Many in the fitness community think that performing steady state cardio will reduce resting metabolic rate. However, this study found no difference in resting metabolism following a 12-week endurance training protocol. The take home message? Cardio won’t kill your metabolism! Losing weight and dieting can reduce your metabolism, however, so make sure to follow our other tips to get the most out your training and nutrition.
Source: Broeder, C. E., Burrhus, K. A., Svanevik, L. S., & Wilmore, J. H. (1992). The effects of either high-intensity resistance or endurance training on resting metabolic rate. The American Journal of Clinical Nutrition, 55(4), 802-810.