Why Does My Treadmill Belt Lag?

Woman running on treadmill in gym.

If you are walking or running on your treadmill and the belt slows suddenly, you should attend to the problem immediately. There are several possible causes for a lagging treadmill belt. You can troubleshoot the problem yourself, but depending on the actual cause, you may need to have your unit serviced by a professional.


If the walking belt stalls or lags, it is a potential safety hazard to anyone using the machine. This safety hazard could result in a trip or fall, and possible injury. The faster you are running, the higher the risk for serious injury if the belt suddenly lags or hesitates.


Icon Health and Fitness manufactures several brands of treadmills, including NordicTrack, ProForm, Epic and Weslo. According to the troubleshooting section of an Icon treadmill user's manual, if your belt slows when walked on, check that the treadmill is plugged in properly. Treadmills require a lot of power and each manufacturer outlines power specifications that must be met for your treadmill to run smoothly. If your treadmill experiences power surges, the belt could stall or lag. Make sure your machine is plugged into a properly grounded outlet with a surge suppressor as outlined in your user's manual.

Belt Lubrication

Depending on the age and model of your treadmill, the walking deck may require regular lubrication. Some treadmills come pre-lubricated from the factory and don't require any further applications. If your treadmill deck does need to be lubricated regularly, and it hasn't been for a while, this increases the friction between the deck and the belt, possibly causing the belt to lag. Refer to your owner's manual and lubricate the deck as directed.

Worn Belt

A worn belt is the most common cause of the belt lagging, according to Treadmilldoctor.com. Visually inspecting the belt is not a reliable method for determining whether it is worn. The only certain way is to use an ammeter and test the amp draw of your treadmill. Contact your manufacturer or a treadmill service professional to conduct this test.

Belt Tension

A lagging belt may be too tight. Walking belts need to be adjusted regularly for centering and proper tension. This is a relatively simple procedure. You use an Allen wrench to adjust the rear roller bolts on the back of the machine. If you have adjusted your belt recently, it is possible that you over-tightened it. Lift the middle of the belt on one side of the machine. If it doesn't raise about 3 inches off the deck, the belt is too tight. Follow the instructions in your owner's manual to adjust the tension.