Impact of Duration of Recovery from COVID-19 Infection on Physical Performance in Post-COVID-19 Patients

Abstract

Background: To evaluate and compare cardiorespiratory function, assessed by the 6-minute walk test (6MWT), and musculoskeletal function, assessed by the handgrip strength test and the sit-to-stand test (STS10) in post-coronavirus disease 2019 (COVID-19) patients. Participants were stratified based on the time since infection (≤6 months and >6 months) and compared with matched healthy controls. Methods: A total of 111 participants were recruited and divided into three groups (n = 37/group). Cardiorespiratory function was assessed using the 6MWT, while musculoskeletal function was evaluated through the handgrip strength test and the STS10. Results: All three groups had normal body mass index values. Group 2 demonstrated significantly lower handgrip strength and a shorter 6MWT distance compared to both Group 1 and Group 3. Additionally, Group 2 required significantly more time to complete the STS10 than Group 1. Following the 6MWT, Group 2 exhibited significantly higher heart rate and systolic blood pressure compared to both Group 1 and Group 3. Diastolic blood pressure was significantly lower in Group 3 compared to the other two groups. Furthermore, Group 2 had significantly lower pulse oxygen saturation than both Group 1 and Group 3. The rate of perceived exertion was significantly lower in Group 1 than in Group 2. Additionally, leg fatigue was significantly lower in Group 1 compared to both Group 2 and Group 3. Conclusions: These findings highlight significant differences in physical performance and physiological responses between post-COVID-19 patients and healthy individuals, emphasizing the potential long-term effects of SARS-CoV-2 infection on cardiorespiratory and musculoskeletal function.

1. Introduction

The cardiovascular system is the primary system affected by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1]. In addition, cardiovascular symptoms are among the most commonly observed in individuals recovering from COVID-19, increasing the risk of new-onset hypertension and heart failure in these populations [2,3,4]. However, the systemic infection caused by SARS-CoV-2 extends beyond the respiratory system, contributing to both acute disease burden and long-term cardiovascular complications [5]. SARS-CoV-2 adversely affects cardiac tissues, triggers systemic inflammatory responses, and causes immune system dysregulation, leading to endothelial dysfunction, myocarditis, and arrhythmia, thereby contributing to increased morbidity and mortality rates [6,7]. In addition to its cardiovascular effects, COVID-19 also impacts the musculoskeletal system, leading to disorders such as myalgia, arthralgia, and muscle weakness. These conditions result from a spectrum of myopathic changes induced by the COVID-19 virus, as SARS-CoV-2 binds to the angiotensin-converting enzyme 2 (ACE2) receptor on the surface of skeletal muscle cells [8,9,10]. The systemic inflammatory response associated with COVID-19 not only exacerbates cardiovascular complications but also plays a key role in musculoskeletal dysfunction, further contributing to post-COVID-19 fatigue and mobility impairments. Given the high prevalence of mild or asymptomatic COVID-19 cases, many individuals may be unaware of underlying cardiovascular involvement. A thorough understanding of these hidden complications is crucial for early detection, effective management, and improved long-term outcomes.

Asymptomatic COVID-19 encompasses two categories: asymptomatic infected individuals and presymptomatic infected individuals. Asymptomatic infected individuals are those who test positive for reverse transcription-polymerase chain reaction (RT-PCR) but never exhibit any signs or clinical symptoms of COVID-19. In contrast, presymptomatic infected individuals are those who test positive for RT-PCR without showing any signs or clinical symptoms at the time of testing but later develop symptoms [11]. A previous study reported that the SARS-CoV-2 virus is transmitted through exhaled droplets containing the virus, which are inhaled by susceptible individuals. These droplets enter the nose and throat, where the virus binds to a cell-surface receptor known as ACE2. Since SARS-CoV-2 is a novel pathogen to the individual, the immune cells fail to recognize it, allowing the virus to evade the body’s defenses and replicate within host cells. This replication process destroys the host cells, triggering pathological changes that alert the immune system to combat both the infected cells and the virus [12]. Therefore, if the early immune response can sufficiently suppress viral replication and prevent it from spreading to the lungs, the infected individual may experience no symptoms or only mild symptoms [13]. Although previous reports have identified impaired cardiorespiratory and musculoskeletal function in post-COVID-19 patients compared to healthy individuals [14,15,16], these findings do not provide insights into cardiorespiratory and musculoskeletal function across different durations after infection. Therefore, this study aims to evaluate and compare cardiorespiratory function, assessed by the 6-minute walk test (6MWT), and musculoskeletal function, assessed by the handgrip strength test and the sit-to-stand test (STS10) in post-coronavirus disease 2019 (COVID-19) patients. Participants were stratified based on the time since infection (≤6 months and >6 months) and compared with matched healthy controls.

