Effects Of An Intensified Training Period On Resting Metabolic Rate, Energy Availability, Blood-Biomarkers And Performance

Cyclists often block periodize their training in micro and meso periods with high training volumes to prepare for competition. The effect of such periods on surrogate markers for Relative Energy Deficiency in Sport (RED-S) have not yet been properly investigated. PURPOSE: To determine how a mesocycle of four weeks of interval training affects RED-S associated surrogate markers and performance variables in well-trained male cyclists. METHODS: Twenty-two participants (age: 33.5 ± 6.6 years, height: 181.4 ± 5.2 cm, weight: 76.5 ± 7.4 kg, VO2peak: 63.5 ± 6.6 mL·kg-1·min-1) were recruited for a four-week interval training protocol, consisting of three high-intensity interval training sessions per week with an accumulated work duration of 32 minutes per session. Unlimited low intensity training was permitted. Protocol included pre- and post-intervention assessment of resting metabolic rate (RMR) (ventilated hood), body composition by dual x-ray absorptiometry, blood samples, energy intake and exercise energy expenditure to calculate energy availability (EA), and aerobic- and anaerobic performance. RESULTS: Four weeks of interval training increased aerobic performance (mean ± SD of difference); peak power output [18.5 ± 12.4 W, (p < 0.001)], VO2peak [1.5 ± 2.1 mL.kg-1.min-1, (p = 0.005)], and functional threshold power [17.0 ± 11.8W, (p < 0.001)] as well as testosterone levels [1.35 ± 2.13 nmol. L-1, (p = 0.011)]. However, triiodothyronine (T3) [-0.12 ± 0.18 nmol. L-1, (p = 0.008)], absolute RMR [-52.2 ± 81.4 kcal per. day-1, (p=0.01)], relative RMR [-0.8 ± 1.2 kcal per kg FFM-1, (p=0.01)], and RMRratio [-0.03 ± 0.04, (p = 0.01)] decreased, and cortisol levels increased (49.3 ± 87.3 nmol. L-1, p = 0.02) indicating energy deficiency, while no changes were observed in body weight or -composition, EA, or insulin and insulin-like growth factor 1 (IGF-1). CONCLUSION: A successive four weeks of intensified training increased performance and testosterone levels in this group of well-trained male endurance athletes, although surrogate markers of RED-S such as decreased RMR, T3 and increased cortisol levels were observed. These results indicate the complexity, and the methodological challenges of assessing and evaluating RED-S in male athletes.