I have recently started to stretch to start learning yoga and I have become sore in my muscles, and was wondering if I am sore the next day after stretching, is it okay to stretch the next day when I am still sore?

I have two questions:

(1) What are the benefits of jumping on a mini-trampoline?

(2) Are there any benefits to using a hula-hoop?

As you can probably see, I'm looking for exercises that are fun.

It's been about three months since I worked out regularly. I find that lifting for strength (i.e. 80% of max for 5-8 reps) causes me to feel nauseated about 3/4 through the workout sometimes, so that I can't bring myself to finish. I took a weight training course last semester and was affected the same way every once in a while. I warm up, stretch before and after, breath when I lift, drink plenty of water, take care not to eat 1 hour before working out, skip a day between workouts, don't lift more than I can handle (I reduced the weight from what I ended on in the class to a seemingly suitable weight. I got a 98 in the class incidentally). What's going on?

1) I work out on my treadmill 20 to 30 minutes a day, usually one to two miles. My husband says that there is a minimum and maximum heart rate. Is there a formula that I can use to calculate this information? Please advise.

2) Is there an equation that would relate the relationship between exercise and heart rate. I understand the maximum and minimum heart rate equations for exercising. I would like to know if someone who is at their max. heart rate would be able to predict their heart rate if they increased their intensity. I am looking for something relating work intensity to heart rate.