When planning a fitness program (and do note that having a plan is a good thing), there are four things you should focus on:
1. Type of activity
2. Frequency
3. Duration
4. Intensity
(Fitness professionals use the mnemonic FITT, Frequency Intensity Time Type.)
These are the four aspects of any fitness program that you can (and should) modify to suit your needs: What type of activity will you be doing (e.g., kung fu, running, weight-lifting, &c.)? How often will you do it (e.g., three times a week)? For how long will you do it (e.g., one hour each time)? How intensely will you do it (e.g., jog, trot, or sprint)?
Why is it important to modify these four aspects?
Varying the type of activity, also known as cross-training, is important for several reasons. First, it allows you to take advantage of the strengths (and minimize the weaknesses) of different activities. Swimming, for example, is fantastic for cardio-pulmonary development but terrible for building strength. Weight-lifting is great for building strength but lousy for training agility. Secondly, cross-training minimizes the risk of injury. Doing the same activity over and over, particularly if it is a highly repetetive activity like cycling or running, increases the risk of repetetive strain injuries and promotes the development of muscle imbalances, which can lead to acute injuries. Thirdly, cross-training helps keep you from becoming bored with your workouts. The psychological aspects of training are often ignored, but one of the most important parts of a fitness program is that it has to be something you want to do. For most people, a certain variety is helpful in this respect. Lastly, cross-training helps to produce more complete fitness. Professional athletes will focus on a particular set of physical skills, but for most of us, general, functional fitness is more useful. Spending three hours a day in a batting cage is important for baseball players, but won't help with most of the activites you do in your daily life. Varying the type of activity you do helps you to become generally fit rather than narrowly talented.
Determining the frequency of activity is largely an issue of time management and organization. First, it is important to schedule at least one rest day per week. At least one day out of every seven should be reserved for rest so that your body can repair the small amounts of damage that occur with exercise and so that you can take a mental break as well. Secondly, you want to distribute your workouts so that they complement each other. For example, if Monday is a really intense weight-lifting session, then don't schedule your second really intense weight-lifting session for Tuesday. Try to spread out your workouts so that there is day-to-day variation in type, duration, and intensity. Lastly, your workouts need to fit within your busy life. If you schedule a hard workout at the end of what you know will be a very busy day, you're a lot less likely to do it. Try to plan your workouts so that they fit comfortably within your schedule, and acknowlege that on some days, it's just not going to happen. Work, family, and other obligations are important; working out should be a source of stress relief, not a cause of stress.
Varying the duration of activity, as with frequency, is largely about time management and organization. If you know you will only have a half an hour one day, for example, that's a better day for a high-intensity workout than for a slow jog. It's also important to consider how much time you will need to get the workout you want. Generally speaking, the cardio-pulmonary benefits of biking for 60 minutes may be achieved in 40 minutes of running or 20 minutes of swimming. Also, if you are new to an activity, you should start with a short duration and gradually increase it over time.
Varying the intensity of activity is largely about the trade-off between training benefits and recovery time. Generally speaking, working out at a higher intensity increases the efficiency of your training (i.e., greater benefits in less time) but also increases the recovery time. Recovery is not the same as rest--recovery can occur during performance of an activity--but it is just as important. Furthermore, some levels of intensity train different abilities better. For example, low-intensity activities tend to be better for training endurance, high-intensity activities tend to be better for training power.
A final note about progression. You will no doubt be unsurprised to learn that you must increase "something" in order to improve your level of fitness. Doing the same things week after week will allow you to maintain your current level of fitness/health but will not help you to improve it. But what do you increase and how? Generally speaking, for any particular type of activity, you should increase first the frequency, then the duration, and lastly the intensity. This will make the transition from easier to harder workouts as smooth as possible and minimize the risk of injury.
