Assessment of Ventilatory Efficacy in Patients With Fatigue Associated With SARS-CoV2 Infection After Ingestion of Beet Juice

Long COVID is a multisystem condition that comprises a set of symptoms following a SARS-CoV-2 infection. At least 65 million people around the world present symptoms associated with persistent COVID, an incidence of 10% of infected people is estimated1. The incidence is estimated at 10-30% of non-hospitalized cases, 50-70% of hospitalized cases2,3, and 10-12% of vaccinated cases4,5. Persistent COVID is associated with all ages and severity of illness in the acute phase, with the highest percentage of diagnoses between the ages of 36 and 50 years, and the majority of cases of persistent COVID are found in non-hospitalized patients with a mild acute illness6, as this population represents the majority of overall COVID-19 cases. The most prevalent symptoms in persistent COVID are fatigue, dyspnea and weakness7.

In our first published study the investigators observed that patients with fatigue after SARS CoA2 infection behaved very similarly to COPD patients, observing a decrease in mechanical efficiency (ME) at the first threshold, second threshold and at maximum consumption. of oxygen during an incremental test8. (Figure 1).

Mechanical efficiency (ME) refers to the ability of an individual to transform oxygen consumption into effective work. In other words, poorer efficiency will increase the percentage of maximum oxygen uptake (VO2max) needed to sustain a given mechanical work. A decrease in ME, indicating that more energy is expended in a given work output, could represent an increased energy cost of respiration during exercise, an altered efficiency in ATP production (ATP produced per O2 consumed), or a higher ATP cost of contraction (ATP consumed by work production)9. Patients with a decreased ME would decrease their performance and, therefore, could be limited in terms of physical activity9.

In our second study, the investigators observed that patients recovered from SARS-CoV-2 but with symptoms of fatigue presented significant muscle dysfunction compared to healthy women with similar characteristics. These findings were corroborated by detecting an increase in VO2sc and a deterioration in ME and ventilatory efficiency during the constant load test10. These results guide us towards a problem of oxygen diffusion in the muscle cell that the investigators are confirming with the findings currently obtained in quadriceps muscle biopsies. The hypothesis of causing an increase in the dilation of muscle capillaries to improve oxygen diffusion made us think about the vasodilator and ergogenic effects of beets.

Beet juice (BRJ) has become increasingly popular among athletes looking to improve sports performance. BRJ contains high concentrations of nitrate, which can be converted to nitric oxide (NO) after consumption. NO has several functions in the human body, including a vasodilatory effect, which reduces blood pressure and increases the delivery of oxygen and nutrients to various organs. BRJ consumption also has an impact on oxygen delivery to skeletal muscles, muscle efficiency, tolerance and endurance and can therefore have a positive impact on sports performance12.