Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Master of Science in Interdisciplinary Studies, Biomedical Engineering


Mechanical and Biomechanical Engineering

Major Advisor

Michelle B. Sabick, Ph.D.


Ronald P. Pfeiffer, Ph.D.


Steve Laverson, MD.


Breast hypertrophy is a common medical condition whose morbidity has increased over recent decades. Symptoms of breast hypertrophy often include musculoskeletal pain in the neck, back and shoulders, and numerous psychosocial health burdens. To date, reduction mammaplasty (RM) is the only treatment shown to significantly reduce the severity of the symptoms associated with breast hypertrophy. However, due to a lack of scientific evidence in the medical literature justifying the medical necessity of RM, insurance companies often deny requests for coverage of this procedure. Therefore, the purpose of this study is to investigate biomechanical differences in the upper body of women with larger breast sizes in order to provide scientific evidence of the musculoskeletal burdens of breast hypertrophy to the medical community[sic]

Twenty-two female subjects (average age 25.90, ± 5.47 years) who had never undergone or been approved for breast augmentation surgery, were recruited to participate in this study. Kinematic data of the head, thorax, pelvis and scapula was collected during static trials and during each of four different tasks of daily living. Surface electromyography (sEMG) data from the Midcervical (C-4) Paraspinal, Upper Trapezius, Lower Trapezius, Serratus Anterior, and Erector Spinae muscles were recorded in the same activities. Maximum voluntary contractions (MVC) were used to normalize the sEMG data, and %MVC during each task in the protocol was analyzed. Kinematic data from the tasks of daily living were normalized to average static posture data for each subject. Subjects were divided into groups of normal control subjects (n=12, reported bra-cup size A, B, or C) or hypertrophy subjects (n=10, reported bra-cup size D or larger). To compare results between the groups, a two-tailed independent t-test was performed for each dependent variable with significance set at α=0.05.

Significant differences in torso flexion were found between the normal control group and the hypertrophy group during both the pencil activity (p=0.054) and the step up activity (p=0.001). There were also significant differences in lower trapezius muscle activation during the static trial (p=0.051). Although not significant, women in the hypertrophy group also tended to exhibit greater head flexion, pelvic tilt and torso flexion under static conditions, and also exhibited increased muscle activation in all five muscles under the same conditions.

Results of this study provide scientific information regarding the effects of breast hypertrophy on the musculoskeletal system. While none of the postural alterations seen in women with large breasts were significantly different from those seen in women with smaller breasts, the data presented shows a trend towards altered musculoskeletal alignment due to the size and weight of larger breasts that should be considered when determining the medical necessity of reduction mammaplasty.

Included in

Biomechanics Commons