Effects of long-term Tai Chi practice on balance and H-reflex characteristics

The purpose of the present study was to examine the effects of long-term Tai Chi practice on postural balance and H-reflex. Sixteen healthy volunteers, eight with three or more years of experience in Tai Chi training (Tai Chi Group-TCG), and eight with no experience in Tai Chi training (Control Group-CG) participated in the study. Postural sways were measured under four experimental conditions: (1) Standing still with eyes open (EO); (2) Standing still with eyes closed (EC); (3) Standing and turning head to left and right with eyes open (EOT); and (4) Standing and turning head to left and right with eyes closed (ECT). Paired reflex depression (PRD) of the soleus muscle was measured under two conditions: supine and standing. Less significant postural sway was observed in the TCG than in the CG under four conditions including EO, EC, EOT, and ECT (p \u3c 0.01). The TCG demonstrated 14.1%, 30.6%, 33.3% and 22.7% less postural sway, respectively. Significant PRD change from a supine to standing position was observed between TCG and CG (p \u3c 0.05). A significant correlation between PRD change (from supine to standing) and years of Tai Chi practice was observed (r = 0.80, p \u3c 0.05). The findings of this study support the positive effects of Tai Chi exercise on balance control under different conditions. Long-term Tai Chi exercisers also demonstrated different reflex modulation from a supine to standing position, and long-term Tai Chi practice may lead to a change of PRD modulation as neuroadaptation. © 2011 World Scientific Publishing Company & Institute for Advanced Research in Asian Science and Medicine

Effects of age on the spinal stretch reflex

Revue de la littérature concernant les modifications du réflexe myotatique dues au vieillissement

A REVIEW OF THE LITERATURE CONCERNING THE AGED POPULATION

The aging population in the United States, as well as throughout the world, is increasing at a dramatic rate. In the United States, for example, approximately 4.0 percent of the population were over the age of 65 years in 1900; whereas it is projected that 15-20 percent of the population will belong to this age category in the year 2000. Currently the state of Florida is the only state in which over 15 percent of the population is over the age of 65 years; it is projected that by the year 2020 thirty-one other states will also belong to this group. Even more striking is the number of individuals over the age of 75 years, as the average life expectancy is nearing 80 years. The purpose of this study is to review and summarize the current literature on the aged population. Included in this review are studies of the following aspects: the role of genetics in increasing the average life span, the sociological, psychological, and biological aspects of human aging. Also included in this review are the role of exercise and training in improving the quality of life in the aged population, as well as the role of diet, nutrition and medication. Specific emphasis was placed on the effect of training and performance as they relate to delaying the deleterious effects of aging. A comprehensive computer literature search for pertinent studies was performed, with emphasis being given to the most recent advances in the literature. Where appropriate, landmark studies from the past (e.g., older than 20 years) were included. Although the major part of the review consisted of studies conducted in the United States, studies from many countries were also included. In the final analysis, the researchers were interested in applying the results of this study to improve the quality of life of the aged population, and in dealing with the aged population from a variety of perspectives

RELATIONSHIP OF LEG STRENGTH, H-REFLEXES AND BALANCE IN YOUNG AND OLDER ADULTS.

The purpose of this study was to examine the relationship between leg strength (Hamstring and Quadriceps), H-reflex modulation and static balance ability in young and older subjects. Ten young (mean age - 22.4 yrs) and 18 older (age > 60 yrs) adults were tested. The older subjects were further divided in three groups of 6 subjects (3 males13 females): 60-69 yrs (mean age = 65.1 yrs), 70-80 yrs (mean age = 76.6 yrs) and over 80 yrs (mean age = 82.6 yrs). All older subjects were physically active, with no history of neuromuscular and/or orthopedic disorders. Each subject reported to the lab for one day of testing, during which three tests were administered: 1) H-reflex; 2) leg strength; and 3) static balance. For H-reflex testing, the procedures outlined by Hugon (1973) were followed. Surface electrodes (Therapeutic Unlimited) were applied to the soleus muscle of the right leg, and the soleus H-reflex was administered via a 1 ms electrical squarewave pulse (Grass Instruments S88 stimulator). The H-reflex recruitment curve was determined with the subject standing (maintaining balance), and prone. The Hh4 ratio (ratio of maximum H-reflex to maximum muscle response) was calculated under each condition. Reflex modulation was defined as the difference between the Hh4 ratio in the two conditions. For leg strength, both the quadriceps and hamstrings muscle groups were tested on a Cybex I1 isokinetic dynomameter. Five trials were administered at a speed of 60 degrees per second: Balance was measured with a Kistler force platform. The subject was instructed to stand motionless for six 15-second trials. The amount of sway (sagittal and lateral in mm) and the area of sway (cm2) was calculated with a customdesigned computer program (sample rate - 50 Hz). Of the six trials, three were performed with eyes open and three with eyes closed. Results indicated that the elderly adults had significantly lower H-reflexes than the young subjects in both the standing ( 31. 6% - 59. 9 % ) and the prone (31. 9 % - 7 3. 5 % ) conditions. Also, the young subjects demonstrated modulation of the H-reflex in the two postures, whereas the older adults did not. As expected, the older subjects experienced more sway that the younger subjects in both the eyes open (1668.34 - 1024.86 cm ) and the eyes closed (2268.55 - 1165.5 1 cm2) conditions. Also, without vision, the older subjects increased their sway by 35.9%, whereas the young subjects increased 13.7%. For the older adults, quadriceps strength (r = -0.40) and hamstring strength (r = -0.44) were moderately correlated with postural sway. These results indicate that both H-reflex modulation and leg strength may contribute to postural stability in the older adult. Further, as training induced changes in the reflex system have been established (Wolpaw, 1990), it is concluded that intervention programs targeting Hreflex modulation and leg strength may prove beneficial for fostering postural stability in the older adult

