Lower leg exercise involves muscles from the knee to the ankle and muscles surrounding the ankle. Lower leg muscles are exercised by rotational movements of the foot about the ankle joint. Lower leg exercise machines commonly provide one or two footplates with adjustable resistances against which the user may exert a force. Such exertion, when regularly repeated, results in lower leg muscle strengthening, improved muscle endurance, and increased joint motion flexibility. These results are key to prevention and rehabilitation of lower leg muscle and joint injuries.
As physical exercise for recreation and for cardiovascular fitness increases in popularity, so do the injuries associated with the lower leg. Ankle sprains are the most frequent injuries associated with recreation and fitness exercise. Knee injuries are also common. Running and jumping, for example, are known to cause a knee injury medically described as infrapatellar tendinitis, resulting in pain at the shin just below the kneecap. This particular injury and its rehabilitation exercises are described in an article "How I Manage Infrapatellar Tendinitis" by Joseph E. Black, MD, in the October, 1984, issue of The Physician and Sportsmedicine, pages 86-92. A principal object of the present invention is to enable individuals to perform the recommended exercise to prevent and rehabilitate this injury.
When serious athletes have lower leg injuries, the supervised care of an athletic trainer or physical therapist may be appropriate to hasten the return of the athlete to full competitive ability. However, for the non-athlete, fitness buff, or recreational player, the objective is not the fastest return to competition. It is instead to quickly regain the capability of walking straight ahead on both feet without a limp. Such movement involves the feet pivoting back and forth in a substantially vertical plane. This motion is technically known as dorsiflexion and plantarflexion.
Commercially available lower leg exercise machines are designed for use at centralized facilities, such as sports medicine clinics and university training rooms. These machines provide for foot movement against resistance in two or three different planes simultaneously. Some have built in seats and elaborate resistance measurement feedback systems. They are complex and costly machines that are economically justified by application to multiple patients. Examples include U.S. Pat. No. 4,650,183 to McIntyre, which discloses a two axis machine with seat and hydraulic gage console; U.S. Pat. No. 4,733,859 to Kock et al, which shows a two axis machine with seat; and U.S. Pat. No. 4,452,447 to Lepley et al., disclosing a three axis machine. These machines provide for exercise in the inversion/eversion and adduction/abduction planes in addition to the dorsiflexion/plantarflexion plane in order to provide complete ankle rehabilitation. Missing from the marketplace are affordable, single-axis, lower leg exercisers for individuals to use at their own convenience at home.
In hospitals where patients are bedridden, a nurse often must manually massage a patient's lower legs to stimulate circulation so that varicose veins and the development of thrombophlebitis can be avoided. There is a need for a small and light weight lower leg exerciser that can be attached by a nurse to a supine patient's foot, with means for providing exerciser stability on a bed, so the patient can perform a lower leg exercise by him or herself. Such an exerciser might eliminate the need for manual massage since exercise stimulates blood circulation. Also, leg exercise would help to maintain lower leg muscle strength in the immobile patient.
U.S. Pat. No. 4,159,111 to Lowth, U.S. Pat. No. 3,525,522 to Piller, and U.S. Design Pat. No. 189,011 to Berne disclose single-axis lower leg exercisers. These machines have significant deficiencies for supine patient use, however. Because the footplate pivot points are located opposite the footplate from the user's ankle joint, substantial movement of the patient's leg is required to rotate a footplate. This movement is easily accomplished in a sitting position with the knee bent, but it is difficult in the supine position with the leg straightened. Also, these inventions are shown with horizontal base plates beneath the footplate pivots. The bases of the Lowth, Piller and Berne exercisers would be unstable to torsional moments when resting on a non-rigid bed surface. They would slide and tilt on the bed surface.
Resistance exercise of major body muscle groups is commonly done using free weights grasped by the hands or by using machines which have cables connecting pivoting members to weight stacks. These resistance means are not practical for ankle exercise. The high resistance levels needed for major muscle groups are not needed for ankle exercise. And the relatively small angle of rotation of the foot (short stroke) permits more compact resistance means to be used. Hydraulic cylinders and friction disks are the predominant resistance means used for lower leg exercisers. U.S. Pat. No. 4,605,220 to Troxel shows four hydraulic shock absorbers attached between a footplate and base. U.S. Pat. No. 4,650,183 to McIntyre shows two rotary hydraulic actuators connecting a footplate to a base. And U.S. Pat. No. 4,452,447 to Lepley et al. shows three hydraulic cylinders connected from a base to footplate cranks. Although smooth and speed controlled motion is provided by hydraulic resistance, disadvantages are its high cost and eventual leakage of hydraulic fluid. Friction disks, on the other hand, are inexpensive, more compact, and don't leak. The latter two features are especially important for a portable device for use in a hospital bed, for example.
Most exercise machines provide a constant resistance throughout the range of motion of a body member about its joint. But as the body member moves, the leverage of the muscle(s) being stressed changes. There is a position at which leverage is greatest. At the ends of the range of body member motion the leverage is usually lowest. Thus, if the resistance is set for optimum muscle stress at the greatest leverage position, the range of motion under this resistance will be very limited. On the other hand, if the resistance is set for optimum muscle stress at the ends of the range of motion, the resistance may be too low at the center of the range of motion. It is desired to have the resistance level vary with muscle leverage so that each muscle is evenly stressed throughout its range of movement.