Levers and joints: what do these have to do with movement?

Our bodies are designed to move easily over distances using our legs as long levers. The joints enable flexible movement such as running, jumping, dancing and yoga. The legs house some of the largest muscle groups in the body that cross over a series of joints at the hip, knee, ankle and foot. When any of these muscles and joints along the chain within the lower limb do not move as designed, and move in compensatory ways, the lower limb is predisposed to injury.

Movement with a twist

The hip, knee and ankle joints allow different ranges of motion and directions of movement. The hip is a ball and socket joint and is therefore quite mobile. The ankle and foot at the bottom of the chain of segments and joints also allow for considerable movement. Conversely, the knee joint — the middle joint in these series of joints in the lower limb — operates largely in one plane of movement like a hinge. When one of these joints functions inefficiently, due to weakness in one of the muscles surrounding the joint, the other joints in the chain are affected.

For instance, if the hip becomes stiff or there is weakness in one of the gluteal muscles that results in instability during walking or running, the knee joint is often required to compensate for the limitations of the hip and becomes more ‘mobile’ (often twisting). Because the knee joint primarily moves in one plane, movement becomes painful with extra twisting required to stabilize the lower limb during repetitive movement such as walking or running. Conversely, a stiff foot or ankle will affect joints and muscles up the chain in the lower limb including the knee and hip, requiring them to move in a manner that may lead to joint and muscle injury.

Safe strengthening

Clinicians recognize that safe strengthening and rehabilitation of the knee following injury or surgery is essential to avoid reinjury. “Closed-chain exercises” safely accomplish this. Closed-chain exercises involve the foot or ankle in a fixed position, so you are weight-bearing through the hip, knee, and ankle when you are exercising. An example includes squatting while the feet are stationary and fixed on the floor as you move your body. Cycling is another example of a closed-chain exercise: the foot is fixed on the pedal as the leg moves. Closed-chain exercises result in minimal shearing of the knee joint. Consequently, closed-chain exercises are less likely to irritate a joint as you strengthen the muscles around it. The following exercises are closed-chain:

  • Squats
  • Lunges
  • Wall squats
  • Step ups
  • Cycling

Many of these exercises are integral components of the SimpliMove Health Exercise Programs. See some of the exercise challenges that incorporate these closed chain exercises (Challenge 1, Challenge 2, Challenge 5 or Challenge 7). Closed-chain exercises are typically quite functional and can closely replicate movement during daily tasks. “Open-chain exercises” involve movement of the hand or foot (end segment of the limb) when they are not fixed to the ground or an object. These exercises are usually not as functional as closed-chain exercises, but they are useful for isolating a specific muscle group that may need to be strengthened. Examples include seated leg extensions, calf pumps while sitting, and hamstring curls.

While there are many exercise choices for strengthening the lower limbs for training or rehabilitation after injury, closed-chain exercises such as squats, step ups and those listed above, can be very beneficial. They are typically the exercise of choice for recovery of functional movement.