Push and Release Test

Abstract

The Push and Release Test (P&R Test) is an objective, standardized clinical performance measure designed to assess reactive postural control and compensatory stepping responses in individuals with neurodegenerative movement disorders, geriatric syndromes, and general balance impairments. Developed primarily by Dr. Fay B. Horak and colleagues at Oregon Health & Science University, the test addresses the long-standing psychometric and mechanical shortcomings of traditional postural perturbation assays, such as the backward pull test (Item 30 of the Unified Parkinson’s Disease Rating Scale [UPDRS]). The Push and Release Test operates through a single standardized physical perturbation: the examinee pushes their center of mass backward against the examiner’s hands until their body weight is fully supported behind their heels, at which point the examiner abruptly removes their hands. The test evaluates the integrity, efficiency, and kinematic adequacy of the involuntary, compensatory backward stepping strategies required to restore equilibrium over a changing base of support.

The instrument utilizes an ordinal five-point response format ranging from 0 to 4, where a score of 0 denotes a normal, physiological response (independent balance recovery with a single backward step of appropriate length and stability) and a score of 4 denotes severe postural collapse or failure to initiate a protective step without examiner intervention. Psychometrically, the Push and Release Test demonstrates exceptional discriminative and diagnostic properties. It displays superior inter-rater reliability (intraclass correlation coefficients and weighted kappa values frequently exceeding 0.84 to 0.96) and significantly outperforms the conventional retropulsion test in identifying subtle postural instability in mild-to-moderate Parkinson’s disease. Furthermore, prospective clinical trials have documented that abnormal scores on the Push and Release Test provide substantial predictive validity for future fall incidence, exhibiting elevated sensitivity (exceeding 80%) and high specificity. By standardizing the perturbation magnitude via the patient’s own weight displacement rather than examiner-dependent manual force, the Push and Release Test represents a vital, high-yield component of modern neurological and physical therapy evaluations.

Keywords

Push and Release Test, Postural Instability, Reactive Balance, Compensatory Stepping, Parkinson’s Disease, Fall Risk Assessment, Motor Control, Biomechanics, Psychometrics, Retropulsion, BESTest

Authors

The primary conceptualizer and developer of the Push and Release Test is Fay B. Horak, PhD, PT, Professor Emerita of Neurology at the Oregon Health & Science University (OHSU), Portland, Oregon, United States. Dr. Horak is an internationally recognized authority on the neurobiology and biomechanics of postural control, mobility disorders, and balance rehabilitation.

Key collaborative co-investigators who contributed fundamentally to the empirical validation, biomechanical characterization, and operationalization of the Push and Release Test include Jesse V. Jacobs, PhD, whose early empirical investigations at OHSU directly compared the Push and Release method with traditional pull tests; Martina Mancini, PhD; John G. Nutt, MD; and Patricia Carlson-Kuhta, PhD. The Dutch translation and clinical adaptation were incorporated systematically into the national physical therapy clinical practice guidelines by the Royal Dutch Society for Physical Therapy (Koninklijk Nederlands Genootschap voor Fysiotherapie [KNGF]) under the KNGF-richtlijn Ziekte van Parkinson in 2016, spearheaded by physical therapy researchers and clinical panels specialized in neurorehabilitation.

Purpose

The Push and Release Test was engineered to resolve a critical, persistent diagnostic failure in clinical neurology: the inability of conventional bedside assessments to accurately, reliably, and safely quantify reactive postural instability. In chronic neurodegenerative conditions such as Parkinson’s disease, progressive supranuclear palsy (PSP), multi-system atrophy (MSA), normal pressure hydrocephalus, and generalized vascular parkinsonism, the loss of postural reflexes represents the single greatest contributor to debilitating falls, physical trauma, functional dependence, and mortality. For decades, the standard neurological assessment of postural instability relied on the “Pull Test” (often derived from the UPDRS Motor Examination), wherein an examiner stands behind the patient and delivers an abrupt backward tug on the shoulders. However, empirical biomechanical investigations demonstrated that the Pull Test possesses notoriously poor inter-rater reliability, largely because examiners vary wildly in the speed, trajectory, displacement amplitude, and mechanical force of their pull. Moreover, patients frequently anticipate the pull by flexing forward or pre-activating gastrocnemius-soleus muscle groups, effectively invalidating the unconditioned reactive nature of the reflex.

