Muscle EMG Activity and Arm Force During Functional Tasks: Heart Surgery Implications

Overview

Median sternotomy (or open heart surgery) is performed during cardiac surgery on over 400,000 patients in the US alone each year. Median sternotomy is associated with a variety of complications including infection, bony nonunion / instability, and dehiscence (pulling apart). While patients often must use their arms to assist with functional activities, pushing, pulling, and lifting after open heart surgery is limited to minimize force across the healing sternum. The main purposes of this study were to determine: 1) how accurately patients can estimate arm weight bearing with 10 lb or less of force and 2) if feedback training is effective for improving their ability to estimate arm force and reduce pectoralis major muscle contraction during functional activities. An instrumented walker was used to measure arm force during functional mobility tasks including walker ambulation and sit-stand transfers. Pectoralis major muscle electromyography (EMG) was also measured simultaneously in subjects (n = 21). After baseline testing, subjects underwent a brief session of visual and auditory concurrent feedback training. Data analyses included t-tests and ANOVA (P<0.05). Results showed that self-selected arm force was greater than 10 lb for all tasks (11.7-19.0 lb) but after feedback training it was significantly lower (8.3-9.8 lb). During most trials (67%), subjects over-estimated arm force. Pectoralis major muscle EMG values were < 10% of maximal voluntary contractions and were reduced (3.3-5.6%) after feedback training. In conclusion, the results of this study suggest that patients may not be not good at estimating < 10 lb of arm force during weight bearing activities, which puts them at risk for delayed bone healing and complications. A combination of visual and auditory feedback was effective at reducing arm weight bearing and pectoralis major muscle EMG activity. Objective feedback training while using an assistive device would be useful for patients recovering from not only from median sternotomy but also lower extremity fractures and other surgeries which require limiting the weight placed through a compromised limb.