Trek District Carbon Or Pinarello Paris?

How could anyone possibly help you. You're comparing a single speed belt drive bike to an endurance bike, to a full blown aero race bike. With zero idea what your needs are.
That's not even apples to oranges. That's comparing a chicken nugget to a potato to a steak.

Im looking for a bike to help build leg muscle.

First thing is deciding where are you going to ride, what are the roads/trails like? Then do you live in hills/mtns/beach? What are the weather conditions? Are you fit or a couch potatoe?

I have 6.7% body fat. I live in NJ.

did you ever buy any of these back in 2017?

No i did not..i decided to gym it instead....this would be my first bike

How about getting an electric bike, removing the battery, and deflating the tires. Even better if you can find a full suspension version. That will build the most leg muscles per distance traveled.

RHankey said:

How about getting an electric bike, removing the battery, and deflating the tires. Even better if you can find a full suspension version. That will build the most leg muscles per distance traveled.

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That will definitely give the legs a work out. Just remember to go up as many hills as possible.

Possibly a more practical solution would be a gravel or mountain bike. Either will strengthen those leg muscles quicker than straight road biking, assuming you ride on gravel or off-road.

If you want to strengthen more than just 1 or 2 muscles make sure you get clipless pedals and cleats so you can clip into the clipless pedals.

I strongly suggest visiting a reputable bike shop. They can help you way more than random people on the internet. Test ride bikes and find out what you like and what you don't

Building leg muscle is good, but like any other exercise with good intentions, you need to get something that will keep your interest in the sport rather than being used a few times and then gathering dust. Since you are just starting out, I would rule out the single speed immediately.

I agree with Lombard. Go to a good bike shop. Look at their stuff. Have 'em suggest something to you. Take something out for a test ride.

Just make sure you get a bike with disk brakes, that way if you need more of a workout, you can always drag the brakes. Disk brakes are easier on the fingers!

RHankey said:

How about getting an electric bike, removing the battery, and deflating the tires. Even better if you can find a full suspension version. That will build the most leg muscles per distance traveled.

Click to expand...

How about saving a lot of money and just tying a cinder block on a rope to drag behind whatever bike you can find at a yard sale?

I'm just going to say it.... Riding a bike is not a way to get big leg muscles! It's an aerobic activity. If you want big leg muscles, one needs to do go do some deadlifts, squats, leg curls. Once a week go for a maximum lift.

Define “big”
Relatively speaking, a few of my leg muscles are much bigger than they were a couple years ago before I got a decent bike.