Training induced adaptations in characteristics of postural reflexes in elderly men
Introduction
It is well documented that the aging neuromuscular system is affected by various degenerative processes leading to a general slowing down of neuromuscular performance [44]. As a consequence, the process of aging results in a decrease in muscle strength [22], [30], a reduced ability to develop explosive force [15], [20], [34], and a modulation of reflex pathways on the afferent [38] as well as on the efferent side [24], [43]. The diminished maximal and explosive force capacity is caused by a decrease in number of large alpha-motoneurons [43] accompanied by a reduction in number and size of especially type-II skeletal muscle fibers [6], [27]. The age-related changes in reflex activity can be attributed to a desensitization of muscle spindles [32], [41], a demyelination of sensory axons [26], [38] with a subsequent decrease in number of sensory neurons [29], changes in presynaptic inhibition [5], [31], and a reduction in number of inter-motoneurons [43] as well as alpha- and gamma-motoneurons [24], [25]. As a consequence, these degenerative processes result in a slower onset and smaller magnitude of postural responses to perturbation impulses and therefore dramatically increase the risk of falling in old age [10], [42]. Due to these neuromuscular limitations, it has to be questioned, whether specifically designed training regimen have an impact on structural modifications in the aging neuromuscular system. Several studies [7], [11], [15], [21] investigated the effects of heavy resistance (HR) training on maximum voluntary contraction (MVC) and rate of force development (RFD) in old age. It has been frequently observed, that even in this age group HR training results in an increase in maximal as well as explosive force production capacity [16], [34]. However, little is known concerning the impact of sensorimotor (SENSO) training on the aging neuromuscular system. Gollhofer [9] investigated the effects of a 4-week SENSO training on MVC, RFD and on postural stability in a group of young physical education students. It was observed that SENSO training leads to an increase in RFD as well as an improved postural stability due to an increase in reflex activation. According to the author, no significant changes in MVC were found. These results are confirmed by a recently published study [13]. As the impact of HR and SENSO training on reflex characteristics in the elderly has not been studied from a functional point of view in the elderly population, the purpose of the study was to examine how HR and SENSO training in elderly men (>60 years) influenced their postural and muscle responses to unexpected treadmill perturbations.
Section snippets
Subjects
Sixty retired males between the ages of 60 and 80 years (age 66.5 ± 4.6 years; body mass index 25.34 ± 2.6 kg/m2) provided written informed consent to participate in the study after experimental procedures were explained. The subjects were healthy with no history of serious muscular, neurological, cardiovascular, metabolic and inflammatory diseases. The participants were asked to fill in the validated “Freiburg questionnaire of physical activity©” [8] before the pre-tests and after the post-tests of
Results
After the 13 week training period, Pillai's trace reached the level of significance (p < 0.05) concerning the parameter latency. Pre- to post-tests led to a significant decrease in latency for the SENSO-group, which lasted from 70.167 ± 1.571 to 66.000 ± 1.469 ms (p < 0.01). No significant changes were noticed for the HR-group (Fig. 2).
Pillai's trace did not reach the level of significance (p < 0.05) concerning the parameter pre-innervation level. We also could not find any significant changes in
Discussion
In this study, HR and especially SENSO training resulted in specific adaptations in postural reflex characteristics in subjects between 60 and 80 years of age. This is of great interest, given the fact that in the same study both training regimen caused an increase in MVC and RFD, which has been published elsewhere [11]. However, when it comes to postural reflexes, positive adaptations were primarily seen in the SENSO-group that performed unilateral stabilization tasks and not in the HR-group.
Acknowledgement
The authors would like to thank Dr. Harald Seelig for providing us with statistical advice.
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