The threshold control theory of motor control describes how central regulation of reflexes, including the stretch reflex, results in different motor actions, in particular, muscle relaxation, motion, and isometric torque production in single- or multi-joint systems (Feldman and Levin 1995). Research in animals and in healthy subjects suggests that the tonic stretch reflex threshold (TSRT) may be altered by descending systems mediating both direct and indirect influences on motoneurons. Deficits in TSRT regulation in specific joints may also be related to limitations in the ability of the CNS to find multiple adaptive solutions for tasks involving multiple degrees of freedom (Levin and Feldman 1994). Results of studies of multijoint adaptability (i.e., motor equivalence; Lashley 1951) in patients with stroke will be summarized with an emphasis on goal-directed reaching from sitting (Shaikh et al., 2014; Subramanian et al, in press) and standing (Tomita et al. 2018) and reaching made in egocentric and exocentric space (Rodrigues et al. 2017; Hasanbarani et al, prep.). The implications for motor learning and recovery of motor function after neurological injury or disease will be discussed.

References
Feldman A.G., Levin M.F. The origin and use of positional frames of reference in motor control. Behavioral and Brain Science, 1995;18: 723-744.
Hasanbarani F., Piqué-Batalla M.A, Feldman A.G., Levin M.F. Pointing movements in different frames of reference: deficits after stroke. In preparation
Lashley, K.S. The problem of serial order in behavior. In L. A. Jeffress (Ed.), Cerebral mechanisms in behavior. 1951:112-131. New York: Wiley
Levin M.F., Feldman A.G. The role of stretch reflex threshold regulation in normal and impaired motor control. Brain Research, 1994;657: 23-30. PMID:7820623
Rodrigues M.R., Slimovitch M., Chilingaryan G., Levin M.F. Does the Finger-to-Nose Test measure upper limb coordination in chronic stroke? Journal of NeuroEngineering and Rehabilitation, 2017;14(1):6. DOI: 10.1186/s12984-016-0213-y. PMID: 28114996
Shaikh T, Goussev V., Feldman A.G., Levin M.F. Arm-trunk coordination for beyond the reach movements in adults with hemiparesis. Neurorehabilitation and Neural Repair, 2014;28(4):355-366. doi: 10.1177/1545968313510973. PMID: 24270057
Subramanian S.K., Baniña M.C., Sambasivan K., Haentjens K., Finestone H.M., Sveistrup H., Levin M.F. Inter-segmental coordination is impaired in chronic stroke. Neurorehabilitation and Neural Repair, in press
Tomita Y., Mullick A.A, Levin M.F. Reduced kinematic redundancy and motor equivalence during whole-body reaching in individuals with chronic stroke. Neurorehabilitation and Neural Repair, 2018;32(2):175-186. doi: 10.1177/1545968318760725. PMID: 29554848