Training & Nutrition - Not Much Base Mileage

From what I've read, I should have a good base before moving to interval. However, I joined an indoor class at bike shop, which had already been going a month or so this winter, and it was pretty much just dive right in. Tues. and Thurs. 20 minute warmup, hour and ten interval training, and cool-down. My only question is, what are the implications for my overall improvement? I'm doing a lot of zone 4 work. Is this good, bad , or other with virtually no base mileage? I can take the pain and strain, but how is this helping me?

What are your goals? How much other riding do you do outside of the spin class, and at what intensities? When you say "virtually no base mileage" do you mean this season, or ever?

If you are on a periodized training schedule and looking to build a big base before doing structured high-intensity work I would probably skip the Z4 spin class for now. However, if you're JRA and trying to gain general fitness I think that any exercise you do is better than nothing at all, and if the spin class keeps you motivated I wouldn't sweat the zones and training periods too much. That said, listen to your body, and if you're hurting/crazy fatigued, back it off.

Goals? Not have to think too much about training. Be prepared to do some longer rides, and some southern Wisconsin type hills/rollers while keeping up with others. Ride some hills without dying. Do 60-80 mile rides by late spring. And maybe a century or two this summer. Outside the class, not much riding yet due to the weather. "Virtually no base" refers to this year. Mainly trying to gain general fitness. The spin classes keep me going, force me to work harder than I probably would on my own, and set a schedule to get me on a bike at least twice a week regardless of weather.

The good news/bad news is that my body always wants to go to the point of exhaustion. But no serious hurting/crazy fatigued so far.

So... thanks for the input. I think you've answered my questions/concerns.