Serum skeletal troponin I following inspiratory threshold loading in healthy young and middle-aged men.

The purpose of this study was to determine if serum levels of skeletal troponin I (sTnI, fast and slow isoforms) could provide a sensitive marker of respiratory muscle damage in healthy humans subjected to inspiratory loads. To accomplish this, we studied healthy, young (27 ± 2 years, Mean ± SEM, n = 5) and middle-aged (55 ± 5, n = 5) men to (1) determine the magnitude, pattern, and time course of the presence of sTnI in the serum after a single 60 min bout of inspiratory threshold loading [ITL, ~70% of maximal inspiratory pressure (MIP)], (2) determine the distribution and magnitude of DOMS after loading, and (3) compare fast and slow sTnI levels, and their relationship to other markers/indices of muscle injury including delayed onset muscle soreness (DOMS), serum creatine kinase (CK) levels, and force generating capacity of the respiratory muscles [MIP and maximal expiratory pressure (MEP)]. There was a 24 ± 4 and 27 ± 3% increase in fast sTnI 1 hour (p < 0.01) and 3 days (p < 0.01) after ITL. Slow sTnI was elevated by 24 ± 10% (p < 0.05) 4 days postITL. Other indices of respiratory muscle injury such as CK, MIP and MEP did not show a difference in mean data following ITL; DOMS was slightly but significantly increased following ITL. Our results suggest that sTnI has superior sensitivity compared to other biomarkers/indices of skeletal muscle injury. Future studies examining the impact of respiratory muscle injury with ventilator weaning should consider using sTnI as a sensitive marker of skeletal muscle injury.