It provides equipment ranging from treadmills, ellipticals, bicycles, free weights, and selectorized weight equipment. Ellipticals produce an intermediate range of leg motion between that of stationary bikes and treadmills. The brand also makes treadmills and elliptical machines. NordicTrack treadmills are the top-selling brand worldwide. Somerville has a gym situated beneath Vaughan, with treadmills, cross-trainers and weights. Some luggage carts at airports and exercise treadmills have this feature. It is equipped with modern stations, free weights, treadmills and stands. Some riders also have access to equine treadmills or swimming pools. For athletes, larger and more stable treadmills are necessary. Water was put in buckets and removed using rope conveyors powered by horses on treadmills. Medical treadmills are also active measuring devices. Treadmills as muscle powered engines originated roughly 4000 years ago. Dog/pet and underwater pet treatment treadmills are available for both home and clinical use. The latter are known as manual treadmills. They used underwater and low-gravity treadmills.