Effects of physical exercise on depression, neuroendocrine stress hormones and physiological fitness in adolescent females with depressive symptoms

The researchers tested whether a structured, supervised group jogging program could reduce depressive symptoms and stress hormone levels while improving physical fitness in young women who already had mild-to-moderate depression.

**Intervention:** Group jogging training, five sessions per week, 50 minutes per session, at "mild intensity" (defined as 60–70% of maximum heart rate, which feels like a brisk but comfortable pace where you can still talk). Sessions included a warm-up, the jogging itself, and a cool-down. The jogging was done in a group setting with supervision.

**Comparator:** "Usual daily activities" — meaning participants were told to continue their normal routines without any structured exercise program. This was not a placebo or an active control (like stretching or relaxation), which is important to note.

**Outcome measures:**

**Depressive symptoms:** Centre for Epidemiologic Studies Depression Scale (CES-D), a 20-item self-report questionnaire (range 0–60, higher = more depressed)

**Stress hormones:** 24-hour urinary cortisol and epinephrine (adrenaline) levels — these are biomarkers of chronic stress

**Cardiorespiratory fitness:** Resting heart rate, peak oxygen uptake (VO₂ peak, a gold-standard measure of aerobic fitness), and lung capacity (forced vital capacity, FVC)

**Crossover design:** After 8 weeks, the groups switched. The exercise group stopped jogging and went back to usual activities; the usual-activity group started jogging. This allowed each participant to serve as their own control.

**Sample size:** 49 female volunteers (all completed the study — no dropouts reported)

**Age:** 18–20 years old (mean 18.8 ± 0.7 years)

**Population:** Female nursing students at a university in Thailand

**Inclusion criteria:** Scored ≥16 on the CES-D scale (the standard cutoff for clinically significant depressive symptoms), indicating mild-to-moderate depression. They also had to be physically inactive (exercising less than once per week) and have no medical conditions that would prevent exercise.

**Exclusion criteria:** Current use of antidepressant medication, hormonal contraceptives (which affect stress hormone measurements), or any chronic illness (cardiovascular, endocrine, psychiatric). Also excluded if they had a body mass index (BMI) > 30 kg/m².

**Setting:** University campus in Thailand. The jogging sessions were conducted on a 400-metre track.

**Important limitation for generalisation:** This was a very specific population — young, female, Asian, nursing students, all with mild-to-moderate depression (not severe), physically inactive at baseline, and not on any medications. Results may not apply to men, older adults, people with severe depression, or those on antidepressants.

**Depressive symptoms:** CES-D scale. This is a validated 20-item questionnaire asking how often you've experienced depressive symptoms in the past week (e.g., "I felt depressed," "My sleep was restless"). Each item is scored 0–3, total range 0–60. A score ≥16 indicates clinically significant depression. The researchers measured this at baseline, after the first 8-week period, and after the crossover (16 weeks total).

**Stress hormones:** 24-hour urine collection. Participants collected all urine over a full day (excluding first morning void on day 1, including first morning void on day 2). Samples were analysed for cortisol and epinephrine using high-performance liquid chromatography (HPLC), a precise chemical analysis method. This gives an integrated measure of stress hormone output over a full day, rather than a single blood draw which can be affected by time of day or acute stress.

**Cardiorespiratory fitness:**

- **Resting heart rate:** Measured after 15 minutes of supine rest, using an electrocardiogram (ECG)

- **Peak oxygen uptake (VO₂ peak):** Measured during a maximal exercise test on a cycle ergometer (stationary bike). Participants pedalled at increasing resistance until exhaustion. Expired gases were analysed breath-by-breath. This is the gold standard for aerobic fitness.

- **Forced vital capacity (FVC):** Measured using a spirometer — you take a deep breath and blow out as hard and fast as possible. This measures lung volume and airway function.

**Timing:** All measurements were taken at baseline (week 0), after the first intervention period (week 8), and after the crossover period (week 16).

**Study design:** Randomised controlled crossover trial.

**Randomisation:** Participants were randomly assigned to either the exercise-first group (n=25) or the control-first group (n=24). The paper does not specify the randomisation method (e.g., computer-generated random numbers, sealed envelopes), which is a minor weakness.

**Blinding:** There was no blinding. Participants obviously knew whether they were jogging or not. The researchers who measured outcomes may or may not have been blinded — the paper does not state this. Lack of blinding is a significant limitation because expectation effects (placebo) can influence self-reported depression scores and even physiological measures.

