European Journal of Cardiovascular Medicine

The COVID-19 pandemic, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has significantly impacted global health, affecting individuals across all age groups¹. While young adults generally experienced milder forms of the disease compared to older adults, emerging evidence suggests that even those with mild or moderate COVID-19 may suffer from persistent physiological impairments following recovery². Among these, altered respiratory function, reduced exercise capacity, and persistent fatigue have been commonly reported³.

Oxygen saturation (SpO₂) is a vital physiological parameter reflecting the efficiency of pulmonary gas exchange. While acute COVID-19 infection often presents with hypoxemia, the persistence of oxygen desaturation following recovery remains a concern⁴. Similarly, exercise tolerance, commonly assessed by the 6-Minute Walk Test (6MWT), serves as an indicator of cardiopulmonary endurance and functional capacity. Studies have suggested that post-viral fatigue and dyspnea can impair exercise performance even in previously healthy individuals⁵.

Young adults, typically considered to be at low risk for severe COVID-19 outcomes, may not routinely undergo post-recovery assessment. However, unnoticed reductions in exercise capacity or subtle desaturation on exertion could affect their quality of life, productivity, and long-term health. Understanding these outcomes is crucial for designing targeted rehabilitation and follow-up strategies⁶.

This study aims to assess the impact of COVID-19 on oxygen saturation and exercise tolerance in young adults who recovered from mild to moderate illness, using resting SpO₂ measurements, 6MWT performance, and follow-up symptom assessment.

This observational study was conducted at Andhra Medical College, Visakhapatnam, from March 2020 to June 2020. The study aimed to assess the impact of COVID-19 on oxygen saturation and exercise tolerance in young adults.

Study Population

A total of 100 young adults, aged 18 to 35 years, who had recovered from mild to moderate COVID-19 infection, were enrolled in the study. Patients were included at least four weeks after recovery, confirmed by negative RT-PCR and clinical resolution of symptoms. Individuals with a history of severe COVID-19 requiring hospitalization, underlying cardiopulmonary disease, or musculoskeletal limitations were excluded.

Data Collection

After obtaining informed consent, the following data were collected:

Demographic details: Age, gender, BMI

Resting oxygen saturation (SpO₂): Measured using a pulse oximeter while seated at rest

6-Minute Walk Test (6MWT): Conducted as per American Thoracic Society (ATS) guidelines in a 30-meter hallway. Pre- and post-walk SpO₂, distance walked, and heart rate were recorded

Fatigue score: Self-reported on a 10-point numerical rating scale post-6MWT

Symptomatology: Participants were asked about persistent fatigue, dyspnea, and chest discomfort during follow-up

Statistical Analysis

Descriptive statistics were used to summarize demographic and clinical data. Group comparisons (≥4% SpO₂ drop vs. <4% drop) were performed using independent t-tests for continuous variables and chi-square tests for categorical data. A p-value < 0.05 was considered statistically significant.

A total of 100 young adults who had recovered from mild to moderate COVID-19 were included in this observational analysis.

Demographic Characteristics

The mean age of participants was 26.8 ± 4.9 years. The study population comprised 58 males (58%) and 42 females (42%), with a mean BMI of 24.6 ± 3.2 kg/m² (Table 1).

Table 1: Demographic Characteristics

Baseline Oxygen Saturation

At rest, the mean oxygen saturation (SpO₂) was 96.4% ± 1.8. Among the participants, 12% (n = 12) had SpO₂ levels below 95%, while 88% (n = 88) maintained normal resting SpO₂ (≥95%) (Table 2).

Table 2: Baseline Oxygen Saturation (SpO₂)

Figure No.1 Districution of Resting SpO2 Levels Among Participants

6-Minute Walk Test (6MWT) Outcomes

The average distance walked during the 6MWT was 465.3 ± 54.7 meters. A ≥4% drop in SpO₂ post-walk was observed in 28% of the participants. The mean self-reported fatigue score after the walk was 5.1 ± 1.9 on a 10-point scale. The average heart rate increase post-6MWT was 22.6 ± 6.8 bpm (Table 3).

Table 3: 6-Minute Walk Test (6MWT) Outcomes

Figure No.2. Six-Minute Walk Test (6MWT) Outcomes

Symptomatology During Follow-Up

During follow-up, 37 participants (37%) reported persistent fatigue, 29 (29%) experienced exertional dyspnea, and 11 (11%) had chest discomfort on exertion. Notably, 34 participants (34%) reported no residual symptoms (Table 4).

Table 4: Symptomatology During Follow-Up

Figure No.3. Symptomatology During Follow-UP

Comparative Analysis Between Groups Based on SpO₂ Drop

Participants were stratified into two groups based on the presence or absence of a ≥4% drop in SpO₂ during the 6MWT. Those with a ≥4% drop walked a significantly shorter distance (430.6 ± 48.1 meters) compared to those with <4% drop (478.2 ± 50.3 meters; p < 0.01). The ≥4% drop group also had lower resting SpO₂ (95.1 ± 1.3%) and higher fatigue scores (6.3 ± 1.7) compared to their counterparts (p < 0.001 and p < 0.01 respectively) (Table 5).

Table 5: Comparative Analysis (SpO₂ Drop vs. No Drop Group)

The present study investigated the impact of COVID-19 on oxygen saturation and exercise tolerance in young adults who had recovered from mild to moderate illness. Despite the perception that younger individuals are less susceptible to long-term effects of COVID-19, our findings reveal that a significant proportion experienced measurable physiological impairments during follow-up⁷.

A key observation was that 28% of participants exhibited a ≥4% drop in SpO₂ during the 6-minute walk test (6MWT), indicating residual pulmonary dysfunction. These individuals also had lower baseline resting SpO₂, shorter walking distances, and higher post-exertional fatigue scores compared to those without desaturation. This suggests lingering abnormalities in pulmonary gas exchange and reduced functional capacity even after clinical recovery⁸.

Similar trends have been reported in prior studies where post-COVID individuals, including those with mild disease, demonstrated impaired diffusion capacity and exertional desaturation, attributed to residual alveolar damage or microvascular injury. While the majority of studies have focused on older adults or hospitalized patients, our study highlights that young, previously healthy adults are not immune to post-COVID sequelae⁹.

Persistent fatigue and exertional dyspnea were among the most commonly reported symptoms, affecting 37% and 29% of participants, respectively. These symptoms align with findings from other post-COVID syndrome studies and may result from autonomic imbalance, deconditioning, or ongoing inflammatory responses¹⁰.

Importantly, 34% of participants remained asymptomatic during follow-up, emphasizing the heterogeneity of recovery. The inclusion of non-hospitalized young adults makes this study particularly relevant for public health planning, workplace reintegration, and tailoring post-COVID rehabilitation programs.

This observational study highlights that young adults recovering from mild to moderate COVID-19 may still experience significant post-recovery effects, including decreased oxygen saturation and reduced exercise tolerance. Nearly one-third of the participants showed a ≥4% drop in SpO₂ following the 6-minute walk test, along with increased fatigue and decreased walking distance. Persistent symptoms such as fatigue and exertional dyspnea were also commonly reported. These findings emphasize the need for structured follow-up, even in younger populations, and support the implementation of post-COVID rehabilitation strategies. Early identification of subtle functional impairments can aid in improving quality of life and preventing long-term morbidity in recovered individuals.

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