2. Materials and Methods

2.1. Study Design

A cross-sectional study was conducted to assess cardiorespiratory function using the 6MWT and musculoskeletal function using the handgrip strength test and the STS10 in healthy individuals and post-COVID-19 patients.

2.2. Participants

A total of 111 participants were recruited and assigned to three groups (n = 37/group). The sample size was determined through power analysis, with a statistical power of 0.80, an alpha level of 0.05, and an effect size d of 0.30 [17]. The inclusion criteria were as follows: participants had to be at least 18 years old, with or without a history of mild COVID-19 recovery, and have had a SARS-CoV-2 infection confirmed by polymerase chain reaction (PCR) or antigen test kit (ATK) before the evaluation. They were also required to have a normal body mass index (BMI) ranging from 18.5–24.9 kg/m². Mild COVID-19 symptoms included fever, cough, sore throat, malaise, pain headache, muscle pain, nausea, vomiting, diarrhea, loss of taste and smell, and a peripheral oxygen saturation (SpO₂) of ≥95%), indicating no need for supplemental oxygen therapy or mechanical ventilation. Additionally, eligible participants exhibited a respiratory rate of >20 breaths per minute, were non-hospitalized, or had abnormal chest imaging findings [18]. The exclusion criteria included individuals with visual, communication, or hearing impairments, as well as those with musculoskeletal conditions that restricted their ability to perform daily activities. Participants were divided into three groups: healthy control group (Group 1), participants who had recovered from COVID-19 within ≤6 months (Group 2), and participants who had recovered from COVID-19 infection more than 6 months (Group 3). The study received ethical approval from the Clinical Research Ethics Committee of the University of Phayao, Phayao, Thailand. (IRB code: 1.3/032/65).

2.3. Procedure

Healthy individuals and post-COVID-19 patients were assessed for cardiorespiratory function using the 6MWT and musculoskeletal function using the handgrip strength test and the STS10.

2.3.1. Evaluation of Demographic Data

All participants were assessed for baseline demographic data, including sex, age, height, weight, and BMI.

2.3.2. Evaluation of Symptomatology

The evaluation of symptoms in the included individuals was based on self-reported data collected at the time of assessment. Reported symptoms included headache, cough, shortness of breath, fatigue, muscle pain, ageusia, anosmia, hair loss, memory loss, anxiety, and runny nose [19].

2.3.3. Evaluation of Musculoskeletal Function Using the Handgrip Strength Test

Participants were instructed to stand with their elbows fully extended at the start of the test. They performed three consecutive repetitions, each lasting three seconds, with a 15 s rest between repetitions. The highest peak force from the dominant arm was recorded [20].

2.3.4. Evaluation of Musculoskeletal Function Using the STS10

Participants were instructed to stand up until their hips and knees were fully extended, then sit down with their arms folded across their chest. They were asked to perform this movement as quickly as possible for a total of ten repetitions. The total time taken to complete the test was recorded [20].

2.3.5. Evaluation of Cardiorespiratory Parameters Using the 6MWT

Before starting the 6MWT, cardiorespiratory parameters were assessed, including the heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse oxygen saturation (O₂ sat), rate of perceived exertion (RPE), and leg fatigue. Each participant was asked to wear comfortable clothing and shoes. Participants were then directed to walk as far as possible within 6 minutes without running along a 30 m corridor. The total distance covered during the 6MWT was recorded, and the cardiorespiratory parameters were measured and documented upon test completion [21].

Data were collected by trained research assistants who underwent specific training on study procedures, data collection techniques, and participant interaction to ensure consistency and reliability. One minute after completing the 6MWT, heart rate and pulse oxygen saturation were measured using a finger pulse oximeter (SB200, Rossmax International Ltd., Taipei, Taiwan). Blood pressure was measured with an automatic blood pressure monitor (HEM-8712, Omron healthcare Co., Ltd., Kyoto, Japan). The Borg rating of perceived exertion scale (6–20 scales) was used to evaluate a participant’s perceived exertion, while leg fatigue was assessed using a modified 10-point Borg scale.

