Activities and Brain-Building Tasks in Youth With Neurodevelopmental Disorders.

There is a lack of current research to support the efficacy of a combination of equine-assisted activities (EAA) and brain building activities to influence motor skill competencies in youth with neurodevelopmental disorders (ND). The primary objective of this study was to quantify changes in motor skill proficiency before and after 8 weeks of EAA and brain-building activities in youth with ND. A secondary objective was to quantify changes in motor skill proficiency before and after 1 year of EAA and brain-building activities in youth with ND. Twenty-five youth completed the same 32-week protocol that was separated into 4, 8-week blocks, in the following order: (1) control; (2) EAA-only; (3) washout; (4) GaitWay block (EAA and brain building activities). Before and after each block, motor skills were assessed using the Short Form of the Bruininks-Oseretsky Test of Motor Proficiency-Version 2 (BOT-2). Seven youth continued with the GaitWay intervention for one additional year, and the BOT-2 Short Form was also administered following this intervention. A repeated-measures analysis-of-variance was performed to compare BOT-2 subtest and overall scores between interventions with a significance of 0.05. Manual dexterity was higher at Post-Washout [3.3 (2.4)] vs. Pre-Control [2.2 (2.1); p = 0.018] and Post-Control [2.6 (2.0); p = 0.024], and at Post-GaitWay vs. Pre-Control [3.2 (2.4) vs. 2.2 (2.1); p = 0.037]. Upper-limb coordination was higher at Post-GaitWay vs. Post-Control [6.0 (4.1) vs. 3.9 (3.8); p = 0.050]. When compared to Pre-Control [3.2 (3.0)], strength was higher at Post-EAA [4.9 (3.5); p = 0.028] and at Post-GaitWay [5.2 (2.9); p = 0.015]. Overall scores were higher at Post-GaitWay [39.1 (22.2)] when compared to Pre-Control [32.4 (21.6); p = 0.003] and Post-Control [32.5 (21.9); p = 0.009]. Additionally, motor skills were maintained for 1 year following the Post-GaitWay testing session among seven participants. This is the first known study to include and demonstrate the short-term and long-term effects of a combination of EAA and brain building activities with motor proficiency in youth with ND. Clinical Trial Registration: Motor Skill Proficiency After Equine-Assisted Activities and Brain-building Tasks; www.ClinicalTrials.gov, identifier: NCT04158960.

Meta-analysis of peptides to detect protein significance.

Shotgun assays are widely used in biotechnologies to characterize large molecules, which are hard to be measured as a whole directly. For instance, in Liquid Chromatography - Mass Spectrometry (LC-MS) shotgun experiments, proteins in biological samples are digested into peptides, and then peptides are separated and measured. However, in proteomics study, investigators are usually interested in the performance of the whole proteins instead of those peptide fragments. In light of meta-analysis, we propose an adaptive thresholding method to select informative peptides, and combine peptide-level models to protein-level analysis. The meta-analysis procedure and modeling rationale can be adapted to data analysis of other types of shotgun assays.

Microfluidic Point-of-Care Testing: Commercial Landscape and Future Directions.

Point-of-care testing (POCT) allows physicians to detect and diagnose diseases at or near the patient site, faster than conventional lab-based testing. The importance of POCT is considerably amplified in the trying times of the COVID-19 pandemic. Numerous point-of-care tests and diagnostic devices are available in the market including, but not limited to, glucose monitoring, pregnancy and infertility testing, infectious disease testing, cholesterol testing and cardiac markers. Integrating microfluidics in POCT allows fluid manipulation and detection in a singular device with minimal sample requirements. This review presents an overview of two technologies - (a.) Lateral Flow Assay (LFA) and (b.) Nucleic Acid Amplification - upon which a large chunk of microfluidic POCT diagnostics is based, some of their applications, and commercially available products. Apart from this, we also delve into other microfluidic-based diagnostics that currently dominate the in-vitro diagnostic (IVD) market, current testing landscape for COVID-19 and prospects of microfluidics in next generation diagnostics.

Community members in activated sludge as determined by molecular probe technology.

The use of molecular probe technology is demonstrated for routine identification and tracking of cultured and uncultured microorganisms in an activated sludge bioreactor treating domestic wastewater. A key advantage of molecular probe technology is that it can interrogate hundreds of microbial species of interest in a single measurement. In environmental niches where a single genus (such as Competibacteraceae) dominates, it can be difficult and expensive to identify microorganisms that are present at low relative abundance. With molecular probe technology, it is straightforward. Members of the Competibacteraceae family, none of which have been grown in pure culture, are abundant in an activated sludge system in the San Francisco Bay Area, California, USA. Molecular probe ensembles with and without Competibacteraceae probes were constructed. Whereas the probe ensemble with Competibacteraceae probes identified a total of ten bacteria, the molecular probe ensemble without Competibacteraceae probes identified 29 bacteria, including many at low relative abundance and including some species of public health significance.

