Journal of Sport and Exercise Physiology

Journal of Sport and Exercise Physiology

The acute effect of high- and moderate-intensity endurance exercise on serum concentrations of club cell protein 16 (CC16), surfactant protein D (SP-D), and the CC16/SP-D ratio in active healthy adult men

Document Type : Original Article

Authors
Hadi Pourmanaf
Saeid Nikoukheslat
Vahid Sari Sarraf
Ramin Amirsasan
Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, University of Tabriz, Tabriz, Iran
10.48308/joeppa.2025.241338.1391
Abstract
Background and Purpose: Previous research has shown that increased ventilation during endurance exercise promotes evaporation of the airway epithelial lining fluid and imposes mechanical shear stress on the respiratory system. These physiological responses may compromise airway epithelial integrity and contribute to epithelial cell injury. Nevertheless, the effect of endurance exercise intensity on biomarkers of airway epithelial injury, including club cell protein 16 (CC16), surfactant protein D (SP-D), and the CC16/SP-D ratio, remains unclear. Therefore, the present study was conducted to investigate the acute effects of high- and moderate-intensity endurance exercise on serum CC16, SP-D, and the CC16/SP-D ratio in healthy, physically active adult men.
Materials and Methods: Twenty healthy, physically active adult men (Mean±SD; age, 22±3 years; weight, 75±8 kg; height, 182±6 cm; BMI, 23±1.86 kg/m2) were randomly assigned to a high-intensity endurance group (HE, n = 10) or a moderate-intensity endurance group (ME, n = 10). Participants in both groups completed a single 20-minute continuous treadmill running session. Exercise intensity was prescribed at 85–90% of maximal heart rate (MHR) for the HE group and 65–70% of MHR for the ME group. The initial treadmill speed was set at 9 km/h for the HE group and 7.5 km/h for the ME group and was adjusted throughout the exercise session to maintain the prescribed target intensity for each participant. To determine serum CC16 and SP-D concentrations, 5-mL venous blood samples were collected from the antecubital vein by an experienced laboratory technician using standard procedures at baseline (pre-exercise) and one hour after completion of the exercise session. Analysis of covariance (ANCOVA) was performed to compare post-exercise outcomes between groups, whereas paired-samples t-tests were used to assess within-group changes.
Results: Based on the within-group analyses, serum CC16 (p=0.008) and the CC16/SP-D ratio (p=0.006) increased significantly following high-intensity endurance exercise, whereas no significant change was observed in SP-D concentrations compared with baseline (p=0.064). In contrast, no significant changes were detected in serum CC16 (p= 0.759), SP-D (p=0.072), or the CC16/SP-D ratio (p=0.121) following moderate-intensity endurance exercise. Between-group comparisons revealed significant differences in post-exercise CC16 concentrations (p=0.021) and the CC16/SP-D ratio (p=0.025), whereas no significant between-group difference was observed in SP-D concentrations (p= 0.446).
Conclusion: The findings of the present study demonstrated for the first time that high-intensity endurance exercise induces more pronounced increases in CC16 release and the CC16/SP-D ratio than moderate-intensity endurance exercise, while it did not affect SP-D release.
Keywords
Airway epithelial integrity
Anti-inflammatory proteins
Clara cell protein (CC16)
Surfactant protein D (SP-D)
Subjects
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  • Receive Date 30 August 2025
  • Revise Date 12 October 2025
  • Accept Date 06 November 2025
  • First Publish Date 06 November 2025
  • Publish Date 22 June 2026