Day 1 Assessment, Day 2 Fear Learning, Day 3 Fear Extinction (followed by moderate intensity exercise), Day 4 Recall of Fear Extinction

Other: Day 1 Assessments Other: Day 2 Fear Learning Other: Day 3 Fear Extinction Behavioral: Moderate Intensity Exercise Other: Day 4 Recall of Fear Extinction

Day 1 Assessment, Day 2 Fear Learning, Day 3 Fear Extinction (followed by low intensity exercise), Day 4 Recall of Fear Extinction

Other: Day 1 Assessments Other: Day 2 Fear Learning Other: Day 3 Fear Extinction Behavioral: Moderate Intensity Exercise Other: Day 4 Recall of Fear Extinction

Behavioral: Moderate Intensity Exercise The moderate-intensity aerobic exercise session will consist of walking or running at a moderate intensity (i.e., between 70-75% MHR) for 30 minutes.

Aim 1 fear extinction analyses consists of a 2 (group: low-intensity exercise vs moderate-intensity exercise) x 2 (cue: conditioned fear and safety) x 2 (task phase context: learning context vs extinction context) mixed design focused on Day 4 fear responding (skin conductance responses). SCR data will be acquired on a BIOPAC MP150 Data Acquisition System (BIOPAC Systems, Inc.) with electrodes placed on participant's left hand. Participants will be instructed to select an intensity of a 7/10 on the subjective pain scale, which should be "uncomfortable, but not painful." Average intensity of participant skin conductance will be reported.

Aim 1 fear extinction analyses consists of a 2 (group: low-intensity exercise vs moderate-intensity exercise) x 2 (cue: conditioned fear and safety) x 2 (task phase context: learning context vs extinction context) mixed design focused on Day 4 fear responding (expectancy ratings). Expectancy will be assessed throughout each phase of the experiment to estimate the degree to which the subject believes she will receive a shock following presentation of certain pictures presented during the experiment.

Aim 2 group differences in BDNF consists of a 2 (group: moderate-intensity vs low-intensity) x 2 (cue: conditioned fear and safety) x 2 (task phase context: learning context vs extinction context) x 2 (timepoint: pre condition vs post condition,) mixed design. The hypothesis is BDNF increases following exercise will separately mediate the relationship between aerobic exercise and enhanced fear extinction recall.

Aim 2 group differences in eCB consists of a 2 (group: moderate-intensity vs low-intensity) x 2 (cue: conditioned fear and safety) x 2 (task phase context: learning context vs extinction context) x 2 (timepoint: pre condition vs post condition,) mixed design. The hypothesis is eCBs increases following exercise will separately mediate the relationship between aerobic exercise and enhanced fear extinction recall.

The POMS survey is a 65-item survey scored on a 5 point Likert Scale (0-4) where 0 s 'not at all' and 4 is 'extremely' for the tension, depression, fatigue, confusion, and anger subscales, and reversed for the vigor and esteem-related affect subscales. The range of total possible scores is XX-XX with higher numbers indicating more extreme or negative moods.