Functional overreaching has been linked to alterations in immunity and host pathogen defense, but little is known as to whether or not running and cycling evoke different responses. This study compared inflammation, muscle damage and soreness, and innate immune function responses to a 3-day period of intensified exercise in trained long distance runners (N=13, age 34.4±2.4year) and cyclists (N=22, age 36.6±1.7year, P=0.452). Upper respiratory tract infection (URTI) symptomatology was monitored for 12weeks using the Wisconsin Upper Respiratory Symptom Survey (WURSS), and subjects from both athletic groups came to the lab during week five and exercised 2.5h/day for 3days in a row at 70% VO2max. Blood samples were collected before and after the 3-day period of exercise, with recovery samples collected 1-, 14-, and 38h-post-exercise. Samples were analyzed for muscle damage [creatine kinase (CK), myoglobin (MYO)], inflammation (CRP, IL-6, IL-8, IL-10, MCP), and innate immunity [granulocyte and monocyte phagocytosis (GR-PHAG and MO-PHAG) and oxidative burst activity (GR-OBA and MO-OBA)]. Runners compared to cyclists experienced significantly more muscle damage (CK 133% and MYO 404% higher post-3days exercise), inflammation (CRP 87%, IL-6 256%, IL 8 61%, IL-10 32%, MCP 29%), and delayed onset of muscle soreness (DOMS, 87%). The 3-day period of exercise caused significant downturns in GR-PHAG, MO-PHAG, GR-OBA, MO-OBA by 14- and 38h-recovery, but the pattern of change did not differ between groups. No group differences were measured for 12-week URTI severity (18.3±5.6 and 16.6±4.0, P=0.803) and symptom scores (33.4±12.6 and 24.7±5.8, P=0.477). These data indicate that a 3-day period of functional overreaching results in substantially more muscle damage and soreness, and systemic inflammation in runners compared to cyclists, but without group differences for 12-week URTI symptomatology and post-exercise decrements in innate immune function.
Keywords: Cytokine; Exercise; Immunology; Muscle soreness; Respiratory illness.
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