Aging of the somatosensory system: a translational perspective

Effect of physical exercise and age on knee joint position sense

This study aimed to test the hypotheses that knee position sense declines with age and that regular exercise can attenuate that decline. This cross-sectional study encompassed 69 older and 60 young adults divided in four groups (exercised-old, N=31; non-exercised-old, N=38; exercised-young, N=35; non-exercised-young, N=25) according to chronological age and exercise practice in the past year. Knee position sense was measured by open kinetic chain technique and active positioning and is reported as the absolute and relative angular error. Knee angles were determined by computer analysis of videotape images using the Ariel Performance Analysis System. Compared to their non-exercised counterparts, exercised-young and -old showed lower absolute and relative angular errors. The absolute (1.62+/-0.71 degrees) and relative errors (0.02+/-1.65 degrees) for exercised-young were lower than all other groups (p<0.001). The absolute and relative errors of exercised-old (4.27+/-2.49 degrees and 5.51+/-3.42 degrees) were similar to non-exercised-young (4.74+/-2.67 degrees and 4.18+/-3.40 degrees). The non-exercised-old exhibited higher absolute (9.35+/-4.34 degrees) and relative errors (9.73+/-5.15 degrees) than all other groups (p<0.001). The present data indicates that age has deleterious effects on knee position sense although regular exercise can attenuate that age-related decline.

Interoceptive awareness declines with age

Aging has been shown to increase sensory thresholds for a variety of exteroceptive and proprioceptive stimuli. However, the influence of aging on interoceptive awareness has received relatively little empirical attention. Here we report an inverse association between aging and interoception, as indexed by the ability to sense the heartbeat at rest. In a group of 59 participants ranging in age from 22 to 63 years, age inversely predicted heartbeat detection ability, both within and across several measurement sessions. On average, age accounted for 30% of the variance in heartbeat detection accuracy. Other attribute variables including body mass index and sex were not related to heartbeat detection ability. These findings provide clear empirical evidence that interoception, much like exteroception and proprioception, declines with age.

The effect of reduced somatosensation on standing balance: a systematic review

The objective of this review is to identify and review publications describing the impact of reduced somatosensation on balance. Based on knowledge of the association between specific somatosensory loss and deterioration of balance, conclusions can be made about role of somatosensation in standing balance. A systematic literature review is presented in which publications from the years 1993 through 2007 were searched in Medline and Embase. Medical Subject Headings (MESH) terms and free text words (related to balance, somatosensory loss, and lower limb) were used to perform the searches. Fifteen articles were selected for detailed review based on predetermined inclusion criteria, and three of the included articles described the effect of experimentally reduced somatosensation on balance in healthy subjects. Ten of the articles described balance in diabetic neuropathy (DN). The last two included articles described balance in Charcot-Marie-Tooth (CMT) disease type 1A (CMT1A) or type 2 (CMT2). The literature indicates that the tactile sensation is reduced in DN, CMT1A, and CMT2 and when the plantar surface of the feet was hypothermically anesthetized. Joint motion sensation seems to be impaired in patients with DN, and passive joint position sensation appears to be reduced in healthy subjects with anesthesia of ankle and foot from prolonged ischemia. This reduced somatosensation seems to have a negative effect on balance in patients with DN and CMT2; however, this appeared not to be the case in patients with CMT1A and in healthy subjects.

Effects of plantar hardness discrimination training on standing postural balance in the elderly: a randomized controlled trial

Objective: To investigate the effects of sensory perception exercises for discrimination of surface hardness by the soles of the feet on standing postural balance in the elderly.

Design: A randomized two-group parallel controlled trial.

Subjects: Twenty-four healthy people aged from 61 to 71 years were enrolled and randomly assigned to a perception exercise group (n = 12) or a control group (n = 12).

Intervention: The perception exercise group were given a task designed to train ability to discriminate different degrees of hardness of foam rubber. The training period was 10 days. Control group subjects were instructed to maintain a standing posture on foam rubber for 10 seconds for a total of 10 days.

Measurements: Before and after training we measured centre-of-gravity sway with the subject standing, obtaining sway path length and area of ellipse. The Functional Reach Test was used to measure the forward displacement distance of the centre of gravity.

Results: Our data revealed a significant reduction in centre-of-gravity sway post training in the perception exercise group as well as a significant increase in forward displacement of the centre of gravity. These parameters were unchanged in the control group. As to change values (difference between pre- and post-training values), the perception exercise group had significantly better values than the control group, indicating the efficacy of sensory perception exercises.

Conclusions: We demonstrated that standing postural balance was improved by sensory perception exercises involving the soles of the feet. Used in addition to balance training, such training for hardness discrimination could be effective in the clinical setting to improve balance in the elderly.

Head posture and neck pain of chronic nontraumatic origin: a comparison between patients and pain-free persons

OBJECTIVE

To compare standing head posture measurements between patients with nontraumatic neck pain (NP) and pain-free individuals.