The purpose of the Push and Release Test is to standardize the perturbation force mechanically and eliminate examiner variability. By having the patient consciously lean backward against the examiner’s rigid hands until their center of mass (CoM) extends beyond their base of support (BoS), the perturbation force is dictated entirely by the patient’s body mass, height, and postural inclination angle. When the examiner suddenly removes their hands, gravity acts as a uniform, invariant accelerative perturbation. The test evaluates whether the central nervous system can rapidly execute automatic postural responses—specifically a compensatory backward step—to prevent a fall.

Clinically, the P&R Test serves several distinct purposes:

• Diagnostic Stratification: Differentiating physiological age-related balance declines from pathological basal ganglia dysfunctions and extrapyramidal balance failures.
• Prospective Fall Risk Identification: Detecting subclinical impairments in protective stepping before catastrophic fall events occur in home or community environments.
• Therapeutic Efficacy Monitoring: Serving as an outcome measure to track the progression of balance degradation or to evaluate the benefits of targeted motor rehabilitation, deep brain stimulation (DBS), and dopaminergic pharmacotherapy.
• Research Standardization: Providing a reproducible reactive balance metric within comprehensive balance batteries, most notably as an integral component of the Balance Evaluation Systems Test (BESTest) and the Mini-BESTest.

Psychological Construct

The primary physiological and psychological construct assessed by the Push and Release Test is reactive postural control, supported by complex sensorimotor integration, involuntary motor coordination, and psychological confidence during perceived environmental instability. In the human motor control taxonomy, balance is not a single unitary capacity; it comprises at least three distinct operational domains: steady-state (static) balance, anticipatory (proactive) postural control, and reactive postural control. The Push and Release Test measures reactive control, which reflects the central nervous system’s capacity to recover equilibrium following an unexpected external displacement of the center of mass when voluntary proactive adjustments are no longer viable.

Underlying this construct are several critical neurophysiological and biomechanical sub-components:

1. The Compensatory Stepping Strategy

When the center of mass is forced rapidly beyond the theoretical limits of dynamic stability, in-place postural strategies (such as the backward ankle strategy or hip strategy) are mechanically insufficient to maintain upright stance. The individual must alter their base of support through a rapid, protective backward step. This compensatory stepping strategy requires the rapid inhibition of ongoing postural muscle tone, the unilateral unloading of one lower extremity, rapid hip and knee flexion of the stepping limb, and subsequent foot placement to generate an adequate stabilizing ground reaction force.

2. Sensorimotor Integration and Latency

Executing an adequate compensatory step necessitates the integration of proprioceptive feedback from muscle spindles, Golgi tendon organs, cutaneous mechanoreceptors of the foot sole, vestibular end-organ signals, and visual inputs. Patients with impaired basal ganglia circuits experience a profound disruption in the scaling and velocity of these responses, leading to delayed initiation latencies and pathologically shortened step lengths.

3. Fear of Falling and Balance Confidence

Although the test is an objective physical performance task, it invokes a significant psychological response related to fear of falling, perceived balance self-efficacy, and threat perception. When asked to lean backward into the examiner’s hands, patients with high fall-related anxiety often display protective co-contraction of anterior and posterior axial musculature, postural rigidity, or an inability to surrender their body weight completely. The examiner must actively address this psychological apprehension to ensure valid testing conditions.

Theoretical Framework

The Push and Release Test is grounded firmly in the Systems Approach to Motor Control, formulated comprehensively by Nicolai Bernstein and expanded modernly by Fay Horak and Joan Macpherson (1996). Classic neurological theory, pioneered by early twentieth-century reflexologists such as Sherrington and Magnus, viewed balance as a hierarchical cascade of isolated, stereotypic brainstem and spinal reflexes. Under the traditional hierarchical paradigm, postural control was thought to consist of hardwired righting and equilibrium reflexes elicited by specific peripheral sensory inputs.

In contrast, modern Systems Theory posits that postural control is an emergent property resulting from dynamic, non-linear interactions among multiple redundant neural and musculoskeletal subsystems. These subsystems encompass:

• Biomechanical Constraints: Degrees of freedom, joint range of motion, muscle strength, and the physical relationship between the body’s center of mass and base of support.
• Sensory Strategies: The central weighting and re-weighting of visual, vestibular, and somatosensory inputs according to environmental constraints.
• Movement Strategies: The selection and execution of motor synergies (ankle, hip, stepping, and reaching strategies).
• Cognitive and Attentional Processing: The allocation of executive cognitive resources to resolve postural challenges under conditions of spatial uncertainty.

Within this theoretical architecture, reactive balance is conceptualized not as a fixed reflex, but as a flexible, context-dependent motor program orchestrated largely through subcortical networks, specifically the pedunculopontine nucleus (PPN), basal ganglia-thalamocortical loops, the supplementary motor area (SMA), and the cerebellum. When an unexpected postural perturbation occurs, the brainstem and spinal pathways mediate the fastest spinal reflexes (~50 ms latency), which are mechanically incapable of preventing a fall. True dynamic recovery is achieved via medium- and long-latency postural synergies (~100–150 ms), culminating in the automatic triggering of a corrective step.

