Breast cancer survivor functional changes immediately following treatment: quantifying mechanisms of strength deficits and compensatory kinematic and muscular strategy adaptations

Breast cancer is prevalent among Canadian women, but treatments may cause functional impairments among survivors. Over 22,000 Canadian women join the survivor population yearly (Brenner et al., 2020). Despite this substantial number, minimal research has approached the challenges faced by this population after primary treatment. Particularly, decreases in strength, range of motion and shoulder-related quality of life are widely reported (Harrington, Padua, Battaglini, & Michener, 2013; Lee, Kilbreath, Refshauge, Herbert, & Beith, 2008; Rietman et al., 2004). These factors, linked with changes in kinematics and muscular activation may result in further complications (Brookham, Cudlip, & Dickerson, 2018a, 2018b). Variability in previous studies, in both the population sampled and results make it difficult to isolate potential mechanism disrupting function. Further, this complicates the determination of key deficits to target in the early years of survivorship. Therefore, the purpose of this dissertation was to determine which factors affect breast cancer survivors in the first two years following the conclusion of treatment, if these factors translate to differences during low load functional tasks, and to investigate the feasibility of increasing strength (as a surrogate for function) to help mitigate these factors and increase function. Study 1 and 2 shared an in vivo experimental collection, with Study 3 using input from the collection in an in-silico approach. Briefly, 35 breast cancer survivors within two years since the conclusion of their treatment participated in the experiment. Participants completed a general questionnaire about their diagnosis, three shoulder-related quality of life questionnaires, and a Godin-Shephard leisure-time physical activity questionnaire, followed by a dual energy x-ray absorptiometry (DXA) scan. Eight muscles were monitored on the affected limb (pectoralis major (sternal and clavicular), deltoids (anterior, middle and posterior), infraspinatus, supraspinatus, and latissimus dorsi). Six maximal isometric strength trials were completed (flexion, extension, abduction, adduction, internal rotation and external rotation). Kinematics of the affected limb were collected for the remaining trials. These consisted of 6 maximal range of motion trials (flexion, extension, abduction, scapular abduction, internal rotation and external rotation), as well as 8 activities of daily living. Study 1 clustered participants into two distinct groups, the low score cluster (LSC) and high score cluster (HSC). The variance in treatment, force production, range of motion, body composition and shoulder-related quality of life is well documented in literature, however there is no distinguishing characteristics that separate survivors who may need rehabilitation following treatment. This study determined, through feature reduction, that internal rotation force production, active extension range of motion and 3 shoulder related quality of life variables (energy/fatigue, social functioning and pain) separated survivors within 2 years of treatment into two clusters (LSC and HSC). The LSC participants had higher self-reported disability, role limitations (health and emotion), fatigue, and lower self reported physical well-being, along with lower abduction, adduction, extension and flexion force production (p<0.001). Several other factors differed between groups (p