Three types
Motorized, curved self-powered, and walking pads
Motorized treadmills
A motor drives the belt at a set speed and incline; you keep up. The format for programmed workouts, incline walking and steady runs. SFE Treadmill Pro (3.0 HP, 12.5 mph, 15 percent incline, 58 by 20 inch belt, folds, 300 lb, $1,199), X19 Commercial Touchscreen (3.0 HP rated, 19-inch screen, 12 mph, 20 percent incline, 396 lb, $999), Elite Pro (3.5 HP, 14 mph, 15 percent, 60 by 21 inch belt, $1,799), Commercial Pro (4 HP, 15 mph, 20 percent incline and 3 percent decline, 64 by 24 inch belt, 400 lb, $2,999).
Curved self-powered treadmills
No motor: the curved slat belt moves as fast as you push it and stops when you stop, which burns more energy per mile, suits sprint intervals and sled-style pushes, and needs no outlet. SFE Air Runner Pro (7 resistance levels, $1,999) and Curved Air Runner Elite Pro with sled push ($2,199), MedEq R1000 ($3,250) and R2000 solid wood frame ($3,450). The "manual treadmill" most people search for.
Walking pad
A flat, low-profile belt for walking under a desk. MedEq R500 ($599): folds flat, compact, up to about 2 mph for working hours.