Different types of high-intensity interval training (HIIT) sessions are used by athletes in order to improve their physical performance, but innovative approaches to training are lacking. Therefore, in Part A of this study the physiological response to a standard HIIT and a new decremental exercise training (DECT) will be compared in runners and cyclists. Next, in Part B the training effects of a 4-week block of the HIIT and DECT will be compared.

Inclusion Criteria:

• Age: 18-40 years
• Healthy, i.e. normal physical and mental status (not taking any medication on a regular basis for more than a month, except contraceptive medication)
• Normal Body-Mass-Index (BMI): 18.5-24.9 kg·m-2
• Well-trained athletes: V̇O2max > 55.1 ml·min-1·kg-1 for men and > 50.1 ml·min-1·kg-1 for women
• Normal lung function
• Non-smoking
• Willing to adhere to the general study rules

Exclusion Criteria:

• Women who are pregnant or breast feeding
• Intention to become pregnant during the course of the study
• Known or suspected non-compliance, drug or alcohol abuse
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant
• Previous enrolment into the same part (A or B) of the current study
• Enrolment of the investigator, his/her family members, employees and other dependent persons
• Acute or chronic illness
• Intake of medications affecting performance or the respiratory, cardiovascular or neuromuscular system
• Insufficient training history (<3 yrs of participation in competitive cycling/running) or training volume (<40 km running/week or 150 km cycling/week) in the previous 6 months
• Recent (<3 months) history of orthopaedic injury or participation in structured high-intensity training blocks