During this single session, participants will walk on a treadmill at a moderate-vigorous intensity (65-75% age-predicted HRmax) for 20 minutes. While walking on the treadmill, participants will also watch a 20-minute video clip to match the control condition. Exercise intensity will be continuously monitored using a Polar OH1 heart rate monitor, which will be strapped to the participant's chest prior to starting the exercise session. Age-predicted HRmax will be calculated for each participant using the following formula: (HRmax = 220 - Age). Subjective units of distress related to their perceived exercise intensity will be measured in 3-minute intervals. Following the exercise session, participants will rest until their heart rate returns to within 10% of their resting heart rate (approximately 5 minutes) before starting the post-assessments.

Participants will be guided by a research assistant through a single silent sitting session, which will serve as a time-matched control. During the sitting session, participants will watch a 20-minute video clip while sitting silently. Similar to the aerobic exercise group, participants' heart rate will be continuously monitored via a Polar OH1 heart rate monitor. Following the sitting session, participants will rest for 5 minutes to match the exercise group before starting the post-assessments.

The aerobic exercise intervention is described in the Aerobic Exercise Arm description.

Participants will be presented with a series of negative high arousing and neutral low-arousing images from the International Affective Picture System. Prior to being presented with each image, participants will be cued to either passively view the upcoming image or to use reappraisal to "reinterpret aspects of the upcoming image in order to adopt a more neutral or positive perspective." During the emotion regulation task, "online" emotional arousal during reappraisal and passive view trials will be measured via the late positive potential (LPP).

The LPP is a positive deflecting waveform that has been shown to be activated when viewing highly arousing negative images. In this study, emotion regulation will be measured as the difference in LPP amplitude between reappraise-negative and view-negative trials. Greater view-negative minus reappraise-negative LPP difference scores will reflect greater emotion regulation.

Participants will be presented with a series of negative high arousing and neutral low-arousing images from the International Affective Picture System. Prior to being presented with each image, participants will be cued to either passively view the upcoming image or to use reappraisal to "reinterpret aspects of the upcoming image in order to adopt a more neutral or positive perspective."

At the end of the emotion regulation picture viewing task, participants will be asked to rate their emotional arousal during reappraisal and passive view using a 1 (Very Weak) to 7 (Very Strong) Likert scale. Self-reported emotional arousal will be measured as the difference in emotional arousal scores between reappraise-negative and view-negative trials. Greater view-negative minus reappraise-negative trials will reflect greater self-reported emotion regulation.

The letter flanker task consists of a series of five letters presented in rapid succession. Participants will be instructed to identify the centrally presented letter amid congruent ('UUUUU') and incongruent ('UUVUU') flanking letters via a button click. The letter flanker task consists of 480 trials grouped into six blocks of 80 trials. Each block consists of a different pair of perceptually similar letters (i.e., "MMNMM", "PPRPP").

Neurophysiological indices of cognitive control during the flanker task will be measured using error-related negativity (ERN), error positivity (Pe), and P300. The ERN, Pe, and P300 are common metrics of cognitive control. The ERN, Pe, and P300 will be measured as the difference in amplitude between error and correct trials. Greater error minus correct difference scores will reflect greater cognitive control.