I will concur with Erica, your exercise programme is out of balance, you are neglecting the largest and most powerful muscle groups for small muscle group isolation exercises. Doing the Bowflex and the pushup work is redundant to a degree with the pushups the most beneficial exercise, working more muscle groups and your core. To gain major benefit from the situp challenge do Janda situps to work the abs and not the hip flexors.
Final note what you will build with the challenges is endurance not strength. Nice personal goal of course but not of major benefit for overall fitness in the long run.
It is called WORK-ing out for a reason.
I said getting fit was simple, I did not say it was easy.
Cardio burns calories, strength work burns fat.
Eat well to lose weight, exercise to get fit
You can not build a six pack using twelve packs
Often when we seek a magic bullet for fitness we end up shooting ourselves in the foot.
"I think calories are little germs in food that all moms are afraid of" Dennis the Menace