Experiencing Extreme Height for The First Time: The Influence of Height, Self-Judgment of Fear and a Moving Structural Beam on the Heart Rate and Postural Sway During the Quiet Stance

Falling from elevated surfaces is the main cause of death and injury at construction sites. Based on the Bureau of Labor Statistics (BLS) reports, an average of nearly three workers per day suffer fatal injuries from falling. Studies show that postural instability is the foremost cause of this disproportional falling rate. To study what affects the postural stability of construction workers, we conducted a series of experiments in the virtual reality (VR). Twelve healthy adults, all students at the University of Nebraska were recruited for this study. During each trial, participants heart rates and postural sways were measured as the dependent factors. The independent factors included a moving structural beam (MB) coming directly at the participants, the presence of VR, height, the participants self-judgment of fear, and their level of acrophobia. The former was designed in an attempt to simulate some part of the steel erection procedure, which is one of the key tasks of ironworkers. The results of this study indicate that height increase the postural sway. Self-judged fear significantly was found to decrease postural sway, more specifically the normalized total excursion of the center of pressure (TE), both in the presence and absence of height. Also, participants heart rates significantly increase once they are confronted by a moving beam in the virtual environment (VE), even though they are informed that the beam will not hit them. The findings of this study can be useful for training novice ironworkers that will be subjected to height and steel erection for the first time.

💡 Research Summary

The paper investigates how extreme height, a moving structural beam, and individual fear levels affect physiological and postural responses in a construction‑safety context, using virtual reality (VR) as a testbed. Falling from height is the leading cause of death on construction sites, accounting for roughly three fatalities per day in the United States, and postural instability has been identified as a primary contributor. To explore the underlying mechanisms, the authors recruited twelve healthy university students (six male, six female) and exposed them to a series of controlled VR scenarios that systematically varied four independent variables: (1) height (ground level vs. 17‑meter virtual elevation), (2) presence of VR (real‑world vs. immersive headset), (3) moving beam (absent vs. a structural beam that slowly approached the participant), and (4) self‑reported fear, measured with the James Geer fear questionnaire and the Acrophobia Questionnaire (AQ).

Each trial required participants to stand quietly on an AMTI force plate for 20–30 seconds while looking at their virtual feet. The force plate recorded the center of pressure (COP), from which four sway metrics were derived: total excursion (TE), root‑mean‑square amplitude (RMS), maximum absolute amplitude (Max), and peak‑to‑peak amplitude (PP). Heart rate was captured continuously with a Fitbit Versa, synchronized via a custom app. Data were exported to MATLAB, where normality was confirmed using the Anderson‑Darling test and paired two‑tailed t‑tests were applied to compare conditions.

Key findings are as follows:

1. Height Increases Sway – When participants were placed at the virtual 17‑meter height, TE increased significantly (p = 0.004). This aligns with prior literature indicating that visual elevation disrupts the integration of visual, vestibular, and somatosensory cues, leading to greater postural instability.

2. Self‑Judged Fear Reduces Sway – Participants who reported higher fear scores exhibited lower TE (p = 0.00005). The authors interpret this as a “freezing” response: heightened anxiety may cause increased muscular co‑contraction and conscious effort to maintain balance, thereby reducing sway amplitude.

3. Moving Beam Elevates Heart Rate – The approach of a moving structural beam, even though participants were warned it would stop short of contact, produced a roughly 10 % rise in heart rate (p = 0.00005). This demonstrates that visual threat alone can trigger sympathetic activation, supporting the use of VR to simulate hazardous scenarios without physical danger.

4. VR Itself Affects Posture – Across all conditions, simply wearing the VR headset increased TE and RMS compared with the real‑world baseline, suggesting that the visual fidelity, latency, or limited field of view of current head‑mounted displays can introduce additional postural challenges.

5. Sex and Acrophobia Differences – Female participants showed higher average heart rates than males (p < 0.01). Participants with high AQ scores displayed elevated heart rates and RMS values, but not a consistent increase in TE, indicating that fear may amplify autonomic arousal and overall sway variability without necessarily changing the total excursion.

The study acknowledges several limitations: the small, homogeneous sample (all university students) limits generalizability to seasoned construction workers; the experimental protocol constrained natural movement, which may not reflect real‑world job tasks; and the Fitbit’s heart‑rate accuracy is lower than clinical-grade devices. Future work is suggested to involve actual ironworkers, incorporate load‑bearing equipment, test a broader range of heights, and employ more precise physiological monitoring (e.g., heart‑rate variability, skin conductance).

In conclusion, the research provides empirical evidence that VR‑based simulations of extreme height and moving structural elements can simultaneously provoke physiological stress (heart‑rate elevation) and modulate postural control (sway metrics). The paradoxical finding that self‑reported fear reduces sway while the moving beam raises heart rate highlights the complex interplay between cognitive anxiety and motor output. These insights support the integration of immersive VR scenarios into safety training programs for novice ironworkers, offering a low‑risk yet realistic exposure to the visual‑perceptual challenges they will encounter on actual steel‑erection sites.