•  
  •  
 

DIURNAL EFFECTS OF EXERCISE ON MARKERS OF MUSCLE DAMAGE IN COLLEGE-AGE HEALTHY INDIVIDUALS

Abstract

Titin is a large, structural protein that functions to stabilize sarcomeres and prevent overstretching. There is evidence indicating circadian turnover of the protein titin in animals. Subsequent pilot studies in humans have shown greater muscle damage following eccentric exercise in the evening, when titin turnover would be high, compared to morning. PURPOSE: The purpose of this study was to examine differences in muscle damage (between a eccentric exercise performed in the morning and evening) and determine if any differences are related to differences in urinary titin level. METHODS: Twenty-eight participants were recruited and randomized into two groups (14 each). Participants arrived at 7:00 am or 5:00 pm and performed 3 sets of 10 eccentric bicep curls at 120% of their one repetition concentric maximum. Maximal isometric strength (MVC) was assessed before and after. Elbow range-of-motion (ROM), delayed onset muscle soreness (DOMS), circumference, and muscle thickness were also assessed before and immediately post-exercise. Markers of muscle damage were reassessed, 24, 48, 72 and 96-hours post exercise, and urinary titin was measured at baseline and 96 hours post-exercise. RESULTS: There were no between-group differences for % ΔMVC [Morning Group: -35.85 ± 3.56, Evening Group: -39.18 ± 3.56, (p = 0.51)], % Δ ROM [Morning Group: -21.33 ± 3.27, Evening Group: -17.07 ± 3.27, (p = 0.37)], DOMS [Morning Group: 25.55 ± 4.00, Evening Group: 33.55 ± 4.00, (p = 0.17)], and % Δ Swelling [Morning Group: 4.86 ± 0.95, Evening Group: 2.53 ± 0.95, (p = 0.81)]. There was no between-group differences for % Δ Thickness [Morning Group: 17.50 ± 2.74, Evening Group: 21.20 ± 2.74, (p = 0.81)], nor baseline measures of pre-exercise urinary titin [Morning Group: 46.47 ± 38.59, Evening Group: 29.97 ± 24.21, (p =0 .34)]. There were observable within-group differences from pre to post for all performance metrics of muscle damage (p < 0.05). CONCLUSION: Our findings suggest the time-of-day when eccentric exercise was performed had no effect on muscle damage. These results could be explained by our lack of finding a circadian variation in titin level as has been observed in animals. Future research should explore the urinary titin response to damaging exercise and the potential diurnal variations in this response.

This document is currently not available here.

Share

COinS