Quadriceps Femoris
Muscle Group
Muscles
The Quadricep muscle group is made up of 4 muscles:
- Rectus femoris
- Vastus intermedius
- Vastus Lateralis (VL)
- Vastus medialis (VM)
- Articularis Genus
Tendon
The quadriceps tendon represents the convergence of all four muscles tendon units
The quadricep tendon inserts into the anterior aspect of the superior pole of the patella2.
Innervation
the femoral nerve (L2, L3, L4) innervates the quadriceps femoris muscles@duttonDuttonOrthopaedicExamination2020. The quadriceps muscles can act to extend the knee when the foot is off the ground, although more commonly, they work as decelerators, preventing the knee from buckling when the foot strikes the ground.14”
Functional Considerations
“In general, the knee extensor muscles produce a torque about twothirds greater than that produced by the knee flexor muscles.47,108 Through their isometric, eccentric, and concentric activations, this extensor torque is used to perform multiple functions at the knee. Through isometric activation, the quadriceps stabilizes and helps to protect the knee; through eccentric activation, the quadriceps controls the rate of descent of the body’s center of mass, such as when sitting, squatting, or landing from a jump. Eccentric activation of these muscles also provides shock absorption to the knee. At the heel contact phase of walking, the knee flexes slightly in response to the ground reaction force. Eccentrically active quadriceps muscles control the extent of the knee flexion. Acting as a spring, the muscle helps dampen the impact of loading on the joint. This protection is especially useful during high-impact loading, such as during landing from a jump, when making the initial foot contact phase of running, or when descending from a high step. A person whose knee is braced or unnaturally held in extension lacks this natural shock absorption mechanism.”3
“In the previous examples, eccentric activation of the quadriceps is employed to decelerate knee flexion. Concentric contraction of this muscle, in contrast, accelerates the tibia or femur toward knee extension. This action is often used to raise the body’s center of mass, such as during running uphill, jumping, or standing from a seated position.”3
Biomechanical Interactions between External and Internal Torques
“In many upright activities, an external (flexor) torque is acting on the knee. This external torque is equal to the external load being moved or supported, multiplied by its external moment arm. The external flexor torque must often be met or exceeded by an opposing internal (extensor) torque, which is the product of quadriceps force multiplied by its internal moment arm. An understanding of how these opposing torques are produced and functionally interact is the focus of this section. This topic is an important component of many aspects of strengthening the quadriceps as part of a rehabilitation program.”3
External Torque Demands Placed against the Quadriceps: Contrasting “Tibial-on-Femoral” with “Femoral-on-Tibial” Methods of Knee Extension
“Many strengthening exercises designed to challenge the quadriceps muscle rely on resistive, external torques generated only by gravity acting on the body. The magnitude of the external torque is highly dependent on the specific manner in which the knee is being extended. These differences are illustrated in Fig. 13.25. During tibial-on-femoral knee extension, the external moment arm of the weight of the lower leg increases from 90 to 0 degrees of knee flexion (see Fig. 13.25A–C). In contrast, during femoralon-tibial knee extension (as in rising from a squat position), the external moment arm of the upper body weight decreases from 90 to 0 degrees of knee flexion (see Fig. 13.25D–F). The graph included in Fig. 13.25 contrasts the external torque–knee angle relationships for the two methods of extending the knee between 90 degrees of flexion and full extension”3
“Information contained in the graph in Fig. 13.25 is useful for designing quadriceps strengthening exercises. By necessity, exercises that significantly challenge the quadriceps also stress the knee joint, patellofemoral joint, and periarticular connective tissues, such as the ACL. Clinically, this stress may be considered potentially damaging or therapeutic, depending on the underlying, if any, pathology of the person performing the exercise. A person with marked patellofemoral joint pain or painful knee arthritis, for example, is typically advised against producing large muscularbased stresses on the knee. A completely healthy person or a high-level athlete in the later phases of postsurgical ACL rehabilitation, in contrast, may actually benefit from such judiciously applied muscular stresses to the knee.”3
