The lymphatic system-lymph nodes and glands, tonsils, adenoids, appendix, spleen and thymus gland-constitutes much of our body's immune system. The lymphatic interstitial fluid carries waste and toxins from tissues and organs to the bloodstream, where they are then eliminated from the body via the liver and kidneys. Keeping this fluid moving is essential for health and for treating minor conditions like allergies, eczema or inflammation.
Because the lymphatic system doesn't have its own pump, as does our circulatory system, any exercise that involves the major muscle groups or forces the lungs to work harder will also prime the flow of lymphatic fluid. Deep breathing, as occurs during hard exercise, also squeezes the thoracic duct, which is responsible for the flow of lymph into the bloodstream.
Although running, jogging or brisk walking all encourage the flow of lymph, rebounding is said to be the most effective of all: jumping, then landing with twice the force of gravity, is thought to boost our lymphatic network.
Rebounding (or 'urban rebound-ing', a term coined by J.B. Berns, one of its major popularizers) is thought to send oxygen and other nutrients into cells, while encour-aging the flow of toxins and waste via the lymphatics. Dr Walker claims that white blood cells, the backbone of immunity, increase dramatically during rebounding. Others claim that this form of movement detox will produce every sort of improve-ment-from eliminating cellulite to quickening hair growth. Walker quoted a study of rebounding by the Karolinska Institute in Sweden from 25 years ago that showed that heart patients using a rebounder dramatically resolved most of their symptoms of breathlessness, palpita-tions, and cold hands and feet. "Rebounding . . . gives any damaged or sick cells the opportunity to heal themselves," wrote Walker (Walker M, Shah H. Everything You Should Know about Chelation Therapy. Stamford, CT: Freelance Communications, 1980).
Rebounding is also extolled as a superior aerobic exercise because bouncing on a forgiving trampoline spares the knees and hips, feet and ankles. Indeed, Berns maintains that it is 87-per-cent less hard on the musculoskeletal system than workouts on a hardwood floor.
Indeed, NASA researchers consid-ered rebounding as a remedial procedure for astronauts, who were routinely exposed to long periods of weightlessness. They concluded that rebounding was more than two-thirds more effective than working out on a treadmill (J Appl Physiol, 1980; 49: 881-7), and kinder because it is low-impact.
Rebounding's main advantage is that it feels a good deal less punishing on the body and takes less time than pounding on a pavement or an outdoor track. You can even get into your 20-minute 'run' in front of the TV set.
A real workout-or not?
But is this easy-does-it form of jogging on a soft target aerobic?
The NASA research showed that rebounding put less stress on the heart and consumed less oxygen. More recent studies of rebounding suggest that it doesn't work you as much as was originally thought.
Researchers from the Human Performance Laboratory at the University of Alabama found that rebounding on its own produced only minor improvements in overall fitness. In one study, 15 men, aged 20-43, worked out on mini-trampo-lines at a particular pace. Oxygen uptake and heart rate were measured while rebounding on its own, then compared with rebounding while the volunteers pumped various sizes of handheld weights.
The researchers found that any size of weights produced significantly higher oxygen uptake and heart rate than simple rebounding alone.
Other evidence from the Alabama lab showed that 1-, 2- or 3-lb hand-weights increased oxygen require-ments from 26 to 60 per cent (Sports Med, 1988; 5: 6-10).
The Alabama researchers conclud-ed that, for true cardiovascular training, people using a mini-trampoline need to consider the additional use of handheld weights(J Cardiopulm Rehabil, 1995; 15: 34-8).
Furthermore, studies of strength training, aerobic power and mobility in inactive older men show that higher-intensity training produces greater gains in strength power, and whole-body physical function (Br J Sports Med, 2005; 39: 776-80).
So, rebounding is useful for senior citizens, the physically handicapped, those who have certain types of physical conditions and those who are recuperating from an accident or injury. But for the rest of us, as fitness guru Kenneth Cooper recom-mends, nothing seems to beat having your feet hit the ground.