Using a novel wearable device to continuously and passively monitor daily life mobility, we found that several domains of mobility were significantly associated with frailty, falls, and physical functioning in prostate cancer survivors treated with ADT. Mobility metrics were similar among participants who were currently on ADT and participants who had been off ADT for at least one year. Daily life mobility metrics clustered into four domains of Gait Pace, Rhythm, Activity, and Balance. These domains were significantly associated with clinically important outcomes, suggesting that passively monitoring daily life mobility could provide a useful, objective marker to identify prostate cancer survivors who have or are developing risk for frailty, falls, and dependence.
Ours is the first study to measure daily life mobility in persons with cancer, a construct that may be a unique reflection of the impact of cancer and treatment on everyday functioning and falls risk. The domains of daily life mobility identified by PCA are consistent with the known side effects of ADT, further validating the utility of daily life mobility measurement to passively monitor for developing risk of frailty, falls and functional decline. Gait Pace and Rhythm accounted for the majority of variance in daily life mobility. The metrics within these domains, including gait speed, heel-strike angle, and toe-off angle, have been linked to fatigue and muscle weakness in populations with neurological diseases,30, 31, 52 but this is the first evidence that these mobility characteristics associate with worse clinical outcomes in prostate cancer survivors on ADT. Fatigue and deconditioning also contribute to low self-report activity levels in patients on ADT, and we observed fewer daily bouts and shorter bout length in participants in our sample who reported more falls, were frailer, and had lower functioning than participants with higher Activity scores.
ADT is a mainstay therapy for the treatment of prostate cancer, and while it markedly improves survival, many patients experience adverse effects that lead to frailty, falls, and functional decline.3, 5, 14–18 However, routine monitoring for signs of frailty or functional decline in clinical practice is lacking, which leaves survivors vulnerable to progressive declines and without opportunities for timely intervention. While assessment tools like the TUG test exist, administration in a clinical setting may be burdensome and difficult to implement often enough to detect early declines. While questionnaires like the FRAIL scale could fill this gap, our results show that survivors vastly underestimate their own frailty when compared to objective measures of frailty. The discrepancy between self-reported and objectively measured frailty underscores the need for objective, low-burden tools to detect decrements in gait quality and activity that could detect the onset of frailty. Indeed, the high acceptability and compliance to wearing the instrumented socks in our sample suggests that further investigation is warranted about the utility of instrumented socks as a clinical assessment tool. Wearable devices that measure daily life mobility, like instrumented socks, could potentially fill a gap in clinical practice by identifying patients at risk for frailty, falls, and dependence, which could provide data for shared decision-making between providers and patients around ADT management.53
Our study had several strengths. The use of a novel device to measure prostate cancer survivors’ gait quality and quantity at home provided us with an unbiased assessment of gait patterns during daily activities. We also captured an average of 6.5 days of daily mobility data, which provided us with a broad observation window for capturing natural variations in activities throughout the week and increased the likelihood that data were representative of each participant’s lifestyle. Our study also had limitations. Most participants had first enrolled in an exercise clinical trial, which was less likely to include men with limited functioning. As a cross-sectional study, we cannot ascertain whether daily life mobility is a cause or consequence of falls, frailty, and/or limited functioning. However, according to most conceptual models of aging, objective measures of strength, gait, and balance are the first signs that frailty, falls, and dependence may be developing.54 Also, racial diversity was limited, so our results may not be generalizable to all men treated with ADT.
In summary, our findings provide evidence that continuous passive monitoring of daily life mobility can detect frailty, falls, and functioning in prostate cancer survivors treated with ADT, which has important implications for understanding and preventing the adverse effects of ADT. Future work should investigate whether wearable sensors, such as instrumented socks, can detect changes in daily mobility over time and thus provide an objective, unobtrusive, and unbiased tool to monitor for mobility changes once men start ADT. Monitoring for declines in daily life mobility after ADT initiation could also provide a way to assess who is most at risk for frailty so interventions, such as those we are currently testing33, can be efficiently applied in resource constrained settings.