Changes in cortisol awakening response during 10 days of high-intensity cycling exercise

Previous studies suggest that the cortisol awakening response (CAR) shows a biphasic pattern—either an increase or a blunting—in response to exercise involving overload, potentially reflecting physiological adaptation. However, its response to continuous high-intensity exercise under controlled experimental conditions has not been sufficiently investigated.

Dr. Yui Ogasawara, Specially Appointed Assistant Professor at Osaka Metropolitan University, and co-researchers examined daily CAR changes during a 10-day high-intensity cycling protocol in two healthy male participants. The protocol involved exercise for 20 minutes per day at 80% of maximal oxygen uptake (VO₂max). The CAR increased during Days 1–4 and returned to baseline levels from Day 5 onward, showing similar trends in acute physiological responses. VO₂max and/or maximum workload improved following the intervention.

These findings support the methodological feasibility of longitudinal CAR monitoring during short-term high-intensity exercise under controlled experimental conditions and suggest that CAR may be a promising non-invasive biomarker for assessing short-term physiological adaptation.

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