This week, our strength work is all about acclimation to the increase in intensity (from the introduction of weights) and volume (as days 2 & 3 move to 8 exercises) that came in week 5. We introduce the fartlek this week with 1-4 miles of 1 min hard/3 min easy. Our main topic for the week is an introduction to the concept of metabolic flexibility. Base building is a key opportunity for experimentation and is a perfect time to work on "fat-adaptation."