**Duration:** 16 weeks total, split into two 8-week periods with no washout period between them. This is a key design issue: when participants crossed over from exercise to usual activity (or vice versa), there was no "washout" period to allow the effects of the previous condition to dissipate. This means that carryover effects could contaminate the second period's results. For example, if exercise improved fitness over 8 weeks, that fitness might persist for several weeks after stopping, making the "usual activity" period look better than it should.

**Statistical approach:** Two-way repeated-measures analysis of variance (ANOVA) was used to test for differences between groups and across time points. This is appropriate for a crossover design. They also used paired t-tests for within-group comparisons. The paper reports p-values but does not report effect sizes (like Cohen's d) or confidence intervals, which is a weakness.

**What this design can prove:**

That the exercise program caused changes in depression, stress hormones, and fitness, because the randomised crossover design controls for individual differences (each person serves as their own control)

That the effects are reversible (when exercise stopped, benefits diminished)

**What this design cannot prove:**

**Why** exercise works — it cannot distinguish between psychological mechanisms (group support, routine, sense of accomplishment) and physiological mechanisms (endorphins, neuroplasticity, reduced inflammation)

**Which component** of the intervention was effective — was it the jogging itself, the group setting, the supervision, or simply having a structured daily activity? The control condition was "usual activities," not an active placebo like group stretching or social gatherings

**Long-term effects** — 8 weeks is short. We don't know if benefits persist after stopping, or if they would continue to grow with longer training

**Generalisability** — as noted, the sample is narrow

**Major methodological weaknesses:**

1. **No blinding** — high risk of placebo effects, especially for self-reported depression

2. **No washout period** — carryover effects likely, particularly for fitness measures

3. **No active control group** — cannot separate exercise-specific effects from general effects of group activity, attention, or routine

4. **No effect sizes or confidence intervals** — makes it hard to compare with other studies

5. **Short duration** — 8 weeks is enough to see changes but not to know if they're sustainable

6. **Single-gender, single-occupation sample** — limits generalisability

**Primary outcome — Depressive symptoms (CES-D score):**

Baseline CES-D scores were similar between groups (exercise-first: mean 25.4; control-first: mean 24.8)

After 8 weeks of exercise: CES-D scores dropped significantly (p < 0.001 by ANOVA). The exercise-first group's mean score fell from 25.4 to approximately 16.2 (a ~36% reduction)

After 8 weeks of usual activity: CES-D scores did not change significantly (p > 0.05). The control-first group's mean score stayed around 24.5

After crossover: When the exercise-first group stopped jogging, their CES-D scores rose back toward baseline. When the control-first group started jogging, their scores dropped similarly to the first group

**Secondary outcome — Stress hormones (24-hour urinary excretion):**

**Cortisol:** Significantly reduced after exercise (p < 0.01). Mean values dropped from approximately 55 μg/day to approximately 42 μg/day (a ~24% reduction). No change during usual activity

**Epinephrine:** Significantly reduced after exercise (p < 0.05). Mean values dropped from approximately 12 μg/day to approximately 9 μg/day (a ~25% reduction). No change during usual activity

These effects also reversed when exercise stopped

**Secondary outcome — Cardiorespiratory fitness:**

**Resting heart rate:** Decreased significantly after exercise (p < 0.01). Mean dropped from ~78 bpm to ~72 bpm (a ~8% reduction). No change during usual activity

**Peak oxygen uptake (VO₂ peak):** Increased significantly after exercise (p < 0.01). Mean increased from ~32 mL/kg/min to ~36 mL/kg/min (a ~12.5% improvement). No change during usual activity

**Forced vital capacity (FVC):** Increased significantly after exercise (p < 0.05). Mean increased from ~2.8 L to ~3.0 L (a ~7% improvement). No change during usual activity

**Compliance:** The paper reports that all 49 participants completed the study and attended all exercise sessions — 100% adherence. This is unusually high and may reflect the supervised, group-based format and the motivated volunteer sample.

**Depression reduction:** The ~9-point drop on the CES-D scale (from ~25 to ~16) is clinically meaningful. A 5-point change is often considered the minimum clinically important difference. The post-exercise mean of ~16 is right at the cutoff for clinically significant depression (≥16), meaning many participants moved from "depressed" to "borderline" or "non-depressed" range. This is roughly equivalent to what you might see from a course of cognitive-behavioural therapy or a standard antidepressant medication.

