Yeah, some peoples' level of fitness is just off the charts. I've started supplementing with 3mg of creatine daily to help with endurance. From what I've read it really helps. I need to work on the endurance as well. I've done fewer long bike rides but do climb up/down seven flights of stairs for 20min three times a day along with kettlebell exercises and burpees.

Good idea about registering for a 5k. Those will be few and far between in MN until spring but would be a good motivator for me.