br Breast cancer survivors had significantly decreased right
Breast cancer survivors had significantly decreased right and left hand grip strengths compared to healthy women. However, non-breast cancer survivors did not have significantly lower hand grip strength than healthy participants. A previous study also showed similar results; the grip strength of young adult breast cancer survivors corresponded to the 10th percentile of healthy aged-matched women (Ibrahim et al., 2018). Another study showed that Trizma maleate breast cancer survivors had sig-nificantly decreased shoulder strength and function compared to healthy women (Harrington et al., 2011). Thus, breast cancer survivors tend to have decreased grip strength compared to age-matched healthy participants.
Furthermore, the breast cancer survivor's subgroup analysis showed that hand grip strength was related to the Mini-BESTest and TUG score but not to CoP length. The non-breast cancer survivor's subgroup ana-lysis showed that the TUG score was related to left hand grip strength and muscle strength of both knees. The Mini-BESTest was not corre-lated with grip strength in non-breast cancer survivors. These findings may indicate that grip strength in breast cancer survivors tend to be related to balance function, while knee extensor strength in non-breast cancer survivors tend to be related to balance function. The relationship between muscle strength and balance function may be characterized by the diﬀerent diagnoses in cancer survivors.
Muscle strength and Mini-BESTest and TUG test scores tend to be correlated in breast cancer survivors and non-breast cancer survivors,
but CoP was not related to muscle strength in both groups. The Mini-BESTest and TUG test both assess dynamic balance functions (mobility, balance, and walking) (Godi et al., 2013; Podsiadlo and Richardson, 1991), but CoP length was measured by postural sway during static standing (Wingert et al., 2014). Muscle strength may be related to dy-namic balance function, such as the Mini-BESTest and TUG test, and not the postural sway test, in cancer survivors. To further understand bal-ance function in cancer survivors, a more directed measurement of the lower limbs and trunk function is required. Although there was no re-lation between balance function and muscle strength in healthy parti-cipants, the healthy women subgroup analysis revealed that right hand grip strength was significantly correlated with the total CoP length. A previous study reported that hand grip strength was correlated with body sway rate (Carmeli et al., 2013), which was similar to our results in healthy women. The present study had small sample sizes in both groups. An increase in the sample size might reveal a significant rela-tion between grip strength and the total CoP length.
5. Study limitations
First, we did not determine how the lower Mini-BESTest scores re-late to the increased risk of falls among cancer survivors. Second, cancer survivors with diﬀerent diagnoses were included in Transgenic animals study. Diﬀerent therapies might aﬀect motor functions, such as balance and strength, diﬀerently in cancer survivors. However, we could not in-vestigate the details of diﬀerent therapies because we did not have the medical records of the cancer survivors. Third, the non-breast cancer survivor group had diﬀerent types of cancer diagnoses and the sample
S. Morishita, et al.
size was small. Thus, we did not show the eﬀect of diﬀerent cancer types on the relation between balance function and muscle strength. In future studies, we should present the possible mechanisms of balance function in cancer survivors with a larger sample size.
Breast cancer survivors had significantly lower hand grip strength and Mini-BESTest scores than healthy women. Additionally, balance function (as assessed by the Mini-BESTest and TUG test) and grip strength were correlated in breast cancer survivors, but not in healthy women. Hand grip strength and Mini-BESTest scores were not sig-nificantly diﬀerent in non-breast cancer survivors compared to healthy participants. Additionally, balance function and knee extension strength were correlated in non-breast cancer survivors. We believe the current findings contribute to the understanding of the changes in balance function and muscle strength in cancer survivors.