The market for dietary supplements to enhance sports performance has exploded in recent years. In fact, you may have tried some of these supplements yourself to improve your workouts. Many common supplements, like caffeine, have been studied in the context of immediate performance enhancement, and are used with that goal in mind. But the effect of chronic supplementation, particularly in endurance training, is not as well understood. Furthermore, it is not as clear how performance-enhancing supplements might influence the adaptive response to exercise training. Training-induced adaptations are the product of repeated stimuli from exercise sessions, as well as accumulated changes in gene expression, which gradually result in adaptive changes like greater muscle mass as well as more efficient muscle contractions. Dietary intake of certain substances can, in theory, affect training adaptations in a couple different ways. They can achieve this by simply increasing the exercise stimulus from a single training bout - basically just enabling an athlete to train longer or harder, or reducing perceived exertion. But they may also be able to affect gains in endurance by altering cellular responses to exercise-induced stress. For instance, supplements like buffering agents and antioxidants may modify the cellular signaling response to training by affecting acid-base balance, reactive oxygen species signaling, or redox status. Importantly, these changes in cell signaling may not be universally beneficial from the standpoint of adaptation. This raises a number of interesting questions. How significant is the impact of these supplements from a practical standpoint? And how do we separate acute effects on training duration and intensity from chronic effects on training adaptations? Is it possible that a supplement could simultaneously make it easier for an athlete to exercise hard, but also have effects on cellular signaling that actually have a long-term negative impact on the adaptive response to training? On this episode of humanOS Radio, we welcome Jeff Rothschild to the show. Jeff is a Registered Dietitian with a Master’s in Nutrition Science, and is a Board-Certified Specialist in Sports Dietetics (CSSD). He has worked with an impressive array of athletes - his clients include multiple Olympians, State Champions, collegiate All-Americans, and professional tennis players, as well as recreational athletes and folks who are trying to complete their first triathlon. Jeff recently wrote a fascinating review exploring the impact of dietary supplements on adaptations to endurance training. He came on the show to discuss his findings, and what they might mean for athletes and generally active people who want to maximize the time and effort that they dedicate to their training. To learn more about how various nutritional supplements might affect your training - both short and long term - check out the interview!