Abstract
Objective: The localized bicep tissue bioimpedance was measured from participants who completed an eccentric exercise protocol with one arm and no exercise with the other arm to compare changes that occur as a result of the exercise protocol over a 96h observation period. Methods: The localized bicep bioimpedance, bicep circumference, and self-reports of bicep pain were collected from 6 volunteers at pre, post, 24h, 48h, 72h, and 96h timepoints after completing an eccentric exercise protocol of the elbow flexor muscles. Results: The unexercised bicep showed no statistically significant differences between the pre-exercise and post-exercise measures at any timepoints for all impedance measures and circumference. The exercised bicep showed statistically significant decreases ( $p ) for 10 kHz, 50 kHz, and 100 kHz impedance (resistance and reactance) and increases of bicep circumference at the 72h and 96h post-protocol timepoints, compared to the pre-protocol measurements. The self-reports of pain of the exercised bicep also showed statistically significant increases ( $p ) at the 48h and 72h timepoints compared to the baseline reports. Conclusion: Completion of the eccentric protocol resulted in increases of bicep circumference and decreases in the magnitude of resistance and reactance components of the localized tissue bioimpedance; with maximum changes of swelling and impedance occurring at the same post-protocol timepoints. These changes support that localized tissue bioimpedance is sensitive to the changes that occur as a result of the exercise protocol with the potential to quantify tissues for exercise induced changes. Significance: Localized tissue bioimpedance is sensitive to the changes that occur from eccentric exercise and may be a potential method to non-invasively quantify tissues for changes due to exercise, fatigue, injury, and recovery.
Highlights
Movement and activity throughout daily living requires a complex orchestration of skeletal muscle contractions
The increases in bicep circumference measured at 72h and 96h after completing the exercise protocol, with no statistically significant changes in the unexercised bicep may indicate that muscle damage and tissue swelling resulted from the eccentric activity
A limitation of this work is that no direct measures of tissue damage were obtained from study participants to assess the level of tissue damage in each individual and the relation with the changes in bioimpedance measures, but warrants future study
Summary
Movement and activity throughout daily living requires a complex orchestration of skeletal muscle contractions. While muscle contractions are necessary for all tasks, repetitive contractions through participation in high-intensity activity (such as sports or resistance training) can cause sarcomere damage [2], shortened connective tissue, passive muscle stiffness, and decreased range of motion (ROM) [3], [4]. Quantifying these skeletal muscle changes is achieved using direct methods such as muscle biopsies or magnetic resonance imaging (MRI) and indirect methods such as force loss, levels of muscle proteins in the blood, and self-reported muscle soreness [5].
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