SPECIFIC CLOSED-KINETIC-CHAIN STRENGTHENING EXERCISES FOR THE LOWER EXTREMITY Minisquats, Wall Slides The minisquat (Figure 3) or wall slide (Figure 4) involves simultaneous hip and knee extension and is performed in a 0 to 40 degree range. As the hip extends, the rectus femoris contracts eccentrically while the hamstrings contract concentrically. Concurrently, as the knee extends, the hamstrings contract eccentrically while the rectus femoris contracts concentrically. Both concentric and eccentric contractions occur simultaneously at either end of both muscles, producing a concurrent shift contraction. These concurrent shift contractions minimize the flexion moment at the knee. The eccentric contraction of the hamstrings helps to neutralize the effects of a concentric quadriceps contraction in producing anterior translation of the tibia.

The half squat produced significantly less anterior shear at the knee than did an open- chain exercise in full extension. A full squat markedly increases the flexion moment at the knee and thus increases anterior shear of the tibia.

Lunges Lunges should be used later in a rehabilitation program to facilitate eccentric strengthening of the quadriceps to act as a decelerator (Figure 5). Like the minisquat and wall slide, it facilitates cocontraction of the hamstring muscles.

Leg Press It provides stability, which decreases strain on the low back. It also allows exercise with resistance lower than body weight and the capability of exercising each leg independently (Figure 6). It has been recommended that leg-press exercises be performed in a 0 to 60 degree range of knee flexion.

Figure 8 Leg-press exercise.

Stair Climbing Stair-climbing machines have two basic designs. One involves a series of rotating steps similar to a department store escalator: the other uses two foot plates that move up and down to simulate a stepping-type movement. When exercising on the stair climber, the body should be held erect with only slight trunk flexion, thus maximizing hamstring recruitment through concurrent shift contractions while increasing the hip flexion moment and decreasing the knee flexion moment. (Figure 11-9).

Figure 7 Stairmaster stepping machine

Lateral Step-Ups Lateral step-ups are another widely used closed-kinetic-chain exercise (Figure 8). Step height can be adjusted to patient capabilities and generally progresses up to about 8 inches. Heights greater than 8 inches create a large flexion moment at the knee, increasing anterior shear force and making hamstring co-contraction more difficult. Lateral step-ups elicit significantly greater mean quadriceps EMG activity than a stepping machine. When performing a step-up. the entire body weight must be raised and lowered, while on the stepping machine the center of gravity is maintained at a relatively constant height. The lateral step-up can produce increased muscle and joint shear forces compared to stepping exercise. In situations where strengthening of the quadriceps is the goal, the lateral step-up has been recommended as a beneficial exercise.

Terminal Knee Extensions Using Surgical Tubing The greatest amount of anterior tibial translation occurs between 0 and 30 degrees of flexion during open-kinetic-chain exercise. Avoiding terminal knee extension after surgery became a well-accepted rule. Unfortunately, this practice led to quadriceps weakness, flexion contracture, and patellofemoral pain.  Closed-kinetic-chain terminal knee extension using surgical tubing resistance have created a means of safely strengthening-terminal knee extension (Figure 9). Application of resistance anteriorly at the femur produces anterior shear of the femur, which eliminates any anterior translation of the tibia.  This type of exercise performed in the 0 to 30 degree range also reduce anterior shear of the tibia. The use of rubber tubing produces an eccentric contraction of the quadriceps when moving into knee flexion.

Figure 9 Terminal knee extensions using surgical tubing resistance.

Stationary Bicycling The stationary bicycle has been routinely used in sport medicine, primarily for conditioning purposes when the injured athlete cannot engage in running activities (Figure 10). However, it also can be of significant value, as closed-kinetic-chain exercise device. The advantage of stationary bicycling over other closed-kinetic- chain exercises for rehabilitation is that the amount of the weight- bearing force exerted by the injured lower extremity can be adapted within patient limitations. The seat height should be carefully adjusted to minimize the knee flexion moment on the down stroke. However, if the stationary bike is being used to regain range of motion in flexion, the seat height should be adjusted to a lowered position using passive motion of the injured extremity.

Figure 10 Stationary bicycle

Balance Board and Minitramp The balance board (Figure 11) and minitramp (Figure -12 ) both provide an unstable base of support that helps to facilitate reestablishing proprioception and joint position sense in addition to strengthening. Working on the Balance board allows the sports therapist to provide stress to the lower extremity in a progressive and controlled manner. It allows the athlete to work simultaneously on strengthening and range of motion, while trying to regain neuromuscular control and balance. The minitramp may be used to accomplish the same goals, but it can also be used for more advanced plyometric training.

Figure11 Balance board exercise.

Slide Boards and Fitter Shifting the body weight from side to side during a more functional activity on either a slide board (Figure 13) or a Fitter (Figure 14) helps to reestablish dynamic control as well improving cardiorespiratory fitness. These motions produce valgus and varus stresses and strains to the joint that are somewhat unique to these two pieces of equipment.

Figure 14 The Fitter is useful for weight shifting

SPECIFIC CLOSED-KINETIC-CHAIN EXERCISES FOR THE UPPER EXTREMITY Weight Shifting A variety of weight-shifting exercises can be done to assist in facilitating glenohumeral and scapulothoracic dynamic stability through the use of axial compression. Weight shifting can be done in standing, quadruped, tripod, or biped (opposite leg and arm), with weight supported on a stable surface such as the wall or a treatment table (Figure 15 A-D), or on a movable, unstable surface such as a balance board, a wobble board, the KAT system, or a plyoball (Figure 16 A-D). Shifting may be done side to side, forward and backward, or on a diagonal. Hand position may be adjusted from a wide base of support to one hand placed on top of the other to increase difficulty.

Figure 15 Weight shifting. A, Standing. B, Quadruped. C, Tripod. D, Opposite knee and arm.

Push-Ups, Push-Ups with a Plus. Press-Ups, Step-Ups Push-ups and/or press-ups are also done to reestablish neuromuscular control. Push-ups done on an unstable surface such as on a plyoball require a good deal of strength in addition to providing an axial load that requires co-contraction of agonist and antagonist force couples around the glenohumeral and scapulothorathic joints while the distal part of the extremity has some limited movement (Figure 17). A variation of a standard push-up would be to have the athlete use reciprocating contractions on a stair climber (Figure 18) or doing single-arm lateral step-ups onto a step (Figure 19). Also, the athlete may perform push-ups in a variety of positions, including to overhead position on the Shuttle (Figure 20). Push-ups with a plus are done to strengthen the serratus anterior, which is critical for scapular dynamic stability in overhead activities (Figure 21). Press-ups involve an isometric contraction of the glenohumeral stabilizers (Figure 22).

Slide Board Upper-extremity closed-kinetic-chain exercises performed on a slide board are useful not only for promoting strength and stability but also for improving muscular endurance. In a kneeling position, the athlete uses a reciprocating motion, sliding the hands forward and backward, side to side, in a "wax on-wax off circular pattern, or both hands laterally (Figure 23). It is also possible to do wall slides in a standing position.