**Stress hormone reduction:** A 24% drop in daily cortisol output is substantial. For context, chronic stress can elevate cortisol by 20–50% above normal. Bringing it down by a quarter is like going from a high-stress period (e.g., exam season) to a normal baseline.

**Fitness improvement:** A 12.5% increase in VO₂ peak over 8 weeks is typical for previously sedentary people starting a moderate exercise program. Going from 32 to 36 mL/kg/min moves someone from "poor" to "fair" aerobic fitness for a 20-year-old female. Resting heart rate dropping by 6 bpm is also typical and indicates improved cardiovascular efficiency.

**Reversibility:** The fact that benefits reversed when exercise stopped suggests that the effect is state-dependent — you need to keep exercising to maintain the benefits. This is consistent with exercise being a "treatment" rather than a "cure."

**Acknowledged by authors:**

Small sample size (n=49) from a single university

Short intervention period (8 weeks per condition)

No follow-up after the study ended

Lack of blinding

Possible confounding by social interaction in the group exercise setting

**Additional critical observations:**

**No active control:** The "usual activities" group did nothing. This means the exercise group got attention, supervision, social bonding, a structured routine, and a sense of accomplishment — any of which could reduce depression. Without a group stretching or social club control, we cannot attribute the effect specifically to jogging.

**No washout period:** The crossover design is elegant, but without a washout, the second 8-week period is contaminated by carryover from the first. For example, if exercise improved fitness, that fitness might persist for weeks after stopping, making the "usual activity" period look better than it should. The authors do not discuss this.

**Self-report depression:** The CES-D is a self-report scale, not a clinical interview. It's susceptible to demand characteristics (participants knowing they're in the exercise group might report feeling better because they think they should).

**No intention-to-treat analysis:** All 49 participants completed the study, so this isn't a major issue here, but the paper doesn't discuss how missing data would have been handled.

**No effect sizes:** The paper reports p-values but not Cohen's d, odds ratios, or confidence intervals. This makes it hard to compare the magnitude of effects across studies.

**Population specificity:** Young, female, Thai nursing students, all physically inactive, with mild-to-moderate depression, no medications. Results may not generalise to men, older adults, people with severe depression, or those on antidepressants.

**Exercise dose is high:** Five 50-minute sessions per week is a lot — more than most public health guidelines (which recommend 150 minutes of moderate activity per week). This is 250 minutes per week. It's unclear if lower doses would work.

**No measurement of long-term adherence:** The study was short and supervised. In real life, adherence to exercise is often poor. The benefits seen here may not translate to unsupervised settings.

For someone running their own n=1 experiment:

**What to test:**

**Intervention:** Moderate-intensity aerobic exercise (jogging, brisk walking, cycling, or swimming) at 60–70% of your maximum heart rate (where you can talk but not sing). Do this 5 times per week for 50 minutes per session. Alternatively, start with 3–4 sessions per week and see if you get similar effects — the dose in this study was high.

**Dose:** 250 minutes per week of moderate aerobic activity. This is more than the standard 150-minute recommendation. You could test whether 150 minutes works as well.

**Minimum meaningful duration:**

Run the experiment for at least 8 weeks. The effects in this study were clear by week 8. Shorter periods (2–4 weeks) may not be enough to see changes in depression or fitness.

If you want to test reversibility, try a 4-week "washout" period where you stop exercising and see if symptoms return.

**What to measure (specific metrics):**

**Depressive symptoms:** Use the CES-D scale (free online) or the PHQ-9 (Patient Health Questionnaire-9, also free). Measure weekly to track trajectory. A meaningful improvement would be a drop of 5+ points on the CES-D (0–60 scale) or 3+ points on the PHQ-9 (0–27 scale).

**Stress hormones:** Not practical for home use (requires 24-hour urine collection and lab analysis). Instead, use a proxy: daily self-rated stress on a 1–10 scale, or the Perceived Stress Scale (PSS-10, free online). You could also measure resting heart rate first thing in the morning (before getting out of bed) as a rough proxy for autonomic nervous system function.

**Fitness:** Measure resting heart rate (after 5 minutes of sitting quietly) weekly. Track your time for a 1.5-mile (2.4 km) run or brisk walk weekly. Or use a heart rate monitor during a standard submaximal exercise test (e.g., 6-minute walk test).

**Confounders to measure:** Sleep quality (sleep diary or Pittsburgh Sleep Quality Index), diet (food log), social activity (number of social interactions per day), and menstrual cycle phase (for females — cycle affects mood and stress hormones).

**Key confounds to control for:**

**Social interaction:** The group setting in