4 Weeks of HIIT Cuts Depression and Anxiety Scores in Normal-Weight Obese Women

Normal weight obesity (NWO) — defined as a normal BMI paired with excess body fat — is increasingly common among young women and carries cardiometabolic and psychological risks that standard weight screening misses. Female college students with NWO often experience elevated rates of depression, anxiety, and poor sleep, yet receive little targeted intervention because their weight appears healthy on standard metrics. This study sought to determine whether high-intensity interval training (HIIT) could address those hidden psychological and sleep burdens.

Researchers at Shanghai University of Medicine and Health Sciences conducted a randomized controlled trial enrolling 35 female students who met NWO criteria (BMI 20–23 kg/m²; body fat >30%). The HIIT group (n=17) completed five supervised sessions per week for four weeks, each consisting of a 10-minute warm-up, nine minutes of high-intensity circuit exercises (opening-closing jumps, squats, push-ups, burpees, and more) performed at >90% VO2max, and a 15-minute cool-down. The control group (n=18) received standard health education only. Validated self-report instruments — PHQ-9 (depression), GAD-7 (anxiety), and PSQI (sleep quality) — were administered before and after the intervention.

After four weeks, HIIT participants showed statistically significant improvements across all three measures. PHQ-9 depression scores fell from 5.8±4.2 to 3.2±2.7 (p<0.01), GAD-7 anxiety scores dropped from 5.1±5.3 to 2.8±2.9 (p<0.05), and PSQI sleep quality scores improved from 5.1±3.4 to 3.5±2.5 (p<0.01). Control group participants showed no significant changes. Importantly, post-intervention analysis in the HIIT group revealed strong correlations between improved sleep quality and reduced depression (R=0.813, p<0.001) and anxiety (R=0.739, p<0.001), suggesting these outcomes are mechanistically linked rather than independent effects of exercise.

The findings are clinically meaningful for several reasons. First, they demonstrate that even a brief, four-week HIIT protocol can produce measurable psychological benefits in a population not typically flagged for intervention. Second, the tight correlation between sleep and mental health outcomes post-HIIT implies that exercise may improve mood partly by regularizing sleep architecture — a pathway warranting further mechanistic investigation involving cortisol, BDNF, or autonomic nervous system changes. Third, the time-efficient format (nine minutes of intense work per session) makes the approach highly accessible for time-constrained college students.

Caveats are notable. The sample size is small (N=35), limiting statistical power and generalizability. The trial was retrospectively registered and relied entirely on self-report measures without objective sleep monitoring (e.g., polysomnography or actigraphy). The absence of dietary controls means nutritional changes could have contributed to outcomes. The exclusively female, single-institution sample restricts generalizability, and the four-week window precludes conclusions about long-term durability of benefits.