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Muscle Memory. It's worth remembering.

Muscle memory has been used synonymously with motor learning, which is a form of procedural memory that involves consolidating a specific motor task into memory through repetition. When a movement is repeated over time, a long-term muscle memory is created for that task, eventually allowing it to be performed without conscious effort. This process decreases the need for attention and creates maximum efficiency within the motor and memory systems. Examples of muscle memory are found in many everyday activities that become automatic and improve with practice, such as riding a bicycle, typing on a keyboard, typing in a PIN, playing a musical instrument, or martial arts.

History Movement and motor learning Movement is a critical part of one's life, and it is a major component of human evolutionary development. It has been suggested that our developed cognitive capacities evolved so we could make movements essential to our survival. For example, cognitive abilities evolved so we could use tools, build shelter, and hunt for animals. The origins of research for the acquisition of motor skills stem from philosophers such as Plato, Aristotle and Galen. Friedrich Bessel is a philosopher who is especially noteworthy, as he was among the first to empirically observe motor learning. Bessel tried to observe the difference in his colleagues with the method in which they recorded the transit time of stars. After the break from tradition of the pre-1900s view of introspection, psychologists emphasized research and more scientific methods in observing behaviours. Thereafter, numerous studies exploring the role of motor learning were conducted. Such studies included the research of handwriting, and various practice methods to maximize motor learning. Research suggests we do not start off with a blank slate with regard to motor memory although we do learn most of our motor memory repertoire during our lifetime. Movements such as facial expressions, which are thought to be learned, can actually be observed in children who are blind; thus there is some evidence for motor memory being genetically pre-wired. One of the earliest and most notable studies regarding the retention of motor skills was by Hill, Rejall, and Thorndike, who showed savings in relearning typing skills after a 25-year period with no practice.

Muscle memory encoding The neuroanatomy of memory is widespread throughout the brain; however, the pathways important to motor memory are separate from the medial temporal lobe pathways associated with declarative memory. As with declarative memory, motor memory is theorized to have two stages: a short-term memory encoding stage, which is fragile and susceptible to damage, and a long-term memory consolidation stage, which is more stable. The memory encoding stage is often referred to as motor learning, and requires an increase in brain activity in motor areas as well as an increase in attention. Brain areas active during motor learning include the motor and somatosensory cortices; however, these areas of activation decrease once the motor skill is learned. The prefrontal and frontal cortices are also active during this stage due to the need for increased attention on the task being learned. However, conflicting evidence suggests that a single plasticity mechanism is not sufficient and a multiple plasticity mechanism is needed to account for the storage of motor memories over time. Regardless of the mechanism, studies of cerebellar-dependent motor tasks show that cerebral cortical plasticity is crucial for motor learning, even if not necessarily for storage.

Muscle memory consolidation Muscle memory consolidation involves the continuous evolution of neural processes after practising a task has stopped. The exact mechanism of motor memory consolidation within the brain is controversial. However, most theories assume that there is a general redistribution of information across the brain from encoding to consolidation. Hebb's rule states that "synaptic connectivity changes as a function of repetitive firing." In this case, that would mean that the high amount of stimulation coming from practising a movement would cause the repetition of firing in certain motor networks, presumably leading to an increase in the efficiency of exciting these motor networks over time.

Though the exact location of muscle memory storage is not known, studies have suggested that it is the inter-regional connections that play the most important role in advancing motor memory encoding to consolidation, rather than decreases in overall regional activity. These studies have shown a weakened connection from the cerebellum to the primary motor area with practice, it is presumed, because of a decreased need for error correction from the cerebellum. However, the connection between the basal ganglia and the primary motor area is strengthened, suggesting the basal ganglia plays an important role in the motor memory consolidation process. To be specific, strength training enhances motor neuron excitability and induces synaptogenesis, both of which would help in enhancing communication between the nervous system and the muscles themselves. This confirms that muscle strength is first influenced by the inner neural circuitry, rather than by external physiological changes in the muscle size. Previously untrained muscles acquire newly formed nuclei by fusion of satellite cells preceding the hypertrophy. Subsequent detraining leads to atrophy but no loss of myo-nuclei. The elevated number of nuclei in muscle fibres that had experienced a hypertrophic episode would provide a mechanism for muscle memory, explaining the long-lasting effects of training and the ease with which previously trained individuals are more easily retrained.

On subsequent detraining, the fibres maintain an elevated number of nuclei that might provide resistance to atrophy; on retraining, a gain in size can be obtained by a moderate increase in the protein synthesis rate of each of these many nuclei, skipping the step of adding newly formed nuclei. This shortcut may contribute to the relative ease of retraining compared with the first training of individuals with no previous training history. Even a small amount of training may be enough to induce neural processes that continue to evolve even after the training has stopped, which provides a potential basis for consolidation of the task. In addition, studying mice while they are learning a new complex reaching task, has found that "motor learning leads to rapid formation of dendritic spines in the motor cortex contralateral to the reaching forelimb". However, motor cortex reorganization itself does not occur at a uniform rate across training periods. It has been suggested that the synaptogenesis and motor map reorganization merely represent the consolidation, and not the acquisition itself, of a specific motor task. Furthermore, the degree of plasticity in various locations is dependent on the behavioural demands and nature of the task. Transitive movements have representations that become programmed to the premotor cortex, creating motor programs that result in the activation of the motor cortex and therefore the motor movements. However, such susceptibility can be reduced with time. For example, if a finger pattern is learned and another finger pattern is learned six hours later, the first pattern will still be remembered. But attempting to learn two such patterns one immediately after the other could cause the first one to be forgotten. Repetitive behaviors, such as typing on a computer from a young age, can enhance such abilities. Therefore, children who learn to use computer keyboards at an early age could benefit from the early muscle memories.

Martin Hunt

London Personal Trainer

Oracle Fitness​

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