**1.3 Proprioception and postural control**

During the execution of all motor tasks, proprioception is required to prepare, maintain, and restore the stability of both the entire body (postural equilibrium) and the segments (joint stability) [14, 15]. Postural control, defined as controlling the position of the body regarding the task in the environment, involves neural control of "postural equilibrium" and "postural orientation". Postural equilibrium consists of the coordination of sensory and motor strategies to maintain balance by controlling the body's center of mass (COM) over its base of support (BOS) to maintain postural stability during both intrinsic (self-initiated) and extrinsic (externally triggered) disturbances. The postural equilibrium controls stability during both static (i.e., quiet standing) and dynamic (i.e., walking and reaching) situations. Postural orientation involves positioning body alignment with respect to gravity, the support surface, visual environment, and other sensory reference frames [22].

Postural control is considered as a complex motor skill derived from the interaction of multiple sensorimotor processes, which are; biomechanical constraints (i.e., BOS, degrees of freedom, strength, limits of stability), movement strategies (i.e., reactive, anticipatory, voluntary), sensory strategies (i.e., sensory integration, sensory re-weighting), orientation in space (i.e., perception of visional verticality, perception of postural verticality), control of dynamics (i.e., gait, proactive), cognitive processing (i.e., attention, learning, reaction time), experience and practice [23]. Impairment of the proprioceptive sensation can disrupt any of these six resources, which contributes to postural control (**Figure 2**). "*Sensory strategies*" are one of the most critical issues to discuss. Sensory information from somatosensory (tactile sense and proprioception), visual and vestibular systems must be integrated to interpret complex sensory environments for achieving postural control. Depending on the environmental conditions, the relative contribution of each sensory system changes, which is referred to as "sensory re-weighting" [24]. Healthy persons rely on somatosensory (70%), vision (10%), and vestibular (20%) information when standing on a stable surface in a well-lit environment (13). On the other hand, when standing on an unstable surface, due to decreased dependence on surface somatosensory inputs for postural orientation, they need to increase sensory weighting to vestibular and visual information [25]. The dynamic regulation or re-weighting of sensory cues is essential for maintaining postural stability when moving between different environments requiring distinct sensorial systems, such as different surfaces (i.e., walking on the sidewalk, walking on grass) or different lighting (i.e., moving in a well-lit room, moving in a dark room) [23]. The interplay between these three sensory modalities is critical for accurate estimates of self-motion and postural control [26].

Besides different sensory cues, different mechanical conditions provide significant advantages to humans for maintaining upright standing [27]. Decreased proprioception could lead to "*biomechanical constraints*" such as abnormal joint biomechanics and decreased muscle strength [28, 29], leading to postural dyscontrol. The "*control of dynamics*" is defined as the ability to perceive body segments relative to one another to stabilize the COM. Maintaining COM requires input from multiple sensory systems, sensorial re-weighting, and multisensory integration to calculate body state, including the COM and heading [30]. "*Movement strategies*" (i.e., postural

#### **Figure 2.**

*Adapted from the framework of the six important resources required for postural control system by Horak, 2006 [23], the contribution of proprioception sensation to postural control.*

**23**

**3. Neurologic correlation**

*Proprioception and Clinical Correlation DOI: http://dx.doi.org/10.5772/intechopen.95866*

sway, ankle strategy, hip strategy) can be used to return the body to equilibrium in a stance position [23]. Without proprioceptive input from the ankle and knee, ankle muscle responses are delayed suggesting that lower leg balance correcting responses are triggered by hip and, possibly, trunk proprioceptive inputs. Especially hip muscle proprioceptive inputs, considered critical for automatic balance correcting responses [31]. Additionally, cervical proprioception is of particular importance for "*orientation in space*". Neck muscle inflow has effects on the perception of body orientation and motion. Prolonged, intense proprioceptive input from neck muscles can induce persistent influences on self-motion perception and cognitive body representation [32]. The loss of proprioception could also impact the "*cognitive processing*" specifically the reaction time, and other factors such as attention, memory, and visuospatial

abilities may contribute to spatial cognitive skills (**Figure 2**) [23].

**2. Clinical implications and evaluation of proprioception**

The loss of proprioceptive afferents may affect the control of muscle tone, disrupts postural reflexes, and severely impairs spatial and temporal aspects of movement [33]. Proprioceptive impairments are associated with various neurological conditions such as stroke [34], Parkinson's disease [35], peripheral neuropathy [36], as well as orthopedic conditions such as low back pain [37], neck pain [38], sports injuries like chronic ankle instability [39], ACL injuries [40], post-operatively such as mastectomy [41], knee arthroplasty [42], and aging [43]. Considering the importance of proprioception for motor control, a detailed evaluation of proprioceptive sense and application of treatment approaches focusing on training the proprioceptive sense is important for restoring motor function. Proprioception

can be measured by using specific and non-specific tests in clinical practice.

test, Rivermead Assessment of Somatosensory Perception] [44].

ceptive system in the performance of many activities of daily living [46].

