The best replacement for treadmills is ellipticals.

The best alternatives to treadmills are rated as following:
★★★★★  ellipticals
★★  elliptical trainers
★★  elliptical
★★  elliptical machines
★★  exercise bikes
★  bikes
★  exercise bike
★  motorized treadmills
★  ellipticals which is better
  treadclimber
  nordictrack
  electric treadmills
  cross trainers
  stationary bikes
  motorized
  steppers
  track
  recumbent bikes
  nordic track treadmills
  bicycles
  image treadmills

Your alternative for treadmills is not listed? Suggest!
Speaking about treadmills, one probably shouldn't forget about incline.

Other search terms related to treadmills and their ratings are:
★★★★★ incline
You have in mind a companion for treadmills and it is not yet here? Propose!



Google Trends

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treadmills
ellipticals
elliptical trainers