Diurnal Effects of Exercise on Markers of Muscle Damage in College-Age Healthy Individuals

Abstract

The primary aim of this study was to examine differences in muscle damage markers (maximal voluntary isometric contraction, range of motion, soreness, swelling, thickness, urinary titin) between a morning group and an evening group. A secondary aim was to determine a correlation between pre-exercise urinary titin concentrations and performance metrics of muscle damage, serving as a predictor of muscle damage. 28 participants were recruited and randomized into two groups (14 each). Participants either arrived at 7:00 am or 5:00 pm and were instructed to perform 3 sets of 10 eccentric bicep curls at 120% of their established one repetition concentric maximum. MVC was assessed before and after to ensure a 40% decline. ROM, DOMS, swelling, and thickness were assessed before and immediately post-exercise. Performance metrics of muscle damage were assessed, 24, 48, 72 and 96-hours post exercise, and urinary titin was measured 96 hours post-exercise to capture peak concentrations. The primary findings were that time of day did not affect the degree of muscle damage, nor baseline measures of pre-exercise urinary titin. Although post-exercise urinary titin concentrations could not be quantified due to extremely high concentrations that exceeded the assay’s top limit of detection, it is clear that the muscle damaging protocol utilized in this project resulted in exaggerated urinary titin response. In the future, we plan to further explore the urinary titin response to damaging exercise and the potential diurnal variations in this response.