Athletes with mild post-COVID-19 symptoms experience increased respiratory and metabolic demands: Α cross-sectional study

Coronavirus Disease 2019 (COVID-19) has significantly affected different physiological systems, with a potentially profound effect on athletic performance. However, to date, such an effect has been neither addressed nor investigated. Therefore, the aim of this study was to investigate fitness indicators, along with the respiratory and metabolic profile, in post-COVID-19 athletes. Forty male soccer players, were divided into two groups: non-hospitalized COVID-19 (n = 20, Age: [25.2 ± 4.1] years, Body Surface Area [BSA]: [1.9 ± 0.2] m², body fat: 11.8% ± 3.4%) versus [vs] healthy (n = 20, Age: [25.1 ± 4.4] years, BSA: [2.0 ± 0.3] m², body fat: 10.8% ± 4.5%). For each athlete, prior to cardiopulmonary exercise testing (CPET), body composition, spirometry, and lactate blood levels, were recorded. Differences between groups were assessed with the independent samples t-test (p < 0.05). Several differences were detected between the two groups: ventilation (${\dot{V}}_E$: Resting: [14.7 ± 3.1] L·min⁻¹ vs. [11.5 ± 2.6] L·min⁻¹, p = 0.001; Maximal Effort: [137.1 ± 15.5] L·min⁻¹ vs. [109.1 ± 18.4] L·min⁻¹, p < 0.001), ratio V_E/maximal voluntary ventilation (Resting: 7.9% ± 1.8% vs. 5.7% ± 1.7%, p < 0.001; Maximal Effort: 73.7% ± 10.8% vs. 63.1% ± 9.0%, p = 0.002), ratioV_E/BSA (Resting: 7.9% ± 2.0% vs. 5.9% ± 1.4%, p = 0.001; Maximal Effort: 73.7% ± 11.1% vs. 66.2% ± 9.2%, p = 0.026), heart rate (Maximal Effort: [191.6 ± 7.8] bpm vs. [196.6 ± 8.6] bpm, p = 0.041), and lactate acid (Resting: [1.8 ± 0.8] mmol·L^-1 vs. [0.9 ± 0.1] mmol·L^-1, p < 0.001; Maximal Effort: [11.0 ± 1.6] mmol·L^-1 vs. [9.8 ± 1.2] mmol·L^-1, p = 0.009), during CPET. No significant differences were identified regarding maximal oxygen uptake ([55.7 ± 4.4] ml·min⁻¹·kg⁻¹ vs. [55.4 ± 4.6] ml·min⁻¹·kg⁻¹, p = 0.831). Our findings demonstrate a pattern of compromised respiratory function in post-COVID-19 athletes characterized by increased respiratory work at both rest and maximum effort as well as hyperventilation during exercise, which may explain the reported increased metabolic needs.