Salivary cortisol concentration after high-intensity interval exercise: Time of day and chronotype effect.
Level 2 - randomized trial
Randomized crossover trial
PubMed 28409690 · doi:10.1080/07420528.2017.1311336
What was done
Twenty-three young adults classified by the Morningness-Eveningness Questionnaire into morning-types (M-types, n = 12; age 21 ± 2 years) and evening-types (E-types, n = 11; age 21 ± 2 years) participated in a randomized crossover study. Each participant performed an acute session of high-intensity interval exercise (HIIE) at 08:00 (morning) and at 20:00 (evening). Salivary cortisol concentrations were measured before exercise (PRE), immediately after (POST), and at 15, 30, 45, and 60 minutes post-exercise.
What was found
Across all 23 participants, cortisol increased from PRE to POST in both morning (4.88 ± 1.19 to 6.60 ± 1.86 ng/mL, +26.1%, P < 0.0001, d > 0.8) and evening sessions (1.56 ± 0.48 to 2.34 ± 0.37 ng/mL, +33.4%, P = 0.034, d > 0.6). During morning HIIE, E-types had significantly higher cortisol concentrations than M-types at POST (8.44 ± 1.08 vs 5.49 ± 0.98 ng/mL, +35%, P < 0.0001, d > 0.8), +15 min (6.61 ± 0.62 vs 4.52 ± 0.42 ng/mL, +31.6%, P < 0.0001, d > 0.8), +30 min (6.21 ± 1.60 vs 4.10 ± 1.44 ng/mL, +34.0%, P < 0.0001, d = 0.7), +45 min (5.80 ± 0.72 vs 3.78 ± 0.55 ng/mL, +34.9%, P < 0.0001, d = 0.7), and +60 min (5.78 ± 1.13 vs 3.53 ± 0.45 ng/mL, +38.9%, P = 0.0008, d = 0.7). No statistically significant differences between chronotypes were detected during evening HIIE.
Why it matters
This study shows that individual chronotype moderates the acute endocrine stress response to exercise timing, suggesting that morning high-intensity interval exercise induces substantially greater physiological stress in evening-oriented individuals.
Limits
The sample size is small (n = 23) and limited to young, trained adults (weekly training volume 7-8 hours), preventing generalization to sedentary, older, or clinical populations. Sex breakdown was not specified in the abstract, and clinical or performance outcomes beyond acute salivary cortisol concentrations were not assessed.
Cited by
- contradicts Intense exercise in the late afternoon or evening can triple or quadruple baseline cortisol levels for several hours.