DESIGN

Single-blind (assessor) cross-sectional study.

SETTING

Hospital and general community.

PARTICIPANTS

Consecutive patients (n=40) with chronic nontraumatic NP and age- and sex-matched pain-free participants (n=40).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Three angular measurements: the angle between C7, the tragus of the ear, and the horizontal; the angle between the tragus of the ear, the eye, and the horizontal; and the angle between the inferior margins of the right and the left ear and the horizontal were calculated through the digitization of video images.

RESULTS

NP patients were found to have a significantly smaller angle between C7, the tragus, and the horizontal, resulting in a more forward head posture than pain-free participants (NP, mean +/- SD, 45.4 degrees +/-6.8 degrees ; pain-free, mean +/- SD, 48.6 degrees +/-7.1 degrees ; P<.05; confidence interval [CI] for the difference between groups, 0.9 degrees -6.3 degrees ). Dividing the population according to age into younger (</=50y) and older (>50y) revealed an interaction, with a statistically significant difference in head posture for younger participants with NP compared with younger pain-free participants (NP, mean +/- SD, 46.1 degrees +/-6.7 degrees ; pain-free, mean +/- SD, 51.8 degrees +/-5.9 degrees ; P<.01; CI for the difference between groups, 1.8 degrees -9.7 degrees ) but no difference for the older group (NP, mean +/- SD, 44.8 degrees +/-7.1 degrees ; pain-free, mean +/- SD, 45.1 degrees +/-6.7 degrees ; P>.05; CI for the difference between groups, -4.9 degrees -4.2 degrees ). No other differences were found between patients and pain-free participants.

CONCLUSIONS

Younger patients with chronic nontraumatic NP were shown to have a more forward head posture in standing than matched pain-free participants. However, the difference, although statistically significant, was perhaps too small to be clinically meaningful.

Dual-task costs while walking increase in old age for some, but not for other tasks: an experimental study of healthy young and elderly persons

BACKGROUND

It has been suggested in the past that the ability to walk while concurrently engaging in a second task deteriorates in old age, and that this deficit is related to the high incidence of falls in the elderly. However, previous studies provided inconsistent findings about the existence of such an age-related dual-task deficit (ARD). In an effort to explain this inconsistency, we explored whether ARD while walking emerges for some, but not for other types of task.

METHODS

Healthy young and elderly subjects were tested under five different combinations of a walking and a non-walking task. The results were analysed jointly with those of a previous study from our lab, such that a total of 13 task combinations were evaluated. For each task combination and subject, we calculated the mean dual-task costs across both constituent tasks, and quantified ARD as the difference between those costs in elderly and in young subjects.

RESULTS

An analysis of covariance yielded no significant effects of obstacle presence and overall task difficulty on ARD, but a highly significant effect of visual demand: non-walking tasks which required ongoing visual observation led to ARD of more than 8%, while those without such requirements led to near-zero ARD. We therefore concluded that the visual demand of the non-walking task is critical for the emergence of ARD while walking.

CONCLUSION

Combinations of walking and concurrent visual observation, which are common in everyday life, may contribute towards disturbed gait and falls during daily activities in old age. Prevention and rehabilitation programs for seniors should therefore include training of such combinations.

[Vertigo and falls in the elderly. Part 1: epidemiology, pathophysiology, vestibular diagnostics and risk of falling]

Disorders of the equilibrium function in the elderly will increase in the coming years due to demographic changes in Germany. In addition to a reduction in the quality of life of affected patients, the risk of suffering from a fall increases with age. At the morphological level age-specific changes of the peripheral vestibular structures, somatosensory pathways and vision can be found, such as degenerative alterations, reduced number of cells and receptors and an accumulation of lipofuscin. Disorders of the equilibrium function in old age are individual-specific, complex procedures which develop from age-related physiological, degenerative alterations in the components of the sensomotor system which maintain equilibrium and can come into being together with vestibular and non-vestibular accompanying diseases as well as psychological factors.

Spinal and supraspinal adaptations associated with balance training and their functional relevance

Traditionally, balance training has been used to rehabilitate ankle injuries and postural deficits. Prospective studies have shown preventive effects with respect to ankle and knee joint injuries. Presently, balance training is not only applied for rehabilitation and prevention but also for improving motor performance, especially muscle power. The recent application of noninvasive electrophysiological and brain imaging techniques revealed insights into the central control of posture and the adaptations induced by balance training. This information is important for our understanding of the basic control and adaptation mechanisms and to conceptualize appropriate training programmes for athletes, elderly people and patients. The present review presents neurophysiological adaptations induced by balance training and their influence on motor behaviour. It emphasizes the plasticity of the sensorimotor system, particularly the spinal and supraspinal structures. The relevance of balance training is highlighted with respect to athletic performance, postural control within elderly people as well as injury prevention and rehabilitation.