While most treadmills require assembly, certain models do not. This is because they are designed to fold flat into a small space, such as a box, and then to unfold to be upright. These treadmills are great space savers because they fold to fit inside a closet or under a bed. Some notable brands that build these no-assembly treadmills are 3G Cardio, Horizon Fitness, LifeSpan, and BH Fitness.
The 80i Fold Flat Treadmill by 3G Cardio won 2013's best buy from Fit-Prof. This specific treadmill folds to a height of 10 inches and comes fully assembled in the box. It is on wheels, so you can roll it to where you want it. It also folds vertically and has wheels that pop out to roll in that vertical position -- with the base locked upright into the handles. The machine itself weighs 225 pounds. It has a 3.0 horsepower motor, goes up to 11 miles per hour and has an incline of 15 percent. It holds up to 325 pounds.
Horizon makes treadmills that require no assembly. One such model is the Evolve SG Compact Treadmill. This treadmill also folds to a height of 10 inches and can roll horizontally or vertically, but it weighs only 99 pounds. It runs on a 1.5 continuous-duty horsepower motor and can hold up to 250 pounds. This treadmill only goes up to 6 miles per hour and has no incline settings. It does come with several pre-loaded workout programs.
The TR200 from LifeSpan Fitness is another treadmill that does not require any assembly. The TR200 folds to a height of 11 inches and can roll vertically or horizontally. It weighs 119 pounds, so it is heavier than Horizon's Evolve SG Compact. The 2014 model reaches speeds of 8 miles per hour with up to a 10-percent incline. It has a 1.5 continuous-duty horsepower motor and can carry up to 250 pounds. It come with six preloaded workouts.
BH Fitness has a technology called plug and run which is used for a variety of their treadmills. This means there is no assembly required; you simply unfold the treadmill, plug it in and run. With several models to choose from, the most powerful has speeds over 11 miles per hour and an incline of 12 percent. They have a variety of weight capacities and sizes. BH Fitness was originally a United Kingdom company, but they do sell their treadmills in the United States.
Other treadmill companies sell treadmills that require little to no assembly or offer free assembly with purchase. These companies include Exerpeutic, ProForm and NordicTrack.