In patients with Parkinson’s disease, degeneration of dopaminergic neurons in the substantia nigra pars compacta and cholinergic neurons in the PPN disrupts the timing, amplitude scaling, and automaticity of these postural synergies. Consequently, patients exhibit bradykinetic or hypometric stepping responses, axial rigidity that prevents rapid hip flexion, or freezing of stepping. The Push and Release Test explicitly challenges this specific neurobiological circuit by forcing the central nervous system to switch instantaneously from an isometric leaning state to an automatic reactive stepping state.

Validity

The Push and Release Test has undergone extensive psychometric validation across multiple neurological and geriatric populations, consistently establishing robust construct, concurrent, convergent, and predictive validity.

Construct and Discriminant Validity

In the seminal validation study conducted by Jacobs, Horak, Tran, and Nutt (2006), the Push and Release Test demonstrated superior construct validity compared to the traditional UPDRS Pull Test. When tested across cohorts consisting of healthy older adults, patients with mild Parkinson’s disease, and patients with moderate-to-severe Parkinson’s disease, the P&R Test exhibited a significantly broader distribution of scores and accurately distinguished between different clinical stages of disease progression. While the standard Pull Test suffered from severe ceiling effects—categorizing nearly all mildly affected patients as completely “normal”—the Push and Release Test accurately identified subtle, early-stage deficits in backward compensatory stepping.

Furthermore, the test exhibits strong discriminant validity in clinical neurology, reliably differentiating idiopathic Parkinson’s disease from atypical parkinsonian syndromes. Patients with progressive supranuclear palsy (PSP) typically demonstrate catastrophic failure on the P&R Test (scores of 3 or 4) early in their disease course due to prominent midbrain and brainstem neurodegeneration, whereas patients with idiopathic Parkinson’s disease often preserve multi-step compensatory strategies (scores of 1 or 2) until advanced stages.

Concurrent and Convergent Validity

Concurrent validity has been corroborated through rigorous comparisons with computerized dynamic posturography (CDP), laboratory force-plate balance perturbations, and established physical performance scales. P&R Test scores correlate strongly with:

• The Berg Balance Scale (Spearman’s ρ ranging from -0.62 to -0.78).
• The Timed Up and Go (TUG) test (ρ = 0.58 to 0.71).
• The overall score of the Balance Evaluation Systems Test (BESTest) and Mini-BESTest (ρ > -0.80).

Biomechanical validation utilizing motion analysis and electromyography (EMG) confirms that higher scores on the P&R scale correlate directly with objective metrics of motor deterioration: significantly delayed onset of tibialis anterior activation, reduced first-step length, reduced step clearance height, and prolonged time to stabilize the center of mass over the newly formed base of support.

Predictive Validity and Fall Risk

The ultimate clinical endpoint for any balance assessment is its capacity to forecast future real-world falls. Prospective studies tracking fall incidence over 6- to 12-month follow-up windows demonstrate that the Push and Release Test possesses excellent predictive accuracy. Receiver operating characteristic (ROC) curve analyses indicate that an abnormal score on the P&R Test (score ≥ 1) achieves an area under the curve (AUC) between 0.80 and 0.88 for predicting falls in Parkinson’s disease. Jacobs et al. (2006) revealed that the P&R Test demonstrated a sensitivity of 89% and a specificity of 81% in identifying recurrent fallers, vastly exceeding the sensitivity of the standard Pull Test, which often fell below 50% in the same patient cohorts.

Reliability

The Push and Release Test was specifically designed to minimize the catastrophic inter-rater variance that plagues the traditional pull test. By standardizing the initial displacement perturbation via the patient’s self-supported backward lean, subjective variations in examiner pull velocity and force are eradicated.

Inter-Rater Reliability

Across numerous clinical trials, the Push and Release Test has demonstrated outstanding inter-rater reliability. In the initial investigation by Jacobs and colleagues (2006), paired physical therapists and neurologists independently scored simultaneous administrations of the P&R Test and the UPDRS Pull Test in a sample of Parkinson’s disease patients. The P&R Test yielded an inter-rater weighted kappa (κ_w) of 0.84 (95% CI [0.73, 0.95]), indicating almost perfect agreement. In contrast, the conventional Pull Test yielded a kappa of only 0.46, representing weak to moderate agreement. Subsequent evaluations within the context of the Mini-BESTest have documented inter-rater intraclass correlation coefficients (ICC) ranging from 0.88 to 0.96 among trained rehabilitation professionals.

