Your husband is being a dick. However, he may not actually SEE just how much you're doing (men are wonderful at not being able to see the obvious). I would suggest writing down exactly what you do in a week so he can literally SEE it right in front of him. You can also write down exactly what he does so you both can compare them side by side. Ask him where HE thinks improvements should be made.
From the above (and of course not knowing you or the situation completely!), it seems to me that your husband wants a traditonal housewife - but also probably needs the money that you bring in by working. Maybe it would help to hire a weekly housecleaning service or to send the laundry out. I told my DH that if I ever went back to work (he wants me to; I'm ambivilant) that the only way our marriage would survivie is if we sent the laundry out and had a housekeeper come in at least once a week. My DH has been spoiled by me running all the errands and taking care of all the household stuff. Even then, we'd still need to wash the daily dishes and pick up the house TOGETHER. Since he's the one working, I do almost all of these things (however this is our arrangement).
If he doesn't care for his alone time while you take the kids to the gym, offer to leave them home but that you NOT going to the gym is simply NOT an option. And bitching about the small things like him having to do 5 minutes worth of toy pick up isn't going to foster any good will on your part.
The other side is that maybe he's jealous you have something that is yours - working out. Does he get any time to take off and do whatever with the boys? Like a weekly poker thing or something? And I think he needs reminding of how having an hour alone in the house while you take the kids to the gym is his opportunity to work on his hobby - whether it's working on an old car, video games, playing music, going to the gym himself, etc.
I'm really sorry you're having to deal with this. If this doesn't bring about a good conversation AND change, then I would suggest marriage counseling.