Whereas strength training provides variety as you move from machine to machine and work different muscle groups, endurance exercise sessions require a lot of time doing the same movements and maintaining a sustained effort level. Basically nothing changes from the beginning to the end of the aerobic activity period. I've noticed that most regular endurance exercisers don't even look at the video displays that provide performance feedback during the workout. Instead, they cover the display with their newspaper, magazine or towel, so that they can't see how much time they have yet to exercise. Generally, they are doing the exercise because they know it is physically beneficial, but they do not find it mentally interesting.

Although there are occasions where a relatively steady pace is essential, such as running a 5K or 10K race, there are more interesting and effective means for conducting your exercise sessions. My preferred approach is known as interval training, and it provides almost unlimited variations in workout designs.

Basically, interval training involves interspersing more demanding and less demanding exercise segments within the workout. The training variables include (1) how hard to make the more demanding intervals, (2) how easy to make the less demanding intervals, (3) how long to make the more demanding intervals, (4) how long to make the less demanding intervals, and (5) how many intervals to perform.

For example, instead of treadmill walking at a steady 3.5 mph pace for 30 minutes, you may try 5 intervals of 6 minutes each. Let's say you begin with 6 minutes of slower-paced walking at 3.0 mph to warm up. You then perform 6 minutes of faster-paced walking at 4.0 mph. Because this is a more demanding pace than you normally do, you follow-up with 6 minutes at the more relaxed 3.0 mph pace. As this permits plenty of recovery time, you can now complete another 6 minutes at the faster 4.0 mph pace. Finally, you cool-down with another 6-minute segment at the slower 3.0 mph pace.

Overall, you have accomplished about the same workout as usual, namely, 30 minutes of treadmill walking averaging about 3.5 mph. However, the 2 faster-paced segments actually enhanced your physical development by requiring a higher work effort than your body normally produces, even for a total of only 12 minutes.

Perhaps just as important, you should find the interval training workout more mentally stimulating due to the variations in walking pace. Many people prefer interval training to steady state exercise because it places a different perspective on the workout duration. For example, when you keep the same pace for 30 minutes, it may seem that the time passes very slowly. However, when you perform higher-effort intervals, you may find that the slower-paced recovery intervals pass almost too quickly and that the total workout time seems considerably shorter than usual.

In the previous treadmill walking example, the harder and easier intervals were equal in duration, 6 minutes each. However, as you become better conditioned, you may make the higher-effort intervals longer and the lower-effort intervals shorter. Consider the following interval training approach to a stationary cycling workout in which the more demanding segments are twice as long as the less demanding segments: