Aerobic exercise impacts bodily processes implicated in the pathophysiology of major depression. Consistent with these effects, aerobic exercise in general, and running in particular, has been repeatedly shown to have both immediate mood elevating and longer-term antidepressant effects. To the investigators' knowledge, all studies of running as a therapeutic intervention for mood have had subjects run in standard running shoes, despite increasing evidence that running barefoot or in shoes with minimal effect on foot strike (i.e. "minimally shod") leads to marked changes in how people run in ways that might have physiological effects of relevance to health. Thus, nothing is currently known about differences in effects on depression-relevant physiological or emotional functioning between running either barefoot or minimally-shod vs. running in standard running shoes (hereafter called "shoed). The current pilot study is designed to begin addressing these issues by examining effects of minimally shod vs. shoed running on non-invasive measures of autonomic nervous system (ANS) functioning and mood state.

Aerobic exercise impacts bodily processes implicated in the pathophysiology of major depression. Consistent with these effects, aerobic exercise in general, and running in particular, has been repeatedly shown to have both immediate mood elevating and longer-term antidepressant effects. To the investigators' knowledge, all studies of running as a therapeutic intervention for mood have had subjects run in standard running shoes, despite increasing evidence that running barefoot or in shoes with minimal effect on foot strike (i.e. "minimally shod") leads to marked changes in how people run in ways that might have physiological effects of relevance to health. Thus, nothing is currently known about differences in effects on depression-relevant physiological or emotional functioning between running either barefoot or minimally-shod vs. running in standard running shoes (hereafter called "shoed). The current pilot study is designed to begin addressing these issues by examining effects of minimally shod vs. shoed running on non-invasive measures of autonomic nervous system (ANS) functioning and mood state. The investigators have selected the ANS as the physiological focus of the current study for several reasons including: 1) running acutely alters ANS activity; 2) running (and aerobic fitness in general) is associated with increased parasympathetic and reduced sympathetic activity at rest; 3) increased parasympathetic tone in the body has been repeatedly associated with emotional well-being and stress resilience, whereas reduced parasympathetic tone has been reliably associated with major depression; 4) given increasing evidence that ancestral humans may have run exceptionally long distances to hunt prey to exhaustion, it is likely that such running was conducted under fairly significant parasympathetic tone to reduce energy expenditure; 5) ancestral humans ran barefoot or minimally shod suggesting that the type of foot strike pattern encouraged by these styles of running may have enhanced parasympathetic tone compared to running with heel strike such as occurs when running shoed; and 6) therefore minimally shod running might differentially impact parasympathetic tone in ways that would make it more effective as a treatment for depression than running shoed.

Inclusion Criteria:

• Male/Female subjects between the ages of 18 and 45 at study entry (per a self report- females must be in the follicular phase of their menstrual cycle, within ~14 days of the end of their last period)
• Fully ambulatory and in good medical health (see exclusion criteria below for specifics)
• Ability to read/understand English
• Consistent practice of running at least three times a week for a total of at least 30 minutes at a time.

Exclusion Criteria:

• Potential subjects will be excluded for a diagnosis of any serious ongoing medical or psychiatric condition that might unduly influence results or increase risk of study participation, including but not limited to:

  • Malignancy
  • Auto-immune disorder
  • Cardiovascular disease (except treated hypertension)
  • Neurologic disorder
  • Endocrinopathy (other than treated hypothyroidism)
  • Chronic infection (i.e. human immunodeficiency virus, hepatitis B or C)
  • Any renal, hepatic or hematological abnormality (other than history of mild anemia)
  • Current major depression or major depression requiring hospitalization or resulting in suicide attempt in past year.

• Subjects will also be excluded for use of medications that might impact ANS functioning, including but not limited to beta-blockers, calcium channel blockers and alpha-blockers, and any medication with anticholinergic properties (e.g., many antihistamines).

Avid barefoot runners and regular 'shoed' runners will be selected from local running groups and clubs.