2.4. Statistical Analysis

Descriptive statistics were used to present demographic data. A one-way ANOVA was conducted to compare cardiorespiratory and musculoskeletal parameters among the healthy control group (Group 1), participants who had recovered from COVID-19 within ≤6 months (Group 2), and participants who had recovered from COVID-19 infection for more than 6 months (Group 3). LSD post hoc tests were conducted to evaluate pairwise comparisons. IBM SPSS Statistics software, version 22.0, was used for analysis, with a p-value of less than 0.05 considered statistically significant.

3. Results

The characteristics of the participants are presented in

Table 1. Characteristics of the participants. Values are presented as means ± SD.

Variables	Group 1 (n = 37; F = 21, M = 16)	Group 2 (n = 37; F = 21, M = 16)	Group 3 (n = 36; F = 17, M = 19)
Age (years)	39.16 ± 18.44	44.38 ± 15.83	36.72 ± 16.99
Weight (kg)	60.24 ± 7.47	55.22 ± 5.24 a	59.94 ± 1.66 b
Heigh (m)	1.66 ± 0.08	1.60 ± 0.06 a	1.66 ± 0.07 b
BMI (kg/m2)	21.70 ± 1.45	21.45 ± 1.78	21.47 ± 2.32

Denote: F = female; M = male; BMI = body mass index; ^a p < 0.05 vs. Group 1 and ^b p < 0.05 vs. Group 2.

. The results indicated that Group 2 had significantly lower weight than both Group 1 and Group 3. However, all three groups had normal BMI values.

All participants in the three groups completed the handgrip strength test, STS10, and 6MWT. Group 2 had a significantly lower handgrip strength test and 6MWT distance compared to Group 1 and Group 3. Additionally, Group 2 took significantly more time to complete the STS10 compared to Group 1 (

Table 2. Comparison of muscle strength and 6MWT distance among the groups.

Variables	Group 1	Group 2	Group 3
Handgrip strength test (kg)	28.65 ± 5.21	24.03 ± 4.30 a	26.97 ± 4.38 b
STS10 (s)	24.14 ± 3.83	26.30 ± 4.48 a	25.53 ± 4.43
Distance of the 6MWT (meters)	537.27 ± 39.90	503.32 ± 41.76 a	541.89 ± 61.08 b

Denote: STS10 = sit-to-stand test; 6MWT = 6-minute walk test. ^a p < 0.05 vs. Group 1 and ^b p < 0.05 vs. Group 2.

).

Before the 6MWT, the results showed that Group 1 had significantly lower HR compared to Group 2 and Group 3. SBP was significantly lower in Group 3 compared to Group 1 and Group 2. DBP was also significantly lower in Group 3 compared to Group 2 (

Table 3. Comparison of cardiorespiratory parameters from the 6MWT among the groups.

Variables	Group 1	Group 2	Group 3
Pre-HR (bpm)	75.05 ± 6.75	81.03 ± 7.97 a	81.89 ± 9.56 a
Post-HR (bpm)	110.35 ± 8.54	118.54 ± 8.51 a	112.50 ± 10.64 b
Pre-SBP (mmHg)	132.86 ± 8.87	132.96 ± 5.60	124.94 ± 11.22 a,b
Post-SBP (mmHg)	142.35 ± 4.73	152.16 ± 10.59 a	139.81 ± 6.24 b
Pre-DBP (mmHg)	78.08 ± 8.82	78.46 ± 5.14	74.92 ± 8.22 b
Post-DBP (mmHg)	81.22 ± 7.11	84.19 ± 3.70 a	77.28 ± 7.46 a,b
Pre-O2 sat (%)	98.57 ± 0.50	98.27 ± 0.69	98.39 ± 0.60
Post-O2 sat (%)	97.22 ± 0.63	96.89 ± 0.70 a	97.08 ± 0.69
Post -RPE	9.97 ± 1.21	10.46 ± 0.90	9.83 ± 1.25 b
Post-leg fatigue	2.95 ± 0.81	3.84 ± 0.83 a	3.72 ± 0.91 a

Denote: HR = heart rate; SBP = systolic blood pressure; DBP = diastolic blood pressure; O₂ sat= pulse oxygen saturation; RPE= rate of perceived exertion. ^a p < 0.05 vs. Group 1 and ^b p < 0.05 vs. Group 2.