*Specific Tests of Proprioception:* assess an individual's status regarding the joint position sense and kinesthesia [21]. *Joint position sense* tests assess precision or accuracy in repositioning the joint at a predetermined target angle and can be measured as active joint position detection (AJPD) [e.g., position matching task, position copying task] and passive joint position detection (PJPD) [e.g., thumb finding test, dual-joint position test] [44]. *Kinesthesia* tests assess the ability to perceive joint movement. For evaluating the perceptual aspect of proprioception, psychophysical thresholds represent the gold standard [33]. These tests are usually performed passively and can be measured by using passive motion detection threshold (PMDT) and passive motion direction discrimination (PMDD) [e.g., distal proprioception

*Non-specific Tests of Proprioception:* for determining the contribution of proprioceptive signals on balance control, functional balance tests can be used to provide an estimate of potential proprioceptive disturbances [33]. These tests involve all body and other sensory and motor functions; therefore, they are considered non-specific tests of proprioception [21]. *Balance tests* can be modified to challenge proprioception, such as unilateral/bilateral stance with eyes open/closed, different supporting surfaces (i.e., stable or unstable), and with/without perturbations [44, 45]. *Stereognosis* and *skilled motor function tests* are important as they indicate the contribution of proprio-

The complexity of sensorimotor systems requires deep knowledge of anatomy and physiology to analyze and localize the symptoms and the signs of the patients.

#### *Proprioception and Clinical Correlation DOI: http://dx.doi.org/10.5772/intechopen.95866*

*Proprioception*

postural control [26].

**22**

**Figure 2.**

*Adapted from the framework of the six important resources required for postural control system by Horak,* 

processing (i.e., attention, learning, reaction time), experience and practice [23]. Impairment of the proprioceptive sensation can disrupt any of these six resources, which contributes to postural control (**Figure 2**). "*Sensory strategies*" are one of the most critical issues to discuss. Sensory information from somatosensory (tactile sense and proprioception), visual and vestibular systems must be integrated to interpret complex sensory environments for achieving postural control. Depending on the environmental conditions, the relative contribution of each sensory system changes, which is referred to as "sensory re-weighting" [24]. Healthy persons rely on somatosensory (70%), vision (10%), and vestibular (20%) information when standing on a stable surface in a well-lit environment (13). On the other hand, when standing on an unstable surface, due to decreased dependence on surface somatosensory inputs for postural orientation, they need to increase sensory weighting to vestibular and visual information [25]. The dynamic regulation or re-weighting of sensory cues is essential for maintaining postural stability when moving between different environments requiring distinct sensorial systems, such as different surfaces (i.e., walking on the sidewalk, walking on grass) or different lighting (i.e., moving in a well-lit room, moving in a dark room) [23]. The interplay between these three sensory modalities is critical for accurate estimates of self-motion and

Besides different sensory cues, different mechanical conditions provide significant advantages to humans for maintaining upright standing [27]. Decreased proprioception could lead to "*biomechanical constraints*" such as abnormal joint biomechanics and decreased muscle strength [28, 29], leading to postural dyscontrol. The "*control of dynamics*" is defined as the ability to perceive body segments relative to one another to stabilize the COM. Maintaining COM requires input from multiple sensory systems, sensorial re-weighting, and multisensory integration to calculate body state, including the COM and heading [30]. "*Movement strategies*" (i.e., postural

*2006 [23], the contribution of proprioception sensation to postural control.*

sway, ankle strategy, hip strategy) can be used to return the body to equilibrium in a stance position [23]. Without proprioceptive input from the ankle and knee, ankle muscle responses are delayed suggesting that lower leg balance correcting responses are triggered by hip and, possibly, trunk proprioceptive inputs. Especially hip muscle proprioceptive inputs, considered critical for automatic balance correcting responses [31]. Additionally, cervical proprioception is of particular importance for "*orientation in space*". Neck muscle inflow has effects on the perception of body orientation and motion. Prolonged, intense proprioceptive input from neck muscles can induce persistent influences on self-motion perception and cognitive body representation [32]. The loss of proprioception could also impact the "*cognitive processing*" specifically the reaction time, and other factors such as attention, memory, and visuospatial abilities may contribute to spatial cognitive skills (**Figure 2**) [23].