“External torques applied to the knee by a constant load vary in a predictable fashion, based on knee angle and orientation of the limb segments. As depicted by the red shading in the graph in Fig. 13.25, external torques are relatively large from 90 to 45 degrees of flexion via femoral-on-tibial extension, and from 45 to 0 degrees of flexion via tibial-on-femoral extension. Reducing these external torques can be accomplished by several strategies. An external load, for example, can be applied at the ankle during ibial-on-femoral knee extension specifically between 90 and 45 degrees of flexion. This activity can be followed by an exercise that involves rising from a partial squat position, a motion that incorporates femoral-on-tibial extension between 45 and 0 degrees of flexion. Combining both exercises in the manner described provides only moderate to minimal external torques against the quadriceps, throughout a continuous range of motion. This strategy of applying external torque has been considered appropriate when attempting to strengthen the quadriceps yet minimize the stress on the underlying patellofemoral joint.261”3
Internal Torque–Joint Angle Relationship of the Quadriceps Muscle
“Maximal knee extension (internal) torque typically occurs between 45 and 70 degrees of knee flexion, with less torque produced at the near extremes of flexion and extension.115,169,171,254,268 The shape of this torque-angle curve varies, however, based on the type and speed of activation and position of the hip. A representative maximal-effort torque versus joint angle curve obtained from healthy male subjects is displayed in Fig. 13.26. In this study, subjects produced maximal-effort (isometric) knee extension torque with hips held fixed in extension.297 As depicted by the red line in Fig. 13.26, maximal-effort knee extension torque remains at least 90% of maximum between 80 and 30 degrees of flexion. This high-torque potential of the quadriceps within this arc of motion is used during many functional activities that incorporate femoral-on-tibial kinematics, such as ascending a high step, rising from a chair, or holding a partial squat position while participating in sports, such as basketball or speed skating. Note the rapid decline in internal torque potential as the knee angle approaches full extension. Most studies report a 50% to 70% reduction in maximal internal torque as the knee approaches full extension.92,171,254 Of interest, the external torque applied against the knee during femoral-on-tibial extension also declines rapidly during this same range of motion (see Fig. 13.25, graph). There appears to be a general biomechanical match in the internal torque potential of the quadriceps and the external torques applied against the quadriceps during the last approximately 45 to 70 degrees of complete femoral-on-tibial knee extension. This match accounts, in part, for the popularity of “closed-kinematic chain” exercises that focus on applying resistance to the quadriceps while the upright person moves the body through this arc of femoralon-tibial knee extension.”3
Extensor Lag
“Persons with significant weakness in the quadriceps often show considerable difficulty completing the full range of tibial-on-femoral extension of the knee, commonly displayed while sitting. This difficulty persists even when the external load is limited to just the weight of the lower leg. Although the knee can be fully extended passively, efforts at active extension typically fail to produce the last 15 to 20 degrees of extension. Clinically, this characteristic demonstration of quadriceps weakness is referred to as an extensor lag.”3
“Extensor lag at the knee is often a persistent and perplexing problem during rehabilitation of the postsurgical or posttraumatized knee. The mechanics that create this condition during the seated position are as follows. As the knee approaches terminal extension, the maximal internal torque potential of the quadriceps is least while the opposing external (flexor) torque is greatest (compare graphs in Figs. 13.25 and 13.26). This natural disparity is not observed in persons with normal quadriceps strength. With significant muscle weakness, however, the disparity often results in extensor lag.”3
“Swelling or effusion of the knee increases the likelihood of an extensor lag. Swelling increases intra-articular pressure, which can physically impede full knee extension.340 Increased intraarticular pressure can also reflexively inhibit the neural activation of the quadriceps muscle.64,212,243 Methods that reduce swelling of the knee, therefore, can have an important role in a therapeutic exercise program of the knee. Passive resistance from hamstring muscles that are stretched across a flexed hip in a seated position can also play a role in limiting full extension.”3