Metastability Strength Training to Prevent Elderly Individuals from Falling

Das Sturzrisiko im Alter ist mit Nachlassenden Fähigkeiten in Kraft-, Gleichgewicht und Koordination assoziiert. In Kombination mit reduzierten kognitiven Ressourcen kann die Fähigkeit, flexibel und robust auf interne und externe Störungen zu reagieren, negativ beeinflusst sein [3]. Einbußen in motorischen und kognitiven Funktionen können zudem dazu führen, dass Situationen mit Unsicherheiten gemieden werden und vorhandene Ressourcen nicht ausgeschöpft werden [4]. Metastabilitätskrafttraining (MKT), ein Krafttraining, bei der Lasten auf „instabilen“ Unterlagen bewegt werden, stellt eine Trainingsform mit unsicherer Gleichgewichtslage dar. Nachfolgend werden vergangene und aktuelle Projekte zu Effekten von MKT auf Motorik und Kognition vorgestellt. Die Wirkungsmechanismen dahinter sollen in weiteren Projekten erforscht werden.

›Using resistance training on unstable supports or with instability devices athletes aim to prepare their neuromuscular system for sudden and unforeseen impairments in equilibrium impeded by the environment or through sports partners. In contrast to athletes, older adults aim to avoid such situations impeded by instability to reduce a possible risk of falling. The goal of this review is to outline the specific benefits of resistance training on unstable supports or with instability devices, denote as metastability resistance training (MRT), in older adults while extending knowledge of past reviews in this field. Existing studies comparing MRT to traditional resistance training (RT) on stable surfaces are reviewed and summarized. Our review shows that MRT: a) is safe for the older adult when properly introduced and supervised; b) requires smaller training loads and stresses larger articular areas while providing similar or larger gains in strength as traditional RT on stable surfaces; c) provides extended gains in functional mobility, balance, and power; d) offers a strengthening of stabilizer muscles whose strength loss is assumed to facilitate falls; e) stabilizes gait performance and, thus, reduces the risk of falls; f) improves cognitive performance reducing reductions the fear of falling and improves executive functions. Moreover, MRT was found to be particularly beneficial for Parkinson’s disease patients. Hence, MRT could be a very useful tool to complement the physical conditioning of older adults.

Cognitive and neurocognitive approaches to human healthy aging attribute age-related decline to the biologically caused loss of cognitive-control functions. However, an embodied-cognition approach to aging implies a more interactive view according to which cognitive control emerges from, and relies on a person’s active encounters with his or her physical and social environment. We argue that the availability of cognitive-control resources does not only rely on biological processes but also on the degree of active maintenance, that is, on the systematic use of the available control resources. Unfortunately, there is evidence that the degree of actual use might systematically underestimate resource availability, which implies that elderly individuals do not fully exploit their cognitive potential. We discuss evidence for this possibility from three aging-related issues: the reduction of dopaminergic supply, loneliness, and the loss of body strength. All three phenomena point to a downward spiral, in which losses of cognitive-control resources do not only directly impair performance but also more indirectly discourage individuals from making use of them, which in turn suggests underuse and a lack of maintenance—leading to further loss. On the positive side, the possibility of underuse points to not yet fully exploited reservoirs of cognitive control, which calls for more systematic theorizing and experimentation on how cognitive control can be enhanced, as well as for reconsiderations of societal practices that are likely to undermine the active maintenance of control resources—such as retirement laws.

Aging is associated with declines in physical and cognitive performance. While there is no doubt about beneficial effects of physical exercise on proxies of strength and balance, the overall evidence for positive effects of resistance and balance training on executive functions is rather inconsistent. Whether the simultaneous exercising of strength and balance, i.e., instability resistance training, promotes executive functions in older adults is unknown. In the present trial, we tested the effects of unstable vs. stable resistance training on executive functions. Sixty-eight healthy older adults aged 65–79 years were randomly assigned to either an instability free-weight resistance training or one of two stable machine-based resistance training programs. Each group exercised twice a week on non-consecutive days for 10 weeks. Four tests to evaluate specific domains of executive functions were administered prior and following training: working memory, processing speed, response inhibition and set-shifting. The instability resistance training group improved working memory, processing speed and response inhibition from pre to post-test. In contrast, we found no improvements in executive functions for both stable resistance training groups. Our results demonstrate that 10 weeks of instability resistance training suffice to improve executive functions in older adults.

