- Cephalocaudal development
- The directional trend in motor development from the head downward toward the feet. Infants first gain control over the head and neck (lifting the head prone, tracking with the eyes at 1–2 months), then the upper trunk (rolling, sitting at 5–7 months), and finally the lower body (standing, walking at 10–15 months). This pattern mirrors the direction of prenatal neurological and muscular maturation, which proceeds in the same head-to-foot direction.
- Proximodistal development
- The complementary directional trend from the body's centre outward to the extremities. Trunk control develops before arm coordination, which develops before precise finger movements. In reaching and grasping, whole-arm sweeping movements (3–4 months) precede ulnar grasp, then radial-palmar grasp, and finally the pincer grip (opposing thumb and forefinger, ~8–10 months). Prenatal development follows the same proximodistal gradient.
- Primitive reflexes
- Involuntary, stereotyped motor responses present at birth, mediated by the brainstem and spinal cord before cortical control is established. Key examples include the Moro (startle) reflex — sudden arm extension then flexion in response to loss of head support; the rooting reflex — head turning toward cheek stimulation to facilitate feeding; the palmar grasp reflex — automatic gripping of objects placed in the palm; and the stepping reflex — walking-like leg movements when held upright. Primitive reflexes typically disappear during the first year as the frontal cortex matures. Their persistence or re-emergence after neurological injury is clinically significant.
- Dynamic systems theory
- Thelen and Smith's account of motor (and cognitive) development as the self-organisation of multiple interacting systems. A motor skill — rolling, walking, reaching — is not encoded in the nervous system waiting to be released by maturation; it emerges when all the relevant subsystems (neural, biomechanical, motivational, perceptual, environmental) reach a threshold of readiness. Because many subsystems interact, changing any one of them can alter the emergent skill. Classic demonstration: suppressing or enhancing the infant stepping reflex by manipulating leg mass (adding weights vs. immersing legs in water) showed that "disappearance" of the reflex at 2 months is not cortical inhibition but biomechanical change.
- Motor milestones
- Normative ages at which most infants in well-nourished samples achieve key gross motor skills. Representative sequence: prone head lift (~1–2 months), rolling back-to-front (~4–5 months), sitting without support (~6–7 months), crawling (~7–9 months), pulling to stand (~9–10 months), cruising (~10–11 months), walking independently (~12–15 months), running (~18 months). Ages vary across individuals and cultures; the sequence is more consistent than the timing.
- Perceptual-motor coupling
- The interdependence of motor and perceptual development throughout childhood. New motor capacities — sitting, crawling, walking — restructure the infant's perceptual world by changing what can be reached, explored, and seen from. Conversely, perceptual learning guides motor action: Gibson and Walk's visual cliff studies showed that crawling but not pre-crawling infants avoid the deep side, suggesting that locomotor experience calibrates depth perception for navigation. Perception and action are not independent developmental streams but coupled and mutually constitutive systems.