Maximal oxidative capacity during exercise is associated with muscle power output in patients with long coronavirus disease 2019 (COVID-19) syndrome. A moderation analysis.

BACKGROUND & AIMS: Long COVID syndrome (LCS) involves persistent symptoms experienced by many patients after recovering from coronavirus disease 2019 (COVID-19). We aimed to assess skeletal muscle energy metabolism, which is closely related to substrate oxidation rates during exercise, in patients with LCS compared with healthy controls. We also examined whether muscle power output mediates the relationship between COVID-19 and skeletal muscle energy metabolism. METHODS: In this cross-sectional study, we enrolled 71 patients with LCS and 63 healthy controls. We assessed clinical characteristics such as body composition, physical activity, and muscle strength. We used cardiopulmonary exercise testing to evaluate substrate oxidation rates during graded exercise. We performed statistical analyses to compare group characteristics and peak fat oxidation differences based on power output. RESULTS: The two-way analysis of covariance (ANCOVA) results, adjusted for covariates, showed that the patients with LCS had lower absolute maximal fatty acid oxidation (MFO), relative MFO/fat free mass (FFM), absolute carbohydrates oxidation (CHox), relative CHox/FFM, and oxygen uptake (V˙˙O2) at maximum fat oxidation (g min-1) than the healthy controls (P < 0.05). Moderation analysis indicated that muscle power output significantly influenced the relationship between LCS and reduced peak fat oxidation (interaction ß = -0.105 [95% confidence interval -0.174; -0.036]; P = 0.026). Therefore, when muscle power output was below 388 W, the effect of the LCS on MFO was significant (62% in our study sample P = 0.010). These findings suggest compromised mitochondrial bioenergetics and muscle function, represented by lower peak fat oxidation rates, in the patients with LCS compared with the healthy controls. CONCLUSION: The patients with LCS had lower peak fat oxidation during exercise compared with the healthy controls, potentially indicating impairment in skeletal muscle function. The relationship between peak fat oxidation and LCS appears to be mediated predominantly by muscle power output. Additional research should continue investigating LCS pathogenesis and the functional role of mitochondria.

Reduced muscle strength in patients with long-COVID-19 syndrome is mediated by limb muscle mass.

Understanding the impact of COVID-19 on muscle strength may help to elucidate the organ systems that contribute to acute and chronic COVID-19 sequelae. We questioned whether patients with postdischarge symptoms after COVID-19 had compromised muscle strength compared with a control group, and if this potential relationship was mediated by the lower appendicular lean mass index (ALMI). A total of 99 patients with long-COVID-19 and 97 control participants were screened. Maximal grip strength was assessed with a TKK 5101 digital dynamometer, and leg extension 1RM was measured using EGYM Smart Strength machines. Body composition (fat mass percentage, lean mass, visceral fat, and appendicular lean mass index) was determined using a whole body dual-energy X-ray densitometer. Results showed that grip strength and leg extension strength were significantly higher in controls than in COVID-19 survivors (mean [SD], 32.82 [10.01] vs. 26.94 [10.33] kg; difference, 5.87 kg; P < 0.001) and (mean [SD], 93.98 [33.73] vs. 71.59 [33.70] kg; difference, 22.38 kg; P < 0.001), respectively). The relationship between long-COVID syndrome and grip/leg strength levels was partly mediated by ALMI, which explained 52% of the association for grip strength and 39% for leg extension. Our findings provide novel insights into the mechanisms underlying the relationship between long-COVID syndrome and grip/leg strength levels, supporting the negative effects of long-COVID syndrome on muscle function.NEW & NOTEWORTHY The causes of post-COVID-19 syndrome are uncertain. Limb muscle wasting common to patients with COVID-19 limits daily activities and exercise. In this cross-sectional study, we found that patients with long-COVID-19 syndrome had significantly lower absolute and relative muscle strength measurements than control participants. Interestingly, we identified that these relationships were mostly mediated by limb muscle mass. Our data thus suggest that the evident reduced upper and lower muscle mass is a putative cause of-or contributor to-the functional limitation of patients with long-COVID-19 syndrome.

Resistance training and clinical status in patients with postdischarge symptoms after COVID-19: protocol for a randomized controlled crossover trial "The EXER-COVID Crossover Study".

BACKGROUND: Physical exercise induces a coordinated response of multiple organ systems, including the immune system. In fact, it has been proposed that physical exercise may modulate the immune system. However, the potential effect of an exercise program on COVID-19 survivors has not been investigated. Thus, the aim of this study is to evaluate the modifications in immunological parameters, physical condition, inflammatory profile, and perceived persistent symptoms after 6 weeks of supervised resistance training (RT), in addition to the standard care on the clinical status of patients with persistent COVID-19 symptoms. The objective of this protocol is to describe the scientific rationale in detail and to provide information about the study procedures. METHODS/DESIGN: A total of 100 patients with postdischarge symptoms after COVID-19 will be randomly allocated into either a group receiving standard care (control group) or a group performing a multicomponent exercise program two times a week over a period of 6 weeks. The main hypothesis is that a 6-week multicomponent exercise program (EXER-COVID Crossover Study) will improve the immunological and inflammatory profile, physical condition, and persistent perceived symptoms (fatigue/tiredness, musculoskeletal pain, and shortness of breath) in patients with postdischarge symptoms after COVID-19. DISCUSSION: Our results will provide insights into the effects of a multicomponent exercise program on immunological parameters, physical condition, inflammatory profile, and persistent perceived symptoms in patients with postdischarge symptoms after COVID-19. Information obtained by this study will inform future guidelines on the exercise training rehabilitation of patients with postdischarge symptoms after COVID-19. TRIAL REGISTRATION: NCT04797871 , Version 2. Registered on March 15, 2021.