Sensing of Leg Position and Movement
Condition: Proprioception
Study type: Observational

Summary: 
      This study will collect information on how people sense leg position and movement. The
      findings may help scientists develop better ways to evaluate and treat joint problems.

      Healthy adult volunteers between 21 and 40 years of age may be eligible for the study.
      Candidates are screened with a brief questionnaire and examination to determine their
      strength, flexibility, and sensation.

      Participants sit on a specially designed chair, with their foot and leg placed in a
      custom-made apparatus that controls knee and ankle movements. The skin is marked to indicate
      the area of interest for ultrasound assessment of muscle. Subjects respond to joint position
      changes for several trials. The procedure takes a maximum of 2.5 hours to complete.

      ...
    

Detailed description: 
      Proprioception can be described as afferent information typically arising from peripheral
      mechanoreceptors that contribute to postural control, joint stability and conscious sensation
      of movement. Sensation of movement can be further divided into joint position sense (JPS) and
      the detection of passive movement sense (DPMS). Collectively, these two sensory modalities
      are commonly referred to as joint kinesthesia. Joint kinesthesia appears dependent on
      specific joint anatomical structure, suggesting different levels of acuity among various
      joints. However, whole limb accuracy appears to be greater than summed error across multiple
      joints of an extremity. Some suggest that it is only JPS errors greater than 3 degrees that
      have any functional significance on gait. However, the authors' calculations of position
      error on gait neglect JPS errors from the ankle and hip, which could also severely influence
      whole limb position sense, impacting gait. We believe that the central nervous system (CNS)
      links together afferent proprioceptive feedback from multiple joints of a limb segment to
      reduce kinesthetic error across a whole limb. The redundancy of the afferent information can
      be used as an "error check" to improve proprioceptive feedback in order to maintain function.
      We have used the term Coupled Joint Proprioception (CJP) in order to describe this
      phenomenon.

      To better understand the relationship between CJP and human function, we would have to
      isolate movement at two adjacent joints, while controlling bi-articular muscle length, to
      determine its influence on single joint kinesthesia. Bi-articular muscles provide a
      mechanical linkage within a limb to transfer forces. Afferent information from bi-articular
      muscles in particular could provide a context with which proprioceptive information from
      other structures (single joint muscles, joint or cutaneous receptors) can maintain or enhance
      proprioception within a limb. The redundant information, provided by the two-joint muscles,
      is the basis on which we describe CJP.

      The overall objective of this non-invasive pilot study is to establish the methodology
      necessary to test the influence of CJP on knee joint kinesthesia and proprioceptive
      capabilities. The primary goal is to establish two experimental conditions in which similar
      motions of simultaneous knee joint extension and ankle joint plantar flexion result in
      shortening and lengthening of all gastrocnemius muscle fibers. Following establishment of
      these conditions, the second goal is to develop and evaluate novel methods for studying the
      influence of CJP on the detection of passive movement and joint position sense at the knee
      joint. The information from this pilot data will also help determine the total number of
      subjects required to undertake a larger clinical investigation of the CJP phenomenon.

      It is important to study CJP, as proprioception is typically measured clinically at a single
      joint in human subjects. Human function usually incorporates multiple joints, suggesting that
      CJP, measured across two joints, could be more representative of human proprioceptive
      function. Therefore, CJP would provide an avenue to better study the influence of
      proprioceptive feedback on human function such as walking. This is especially important
      because maintaining proprioceptive feedback while walking may minimize falls in patients who
      are at risk due to lower extremity injuries or pathologies.
    

Keywords: Kinesithesia; Sensorimotor Function; Somatosensory; Muscle Spindles; Sensory Feedback; Healthy Volunteer; HV