Objective: Muscle weakness is an important risk factor for falls in older adults. Intensity and duration of muscle activity are important determinants of exercise effectiveness in combating muscle weakness. The aim of this paper was to assess the intensity and duration of muscle activity in Virtual Reality (VR) balance games. Materials and Methods: Thirty young and thirty healthy older adults played seven different VR balance games. Muscle activity of the Vastus Lateralis, Vastus Medialis, Soleus and Gluteus Medius was obtained using surface EMG. The processed EMG signals were divided in 200ms blocks, after which each block was categorized by its average normalized EMG activity i.e. >80%, 60-80%, 40-60% or <40% of maximum voluntary contraction (MVC). We calculated the total number of blocks in each category to score intensity, as well as the maximal number of consecutive blocks (MCB) >40% MVC, to identify prolonged muscle activity. Results: Muscle activity during game-play was mostly below 40% MVC and prolonged activation was lacking. Only the games that included more dynamic movements showed activation blocks of higher intensity and resulted in more MCB. Conclusion: Our method allowed us to analyze the overall muscle activity and the distribution of activity over a trial. Although the activation levels during these VR games were low in general, we identified game elements that could potentially provide a strength training stimulus. Future research should aim to implement these elements, such that the intensity, prolonged activity and rest are optimized to sufficiently challenge lower limb muscles in VR training.

Background: Novel balance-targeting exergames controlled with off-the-shelf hardware, were developed based on current recommendations for balance training in healthy older adults and documented shortcomings of existing games. The aim of this study was to explore the feasibility of these novel exergames as training tool for elderly and, more specifically whether these games can elicit more challenging weight shifts and higher levels of muscle activity compared to existing off-the-shelf exergames. Furthermore, the motivational pull in these new games was studied. Methods: Sixteen healthy older adults were recruited to play the novel games and two reference games that were found to be the most challenging ones in terms of weight shifts or muscle activity in previous studies. Weight shifts were expressed relative to participants' Functional Limits of Stability (FLOS). Muscular challenge of the games was quantified by dividing the signal into 200 ms blocks and determining the average muscle activity within these blocks. The muscle activity was normalized to maximal voluntary contractions (MVC) to categorize the blocks in zones of < 40, 40-60, 60-80 and > 80% MVC. Subsequently, the number of blocks per intensity level and the number of consecutive blocks above 40% were determined. Motivation to play the games was assessed using the Intrinsic Motivation Inventory (IMI) and scores between the games were analyzed using Generalized Estimated Equations (GEE). Results: The novel exergames successfully elicited center of mass (COM) displacements with medians of around 80% of FLOS or higher for all directions. Furthermore, the COM displacements in the novel games were larger for each direction than in the reference games, although for one game the sideward left direction reached significance only at the third trial. Compared to the existing games, longer blocks of muscle activation above 40% MVC were found, but overall intensity remained low. IMI scores were high on all subscales, indicating that older adults experienced the games as motivating. Conclusion: We conclude that affordable hardware can be used to create challenging and enjoyable balance training programs using exergames. The exergames that were successful in eliciting challenging weight shifts and muscle activity should now be further studied in longitudinal randomized controlled interventions, to assess effects on balance, muscle strength and eventually fall risk in healthy older adults.

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