Healthy older adults have shown to stabilise the trajectory of the swing foot by kinematic synergies during walking across an even surface. Since surface configuration (e.g.,uneven surface) can alter lower limb kinematics, walking across an uneven surface may affect kinematic synergies, particularly with age. Therefore, the purpose of the study was to quantify age and surface related changes in a synergy index and its variance components using the uncontrolled manifild approach (UCM).Thirteen healthy younger adults and 11 healthy older adults walked across a 10m path under two conditions (even and uneven). Although kinematic synergies exist independent of age during walking across a uneven surface, composition of older adults' joint configuration variance was meaningfully different.

The need to move over uneven terrain is a daily challenge. In order to face unexpected perturbations due to changes in the morphology of the terrain, the central nervous system must flexibly modify its control strategies. We analysed the local dynamic stability and the modular organisation of muscle activation (muscle synergies) during walking and running on an even- and an uneven-surface treadmill. We hypothesized a reduced stability during uneven-surface locomotion and a reorganisation of the modular control. We found a decreased stability when switching from even- to uneven-surface locomotion (p < 0.001 in walking, p = 0.001 in running). Moreover, we observed a substantial modification of the time-dependent muscle activation patterns (motor primitives) despite a general conservation of the time-independent coefficients (motor modules). The motor primitives were considerably wider in the uneven-surface condition. Specifically, the widening was significant in both the early (+40.5%, p < 0.001) and late swing (+7.7%, p = 0.040) phase in walking and in the weight acceptance (+13.6%, p = 0.006) and propulsion (+6.0%, p = 0.041) phase in running. This widening highlighted an increased motor output’s robustness (i.e. ability to cope with errors) when dealing with the unexpected perturbations. Our results confirmed the hypothesis that humans adjust their motor control strategies’ timing to deal with unsteady locomotion.

Locomotor stability is challenged by internal perturbations, e.g., motor noise, and external perturbations, e.g., changes in surface compliance. One means to compensate for such perturbations is to employ motor synergies, defined here as co-variation among a set of elements that acts to stabilize, or provide similar trial-to-trial (or step-to-step) output, even in the presence of small variations in initial conditions. Whereas evidence exists that synergies related to the upper extremities can be trained, the extent to which lower limb synergies, such as those which may be needed to successfully locomote in complex environments, remains unknown. The purpose of this study was to evaluate if resistance training (RT) in unstable environments could promote coordination patterns associated with stronger synergies during gait. Sixty-eight participants between the age of 65 and 80 were randomly assigned to one of three different RT modalities: stable whole-limb machine-based RT (S-MRT), instability free-weight RT (I-FRT), and stable machine-based adductor/abductor RT (S-MRThip). Before and after RT, participants walked across an even lab floor and a more challenging uneven surface with and without holding a weighted bag. The uncontrolled manifold control analysis (UCM) was used to calculate the synergy index (i.e., strength of the kinematic synergy) related to stabilization of our performance variable, the mediolateral trajectory of the swing foot, under each condition. Regardless of RT group, there was no effect of RT on the synergy index when walking across the even lab floor. However, the synergy index during the two uneven surface conditions was stronger after I-FRT but was not affected by the other RT modalities. The stronger synergy index for the I-FRT group was due to improved coordination as quantified by an overall increase in variability in elemental variable space but a decrease in the variability that negatively affects performance. The unstable environment offered by I-FRT allows for exploration of motor solutions in a manner that appears to transfer to challenging locomotor tasks. Introducing tasks that promote, rather than limit, exploration of motor solutions seems to be a valuable exercise modality to strengthen kinematic synergies that cannot be achieved with traditional strengthening paradigms (e.g., S-MRT).