Fitness isn't just about working hard, it's about working smart. So when you're endeavoring to get in shape, make sure you consider the four fitness factors, or FITT: Frequency, Intensity, Type and Time.

Frequency

Ideally, exercise is something you should do every day. However, the frequency of your exercise depends on the type of workout you do.

Bodybuilding: Using the muscles too frequently will cause muscle damage, so you need a break between each day of workout. If you perform high-intensity exercises, you need to give the muscles worked at least one day of rest--or two if you push them very hard with low-rep, high-weight exercise (for power).

Aerobic: Some aerobics should be done every day in order to promote good cardiovascular conditioning. Intense aerobic exercise (sprinting, for example) should be done every two or three days, as the muscles used need to recover. Low-intensity and steady-state aerobics can be done every day.

Other: Yoga, martial arts, dance, and all the other forms of exercise can be done daily.

Intensity

Just how intense should you go when exercising?

Low Intensity (60 to 70% of Max HR): Low intensity exercise is good for weight loss as well as cardiovascular conditioning. At 60 to 70 percent of Max Heart Rate your body will be burning fat, pumping blood and using up your energy at a steady rate--but not so much that you'll be exhausted. You can usually go for 30 to 60 minutes every day at this level of intensity.

Medium Intensity (70 to 85% of Max HR): Once you crack 70 percent of your Max Heart Rate, your body starts to feel it. You can't do daily workouts, as your body needs time to recover. The average exercise time will be about 20 to 30 minutes, but no more than 60 minutes. You should only perform at medium intensity three to five times per week.

High Intensity (85 to 95% of Max HR): Between 85 and 95 percent of your Max Heart Rate is ideal for weight loss, as it burns large amounts of energy in a short period of time. Endurance athletes (triathletes, marathon runners) usually go for this intensity level, as it improves their performance. Exercise will usually last no longer than 20 minutes--with plenty of rest in between the bursts of high-intensity intervals--and done every two or three days.

Note: You should never reach 100 percent Max Heart Rate--it's just too much for your heart to take!

Type

The type of exercise you choose is entirely up to you and depends on your goals:

Getting in Shape/Losing Weight: High-intensity training is highly recommended, so sprint training, HIIT and CrossFit are great! Jogging, cycling and other low-intensity steady-state aerobics can be good, but weight loss will really only occur if you combine weight-training with this low-intensity exercise. All forms of aerobic exercise are good, including dance, martial arts, swimming and spinning.

Building Muscles: For the man or woman looking to bulk up, power (1 to 3 reps) and strength (4 to 6 reps) training with weights is the ideal type of exercise--with 20 minutes of low-intensity aerobics thrown into the mix every day.

If You're Older: Older men and women have to take a different approach to exercise. They can't always do high-impact exercise (running or martial arts), but they need to focus on the low-impact exercise types (cycling on a recumbent bike, moderate weightlifting, Yoga, Pilates, swimming).

Time

The amount of time you spend training will depend on the intensity of the exercise you do:

Low Intensity: You may have to work up to it, but you should be able to keep your steady-state, low-intensity workouts up for at least 40 to 60 minutes per day.

Medium Intensity: It's not recommended to push your body beyond 30 minutes.

High Intensity: You'll be wiped after just 10 minutes, and you shouldn't train for longer than 20 minutes.