Metabolic rates were similar across trials and were moderate intensity (48.5-59.8% of VO2max). Walking slower uphill significantly reduced loading rates and lower extremity net muscle moments compared to faster level walking. Peak knee extension and adduction moments were reduced by ~ 19% and 26%, respectively, when subjects walked up a 6[degrees] incline at 0.75m/s vs. level walking at 1.50m/s.So, ramp up your incline and walk, but please do me a favor and do not hold on to the handle in front of you, like some of the overweight mamas at my gym do. This will not only reduce the work-intensity and thus diminish the metabolic effect, it may as well ruin your back.
Edit: Dr. Rouse was kind enough to remind me that there is a world beyond the gym (cf. my Facebook page) and that just walking outside would be a better alternative - thanks Peter ;-)