The American College of Sports Medicine recommends that adults achieve at least 30-50 minutes of moderate-intensity cardiorespiratory exercise 5 days per week or 20-60 minutes of vigorous-intensity exercise 3 days per week. While these minimum guidelines are clearly described, there are currently no maximum guidelines, particularly with respect to high-intensity time and frequency, for the prevention of overtraining.
PURPOSE: To evaluate the correlation between salivary hormones, time in varying heart rate zones, and psychosocial stress variables in order to prevent overtraining and improve fitness. Our hypothesis is that chronic exercise durations greater than 1 hour per week in the high intensity (greater than 90% maximum heart rate) zone will lead to decreased variation in the production of stress hormones, decreased ability to reach heart rate max and increased self-reporting of tension as well as fatigue.
METHODS: Twelve healthy adults between 25-50 years who regularly exercised more than 8 hours per week recorded their heart rate during every training session and answered daily surveys regarding their mood for 3 weeks. Next, they completed an experimental day composed of 2, 30-minute high-intensity interval sessions separated by 4-hours of non-active recovery. We collected saliva samples prior to each exercise session, immediately following, and 30-minutes post to assess changes in cortisol and testosterone concentrations. Heart rate was monitored throughout the experimental day to determine exercise and recovery values.
RESULTS: There was a correlation between weekly time training at an intensity greater than 90% maximum heart rate and the variables associated with overtraining. Cortisol and testosterone saliva concentration fluctuated less in the participants who exercised in this extreme zone for more than 50 minutes per week. To add, these participants were not able to reach the same intensity during the second-high intensity session on the experimental day and reported greater tension as well as fatigue on the surveys in the weeks prior to testing.
CONCLUSIONS: Our data demonstrate that 50 minutes of high-intensity training per week is a suggested maximum, cumulative time in order to prevent symptoms related to overtraining.