I've been doing 4 min intervals times 7 with 4 minutes rest between each as part of my preparation for time trialing. Mostly because of weather and convenience I've been doing them on the computrainer. My more experienced and much faster friend tells me I would get a better workout outside. I tried it and found too much variation due to wind, inclincation, intersections, poor roads etc. With the computrainer I can monitor speed, wattage and heartrate easier and I find I can do more consistent efforts. I do all of my other training outside so am I doing myself a big disservice by doing these intervals inside?