Apparently earths gravitational pull has increased, this is due to a significant rise in people frequenting fast food outlets, & this effect is more noticable in areas where obese people congregate, i.e - mcdonalds, outsize clothing stores, 4x4 dealers etc..
..or possibly the electric motor on your treadmill has seen the last of it's days, 4 years aint bad i s'pose.
Peter
September 2008