Spatiotemporal gait parameters in young individuals wearing an age simulation suit compared to healthy older individuals

The present pilot study aimed to determine the effect of an age simulation suit on spatiotemporal gait parameters of healthy young adults and compare these parameters with healthy older controls without wearing such a suit. It was hypothesized that wearing an age simulation suit changes the gait characteristics of young people. Furthermore, it was hypothesized that the age simulation suit-induced gait characteristics of young subjects approximate those of the healthy older controls.

Wearing the suit reduced the walking speed (4.1 ± 0.7 to 3.3 ± 0.5 km/h) and the number of steps per minute (from 103 to 92 steps/min) in the younger group. Furthermore, the step length, stride length, step time and stride time were reduced by wearing the suit. However, not every change matched the healthy older controls. Velocity (km/h) was the only marker that differed between older and younger subjects before wearing the suit, but not when younger subjects wore the age simulation suit. The step length for left and right foot and the stride length trended towards the older controls but were still significantly different.

Our study gave similar results to the step length and stride length they seem to decrease with age [3], but both step and stride length were reduced compared to other results [12, 13]. Similar to the parameters mentioned previously, the differences observed for velocity and cadence in younger and older participants are supported by other findings, but absolute values for velocity and cadence in this current study are also lower than those which others had found before [13]. Temporal gait parameters assessed in this study (step time left and right, stride time) did not differ between younger subjects without the suit and older subjects. Our results are in contrast to the results of [3], where age differences in temporal gait parameters were found.

We found differences in the walking speed between healthy young and older individuals; this is in line with published studies [12, 13]. Compared to the study by Chiu and Lusardi, young subjects in our study had a slower walking speed,the walking speed of older individuals was comparable.

We did not find a significant difference in the step width between younger and older subjects, which is in line with previous research for healthy individuals [13, 14]. Only one study [9] assessed gait characteristics while wearing this particular age simulation suit (GERT). Compared to their results, our young subjects walked considerably more slowly (3.1 vs. 4.3 km/h), showed a decreased step length (58.7 vs. 69.7 cm), increased step times (656 vs.550 ms) and comparable step widths (12.1 vs.11.5 cm). While we used a treadmill, [15] assessed walking on a ground-level surface with a length of four meters (GAITRite®).

Regarding markers of gait variability, we found significant differences between COV of step length left and right, stride length, step time left and stride time between young individuals with and without the age simulation suit. No significant difference was observed in the COV of any variable between younger and older subjects or between younger subjects wearing the suit and older subjects. Markers of gait variability seem to be highly variable between individuals and are rarely assessed in younger adults, which makes it difficult to compare these findings to others [13]. The standard deviation of lateral symmetry (a marker specific to this Zebris treadmill), which also serves as a marker of gait variability in this study, showed an increase in younger subjects when wearing the age simulation suit on the same level as the older subjects.

Some of the results might be explained by the methodological framework of the study. Firstly, this study assessed the effect of an age simulation suit on participants walking on an instrumented treadmill. The naivety of subjects towards walking on a treadmill has not been assessed and the relatively long familiarization phase of about five minutes was implemented to reduce the risk of falling or instability regarding walking on the treadmill. It is highly likely that our young subjects are not naïve to treadmills. The walking speed was self-selected and did not change after the initial velocity was achieved and the walking speed of young individuals was similar to the results of other experiments when walking on an instrumented treadmill [16]. However, the same study found subjects walked faster when they had the chance to change the walking speed while walking on the treadmill. This might be a possible explanation of why subjects in this study walked slower than assessed elsewhere. The most important spatiotemporal gait parameters seem to be reliable when assessed on the treadmill used in this current study as stated by Faude et al. [17]. On the contrary, parameters of gait variability inherited less reliability and should be carefully interpreted. In addition the treadmill, it is also important to consider the suit itself. A slower walking speed in younger subjects with the age simulation suit was achieved by increasing the stride time more than in the older group as well as decreasing the stride length to a small extent. Regarding some parameters (e.g., cadence), the suit might have added more mechanical resistance and stiffness than the older participants experienced, whereas other gait characteristics of older individuals were mimicked quite well when wearing the suit. Since we only assessed one specific age simulation suit [18], the results reported are limited to this specific age simulation suit and must not be generalized to different implementations of age simulation suit. It should be noted that wearing the age simulation suit was not reported to be uncomfortable for any of the younger participants regardless of the height or weight of the individual subject. Lastly, differences between groups were assessed with the appropriate statistical tests.

We want to point out that our study design may have influenced our results in several regards: first, the young adults had to perform two consecutive sets of 15 min treadmill walking, in all cases first without and then with the age simulation suit, whereas the older adults only walked once for 15 min. This may have reduced the difference between the groups because of familiarization of the younger adults to treadmill walking. Our method unfortunately does not allow us to re-analyze shorter time fragments, so that we cannot analyze how familiarization (e.g. in the second or third 5 min subsegment) affects outcome. Second, the younger adults have a high level of physical activity (5.9 ± 3.8 yours sport per week). Therefore, they may have shown less difference between normal and age simulation suit than a young adult with lower fitness level. Third, our sample size was smaller than planned (initially planned for 15 participants in each group): we had to stop recruitment due to restrictions during the covid 19 pandemic (study subjects were not allowed within the hospital.) Because of the small sample size, power analyses have not been conducted. Finally, it should be noted that the adaption capabilities to changes in biomechanical parameters can have a large impact on handling the additional influences of the age simulation suit Shadmehr et al. [11] stated that especially young healthy subjects can quickly adjust their locomotor behavior to environmental changes. However, older subjects, who are naturally affected by gait deterioration due to aging processes, do not lose the ability to recalibrate their locomotor system to changes [19]. Moreover, older subjects are used to continuously adapt their gait behavior to possibly highly non-linear changes in movement capabilities [10] showed no significant difference in adaption capabilities between young an older subjects; this is a controversial discussion also in current research. As part of our future work, we will redesign the study protocol in order to investigate the temporal dependencies of adjusting the individual gait behavior to the age simulation suit-induced gait impairments.

In summary, this study reports that wearing this specific age simulation suit during walking on an instrumented treadmill alters most of the spatiotemporal gait parameters of healthy younger individuals, but not every parameter shifts towards gait characteristics of healthy older adults. Regarding gait variability, the standard deviation of the in-house marker of the instrumented treadmill was the single significant difference between younger and older participants. The fact that we only tested on treadmill does not allow us to extrapolate on more complicated, closer to real life gait challenges Testing age simulation suits on normal, uneven or inclining ground would add scientific evidence to the already widespread use of age simulation suits within the education of medical students, nurses, physiotherapists, and others.

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