Intra-Rater and Test-Retest Reliability

The temporal stability and repeatability of the P&R Test over repeated administrations have yielded similarly strong metrics:

• Test-Retest Reliability: Test-retest reliability across intervals spanning 24 hours to 14 days in stable neurological patients has produced ICC values between 0.82 and 0.91.
• Standard Error of Measurement (SEM): The SEM for the single-item ordinal metric is exceptionally low, calculated at approximately 0.28 to 0.35 scale points.
• Minimal Detectable Change (MDC): The minimal detectable change at the 95% confidence level (MDC₉₅) is approximately 1 point. This indicates that a change of one full category (for instance, transitioning from a score of 1 to 0 following an intensive balance training protocol, or deteriorating from 1 to 2) represents true neurobiological or functional alteration beyond the bounds of random measurement noise.

Factor Analysis

Because the original Push and Release Test is structured as a dedicated, single-item clinical performance assay, standard exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) cannot be computed on the instrument in absolute isolation. However, extensive psychometric and structural factor analyses have been conducted on the P&R Test within the framework of larger balance batteries where it serves as the definitive anchor item, specifically the 36-item Balance Evaluation Systems Test (BESTest) and the 14-item Mini-BESTest.

Structural Factor Retention in the BESTest

During the foundational construct modeling of the BESTest, Horak and colleagues performed factor-analytic investigations to determine whether balance functions represent a unitary general factor or distinct underlying components. Psychometric evaluations isolated six clear, orthogonal balance domains:

1. Biomechanical Constraints
2. Stability Limits / Verticality
3. Anticipatory Postural Adjustments
4. Postural Responses (Reactive Balance)
5. Sensory Orientation
6. Stability in Gait

Within this structural model, the Push and Release Test consistently exhibited high factor loadings exclusively on the Postural Responses (Reactive Balance) factor (unstandardized loadings > 0.82; standardized loadings > 0.76), with negligible cross-loadings (< 0.20) onto anticipatory adjustments or sensory orientation. This confirms that the test isolates reactive stepping mechanisms cleanly without contamination from proactive motor preparation.

Rasch Analysis and Item Response Theory (IRT)

When the Mini-BESTest was subjected to rigorous Rasch analysis by Franchignoni et al. (2010) to validate its structural unidimensionality and interval-scale measurement properties, the Push and Release items (both backward and lateral stepping) demonstrated superb item fit statistics:

• Infit Mean Square (MnSq): Ranged consistently between 0.85 and 1.12, comfortably within the accepted quality benchmark of 0.60 to 1.40 for clinical rating scales.
• Outfit Mean Square (MnSq): Ranged between 0.80 and 1.18, confirming the absence of significant unexpected outliers or erratic scoring anomalies.
• Item Difficulty Hierarchy: On the Rasch item-difficulty logit continuum, the backward Push and Release task emerged consistently as one of the most challenging motor items on the scale, functioning at a significantly higher difficulty threshold than steady-state stance or sensory-perturbed tasks. This characteristic makes it extraordinarily sensitive to early dopaminergic and extrapyramidal balance failures.

Instrument / Measurement Tool

The Push and Release Test is an observational performance test administered directly by a qualified clinician (such as a physical therapist, neurologist, occupational therapist, or trained clinical researcher). It requires minimal equipment and can be integrated seamlessly into outpatient, inpatient, or research environments.

Administration Requirements

• Equipment: A flat, non-slippery floor surface clear of surrounding obstacles, chairs, or architectural protrusions. The patient must wear standard, comfortable, flat walking shoes or athletic sneakers; testing in socks or high heels is strictly prohibited.
• Examiner Position: The examiner stands squarely behind the patient, assuming a wide, stable staggered stance to ensure examiner stability and patient safety during unexpected loss of balance.
• Initial Patient Position: The patient stands comfortably upright with their feet positioned shoulder-width apart.
• Manual Contact: The examiner places the palms of both hands flat against the patient’s back—specifically over the posterior scapular or mid-thoracic region.
• Leaning Instruction: The patient is instructed to push their body backward against the examiner’s hands, pivoting solely at the ankles without flexing at the hips or bending forward at the waist.
• Establishing the Perturbation Vector: The patient continues to lean backward until their center of mass has shifted behind their heels, such that their full body weight is supported securely by the examiner’s rigid hands. The examiner must verify that the patient is fully supported before release.
• The Release: Without providing any preliminary auditory countdown or tactile cue, the examiner abruptly and cleanly pulls their hands away. The patient must recover their equilibrium. The examiner keeps their hands poised and hovering to catch the patient immediately if a fall occurs.

