Perhaps, like me you have had times in your life when you were struck by a realization about the seemingly serendipitous interconnectedness of things you had not previously thought to be related. With so much discussion of late regarding the movement system, patterns have started to become evident regarding how many aspects of life influence, and in turn, are influenced by, movement. I can say with certainty that the relationships that I describe in my musings below surely represent just a small portion of the existing movement-related interactions, and I invite you to share others that you have noticed in JNPT's online blog site.
One of the statements that stands out from lectures during my graduate school years was that the nervous system evolved primarily for the purpose of movement and in response to movement-related needs—the need to find/capture food or, conversely, to avoid becoming food for another animal. When one reviews the history of evolution in the animal kingdom, it seems evident that over the eons as nervous systems evolved and became more sophisticated, so did the movements they could generate. Evidence indicates that bipedal locomotion may have evolved because of the advantages it brought for carrying food,1 and that movement is central to the evolution of the human species.2 An interesting finding from recent studies confirms that the opposite is also true, that the relationship between movement and the evolution of the nervous system is bidirectional; just as developmental advances in the nervous system impel more complex motor outputs, changes in movement drive the evolution of the nervous system.3
Evolution is but one of the many examples of reciprocal interactions related to movement. In the neurophysiologic basis of movement, we recognize numerous instances of reciprocity, from elemental reciprocal inhibition in the spinal cord, to efference copy in the premotor circuits, to the iterative motor loops formed by the basal ganglia and cerebellum. Furthermore, from the perspective of motor outputs, there are striking reciprocal relationships that offer opportunities to access and modulate the nervous system. While lack of movement and movement-related afferent input seems to be a key element of reflex dysregulation,4 conversely, movement provides afferent input that can have a beneficial modulating effect on reflex excitability.5
Likewise, beyond the widely acknowledged effects of movement repetitions on development of skill in motor functions, over the past decade, it has become irrefutably clear that motor activity strongly influences not only motor function but also cognitive function.6 The relationship between movement and cognition is also bidirectional, as the influence of cognitive activity on motor function is evident in studies of dual-task interference. The ability to perform a cognitive task simultaneously with a motor task is a hallmark of the consolidation of motor learning.7 Just as motor activity and cognitive health are intertwined, similar reciprocal relationships hold true for psychological health. Individuals with more positive affect are more likely to be physically active, and, conversely, physical activity appears to be a valuable tool in the prevention of depressive symptoms.8 On a larger scale, group exercise has been shown to be related to increased social bonding, and the reverse is also true—the social bonding that comes with group exercise can enhance motor performance.9
In the end, there are aspects of movement wherein we are only just beginning to understand the reciprocal relationships. Nowhere is this more true than the relationship between genetics and movement. As neurologic physical therapists, our experiences with patients whose genetic makeup puts them at risk for, or causes, motor disorders such as Parkinson disease, Huntington disease, dystonia, ataxia, or chorea have made clear to us the impact of genetics on motor function. Not only do genetic factors cause movement-related dysfunction but there is also more and more evidence accumulating about how genetic factors influence responsiveness to movement-related interventions.10 Auspiciously, the converse relationship also exists. In his 48th McMillan Lecture, Richard Shields, PT, PhD, FAPTA, described his studies that reveal the powerful regulatory effects that muscular contractions associated with movement have on gene expression.11 The full text of his lecture will be available in an upcoming issue of our sister journal Physical Therapy (PTJ); I invite you to ponder this, and all the other aspects of the astounding reciprocity of movement-related interactions, and share your insights into our JNPT community blog. For us as clinician-scientists for whom movement represents our primary domain of expertise, the many ways in which we can transform society by optimizing movement to improve the human experience seem incalculable.
1. Hewes GW. Hominid bipedalism: independent evidence for the food-carrying theory. Science. 1964;146(3642):416–418.
2. Kuhn SL, Raichlen DA, Clark AE. What moves us? How mobility and movement are at the center of human evolution. Evol Anthropol. 2016;25(3):86–97.
3. Aiello BR, Westneat MW, Hale ME. Mechanosensation is evolutionarily tuned to locomotor mechanics. Proc Natl Acad Sci U S A. 2017;114:4459–4464.
4. Lundbye-Jensen J, Nielsen JB. Immobilization induces changes in presynaptic control of Group Ia afferents in healthy humans. J Physiol. 2008;586:4121–4135.
5. Estes SP, Iddings JA, Field-Fote EC. Priming neural circuits to modulate spinal reflex excitability. Front Neurol. 2017;8:17.
6. Sáez de Asteasu ML, Martínez-Velilla N, Zambom-Ferraresi F, Casas-Herrero Á, Izquierdo M. Role of physical exercise on cognitive function in healthy older adults: a systematic review of randomized clinical trials. Ageing Res Rev. 2017;37:117–134.
7. Smith E, Cusack T, Cunningham C, Blake C. The influence of a cognitive dual task on the gait parameters of healthy older adults: a systematic review and meta-analysis. J Aging Phys Act. 2017:1–35.
8. Lindwall M, Larsman P, Hagger MS. The reciprocal relationship between physical activity and depression in older European adults: a prospective cross-lagged panel design using SHARE data. Health Psychol. 2011;30:453–462.
9. Davis A, Taylor J, Cohen E. Social bonds and exercise: evidence for a reciprocal relationship. PLoS One. 2015:10(8):e0136705.
10. Goldberg A, Curtis CL, Kleim JA. Linking genes to neurological clinical practice: the genomic basis for neurorehabilitation. J Neurol Phys Ther. 2015;39(1):52–61.
11. Petrie MA, Kimball AL, McHenry CL, et al. Distinct skeletal muscle gene regulation from active contraction, passive vibration, and whole body heat stress in humans. PLoS One. 2016;11(8):e0160594.