chicken and egg part 2: Pain & Weakness

In a study published in 2007 in Medicine and Science in Sports and Exercise, there was confirmation that a correlation exists between knee pain and hip muscle weakness on that same side. So, what comes first, knee pain or hip weakness? To date, it has been difficult to assess if the chicken comes before the egg (you pick which is which). What other studies demonstrate is that pain sensation leads to inhibition of muscles proximal or distal to the site of pain. In a study in Experimental Brain Research in 2005, pain was elicited via injection of an irritant into upper extremity muscles and it was found that, while pain did not alter the type and magnitude of arm movement during a repetitive task, the muscle recruitment patterns of neck and forearm muscles were significantly altered in the experimental (painful) group. The control (nonpainful) group demonstrated more consistent muscle activity to complete the repetitive task. So, it is plausible that knee pain causes inhibition over time of hip musculature, which leads to weakness. However, further longitudinal study is needed to determine whether weakness leads to knee pain.

Additionally, experimentally induced pain produced through injection of hypertonic saline directly into the upper, middle, and lower divisions of the trapezius in otherwise healthy subjects, resulted in decreased upper trapezius and increased lower trapezius activation on the painful side and increased trapezius activation on the contralateral side during repetitive bilateral flexion (research here). Further investigation of the influence of induction or removal of pain and the relationships between pain state, muscle activation, and kinematics is needed.

From our perspective, thankfully, knowing the relationship between pain and weakness/muscle control deficits up and down the kinetic chain is enough. That knowledge, in combination with a standardized movement assessment allows us to differentiate true weakness from altered muscle control and adds precision to our treatment paradigm in treating a multitude of movement impairments, including painful conditions. Treatment efficiency is the direction healthcare is moving. We are enthusiastic about empowering patients to manage their symptoms as soon as possible, to expedite painless return to activity and improved quality of life.