Is it worthwhile to integrate interval sprinting into F1/H1 training? If so, how many times per week would you recommend and on which day(s)? Based on the studies below I am thinking of adding 15 minutes of sprint intervals at 80% of maximal speed in a decreasing fashion (400m, 300m, 200m, 100m) at the end of H1 days preprandial. Recent studies show sprint interval training leads to a significant increase in lactate and the anabolic factors growth hormone, insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3), and testosterone levels http://www.ncbi.nlm.nih.gov/pubmed/21785293 http://www.ncbi.nlm.nih.gov/pubmed/19057403