The IDO Metabolic Trap Hypothesis for the Etiology of ME/CFS.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating noncommunicable disease brandishing an enormous worldwide disease burden with some evidence of inherited genetic risk. Absence of measurable changes in patients' standard blood work has necessitated ad hoc symptom-driven therapies and a dearth of mechanistic hypotheses regarding its etiology and possible cure. A new hypothesis, the indolamine-2,3-dioxygenase (IDO) metabolic trap, was developed and formulated as a mathematical model. The historical occurrence of ME/CFS outbreaks is a singular feature of the disease and implies that any predisposing genetic mutation must be common. A database search for common damaging mutations in human enzymes produces 208 hits, including IDO2 with four such mutations. Non-functional IDO2, combined with well-established substrate inhibition of IDO1 and kinetic asymmetry of the large neutral amino acid transporter, LAT1, yielded a mathematical model of tryptophan metabolism that displays both physiological and pathological steady-states. Escape from the pathological one requires an exogenous perturbation. This model also identifies a critical point in cytosolic tryptophan abundance beyond which descent into the pathological steady-state is inevitable. If, however, means can be discovered to return cytosolic tryptophan below the critical point, return to the normal physiological steady-state is assured. Testing this hypothesis for any cell type requires only labelled tryptophan, a means to measure cytosolic tryptophan and kynurenine, and the standard tools of tracer kinetics.

Combining newborn metabolic and DNA analysis for second-tier testing of methylmalonic acidemia.

PURPOSE: Improved second-tier tools are needed to reduce false-positive outcomes in newborn screening (NBS) for inborn metabolic disorders on the Recommended Universal Screening Panel (RUSP). METHODS: We designed an assay for multiplex sequencing of 72 metabolic genes (RUSPseq) from newborn dried blood spots. Analytical and clinical performance was evaluated in 60 screen-positive newborns for methylmalonic acidemia (MMA) reported by the California Department of Public Health NBS program. Additionally, we trained a Random Forest machine learning classifier on NBS data to improve prediction of true and false-positive MMA cases. RESULTS: Of 28 MMA patients sequenced, we found two pathogenic or likely pathogenic (P/LP) variants in a MMA-related gene in 24 patients, and one pathogenic variant and a variant of unknown significance (VUS) in 1 patient. No such variant combinations were detected in MMA false positives and healthy controls. Random Forest-based analysis of the entire NBS metabolic profile correctly identified the MMA patients and reduced MMA false-positive cases by 51%. MMA screen-positive newborns were more likely of Hispanic ethnicity. CONCLUSION: Our two-pronged approach reduced false positives by half and provided a reportable molecular finding for 89% of MMA patients. Challenges remain in newborn metabolic screening and DNA variant interpretation in diverse multiethnic populations.

A biosensor-based approach reveals links between efflux pump expression and cell cycle regulation in pleiotropic drug resistance of yeast.

Multidrug resistance is highly conserved in mammalian, fungal, and bacterial cells, is characterized by resistance to several unrelated xenobiotics, and poses significant challenges to managing infections and many cancers. Eukaryotes use a highly conserved set of drug efflux transporters that confer pleiotropic drug resistance (PDR). To interrogate the regulation of this critical process, here we developed a small molecule-responsive biosensor that couples transcriptional induction of PDR genes to growth rate in the yeast Saccharomyces cerevisiae Using diverse PDR inducers and the homozygous diploid deletion collection, we applied this biosensor system to genome-wide screens for potential PDR regulators. In addition to recapitulating the activity of previously known factors, these screens identified a series of genes involved in a variety of cellular processes with significant but previously uncharacterized roles in the modulation of yeast PDR. Genes identified as down-regulators of the PDR included those encoding the MAD family of proteins involved in the mitotic spindle assembly checkpoint (SAC) complex. Of note, we demonstrated that genetic disruptions of the mitotic spindle assembly checkpoint elevate expression of PDR-mediating efflux pumps in response to exposure to a variety of compounds that themselves have no known influence on the cell cycle. These results not only establish our biosensor system as a viable tool for investigating PDR in a high-throughput fashion, but also uncover critical control mechanisms governing the PDR response and a previously uncharacterized link between PDR and cell cycle regulation in yeast.

Red blood cell deformability is diminished in patients with Chronic Fatigue Syndrome.

BACKGROUND: Myalgic encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a poorly understood disease. Amongst others symptoms, the disease is associated with profound fatigue, cognitive dysfunction, sleep abnormalities, and other symptoms that are made worse by physical or mental exertion. While the etiology of the disease is still debated, evidence suggests oxidative damage to immune and hematological systems as one of the pathophysiological mechanisms of the disease. Since red blood cells (RBCs) are well-known scavengers of oxidative stress, and are critical in microvascular perfusion and tissue oxygenation, we hypothesized that RBC deformability is adversely affected in ME/CFS. METHODS: We used a custom microfluidic platform and high-speed microscopy to assess the difference in deformability of RBCs obtained from ME/CFS patients and age-matched healthy controls. RESULTS AND CONCLUSION: We observed from various measures of deformability that the RBCs isolated from ME/CFS patients were significantly stiffer than those from healthy controls. Our observations suggest that RBC transport through microcapillaries may explain, at least in part, the ME/CFS phenotype, and promises to be a novel first-pass diagnostic test.

Acute Cardiometabolic Responses to Three Modes of Treadmill Exercise in Older Adults With Parkinson's Disease.

The purpose of this study was to compare acute cardiometabolic responses to 3 modes of treadmill exercise in adults diagnosed with Parkinson's disease (PD). Eight elderly adults with PD (67.9 ± 3.0 yr) completed 1 session each on a land, aquatic, and antigravity treadmill at 50% body weight. Participants walked from 1 to 3 mph in 0.5-mph increments at 0% grade for 5 min at each speed. Heart rate, energy expenditure, blood pressure, and rating of perceived exertion were measured at rest and during exercise. All variables except diastolic blood pressure increased with speed on all treadmills (p < .001). At all speeds except 1.5 mph, heart rate was higher on the land treadmill than the antigravity treadmill (p < .05). Exercising on an aquatic or antigravity treadmill elicits similar submaximal physiologic responses to exercise on a land treadmill in adults with PD.