Motor Control And Aging

Class Project 2- Motor Control and Aging

It is often assumed that as all humans age, their motor function becomes more and more impaired. Many people in the elderly population experience problems with posture and balance that can lead to falls. Falls that cause serious injury, such as bone fractures, are known to increase the mortality rate in the elderly. This subject is of particular interest to me as I work in Cardiac Rehabilitation and have seen many patients health spiral downward and eventually lead to death as a result of loss of motor control. Fifty percent of all people older than 80 years fall each year. Of those who fall, 20-30% have moderate to severe injuries such as hip fractures or head injures that decrease mobility and independence, and increase the risk for premature death. These figures make it clear that clinicians are in need of rehabilitation tools that can prevent the occurrence of falls in balance-impaired older adults.

Motor function incorporates a variety of cortical structures in both the central and peripheral nervous systems that work to control different aspects of movement. However, motor function is not a unitary process, and the association between characteristics like motor performance and muscle strength can differ. In a study by Buchman et. al entitled "Change in Motor Function and Risk of Mortality in Older Persons," researchers sought to discover whether change in motor function contributes to increased mortality rate after controlling for baseline motor function. The study also sought to find out whether the associations between motor performance and muscle strength and mortality vary, since motor function is not a collective process.

The results of the study were quite profound. Motor performance was found to be inversely related to age, positively associated with education, and men having higher levels of motor performance than women. Strength was also found to be inversely related to age, positively associated with education, and men having higher strength levels than women. During a mean follow-up time of 2.2 years, 81 of the 837 study participants died. In a proportional hazards model adjusted for age, sex, education and body mass index (BMI) , each one-unit annual increase in motor performance was associated with an approximately 11% decrease in the risk of mortality. In addition, each unit of increase in the level of baseline motor performance was associated with an approximately 9% decrease in risk of mortality. Similarly, each one-unit annual increase in strength was associated with a 10% decrease in the risk of mortality. Although men and women were analyzed together in the study, the results were similar when men and women were analyzed separately and after controlling for factors such as chronic disorders, cognition and physical activity levels. When both muscle strength and motor performance were examined in a single model, only annual and baseline change in motor performance were associated with mortality.

According to an article by Koceja et. al called "Age Differences In Postural Sway During Volatile Head Movement," postural sway in the elderly and the young are quite different and could be a main cause of falls and death in older adults. Ten young adults and ten older adults were tested on their postural sway characteristics using a Kistler force platform, and were tested under four experimental conditions: static postural sway with vision, static postural sway without vision, postural sway with vision and self-paced head turn movement, and postural sway with no vision and a self-paced head turn movement. The results of the study showed that during static conditions young subjects produced significantly less postural sway than the elderly in the vision and no-vision conditions. When asked to initiate the head turn, elderly subjects also increased their mean sway amplitude and decreased their frequency of sway whereas younger subjects made no such alterations to their sway profiles. The results of this study demonstrate the differences in postural sway amongst the two age groups, and the inefficient and mechanically wasteful way the elderly stand and perform tasks with respect to their postural stability.

Similarly, in a study entitled, "Attentional control of postural stability in institutionalised elderly people: effects of a physical exercise program" by Albinet et al., twelve older adults with a mean age of 81 years participated in the physical activity program, posture-balance-mobility (PBM) twice a week (1 hour per session) for 12 weeks. The researchers analyzed stabilometric data for surface and length of the center of pressure (COP) sway, with eyes open and eyes closed, under single-task and dual-task conditions on a firm floor before and after the training program. During the static postural evaluation and under the dual-task condition, subjects performed an attention-demanding cognitive and a random number generation task. The results of the training program suggested that elderly subjects could improve their ability to perform an attention-demanding cognitive task while standing still, in particular with their eyes closed. Although balance seemed to be less stable under the dual-task condition than under the single-task condition, these results could be interpreted as an improvement of the attentional control of postural stability.

In a study entitled "Effect of High-Intensity Strength- Training on Functional Measures of Balance Ability in Balance-Impaired Older Adults" by Hess and Woollacott, the researchers sought to evaluate the effect of a ten week, high intensity strength-training program targeting key lower extremity muscles for the purpose of improving postural control in balance-impaired adults in order to decrease fall risk and the subsequent problems associated with falling. After strength training, those who participated in the program were significantly stronger than the control subjects and improved significantly on the Berg Balance scale and the Activities-Specific Balance Confidence Scale which were used to measure their postural stability. Because of these significant improvements in balance and perceived balance, these changes were associated with a decrease in fall risk. This study shows that high-intensity strength