A Biomechanical Analysis of the Contributing Factors to Increases in Vertical Jump Height Following Exercise with Weighted Vests

Background: It has been shown that a bout of jumping exercise with weighted vests increases the subsequent countermovement jump height. However, it is not clear whether the improvement in jump height is due to the enhancement of joint power or due to other mechanisms such as neural adaptations. Methods: To investigate this dichotomy, we tested the acute neuromechanical changes following a preloaded exercise protocol (3 sets of 5 consecutive CMJs with a weighed vest equal to 15% of the body mass of the participant) that successfully increased the subsequent jump height. On average, jump height increased 1.52 cm (5.40%) after this exercise as compared to CMJs prior to the exercise protocol. Results: A significant decrease in the time from the start of the movement to take off (pre-take off duration) was observed. This decrease was exclusively caused by exercising with a weighted vest, since such a change was not observed in the control sessions in which participants exercised without the weighted vest. Our data showed that jumpers leave the ground with some degrees of knee flexion and upon exercising with weighted vest this amount of flexion increased and hence an increase in the jump height. However, no significant changes in peak values of lower limb joint angle, velocity, moment and power were observed. Conclusion: It is suggested that for designing weighted vest exercise protocols with the aim of increasing jump height, the idea of modifying the timing of the movement should be considered as a cause of the enhancement. This novel idea adds another mechanism for increasing the jump height following weighted vest exercise, along with the general belief of muscle potentiation

Effects of age vestibular and visual systems on the soleus H-reflex

The vestibular system, visual and proprioceptive pathways provide information about control of posture, movement and balance. Loss of postural control directly leads to a greater incidence of falling in the elderly population causing serious health problems. One important neuromuscular mechanism instrumental in the control of posture and balance is the reflex system. However, the age-related changes of vestibular and visual systems and their relationship with the reflex system are not clear. The purpose of this study was to investigate the effects of age, the vestibular and the visual systems on the modulation pattern of the soleus H reflex. Seventeen neurologically healthy volunteers were categorized by age in two groups: young (n = 8, mean age = 22.1 ± 5.0 yr.) and elderly (n = 9, mean age = 59.3 ± 12.8 yr.). Maximal soleus H-reflex (H-max) and motor response (M-max) amplitudes were determined prior to testing at each condition while subjects were lying supine on a tilt table for standardization. Stimulation intensity was set to evoke a 5-10% M-wave on each trial. Participants received 5 test H-reflex stimuli in two conditions, static 60º and dynamic 60º on a tilt table. Both tilt conditions were performed with vision and no vision. A 3-way repeated-measures analysis of variance (ANOVA) 2 (groups: young/old) x 2 (condition: static/dynamic) x 2(vision: vision/no vision) was used to assess changes in H-reflexes. All data were expressed relative to the H-reflex amplitude at 0º static on the tilt table. The results showed a significant 3-way interaction (p = .038). The old group showed greater H-reflex amplitude in the no vision condition at static 60º (vision:0.97; no vision:1.23) whereas in the young group less modulation was demonstrated in the same condition (vision:1.15; no vision:1.12). These results suggest in young subjects the vestibular system produced a suppression of the H-reflex with or without visual input; however, in the old group vision was necessary for this suppression. The interaction between the visual and vestibular systems as we age needs to be further explored.This work was funded by 2219- International Postdoctoral Research Scholarship Programme of The Scientific and Technical Research Council Of Turkey (TUBITAK) Scientific Human Resources Development. Award number:1059B191700345 and by the Spanish Ministry of Science and Innovation (PID2019-110074GB-8 I00/AEI/10.13039/501100011033)

Residential Proximity to Agricultural Fields and Neurological and Mental Health Outcomes in Rural Adults in Matlab, Bangladesh

Pesticide exposure is an important rural public health concern that is linked to a spectrum of health outcomes in farmers. However, little is known about these effects on residents living in close proximity to agricultural fields and who are not involved in regular farming. This paper compared the effects of residential proximity to farming lands on a number of neurological and mental health outcomes in adults. A cross-sectional study was performed on 57 adults involved in farming only occasionally in rural Matlab in Bangladesh. A health and demographic surveillance system (HDSS) and geocoding were used to define proximity to the agricultural field. Neurological health was measured using the trail making test, vibrotactile threshold measurement, and dominant ulnar nerve conduction velocity (NCV) amplitude. An adapted Center for Epidemiological Studies Depression scale (CES-D) questionnaire was used to evaluate mental health. Results indicated that respondents living near agricultural fields had significantly higher vibrotactile threshold in big toes (p < 0.004) and needed a longer time to complete the trail making test (p < 0.004) than those living far from fields after accounting for the covariates. Results of this pilot study suggest further investigations to establish the impact of pesticide exposure among occasional and non-farmers on neurological health outcomes