Answer:

Spinning is a great way to do cardio work on the stationary bike. Here are some recommendations for your goals.

Fat Burning:

1. Do your spinning class on a fasting state. What this means is that you should not eat or drink anything with calories in it for several hours before your class. The absolute best example of this is first thing in the morning.

You can burn about 300% more fat if you do your cardio first thing in the morning before eating or drinking anything (except water). If your class is later in the day, be sure to have your closest meal before it at least 2 to 3 hours prior to the class or in at least enough time for it to be fully digested.

What the fasting state does for you is put you in a condition of low blood sugar. If your body doesn't have much blood sugar (carbohydrates) to fuel your exercise, it will dip into your fat stores much sooner. Be aware, however, that you may not feel as though you have as much energy to train when you first start doing this, especially if you are used to eating right before you train.

2. Do not eat anything right away after the spinning class. Your body will continue to burn fat after the class because you have cranked up your metabolism. Wait about an hour, then eat protein and carbs to help fuel your recovery.

Cardio:

1. Your frequency of classes is good. I wouldn't recommend going much over 3 to 4 times per week. This gives your body a chance to recover. You didn't mention how long your classes were but another option towards increasing your endurance may be to get there a few minutes early and stay a few minutes late just doing some low-intensity pedaling.

2. Increasing the resistance on the bike, naturally, will make the workload harder and build leg strength as well.

3. Increasing your cadence (leg speed/r.p.m.'s) will also increase your workload.

4. I am assuming that your class consists of interval training where the resistance and speed is varied during the workout. One trick you may want to try at the very end of your workout is one all out sprint with everything you've got on a high resistance until you feel you can't go any more -- then do five more seconds.

Not only has an all-out, lactic-acid churning sprint like this been shown to increase growth hormone levels in your body, it will build up your wind and give you a good challenge. Keep track of how long that last sprint lasts and try to increase it's time each session you do it.