Table 1.

Parkinson’s disease (PD) specificbalance components, constraints affectingbalance and exercises designedto reduce these constraints

Balance components	Constraints in PD	Exercise principles	Exercise objectives
SENSORY INTEGRATION
Integration of sensory information (somatosensory, visual and vestibular) for estimation of body position	- Impaired somatosensory integration	Walking tasks on varying surface with or without visual constraints	Improve interpretation of and reliance on somatosensory information
	- Poor proprioception
	- Visual dependency
APAs
Prediction and control of perturbation related to voluntary movements	- Poorly timed and scaled APAs	Voluntary arm/leg/trunk movements focusing on movement velocity and amplitude, and postural transitions	Improve APA strategies regarding quality (timing, amplitude) and task- specific adaptation
	- Bradykinesia
MOTOR AGILITY
Coordination between body parts and movement adaptation, e.g. regulation of movement and quick shifts between tasks	- Bradykinesia	Whole-body coordination during varying gait conditions and reciprocal movements. Quick shifts of movement characteristics (velocity, amplitude and direction) during predictable and unpredictable conditions	Improve whole-body coordination, ability to adapt movement and quick shifts between different tasks
	- Impaired whole-body coordination
	- Biomechanical constraints
	- Inflexible motor programming
STABILITY LIMITS
Whole-body regulation relative to the BoS	- Reduced functional stability limits	Voluntary leaning tasks in standing with varying BoS-stimulating weight shifts in multiple directions through arm and trunk movements	Improve the ability to safely control CoM within BoS to increase functional limits of stability
	- Biomechanical constraints
	- Poor proprioception
	- Impaired somatosensory integration

APAs = anticipatory postural adjustments; BoS = base of support; CoM = centre of mass.