The matched eyes-open treadmill exercise condition used the same individualized 25-minute treadmill protocol, 0% incline, five-phase structure, safety harness, front-handle contact requirement, laboratory supervision, and staff-controlled speed transitions as ECI-AE. Participants kept their eyes open. Before the bout, participants were told that a science audiobook would be played and that they could attend to or ignore it. No ECI-AE verbal reminders or meditative background music were delivered. The audiobook provided a standardized externally oriented audio context and avoided exercise-, emotion-, or meditation-related content. Before each experimental treadmill session in both conditions, participants were told they could breathe through the nose when possible.

Emotional feeling was measured using the Feeling Scale, an 11-point single-item measure ranging from -5 to +5, with higher scores indicating more positive affective valence. Mean or model-estimated mean scores were summarized by condition and treadmill phase.

Physical comfort/tiredness was measured using an 11-point single-item rating ranging from -5 to +5, with higher scores indicating greater physical comfort or lower tiredness. Mean or model-estimated mean scores were summarized by condition and treadmill phase.

Data completeness was summarized as the percentage of expected observations obtained for emotional feeling, physical comfort/tiredness, perceived attentional/interoceptive cue-following, and final comparative interview responses.

Perceived attentional and interoceptive cue-following was measured after each experimental treadmill session using a custom single-item scale titled the Perceived Attentional and Interoceptive Cue-Following Rating. Possible scores ranged from 1 to 10. Higher scores indicate greater perceived success clearing the mind and focusing on breathing during exercise, representing stronger engagement with the intended attentional and interoceptive exercise instructions. Mean scores were summarized by condition and exposure.

Condition preference was summarized as the number and percentage of participants who preferred ECI-AE, preferred the matched eyes-open control condition, or reported no preference during the final comparative interview.

Adaptation to ECI-AE was summarized as the number and percentage of participants who described the second ECI-AE exposure as better, worse, or the same compared with the first ECI-AE exposure. Open-ended explanations were used to characterize perceived familiarity, comfort, confidence, or remaining concerns.

Postexercise seated-recovery emotional feeling was measured using the Feeling Scale, an 11-point single-item measure ranging from -5 to +5, with higher scores indicating more positive affective valence. Mean scores were summarized by condition and exposure.

Postexercise seated-recovery physical comfort/tiredness was measured using an 11-point single-item rating ranging from -5 to +5, with higher scores indicating greater physical comfort or lower tiredness. Mean scores were summarized by condition and exposure.

State anxiety was measured before and after each experimental session using the State-Trait Anxiety Inventory-State Form. The scale includes 20 items rated from 1 to 4, producing a total score ranging from 20 to 80 after appropriate reverse scoring. Higher scores indicate greater state anxiety. Change scores were calculated as post-session score minus pre-session score and summarized by condition.

Exercise-induced affective state was measured before and after each experimental session using the Exercise-Induced Affect Scale questionnaire. Mean item scores ranged from 1 to 5, with higher scores indicating greater intensity of the specific affective state being rated. Change scores were calculated as post-session score minus pre-session score and summarized by condition.

Exercise attitude was measured after each experimental session using custom bipolar adjective ratings of the completed exercise condition. Items were rated from 1 to 9. Higher scores indicate a more favorable attitude toward the completed exercise condition. Mean scores were summarized by condition.

Exercise intention was measured after each experimental session using custom condition-specific items rated from 1 to 5. Higher scores indicate stronger intention to perform the relevant exercise type in the future. After matched eyes-open control sessions, items assessed intention and motivation for treadmill exercise. After ECI-AE sessions, items assessed intention and motivation for meditation-infused or eyes-closed interoceptive aerobic exercise. Mean scores were summarized by condition.

Heart-rate variability was derived from heart-rate recordings collected during seated rest and postexercise seated recovery periods. HRV indices, such as root mean square of successive differences or other protocol-specified HRV metrics, were summarized by condition and time period. Higher scores indicate greater heart-rate variability for the specific HRV metric reported.

Systolic and diastolic blood pressure were measured in millimeters of mercury before treadmill exercise, immediately after treadmill exercise, and after postexercise seated recovery at each experimental visit. Change scores were summarized by condition. Higher values indicate higher blood pressure.

Cognitive performance was measured using a Stroop task before and after the treadmill exercise and recovery procedures at each experimental visit. Outcomes included reaction time, accuracy, and/or Stroop interference indicators. For reaction time and interference scores, higher values generally indicate slower or greater interference. For accuracy, higher values indicate better performance.

Open-ended responses from the final comparative interview were coded to summarize participant-reported reasons for better, worse, or similar experiences between ECI-AE and the matched control condition. Themes included perceived benefits, burdens, safety concerns, adaptation, breathing focus, mental quiet, physical tiredness, music or audio experience, and condition preference. The number of participants endorsing each theme was summarized.