Well, maybe not in this case. But it can make your sides hurt. I’m talking about interval training speedwork. This week I decided that since I now have a decent base at about 20 miles per week, I should work on my speed. So three days this week I did intervals as part of my morning run. After a warm up I did 2 minute fast repeats with 1 minute jog in between. It was definitely a harder workout than my normal easy morning run but it felt good. Until late in the day when my sides hurt. I wasn’t sure why they hurt but I remembered my son saying his sides hurt early in the track season after he did speedwork. Apparently speedwork uses some different core muscles than easier running does? Maybe it’s the arm pumping or something else but it makes a difference. Wasn’t killing me but it was certainly noticeable. But hopefully it will pay off in the first 10k of the year, June 5.