Paul B. Laursen, PhD, is an endurance coach, a sport scientist, and an adjunct professor for Auckland University of Technology in New Zealand. He earned his doctorate in exercise physiology from the University of Queensland, was formerly the physiology manager for High Performance Sport New Zealand, and now resides in British Columbia, Canada. Laursen is well known throughout the international sport and strength and conditioning communities for his knowledge and research of high-intensity interval training. His other interests include health, longevity, heart rate variability, thermoregulation, and artificial intelligence application to training. He has published more than 125 peer-reviewed manuscripts in exercise and sport science journals; his publications with coauthor Martin Buchheit are among the most cited. He is an active endurance athlete, having completed 18 Ironman triathlons. Martin Buchheit, PhD, is a sport scientist, a strength and conditioning coach, and the head of performance for the Paris Saint-Germain Football (Soccer) Club. He is also an adjunct associate professor of exercise science for Victoria University in Australia. He previously worked as an exercise physiologist for ASPIRE Academy in Qatar, and he has served as a lecturer, consultant, and strength and conditioning coach for various organizations. Buchheit received his doctorate in physiology from the University of Strasbourg in France. He has published more than 160 peer-reviewed manuscripts, with much of his research focusing on high-intensity interval training. The training tools he has developed include the 30-15 intermittent fitness test, used to program high-intensity training, and the 5-5 running test, used to monitor training status using heart rate variability. Buchheit also has experience with match analysis and talent development and identification. He is an endurance athlete who has a personal best time of 2:54 in the marathon.