As people get older, neuromuscular changes often result in an impaired ability to produce rapid force. Such a reduction in muscular power can then lead to functional mobility impairments, poor balance and an increased risk for falls. However, the mechanistic understanding of how reduced muscular power affects function and balance recovery, and how we can counteract it, is still lacking. This review selected studies that would provide further insight about the mechanisms that lead to the reported age-related loss of muscular power and functional impairments, as well as the benefits of power training compared to the traditional strength training approach for muscular performance, function and balance.

Our narrative review demonstrated that age-related reductions in nerve conduction velocity, discharge rate, number of functional motor units and available motorneurons are well-established.  Furthermore, muscle architecture and composition, muscle contractility and selective denervation of type II skeletal muscle fibers (high force and fast contraction fibers) are also affected by old age. These age-related changes lead to reduced neural drive, rate of neuromuscular activation and reduced muscle mass, classically known as sarcopenia. Ultimately, these changes have an impact on muscular performance and the rate of force development, which are both a crucial for generating muscle power. This could explain why impaired muscle power is such a potent predictor of functional independence, functional impairments and falls.

It seems quite clear from the literature that these age-related changes in our muscles areinevitable. So should we just give up and accept our fate? Or can we actually defeat the laws of nature and reduce (or even reverse!) the rate of age-related decline through exercise training. There is evidence that strength resistance training can prevent neuronal denervation and increase neural drive resulting in a greater neuromuscular performance. However, this type of resistance training has limited effects on power production because it does not focus on velocity of execution. A potentially viable alternative is power training. This alternative focuses on fast, explosive movements to have a stronger effect on muscle power.

Our literature review revealed a large variability in the paradigms used for traditional strength and power training, which makes it difficult to draw firm conclusions. Nonetheless, there seems to be some evidence suggesting that muscle power training might be beneficial in older individuals for improving muscular performance and functional mobility. Future research could look at whether power training could also prevent falls and investigate the optimal dose to have a maximal effect on functional mobility.

Figure. Conceptual model for age-related changes that lead to functional impairments and how strength and power training can affect these changes.

Publication

Inacio, M. (2016). The Loss of Power and Need for Power Training in Older Adults. Current Geriatrics Reports, 5(3), 141-149. doi: 10.1007/s13670-016-0176-7.

https://link.springer.com/article/10.1007/s13670-016-0176-7

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Perhaps you, like many members of our ISPGR community, have been engaged in the development and evaluation of interventions to improve postural balance and ambulation? Most likely, this was for frail members of our society who have an increased risk of falling due to reduced muscle strength/power, or in patient populations who suffer from musculoskeletal disease or degeneration?  In that case it is unlikely that you often venture into the sports medicine literature, let alone literature that establishes a theoretical framework for sport scientists who are engaged in the daily monitoring of elite athletes. In this blog, I would like to offer some creative ideas on how to evaluate physiological adaptations from a strength training programme for the frail elderly person, or how to monitor neuromechanical adaptations from ballroom dancing classes for the baby boomers.

In our recent perspective paper in Sports Medicine, we reviewed some of the sports science and sports medical literature on the recent developments of player load monitoring. The scientific field of player load monitoring has grown rapidly, and we believed that there was a lack of theoretical framework to justify the daily monitoring of a vast amount of variables in sports environments, ranging from subjective ratings of perceived exertion to a host of complicated derivatives from GPS-based position tracking. Historically, this has been the domain of exercise physiologists, who have gained extensive knowledge on physiological processes and the effects of different types of training regimes. Very few biomechanists have looked into this, and the knowledge on so-called ‘mechanobiological’ adaptations from training and exercise is still very limited. In order to address this important knowledge gap, we developed a theoretical framework that firstly separates a biomechanical load-adaptation pathway from the physiological load-adaptation pathway (see Figure). Secondly, the framework helps to identify observations that are associated with the external load (how is the body moving through and interacting with its environment), and observations that represent internal load (what is the stress on the internal structures and systems). The availability (and affordability) of wearable sensor technologies has made it possible to monitor external load more easily. Monitoring of the internal load and of the adaptations that are constantly taking place as a consequence of those loads, however, remain a huge challenge. For example, whilst sports scientists embrace the concept of supercompensation to explain the progressive physiological benefits from training and exercise, there are few experimental observations available that allow one to monitor this wonderful phenomenon actually taking place. Therefore, our perspective paper also addresses the practical implications and to some extent the pitfalls around measuring loads and adaptation outside a laboratory, some of which may well apply to other contexts than elite athlete monitoring.

