Concerns about cardiac damage following coronavirus disease 2019 (COVID-19) and society-wide mitigation strategies disrupted children's lives during the COVID-19 pandemic, particularly during the early stages. Policies, such as school and sport restriction, dramatically altered daily routines, leading to more school-based and leisure screen time and less time in active play with their peers (1). Decreased physical activity because of COVID-19 related restrictions has been shown in multiple studies in pediatrics (1–3). Little is known about the effect this has had on fitness and body composition in pediatric and congenital heart disease (CHD), individuals who are often already deconditioned. The only known pediatric CHD study included a combination of individuals with and without heart disease, reporting a decline in peak oxygen consumption (VO₂) on serial exercise testing performed during the pandemic (4).The aims of this study were to: (1) understand how COVID-19 mitigation strategies affected fitness and also body composition in youth with heart disease, and (2) determine if children with heart disease and pre-existing exercise restrictions were more likely to have alterations in their fitness or body composition compared to without such restriction.

This study was approved by the Cincinnati Children's Hospital Medical Center Institutional Review Board, and informed consent was not required for this study.

There were a total of 48 patients who underwent serial testing, with the first test performed within 12 months before and the second test performed within 12 months after the COVID-19 lockdown. There were 15 patients excluded (6 tested because of concern for clinical decompensation, 6 submaximal effort tests, 3 missing data). There were 33 remaining patients (mean age 15.3 ± 3.4 years at the time of the first test; 46% male) who were included in the analysis. Underlying cardiac diagnoses are presented in Table 1. Primary diagnosis was related to electrophysiologic disease in 18 patients, while 15 had structural heart disease. Of note, 36% (12/33) were restricted from sports before COVID-19 with the reason for sports restriction being concern about ventricular arrhythmia in 10 patients and severe left ventricular outflow tract obstruction in 2 patients. In the COVID group, 58% (19/33) were prescribed beta-blockers. None had a cardiac pacemaker, had medication changes, or experienced unexpected arrhythmias during the test.

There was no significant difference in sport restriction and beta-blocker usage between the post COVID-19 lockdown and historical control groups. No patients were diagnosed with COVID-19 prior to their exercise test.

In the COVID-19 lockdown group, the mean time between tests was 1.1 years, ranging from 0.6 to 1.5 years. There was an increase in weight (58.7 ± 21.5–63.9 ± 22 kg, p < 0.0001), skeletal muscle mass (24.1 ± 9.2–25.9 ± 9.1 kg, p < 0.0001), and body fat percentage (22.7 ± 9.4–24.7 ± 10.4%, p = 0.04) without significant change in height (165.5 ± 16.4–167 cm ± 14.2 cm, p = 0.1) or body mass index (21.7 ± 4.8 vs. 22.5 ± 5.5 kg/m², p = 0.2) (Table 2).

There was an increase in absolute peak VO₂ (1,832.9 ± 784.8–1,958.2 ± 835.9 ml/min, p = 0.03), but no change in peak VO₂ when expressed as a percent of predicted values or when indexed to body mass (78.6 ± 13.1–79.3 ± 16.9%, p = 0.8; 31.2 ± 7.5–31.1 ± 8.9 ml/kg/min, p = 0.9). There was no significant change between tests in any of the other exercise variables (Table 2).

When further evaluating the COVID-19 lockdown group, body composition and CPET differences by sex are provided in Table 3. Of note, male patients had an increase in weight (68.9 ± 24–74.6 ± 24.2 kg, p = 0.02) and skeletal muscle mass (29.5 ± 9.1–32.7 ± 8.3 kg, p = 0.002) without a significant change in adiposity (18.9 ± 10–18.8 ± 9.5% body fat, p = 0.8) or height (176.1 ± 12.2–176.4 cm ± 11.9 cm, p = 0.9). Female patients had an increase in height (155.4 ± 13.3–158.2 cm ± 10.2 cm, p = 0.008), weight (49 ± 13.253.8 ± 14 kg, p < 0.0001), skeletal muscle mass (18.7 ± 5.4–19.8 ± 4.2 kg, p = 0.005), and body fat (26.4 ± 7.3–29.8 ± 8.4%, p = 0.03). Male patients had a significant difference between absolute peak VO₂ but not peak VO₂ indexed to weight or as a percent of predicted values. There were no other significant differences based on sex.