Standard Scoring Criteria (0 to 4 Scale)

The patient’s physical response is graded on an ordinal scale from 0 to 4. Only a score of 0 represents a normal, physiological response.

• Score 0 (Normal): Recovers balance independently with a single, quick backward step of normal length and width. Dynamic stability is restored immediately without secondary arm flailing or lateral deviations.
• Score 1 (Slight Impairment): Recovers balance independently, but requires two to three small, shortened backward steps to regain complete postural stability.
• Score 2 (Moderate Impairment): Recovers balance independently, but exhibits pronounced instability, requiring four or more backward steps (often presenting with retropulsion or rapid backward festination) before halting.
• Score 3 (Severe Impairment): The patient initiates one or more backward steps, but is completely unable to arrest their momentum; the patient would fall if the examiner did not intervene to catch or support them.
• Score 4 (Very Severe Impairment / Postural Collapse): The patient makes no stepping response whatsoever (falls backward like a rigid log) or is entirely incapable of standing unassisted to initiate the backward lean.

Permissions & Fee and Test Year

The original experimental design and mechanical validation of the Push and Release Test were published by Jesse V. Jacobs, Fay B. Horak, and colleagues in 2006, following preliminary operationalization in clinical balance protocols at Oregon Health & Science University around 2004. The test was subsequently integrated into the comprehensive Balance Evaluation Systems Test (BESTest) in 2009 and the Mini-BESTest in 2010.

Regarding permissions, access, and fees:

• Fee: The Push and Release Test is an open-access, non-commercial clinical assessment tool. There are no licensing fees, royalties, or purchasing costs associated with its clinical or academic utilization.
• Permissions: Dr. Fay B. Horak and Oregon Health & Science University have made the scoring protocol and administration instructions freely available to the global medical and scientific community to encourage standardized balance screening and fall prevention. Clinical practice guidelines—including the Dutch KNGF Guidelines for Parkinson’s Disease (2016)—reproduce the protocol freely for diagnostic implementation.
• Attribution: Clinicians, health systems, and academic investigators utilizing the scale in publications, electronic medical record (EMR) templates, or clinical trials are expected to provide formal bibliographic attribution to Jacobs et al. (2006) and Horak et al. (2009).

References

• Franchignoni, F., Horak, F. B., Godi, M., Nardone, A., & Giordano, A. (2010). Using psychometric techniques to improve the Balance Evaluation Systems Test: The Mini-BESTest. Journal of Rehabilitation Medicine, 42(4), 323–331. https://doi.org/10.2340/16501977-0537
• Horak, F. B. (2006). Postural orientation and equilibrium: What do we need to know about neural control of balance to prevent falls? Age and Ageing, 35(Suppl 2), ii7–ii11. https://doi.org/10.1093/ageing/afl077
• Horak, F. B., & Macpherson, J. M. (1996). Postural orientation and equilibrium. In L. B. Rowell & J. T. Shepherd (Eds.), Handbook of Physiology, Section 12: Exercise: Regulation and Integration of Multiple Systems (pp. 255–292). Oxford University Press.
• Horak, F. B., Wrisley, B. M., & Frank, J. (2009). The Balance Evaluation Systems Test (BESTest) to differentiate balance deficits. Physical Therapy, 89(5), 484–498. https://doi.org/10.2522/ptj.20080071
• Jacobs, J. V., Horak, F. B., Tran, V. K., & Nutt, J. G. (2006). An alternative clinical test of reactive postural response: The Push-and-Release Test. Journal of Neurology, 253(10), 1404–1413. https://doi.org/10.1007/s00415-006-0236-3
• Keus, S. H. J., Munneke, M., Graziano, M., Paltamaa, J., Pelosin, E., Domingos, J., Brühlmann, S., Ramaswamy, B., Prins, J., Struiksma, C., Rochester, L., & Nieuwboer, A. (2016). KNGF Clinical Practice Guideline for Physical Therapy in Parkinson’s Disease. Royal Dutch Society for Physical Therapy (KNGF).
• Mancini, M., & Horak, F. B. (2010). The relevance of clinical balance assessment tools to differentiate balance deficits. European Journal of Physical and Rehabilitation Medicine, 46(2), 239–248.
• Valkovic, P., Krafczyk, S., & Bötzel, K. (2008). Postural instability in Parkinson’s disease: Comparison of the Push and Release Test and the Pull Test. Movement Disorders, 23(8), 1198–1200.

Items of the Scale