During stance phase, the knee is not stabilized by a single muscle, but by 𝗯𝗮𝗹𝗮𝗻𝗰𝗲𝗱, 𝘄𝗲𝗹𝗹-𝘁𝗶𝗺𝗲𝗱 𝗰𝗼-𝗰𝗼𝗻𝘁𝗿𝗮𝗰𝘁𝗶𝗼𝗻 𝗼𝗳 𝘁𝗵𝗲 𝗾𝘂𝗮𝗱𝗿𝗶𝗰𝗲𝗽𝘀 𝗮𝗻𝗱 𝗵𝗮𝗺𝘀𝘁𝗿𝗶𝗻𝗴𝘀. At the same time, the 𝗴𝗿𝗼𝘂𝗻𝗱 𝗿𝗲𝗮𝗰𝘁𝗶𝗼𝗻 𝗳𝗼𝗿𝗰𝗲 (𝗚𝗥𝗙) acting on the limb is constantly changing in both 𝗺𝗮𝗴𝗻𝗶𝘁𝘂𝗱𝗲 𝗮𝗻𝗱 𝗱𝗶𝗿𝗲𝗰𝘁𝗶𝗼𝗻 from heel strike, through mid-stance, to push-off.

What the nervous system must learn is therefore not strength alone, but a 𝗱𝘆𝗻𝗮𝗺𝗶𝗰 𝗸𝗻𝗲𝗲 𝘀𝘁𝗮𝗯𝗶𝗹𝗶𝘇𝗮𝘁𝗶𝗼𝗻 𝘀𝗸𝗶𝗹𝗹 that continuously adapts to these changing forces.

Many stroke patients begin walking 𝗯𝗲𝗳𝗼𝗿𝗲 𝗳𝘂𝗹𝗹 𝗿𝗲𝗰𝗼𝘃𝗲𝗿𝘆, when weakness, poor balance, or impaired control is still present. To avoid collapse, they often discover an effective but maladaptive solution: 𝗹𝗼𝗰𝗸𝗶𝗻𝗴 𝘁𝗵𝗲 𝗸𝗻𝗲𝗲 𝗶𝗻𝘁𝗼 𝗵𝘆𝗽𝗲𝗿𝗲𝘅𝘁𝗲𝗻𝘀𝗶𝗼𝗻. This strategy allows stance stability with minimal control demand. The problem is that once learned, this motor solution can persist. Even when selective motor control of the knee later improves, the patient may 𝗻𝗼 𝗹𝗼𝗻𝗴𝗲𝗿 𝗸𝗻𝗼𝘄 𝗵𝗼𝘄 𝘁𝗼 𝘀𝘁𝗮𝗯𝗶𝗹𝗶𝘇𝗲 𝘁𝗵𝗲 𝗸𝗻𝗲𝗲 𝘄𝗶𝘁𝗵𝗼𝘂𝘁 𝗵𝘆𝗽𝗲𝗿𝗲𝘅𝘁𝗲𝗻𝘀𝗶𝗼𝗻.

In other words, the issue is not that the muscles cannot work, but that the nervous system has learned the wrong solution to the stabilization problem.

Of course, knee hyperextension is not always purely a learned control issue. In some patients, additional factors push the knee into recurvatum during stance, such as:

- plantar-flexor spasticity or ankle contracture,

- severe weakness of the quadriceps or hamstrings,

- impaired proprioceptive sense at the knee joint.

Understanding 𝘄𝗵𝗶𝗰𝗵 𝗺𝗲𝗰𝗵𝗮𝗻𝗶𝘀𝗺 𝗱𝗼𝗺𝗶𝗻𝗮𝘁𝗲𝘀 in a given patient is crucial, because strengthening alone rarely solves the problem if the core issue is motor control and sensory prediction.

In an upcoming case report in the ASEAN Journal of Rehabilitation Medicine (January 2026), I describe 𝗿𝗲𝘃𝗲𝗿𝘀𝗮𝗹 𝗼𝗳 𝗰𝗵𝗿𝗼𝗻𝗶𝗰 𝗸𝗻𝗲𝗲 𝗵𝘆𝗽𝗲𝗿𝗲𝘅𝘁𝗲𝗻𝘀𝗶𝗼𝗻 𝘁𝘄𝗼 𝘆𝗲𝗮𝗿𝘀 𝗮𝗳𝘁𝗲𝗿 𝘀𝘁𝗿𝗼𝗸𝗲.

The locomotor training device used in that case can be seen at

http://www.sensiblestep.org

Source: Stroke Boot Camp : Neurological Rehabilitation

Why do some stroke patients with good leg strength still walk with knee hyperextension (genu recurvatum)?