).

After the 6MWT, the results revealed that Group 2 exhibited significantly higher HR and SBP compared to both Group 1 and Group 3. DBP was significantly lower in Group 3 when compared to Group 1 and Group 2. O₂ sat was significantly lower in Group 2 relative to both Group 1 and Group 3. The RPE was significantly lower in Group 1 than in Group 2. Additionally, leg fatigue was significantly lower in Group 1 compared to both Group 2 and Group 3 (Table 3).

4. Discussion

This study aimed to evaluate cardiorespiratory and musculoskeletal function in individuals recovering from COVID-19, comparing them with healthy controls. The findings reveal significant differences in physical performance and physiological responses between post-COVID-19 patients and healthy individuals, shedding light on the potential long-term consequences of SARS-CoV-2 infection.

The study’s musculoskeletal findings indicate significant impairments in individuals recovering from COVID-19, particularly in Group 2, which includes participants who recovered within the past 6 months. This group demonstrated lower handgrip strength and shorter distances in the 6MWT compared to both Group 1 and Group 3, indicating a reduction in both muscle strength and endurance. Decreased handgrip strength is a notable marker of overall muscle weakness and is often associated with poor functional outcomes, including difficulty in performing daily activities that require hand strength [22]. The 6MWT results further suggest that COVID-19 recovery might impair aerobic capacity, stamina, and endurance. A shorter walking distance in this test may reflect limitations in cardiovascular fitness, lung capacity, or both, as well as diminished muscle endurance due to prolonged bed rest, reduced physical activity during illness, or the effects of post-viral fatigue. Previous research has demonstrated that COVID-19 can cause lingering fatigue even in asymptomatic or mild cases, which may persist for months after recovery and contribute to a general reduction in functional capacity [14,16]. Additionally, Group 2 took longer to complete the STS10, indicating challenges in lower body strength and mobility. The STS is a widely used measure of lower body strength, balance, and functional mobility. It requires participants to rise from a seated position and return to a seated position multiple times in quick succession. Slower performance on this test indicates reduced strength in the legs and difficulty with postural control, both of which are essential for independent mobility and quality of life. Since the lower extremities play a crucial role in walking, climbing stairs, and standing, these findings suggest that post-COVID-19 individuals, particularly those recently recovered, may experience difficulties in these basic functional movements due to muscle weakness or fatigue [23,24]. The impairments in both handgrip strength and functional mobility observed in Group 2 are likely multifactorial. One possible contributing factor is the direct effect of the SARS-CoV-2 on skeletal muscles. The virus binds to the ACE2 receptor, which is present on muscle cells as well as in the lungs, heart, and other organs [8,9,10]. Infected muscle tissue can suffer from myopathy, characterized by muscle fiber damage and inflammation, which can contribute to muscle weakness, pain, and decreased function. Additionally, the inflammatory response to the virus, which includes the release of cytokines and other immune system signals, may further exacerbate muscle breakdown and fatigue. This systemic inflammation can persist even after the infection has been cleared, leading to prolonged musculoskeletal dysfunction in some individuals [5,7]. The findings of this study align with the existing literature reporting musculoskeletal impairment as a common long-term effect of COVID-19, which can persist well beyond the acute phase of the illness. The combined effects of viral damage to muscle tissue, systemic inflammation, and physical deconditioning all contribute to the observed reductions in strength, endurance, and mobility in post-COVID-19 patients [8,9,10].

