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Objective: This study compared the muscle activities of the erector spinae (ES), the external oblique (EO), and the rectus abdominis (RA) on three different surfaces. The purpose of this study was to determine which surface induces the highest muscle activity during the plank exercises. The information from this study can be used to recommend plank exercises to athletes and patients with weak core muscles. Design: Cross-sectional study. Methods: The subjects include 20 adult males attending S University in Seoul. Participants completed each plank exercise on three different surfaces. To measure muscle activities, researchers used the values from electromyography. The measurement excluded the initial two and final two seconds and collected information on the RA, EO, and ES in each posture of each subject. Results: The left external oblique showed significant differences between the plank position on stable ground (ST) and the plank position using a suspension device (SL) (p<0.05) and between the plank position on the unstable ground (US) and SL (p<0.05). The right rectus abdominis and left rectus abdominis displayed statistically significant differences between the ST and the US (p<0.05) and between the ST and the SL (p<0.05). The right erector spinae had a statistically significant difference between ST and US (p<0.05). Conclusions: The plank exercise strengthens the core muscles effectively, and muscle activity is related to the posture of the exercise and the location of the muscle. These results suggest that plank exercises improve muscle activities. Additionally, plank exercises can be applied to general medical care.

Given the growing threat of housing instability in the United States, this study explores the variability in housing instability experiences in terms of severity and persistence by tracking low-income households in the Panel Study of Income Dynamics data from 2003 to 2017. First, this study examines the associations between one housing instability incident at a particular time and subsequent mobility trajectories. Second, by incorporating sequence analysis, this study explores the conditions under which low-income households are likely to suffer from more chronic forms of housing instability. The results reveal that the more severe one housing instability incident is, the more prolonged the entire housing instability experience is likely to be over time. The ability to maintain homeownership, repeated transitions in partnerships, job insecurity, and repetitively moving across distressed neighborhoods are the conditions for housing instability that occurs more frequently. Moreover, younger households and households with a member with health problems are likely to suffer from more chronic forms of housing instability.Along with the housing affordability crisis happening in major cities across the world (Florida & Schneider, 2018), achieving and maintaining housing stability becomes challenging for many low-income households in the United States, where approximately one in every four renters is severely cost burdened, spending more than half of their household income on housing costs (Joint Center for Housing Studies of Harvard University [JCHS], 2020). The prevalence of high housing cost burdens implies that millions of households' housing situations can be easily destabilized by minor financial shocks. One important by-product of the severe shortage of affordable housing is housing instability, often represented by frequent and involuntary residential moves. Although there is no universally accepted definition of housing instability (Cox et al., 2017), it usually refers to various residential situations where households do not have sufficient control over their residential environments (Beer, 2011). Housing instability is often represented by living in unaffordable,

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