Figure: A theoretical framework that separates a physiological load-adaptation pathway (left) from a biomechanical load-adaptation pathway (right). Measures that are indicative of what the body is doing (external load) are also separated from measures that represent the internal consequences to our body (internal load). Eventually, this internal load will cause adaptations which can be associated to each of these pathways, even if not exclusively so.

We hope that our perspective paper will assist the ISPGR community to consider using established methodologies from sports and exercise contexts into more clinical applications. For example, technologies developed by (and for) sports science could be used to evaluate physical loads due to therapeutic interventions. Or, established ratings of perceived effort multiplied by session time, may well be a useful tool in exercise programmes for the elderly or patient populations. Finally, we hope that the complex systems approaches to evaluate intricate interactions between various types of loads and load-adaptation pathways, could provide members of the ISPGR community with new ideas to better interrogate the multifactorial responses to multi-component exercise programmes within their clinical trials.

Publication

Vanrenterghem, J., Nedergaard, N.J., Robinson, M.A., Drust, B. (2017) Training load monitoring in team sports : A novel framework separating physiological and biomechanical load-adaptation pathways. Sports Medicine, Published Online First.

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Step training has recently been shown effective in preventing falls most likely because of its high task-specificity to rapid movements required to avoid falls. Step training systems using interactive video game technology have the potential for widespread implementation because they are low-cost and can be used unsupervised by older people at home. While this is all very promising, there is one thing we need to consider. Most stepping systems only train in a few directions (e.g., anterior-posterior and lateral directions). This is concerning because a randomised controlled trial (RCT) showed that upper-limb resistance training with limited directions deteriorated rapid movements in untrained directions in older adults. Therefore, to ensure the safety of home-based step training system, we conducted this study to examine transfer effects of step training on stepping performance in untrained directions among older adults.

We conducted an RCT with 54 older adults aged 65 years or older. The participants were randomly allocated to one of three groups; forward step training (FT), lateral plus forward step training (FLT) and no training (NT) groups. A choice stepping reaction time (SCRT) system was used for the training as well as assessments (see Figure). The FT group completed 200 forward steps, while the FLT group completed 100 forward steps and 100 lateral steps. The NT group rested for 15-min between the pre- and post-assessments. Prior to and immediately after the training or rest periods, the participants underwent a 2-min CSRT assessment. During the assessments, participants wore 14-mm diameter reflective markers to the lower limbs and their stepping movements were recorded using a 6-camera Vicon Bonita motion capture system. We used choice stepping reaction time and stepping kinematics in untrained, diagonal and lateral directions as outcome measures. Results indicated that FT induced delayed response time (a negative transfer effect) and faster peak stepping speed (a positive transfer effect) in the diagonal direction during the first step after the training. However, these effects were no longer apparent in the subsequent steps. Moreover, no such effects were seen in the FLT group.

Figure. A) The step mat and screen display used in the step training and stepping performance assessments. B) A typical example of stepping trajectory for one participant.

Our results suggest that if participants receive a step training program that only trains steps in the forward direction, this will improve stepping speed but may acutely slow response times in the untrained diagonal direction. However, this acute effect appears to dissipate after a few repeated steps. Step training in both forward and lateral directions appears to induce no negative transfer effects in untrained diagonal stepping. These findings suggest home-based step training systems (usually with 6 directions) present low risk of harm through negative transfer effects in untrained stepping directions.

Publication

Okubo Y, Menant J, Udyavar M, Brodie MA, Barry BK, Lord SR, Sturnieks DL. Transfer effects of step training on stepping performance in untrained directions in older adults: A randomized controlled trial. Gait & Posture 54 (2017) 50–55

http://www.gaitposture.com/article/S0966-6362(17)30048-6/abstract

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