Use the force . . . . but not to break things

The "C" on the head unit of the PowerTap is cadence.

Short ride for today's training had me doing a 'force' workout - simulating hill work. Low cadence and semi threshold'ish riding for 3 minutes, followed by three minute rest at endurance wattage, and repeat four times (see power plateaus below in graph).

After the first forty minutes or so I did a few form sprints (the spikes on the graph) and some isolated leg intervals to finish off.

- soaked handkerchief, el cheapo wheel stand and my cheat sheet (all my power zones on one side and specific workouts on the other kept for handy reference during rides)

After one of the form sprints (10 seconds all out while maintaining good form and pedal stroke), I looked down between my legs and saw this. Earlier in the ride I heard a noise, sounded like a squeak, but paid no heed to it.

Could I be that powerful that I can break the seat tube?! It's not the first thing I've broken in the past week. I'm guessing it has more to do with my pre-season heftiness . . . . yes, I am fat.