Estimating Muscle Forces for Breast Cancer Survivors During Functional Tasks

Breast cancer survivors have known scapular kinematic alterations that may be related to the development of secondary morbidities. A measure of muscle activation would help understand the mechanisms behind potential harmful kinematics. The purpose of this study was to define muscle force strategies in breast cancer survivors. Shoulder muscle forces during 6 functional tasks were predicted for 25 breast cancer survivors (divided by impingement pain) and 25 controls using a modified Shoulder Loading Analysis Module. Maximum forces for each muscle were calculated, and 1-way analysis of variance (P < .05) was used to identify group differences. The differences between maximum predicted forces and maximum electromyography were compared with repeated-measures analysis of variance (P < .05) to evaluate the success of the model predictions. Average differences between force predictions and electromyography ranged from 7.3% to 31.6% but were within the range of previously accepted differences. Impingement related pain in breast cancer survivors is associated with increased force of select shoulder muscles. Both pectoralis major heads, upper trapezius, and supraspinatus peak forces were higher in the pain group across all tasks. These force prediction differences are also associated with potentially harmful kinematic strategies, providing a direction for possible rehabilitation strategies.

The Effect of Two Movement Strategies on Shoulder Resultant Joint Moment During Elastic Resistance Exercise

Despite the common use of elastic resistance in training, only the static loading characteristics have been studied, whereas the dynamic components remain undetermined. The purpose was to determine the effect of two movement strategies on the shoulder resultant joint moment (RJM) during internal/external rotation exercise with elastic load. Ten healthy subjects performed sweep and step movement strategies over a constant range of motion and cadence (1:1). Shoulder RJM was determined using a Newtonian model with elastic force measured by force transducer, joint angle by electrogoniometer, and limb acceleration by accelerometer. Relative to the sweep strategy, the step strategy revealed a 49% increase in angle-specific RJM during the initial phase, RJM was reduced to 67–69% during midrange, and increased to over 110% at the end of the repetition. These RJM differences were wholly attributable to strategy-dependent changes in limb acceleration. Shoulder RJM in the sweep strategy was almost entirely explained by moment of elastic force. Movement strategy can substantially alter shoulder loading despite constant range of motion and cadence, impacting the magnitude and nature of the stimulus for neuromuscular adaptation. These acceleration-dependent changes in shoulder RJM may be important to consider for exercise efficacy and safety.