Following the 6MWT, Group 2 exhibited significantly higher HR and SBP compared to both Group 1 and Group 3. This suggests greater cardiovascular stress and impaired recovery following physical exertion. Increased HR and SBP post-exercise indicate that individuals in this group may have a diminished ability to regulate cardiovascular responses during and after physical activity, possibly due to lingering effects of SARS-CoV-2 infection. Previous studies suggested that COVID-19 may contribute to cardiovascular dysfunction through mechanisms such as endothelial damage, myocarditis, and autonomic dysregulation, all of which can impair circulatory efficiency and lead to an exaggerated cardiovascular response to exercise [6,7]. Persistent endothelial dysfunction may lead to inadequate vasodilation and oxygen delivery to active muscles, further exacerbating cardiovascular strain. Additionally, Group 2 exhibited significantly lower O₂ sat levels following the 6MWT, suggesting potential impairments in oxygen uptake, delivery, or utilization during physical exertion. Reduced oxygen saturation could indicate persistent pulmonary complications, such as impaired alveolar gas exchange or residual lung inflammation, which have been observed in post-COVID-19 patients even months after recovery. These findings align with prior studies demonstrating that SARS-CoV-2 infection can lead to long-term respiratory impairments, including decreased lung diffusion capacity, ventilation-perfusion mismatching, and interstitial lung abnormalities [8,9,10]. The observed reduction in oxygen saturation may also reflect microvascular dysfunction, contributing to inadequate oxygen supply to tissues and potentially explaining the greater cardiovascular strain experienced by Group 2 during exertion. The RPE was significantly lower in Group 1 than in Group 2, indicating that individuals recovering from COVID-19 perceive physical tasks as more challenging. This heightened perception of effort could be due to a combination of lingering fatigue, autonomic nervous system dysfunction, and reduced cardiovascular and musculoskeletal efficiency. COVID-19-related fatigue has been widely documented, with possible contributing factors including mitochondrial dysfunction, systemic inflammation, and dysregulation of energy metabolism. Persistent inflammatory markers such as elevated cytokines and C-reactive protein (CRP) have been reported in post-COVID-19 individuals, potentially leading to prolonged fatigue and reduced exercise tolerance [11,12]. The increased exertion perception in Group 2 may also be linked to muscle deconditioning due to prolonged inactivity during illness, further reduced physical resilience. Furthermore, leg fatigue was significantly lower in Group 1 compared to both Group 2 and Group 3, suggesting that post-COVID-19 individuals, even those recovered for more than six months, may experience persistent muscle fatigue and mobility limitations. The presence of leg fatigue in Group 3, albeit to a lesser extent than in Group 2, indicates that some individuals may experience prolonged recovery periods, with residual musculoskeletal impairments persisting beyond six months post-infection. This could be attributed to muscle fiber atrophy, chronic inflammation, or reduced neuromuscular function following SARS-CoV-2 infection [13,14]. In addition, comprehensive physical recovery following COVID-19 should address dietary and nutritional changes, exercise interventions, and appropriate medication use. Proper nutrition supports muscle repair and overall recovery, while gradual and supervised exercise programs can improve cardiovascular and musculoskeletal function. Pharmacological management may be necessary in certain cases to control symptoms or complications. Emphasizing a multidisciplinary approach that includes nutritionists, physiotherapists, and healthcare providers is essential for optimizing rehabilitation and improving long-term outcomes in post-COVID-19 patients.

Limitations of This Study

This study has several methodological limitations that should be acknowledged. First, although participants were stratified into three groups with equal sample sizes, no formal matching was conducted based on demographic characteristics or baseline physical activity, which may have introduced selection bias. Future studies should consider matching participants or adjusting for potential confounding variables statistically. Second, data on comorbidities, medication use, and lifestyle factors such as smoking, alcohol consumption, and habitual exercise were not collected, all of which may influence cardiorespiratory and musculoskeletal performance outcomes. Additionally, the study relied on self-reported symptomatology to classify the severity and duration of COVID-19 symptoms, which may be subject to recall bias. Importantly, pre-infection baseline data were not available due to the cross-sectional nature of this study, limiting the ability to assess changes in physical performance attributable to COVID-19. Furthermore, assessors were not blinded to group assignments, which may have introduced measurement bias. Although standardized procedures were followed, the reliability of outcome measures such as the 6MWT, STS10, and handgrip strength was based on previously published protocols and not re-evaluated in this specific cohort. Lastly, although one-way ANOVA was used to compare group differences, post hoc comparisons and effect sizes were initially not reported. These have been added to enhance interpretability. These limitations should be considered when generalizing the findings, and future research should employ a longitudinal design with comprehensive baseline assessments and control for confounding variables to better elucidate the long-term effects of COVID-19 on physical function.

5. Conclusions

These findings emphasize the importance of structured rehabilitation interventions aimed at restoring muscle strength, endurance, and overall mobility in individuals recovering from COVID-19. Given the high prevalence of mild or asymptomatic cases, many individuals may be unaware of the potential long-term effects on physical health. Rehabilitation programs should incorporate targeted exercises to improve musculoskeletal function, cardiovascular efficiency, and fatigue management, helping post-COVID-19 individuals regain optimal physical health.