For the past few weeks, I have been answering a question from a reader who hated winter because it was so difficult to maintain an exercise program when it gets cold. I have been discussing the advantages and disadvantages of various types of indoor exercise equipment and have covered exercise bikes (ergometers), treadmills and rowing machines. This week, I will try to finish this question.

Stepping machines. Anyone who has climbed stairs knows how difficult this activity can be; thus, one of the simplest indoor exercise activities is stair climbing. If you have stairs in your house, you can get an excellent workout just by climbing them for 30 minutes or so each day. Some people modify the stair climbing activity by buying or making a small step or stool between 8 and 15 inches high, and stepping up onto the stool and back down using a rhythmic cadence.Using the stepping principle, several companies have developed very nice stepping machines. The simplest of these machines uses a hydraulic shock absorber on each pedal and the pedals are pushed down with a stepping motion by the person using the machine. Another variation of the stepping machines uses a flywheel that is put into motion as you step on the pedal, and the flywheel can be adjusted to offer more or less resistance as needed. Sometimes this flywheel is a fan of some type, much like the flywheel on the exercise bikes discussed two weeks ago, or they can be electronically braked. Almost all of these machines are constructed so that the one stepping lever goes up as the other goes down.

An interesting and more expensive variation of the stepping machine is constructed like a small escalator. Working on this machine is much like trying to go up a down escalator in a store except the speed of these machines can be varied to suit the individual's fitness level. These machines are often used by physical therapists for rehabilitation, but are fun to use and provide an excellent workout.

Another variation of the stepping machine is called a "climber." With this device there are adjustable arm levers that are connected to foot levers and the exercise involves a motion much like climbing up a ladder. Again, the resistance and speed can be varied and the makers claim that a better workout is possible because of the increase in the number of muscles used.

Ski machines. One of the most popular of the newer indoor exercise machines is designed to simulate cross country skiing. These machines are designed with two parallel tracks that require the legs to move forward and back using a motion very much like that required to cross country ski in the snow. Almost all of these machines have some type of arm lever or pulley so that the upper body can be involved, just like in real skiing. These machines have an obvious advantage for people who ski because the motion is so much like the real motion of skiing.

One of the most interesting of the ski machines is the Skiers Edge or Fitness Edge. This machine is designed to allow the side-to-side motion involved in downhill skiing. Because it uses the large muscles of the hips and legs rhythmically, and because this motion can be maintained for a long period of time, it can be an effective machine for aerobic conditioning as well as a specific conditioner of the skiing muscles. Because of the number of questions I have received about this device, I have borrowed one from Scientific Sports Systems. I will report on this in some detail in a few weeks.