When comparing with the cohort that had testing in the years prior to the COVID-19 pandemic (historical control) (N = 65; mean age 14.9 ± 3.3 years at the first test; 49% male), there was no difference in the sex, diagnoses, age, or size between groups. On comparing baseline CPET results between the COVID-19 lockdown and historical control groups, there were no significant differences in any of the CPET parameters studied. In the historical control group, there was no significant change in absolute peak VO₂ (1,826.8 ± 696.8–1,866.7 ± 655.6 ml/min, p = 0.4) or percent predicted peak VO₂ (78.3 ± 15.3–75.9 ± 17.7%, p = 0.2), though there was a decrease in peak heart rate (82.1 ± 11.4–78.1 ± 14.0%, p < 0.001). The ventilatory anaerobic threshold was lower on serial testing in the cohort with testing before the pandemic (54.3 ± 13.2–50.9 ± 14.6, p = 0.02) (Supplementary Table S1).

Findings from this observational study revealed no significant change in the aerobic capacity or body composition, beyond those associated with puberty, from before to after the COVID-19 pandemic and related societal lockdown. This is notable, as there has previously been concern that COVID mitigation could affect exercise habits in this population (1, 11). There were no differences in fitness when comparing serial testing separated by either sex, activity restriction, or in the matched paired historical control group. There were changes in body composition seen between tests, but this was likely secondary to normal pubertal maturation in a largely pediatric cohort.

There have been reports of decreased physical activity related to COVID-19 mitigation strategies both in healthy children and in those with heart disease (1, 11). Whether or not our cohort engaged in less physical activity is unknown, but their objective measures of fitness did not change, which is the opposite of what was reported by Burstein DS et al. (4). This may mean many of the patients were already deconditioned at the time of the initial CPET, as evidenced by an average peak VO₂ of ∼78% of predicted, compared to ∼96% in the Burstein DS et al. cohort (4). Additionally, the lack of change in fitness may be secondary to pre-existing activity restrictions applied by the patients' medical teams, although the lack of change in VO₂ in those not activity restricted argues against this. Lastly, this may mean that the introduction of lockdown measures did not alter their physical activity as they were already sedentary and deconditioned, which is not unusual for a typical congenital heart disease cohort. Prior to COVID-19, youth with congenital heart disease were shown to be more sedentary than their peers (12, 13). Thus, the introduction of lockdown measures may not have resulted in a significant change in their physical activity levels. This is further supported by the lack of change in the already low peak VO₂ on serial testing in the pre-COVID control group.

This study continues to highlight the need to encourage physical activity in youth with congenital heart disease. While the absence of direct negative effects from the lockdown on fitness in children with heart disease is reassuring, this population, both in our cohort and others, has been shown to be significantly deconditioned (14–16). This is meaningful, since decreased peak VO₂ has both negative prognostic and functional implications (17–19). Recreational and competitive activities should be encouraged in this population with an eye towards the risk: benefit calculation, balancing the concerns for sudden cardiac arrest during athletics, and the long-term morbidity and mortality that arises from sedentary behaviors. For individuals so severely deconditioned that participation in organized sports would be impractical, exercise prescription and structured cardiac rehabilitation should be encouraged to improve cardiopulmonary fitness (20).

While this study focused on evaluating the effect of COVID-19 mitigation strategies on the body composition of children and young adults with heart disease, body composition changed during the study period in a pattern that is likely consistent with normal pubertal changes (21). Increase in both skeletal muscle mass and body fat percentage results in an increase in total weight in a pubertal population, which was seen in our cohort. The increase in the total weight for the males was largely driven by increases in skeletal muscle mass while the increase in weight for the females was largely due to increased adiposity; this is in keeping with typical sex-specific pubertal body composition changes (21). These changes remained when the 7 patients older than 18 years-old were removed from the analysis, again supporting expected somatic growth as the likely explanation. The lack of significant change in predicted peak VO₂ in this cohort further supports that these body composition changes were most likely related to normal, expected growth. Unfortunately, secondary to the retrospective design of this study we do not have specific information on the exact pubertal stage of these patients. This should be taken into account for future pediatric studies involving serial body composition measurements.

There were other limitations to this analysis. The available sample size limits statistical power, and a subset of the null findings may represent false negative findings, particularly those with a small effect size. The comparison group lacked body composition data, as the InBody Bioimpedance scale was not widely used in our laboratory until early 2019; thus it is unknown if the changes in body composition in the study cohort is reproduced in the age, sex, and diagnosis-matched cohort. Additionally, questions on specific exercise habits and sports participation are not routinely asked by all of the providers in our hospital. Additional sampling bias may also exist secondary to the retrospective design of the study.

The COVID-19 pandemic and related lifestyle changes do not appear to have had an substantial negative impact on aerobic fitness in children and young adults with heart disease. While this is largely reassuring, these finding may be in part related to pre-existing chronic deconditioning, pre-limited participation in organized sport, or sampling bias.