Will walking on a treadmill on a deep incline help tone thighs?

In general, walking on a treadmil set at a zero degrees incline will add a minimal amount of leg muscle. Greater levels of leg muscle mass can be obtained via sprinting on a treadmill or walking/running uphill on a treadmill, but the muscle gain will not be significant as compared to the results obtained through heavy progressive resistance training (though similar results can be obtained through heavy sprinting training).