Striders / gliders / flyers.
These current "darlings" of TV infomercials simulate the motion of cross-country skiing with a twist - you swing your legs on foot pedals that are suspended on air. The good points of the machines are that they are easy to use, affordable and non-impact. Some versions use the arms and legs simultaneously. The disadvantage is that since the foot pedals allow such a wide range of motion using momentum, it is easy to hurt the lower back as the user swings the legs behind.
In 1997, the American Council on Exercise (ACE) commissioned researchers at the California State University, Northridge to evaluate two brands of gliders - the Airofit and the Fitness Flyer. The scientists found that the gliders were appropriate for individuals with low to moderate fitness levels but that for "those who desire a vigorous workout, the effectiveness of the Fitness Flyer and the Airofit is questionable". The men in the study were unable to reach high-intensity levels. This was in spite of the fact that the Fitness Flyer had adjustable knobs to increase resistance.
The reason for this could be that since the pedals are suspended in air, they couldn't re-create the friction that occurs when gliding on a real cross-country skiing machine. The researchers noted that their observation about these two brands probably also holds true for other brands because of similarity in basic design. The scientists advised consumers to check out the sturdiness of the gliders that they desire to purchase. They found that several bolts on the Fitness Flyer came loose and the digital display wobbled so much that it had to be removed.
In another ACE-commissioned study, this time at the San Diego State University, researchers found that the Fast Track, a hybrid glider/cross-country skiing machine, could effectively accommodate all fitness levels. They also found the machine to be well made with a durable plastic construction. The Fast Track does not hurt the lower back because the length of the tracks controls excessive momentum when swinging the legs behind. The only major disadvantage was the noisiness of the machine.
Riders.
These machines look like a combination bike and bronco-riding contraption. Brands that were put to the test by a study at the California State University included the Healthrider, Cardioglide, and E-Force.
The researchers found that the aerobic riders burned significantly fewer calories than a motorized treadmill or a cross-country skiing machine. Mitch Simon, exercise physiologist at the National Academy of Sports Medicine, suspects that the riders' momentum creates most of the work.
Study leader Patrice Pinachio observed that someone who is sedentary would likely find the riders challenging for up to a year - maybe longer if one is trying to maintain only a modest level of fitness. She says that people who are already fit will not be able to achieve a satisfactory workout. The lower back can also be put at risk by using aerobic riders. Five out of seven people involved in the study complained of lower back pain.
Electrical muscle stimulation machines.
EMS machines were originally invented to reduce muscle shrinkage in bed-ridden individuals. They are legitimately used by physical therapists to relax muscle spasms and to speed up the rehabilitation process of injured muscles.
The machines are designed to deliver a mild electrical shock to contract and relax your muscles. The machines are now being hawked over TV as a simple, no sweat way of getting fit "without having to do any work". One ad claims you do the equivalent of 450 sit-ups in 30 minutes!
Actually, the "passive exercise" concept is not new. In the 60's, the Relax-A-Cisor was promoted aggressively as a pleasant and effortless way to reduce. According to Stephen Barrett, author of The Health Robbers, it took years of investigation and a five-month court battle to put this profitable gizmo out of business.
Forty witnesses testified that the Relax-A-Cisor could be hazardous in a wide range of conditions including gastrointestinal, orthopedic, muscular, neurological, vascular, skin, kidney and female disorders. The judge found it could even cause miscarriages.
What does research say about today's modern versions? A study by the Utah State University that was presented at the 1997 American College of Sports Medicine conference concluded that "EMS machines may strengthen muscles to a point, but probably will not help individuals lose weight, lose fat, or change their basic body dimensions".
Liz Neporent claims, in her book, Weight Training for Dummies, that "electronic stimulation devices aren't just a waste of money; they're also potentially dangerous". She recounted that she developed deep red splotches on her thigh when she tried an EMS device for the first time.
Strength training machines.
Muscle strengthening is an important aspect of fitness. Strength training machines are useful in reshaping the body and building muscle mass to burn more calories. Machines sold over TV are normally cheaper than weight training machines sold in sports stores because they use giant rubber bands or body weight as resistance instead of expensive weight stacks.
Another advantage is that they occupy less space and yet, by rearranging pulleys and seat positions, allow you to perform dozens of exercises. Unfortunately, they are usually not as well made as their more expensive cousins.
According to Liz Neporent, these are the things to consider when buying a multi-exercise strength training machine from TV: Check that the resistance is even on both sides. Many machines have rickety levers and weak metal bars. Watch out for movements that are sticky and jerky. Some machines require such complicated maneuvers with the bars, cables and/or levers that working out can be quite time-consuming. Many of these machines promise at least 40 exercise variations. Not all the positions are safe or effective. Usually, it is the shoulder joint that is compromised.
General guidelines
Here are general guidelines to consider when buying fitness equipment of any kind to ensure that you are making a good investment.