PT on the Net Research

Single Leg Weakness


I have a client who has developed weakness in the right leg. There is no pain, no problem walking or doing any lifts. However, when he tries to run, he loses some control of the right leg during the swing phase, making foot plant weak and erratic. He has no known injuries. There was soreness of peroneus longus at about the same time this started, although it is no longer sore. On lunges, the right knee wobbles when the foot is planted. He says it almost feels like the hip, knee and sometimes ankle need to just click into place for it to feel right (if that makes any sense). Thanks for any suggestions you may have. He is having a bout of bursitis in the right shoulder, in case there could be any link there.


Although there is no “known” injury, there is apparently some interference with normal motor control based on your client’s subjective reporting to you. And poor motor control goes hand in hand with poor or blocked feedback from the proprioceptors.

Your description of the problems with running raises the possibility that it is not an “erratic” leg during the swing phase but instead an unstable right lower extremity. I say this because you also mention his instability at the knee and hip during lunges. Remember, the moment the foot touches the ground everything changes.

The soreness in the peroneus longus is another possible clue. The area of the peroneus longus is a common referral site from the sciatic nerve. Pain or soreness can skip right to another area of distribution of the lumbar nerve, without the individual ever experiencing back pain or sciatica further up the leg or buttocks.

Going back to the fact that there is no known injury, it is very possible that this reduced motor control and proprioception developed over time. It probably started out as some altered movement pattern (for numerous possible reasons), eventually exhausting the body’s capacity to deal with it. The client’s description of “clicking into place” for things to feel right is probably accurate. There may be a reflexive inhibition of one or more joints at the knee, hip, pelvis or lower back.

My first suggestion is to assess your client’s posture. Check for things like pelvic obliquity, leg length discrepancies, asymmetrical anterior-posterior rotations of the innominates and increases or decreases in lumbar lordosis. This will provide insight into the involvement of the lumbar spine and the S.I. joints.

Next, you’ll want to assess his ability to distribute the ground reaction forces unilaterally by having him do a one-legged stork stance. Compare both sides to one another. Look for the knee going excessively valgus, the pelvis shifting laterally over the support leg and/or the torso flexing laterally away from the support leg. This assessment is most sensitive to weakness or inhibition of the gluteus medius. Once you’ve completed your assessment, you’ll want to incorporate the appropriate corrective exercises to influence your client’s motor patterns. Extremely effective corrective exercises can be found on my DVD, “Corrective Exercises for Powerful Change.” It is also important to avoid exercises such as the lunge (especially with added resistance) that may predispose your client to injury. If the instability goes unaddressed, exercises such as the lunge and running will promote altered movement patterns and further compensation.