I agree with those who are doing the 6 month rotation and extending Meso 1, which I believe is for endurance. That's what you want to focus on for marathon and/or half-marathon training. Also, you'd be wise to work it so the leg workout portion of STS is not do right before or right after your long run. Remember, you need 48 hours to recover before you work the same body part. If your long run is on a Saturday, then make sure you do the leg portion no later than Thursday. Wednesday would even be better. Keep in mind that I don't have STS and have not seen the leg portion.