In order to facilitate and accelerate many physical rehabilitation processes, it is best to incorporate functionally oriented, task-specific exercises and movements into the rehabilitation program. For example, when it is desired that a patient recovering from a knee, leg or ankle injury be able to resume walking, running, squatting as soon as possible, the rehabilitation program will preferably include walking, rnmning, or squatting movements. Unfortunately, unless a portion of the patient's body weight is somehow "unloaded" from the injured knee, leg, ankle, or other weight-bearing member, the patient often will not be able to engage in such task-specific movements and activities without pain and/or possible additional injury.
As used in the art, the term "unloading" refers to exercise, therapeutic rehabilitation, and athletic training techniques wherein, while performing beneficial exercises and movements, a portion of the person's body weight is continuously unloaded (relieved) from the weight-bearing parts of the person's body. If, for example, a patient recovering from knee surgery weighs 150 pounds but is only capable of bearing a standing body weight of 50 pounds, the patient will not be able to exercise in a standing position unless at least 100 pounds of the patient's body weight are somehow continuously unloaded/relieved from the person's knees throughout the activity in question. Stated another way, at least 100 pounds of the patient's body weight must be lifted and supported in such a manner that the patient's knees are required to bear no more than 50 pounds of the patient's body weight during the exercise activity.
In the context of physical therapy, the ability to reliably, precisely and continuously unload a portion of the patient's body weight is particularly desirable in situations where, for example: (a) fall weight-bearing is painful to such a degree that the patient's ability to engage in task-specific, functional activity is significantly limited; (b) due to muscular weakness, impairment of balance, and/or proprioception, functional movements are essentially impossible without physical assistance; and/or (c) the patient's general fitness condition is such that necessary movement and exercise is overly fatiguing.
In the context of aerobic exercise and athletic training, unloading techniques can be used to: maintain a targeted heart rate over a substantial period of time; reduce stress and impact on the person's limbs and joints; improve reflexes, reaction times and quickness; and reduce injuries, both on and off the field. Over-speed training, for example, conducted under unloaded conditions can be used to improve an athlete's coordination when moving at top speeds.
The concept of reducing the effects of body weight and gravity during rehabilitation and training is familiar to most athletic trainers, physical therapists, and other health-care practitioners. Aquatic therapy is often prescribed, for example, for patients with back or other injuries. Unfortunately, aquatic therapy has significant shortcomings in that (a) it is typically not possible to precisely control the amount of weight unloaded from the patient and (b) it is typically not possible, when immersed in water, to practice task-specific movements at normal or accelerated speed.
Various types of devices for unloading body weight while walking, jogging, or running on treadmills, or while engaging in other exercises, are known in the art. As on example, French patent publication 2,252,108 discloses a cable and pulley arrangement wherein a pneumatic cylinder is used to provide and adjust the lifting force imparted to the user. As another example, U.S. Pat. No. 3,761,082 discloses a harness assembly for stationary exercise and walking wherein a short, overhead tension spring is used to "counterbalance" a portion of the user's weight.
Unfortunately, common unloading systems utilizing air or gas cylinders, hydraulic cylinders, or springs have significant shortcomings. When walking or running on a treadmill, a person's torso repeatedly moves up and down (oscillates) as much as three inches or more. The rate of oscillation increases significantly as the exercise speed proceeds from walking to jogging to running. The air, gas, or hydraulic cylinder systems known heretofore have typically been capable of accommodating relatively low oscillation speeds such as occur when the person is walking at a speed of less than two miles per hour. However these prior systems cannot respond quickly enough to accommodate higher oscillation rates such as occur when jogging or running. Thus, when exercising at higher speeds, the user will experience abrupt jolts and jerking forces which are uncomfortable and can potentially cause significant harm.
In contrast to the common systems utilizing air, gas, or hydraulic cylinders, spring devices such as the one disclosed in U.S. Pat. No. 3,761,082 are capable of responding to both low and high frequency oscillations. Unfortunately, however, the amount of lifting force imparted by a spring of the type employed in U.S. Pat. No. 3,761,082 changes tremendously as the spring stretches and contracts over the normal oscillation range. Thus, rather than providing a desirably constant unloading force, the spring will typically provide a greatly exaggerated lifting force when the torso is positioned at the bottom of the oscillation interval but may provide almost no lifting force when the torso is positioned at the upper end of the oscillation interval.
In comparison to the devices just described, a greatly improved therapeutic unloading system is disclosed in U.S. Pat. No. 5,273,502. The improved system comprises: a frame; an electrical winch and associated load cell mounted at the bottom of the frame; a relatively long, low constant spring positioned within a vertical side rail of the frame; a first cable segment extending from the winch to the lower end of the spring; and a second segment of cable having one end secured to the top of the spring and a second end extending downwardly from the top of the frame for attachment to a harness. The control circuitry of the improved device continuously monitors the unloading force acting on the patient and causes the winch to respond automatically to changes in the patient's position. The winch is fast acting so that it reacts very quickly. Moreover, the spring employed in the improved device compliments the winch system and assists in maintaining a more constant unloading force. In contrast to the springs used in other systems, the spring employed in the improved system is relatively long (typically about three feet in length prior to stretching) and has a low spring constant value such that it must be stretched a significant distance (possible up to twice its original length or more) when initially setting the desired unloading force to be applied to the patient. As a result, the spring is able to absorb and dampen small positional movements, regardless of speed, such that no significant change in the total applied unloading force occurs.
Although highly effective for absorbing and dampening small oscillations and movements, regardless of speed, the use of a long, low constant spring can limit the adaptability, size and/or uses of a system of the type disclosed in U.S. Pat. No. 5,273,502. As the required amount of unloading force increases, the spring must be stretched to a greater and greater degree. However, as the height of the user increases, the maximum available length to which the spring can be stretched decreases. Thus, for a very tall user, the amount of unloading force obtainable may be significantly limited. Although the apparatus can certainly be enlarged to accommodate the taller user, the larger apparatus may not function as well for smaller users and could be too large to fit within the particular room and/or ceiling space available.
Thus, a need exists for an unloading system which is at least as effective as the system of U.S. Pat. No. 5,273,502 and overcomes its limitations. Of course, any further improvement in the responsiveness of the unloading system and/or the ability, regardless of the speed, to maintain a constant unloading force would also be desirable and beneficial.