Force Absorption Through Bent Knees

The knees are very important in managing the force generated in the body during movement. This is because they are intermediaries between the upper body and the ground (via the feet). As such, the knees are themselves one of nature's engineering marvels; they need to support almost all of the weight of the body while also providing mobility.

To achieve these very difficult tasks, the knees have evolved into a complex yet very effective structure. The knee joint is actually composed of functional compartments which describe the interaction between the femur (upper leg bone) and patella (knee cap) and between the femur and tibia (lower leg bone). These are supported by various structures such as the bursae, cartilage, menisci, and ligaments that ensure smooth movement of the knee. To allow movement, the knee is surrounded by the largest and most powerful muscles of the body. Knee extension is provided by the quadriceps while flexion is provided by a complex of muscles at the back of the leg. Interaction by these muscles also provides for internal and external rotation movements of the knee.

The knees transfer forces between the ground and the body on a fairly continuous basis. Normal standing only generates about 1.0 times the person's body weight. Walking on the ground generally generates around 2.6x , treadmill walking is 2.05x, while biking is only 1.3x. Playing tennis generates up to 3.8x especially during serving and jogging produces around 4.3x. This means that the knees of an 80kg person will have to deal with around 4 times that weight during jogging. In spite of these massive forces, the knees are generally able to absorb them considering its size and the number of structures supporting it.

During activities, the forces generated on the knees are not confined to the knees. They are also transferred to the upper body via the pelvis, lower back, and to the rest of the upper body. For example, it is said that the most powerful punches are made when the muscles of the legs are recruited. This is because of the sheer size of the leg muscles. Experienced fighters can generate powerful forces through their legs which are transferred to the upper body and finally delivered by their shoulders, arms, and fist. One point that needs to be considered is the lower back. These are very important in the transfer of force from the legs to the upper body. However, compared to the knees, they are not as heavily fortified. In fact, the muscles supporting the legs are not as large and powerful. Instead, they are built for endurance since their main purpose is maintaining the proper posture of the body; hence the adage that states that we should lift with our legs and not with our backs.

There are certain activities and exercises where keeping the knees bent are especially important in protecting the spine. If the knees are not bent upon landing in certain activities, the force generated can overload the bones and discs of the spine, eventually leading to degeneration, disc prolapsed, back pains, and possible nerve root impingements. Essentially, exercises that require jumping and landing should be done with bent knees to help absorb the shock that would otherwise harm the spine, knee joint, and leg bones. The legs muscles are recruited and act as springs that help cushion the force generated on the knees during soft landings making them stronger.

For example, lifting a weight while jumping is best done with a soft landing with the knees slightly bent. The muscles of the knees in this position act as springs that absorb the force generated. If this were done with knees straight, the knees and the lower back will absorb the brunt of this force and cause damage in the long run. Dancers executing leaps and jumps are usually told to "go through the foot" which means executing a soft-landing starting from the toes to the heel. This is often extended by landing on slightly bent knees and hips because in this position, the knee and hip extensors are able to absorb a great amount of the force. In some sports such as basketball and soccer, soft landing with the knees are said to prevent injury and also allows for instant movement after the landing because the leg muscles are already placed on an optimal position to contract. Squat jumps are best done by jumping off the ground from the basic squat position. However, landing should be done with the knees slightly bent because landing on a completely straight leg can overly stress the leg bones and knee joint similar to how gymnasts injure their legs. Other exercises where soft landings with slightly bent knees should also be used include ankle hops, tuck jumps, standing long jumps, 180-degree jumps, split-squat jumps, single leg jumps, and box jumps.

Looking for a personal trainer in Brisbane who knows about knee absorption? Try Executive Results who has been in business since 2004. Force Absorption Through Bent Knees