Influence of steps per day on health-related quality of life in schoolchildren: the mediator role of cardiorespiratory fitness

doi:10.21203/rs.3.rs-3219966/v1

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Research Article

Influence of steps per day on health-related quality of life in schoolchildren: the mediator role of cardiorespiratory fitness

https://doi.org/10.21203/rs.3.rs-3219966/v1

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Journal Publication

published 18 Nov, 2023

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Objectives

To analyse the relationship between steps per day and HRQoL and cardiorespiratory fitness (CRF) and to examine whether the relationship between steps per day and HRQoL is mediated by CRF in schoolchildren.

Methods

This was a cross-sectional study including 501 schoolchildren (aged 9–12 years, 47.3% girls), from Cuenca, Spain. Steps per day were measured using the Xiaomi MI Band 3 Smart Bracelet, HRQoL was estimated by the KIDSCREEN-27 questionnaire and CRF was assessed using the 20-m shuttle run test.

Results

ANCOVA and MANOVA models showed that children with a higher mean number of steps per day (> 9,000 steps/day) had better HRQoL (global score and physical and psychological well-being) and higher CRF levels than their peers with a lower number of steps per day (p < 0.05); however, these differences were attenuated when controlling for sex, age, mother’s education level and CRF (p > 0.05). Linear regression models estimated that each 1000-step increment was associated with better CRF (β = 0.350). In addition, the relationship between steps per day HRQoL global score and physical and psychological well-being is partially mediated by CRF (p < 0.05).

Conclusion

Steps per day is a good metric to estimate daily physical activity because of its positive relationship with CRF. Moreover, those children taking more than 9,000 steps per day have better physical and psychological well-being. Finally, a substantial part of the improvement in HRQoL achieved through the increase in physical activity (steps per day) is mediated by CRF.

physical activity

wearables

physical fitness

children

daily steps

Physical inactivity increases the risk of major noncommunicable diseases [1], and it is considered by the WHO as the 4th cause of mortality [2]. In children, physical inactivity has been related to a worse cardiometabolic profile [3] and a higher risk of mental disorders [4]. Conversely, physical fitness has been associated with improvements in HRQoL and academic achievement [5]. However, more than 80% of children and adolescents worldwide are insufficiently physically active due to time spent in sedentary behaviour, a trend that has increased over the last decades, and has intensified due to the COVID-19 pandemic [6].

Health-related quality of life (HRQoL) refers to the perception of the physical, psychological, and social domains of health, seen from a subjective point of view. It considers distinct environments, such as family, friends, and school, which are influenced by a person's experiences, beliefs, expectations, and perceptions [7]. In this sense, physical activity has repeatedly been associated with both cardiorespiratory fitness (CRF) [8] and HRQoL [9].

Current physical activity guidelines recommend ≥ 60 minutes of moderate to vigorous physical activity (MVPA) per day [10]. However, these recommendations are not adapted to wearable physical activity trackers, nor are they appropriate for steps per day-based metrics, although these devices have proven their effectiveness in increasing physical activity and improving psychosocial outcomes and HRQoL [11]. In children, Gu et al. [12] found that both physical fitness and steps/minute (cadence) were related to HRQoL, suggesting that steps per day interventions at schools could improve children's physical and mental health. Furthermore, children and adolescents with higher levels of CRF took more steps per day (13), requiring further understanding of the role of CRF in the relationship between steps per day and HRQoL.

Although it appears that physical activity improves HRQoL (14), to date, no research in paediatric populations has provided empirical evidence about how many steps per day would be necessary to increase HRQoL and CRF and whether this relationship is mediated by CRF. Accordingly, the aims of this study were 1) to analyse the relationship between steps per day, CRF, and HRQoL in schoolchildren and 2) to investigate whether the relationship between steps per day and HRQoL is mediated by CRF in this population.

We conducted a cross-sectional analysis of baseline data (collected on February-March and October-November 2022) from the e-MOVI study aiming to study physical activity and diet behaviors, lifestyle and cardiovascular risk that occur during childhood. The study included 904 schoolchildren aged 9 to 12 years old from 8 public primary schools in the province of Cuenca, Spain.

The study protocol was approved by the Clinical Research Ethics Committee of the Hospital Virgen de la Luz in Cuenca (REG: 2019/PI1519). After the Board of Governors of each school approved the study, a letter was sent to the parents of all 4th, 5th and 6th graders inviting them to a meeting. At this meeting, we explained the objectives of the study and asked for written approval for their children's participation. All procedures performed in this study were in accordance with the Declaration of Helsinki and its later amendments or comparable ethical standards for experiments involving humans.

Height and weight were measured twice and averaged for analysis. Height was measured to the nearest millimetre using a wall-mounted stadiometer (SECA 222, Vogel and Halke, Hamburg, Germany), with the children standing straight against the wall without shoes, to align the spine with the stadiometer. The head was positioned so that the chin was parallel to the floor. Weight was measured to the nearest 100 g using a calibrated digital scale (SECA 861; Vogel & Halke, Hamburg, Germany) with the children lightly dressed and without shoes. Body mass index was calculated as weight in kilograms divided by the square of height in meters (kg/m2) using the means of the weight and height measurements.

Steps per day were measured by a Xiaomi Mi Band 3 Smart wristband, which presents a good validity for step count [15]. The mean of the steps per day in the two weeks following the baseline measurements was used. Only data from participants whose wristbands had records of at least 4 days per week, with at least 1 weekend day, were considered. The steps per day were recorded by the children in a daily steps log that was collected weekly at the school by a member of the research team.

The 20-m shuttle run test was used to assess the CRF. Participants ran between two lines separated by 20 m while keeping pace with audio signals emitted by a pre-recorded compact disc. The initial speed was 8.5 km/h and increased by 0.5 km/h every minute. Children were encouraged to keep running as long as possible during the test. When children failed to follow the pace in two consecutive intervals, they were asked to stop, and the stage completed (full laps) was recorded. Leger’s formula was used to estimate maximal oxygen consumption (VO₂max) [31.025 + (3.238 × velocity) − (3.248 × age) + (0.1536 × age × velocity)] as an indicator of CRF.

Health-related quality of life was evaluated using the validated Spanish version of the KIDSCREEN-27 questionnaire [16], which consists of 27 items, referring to the previous week, assessing 5 domains of HRQoL: physical well-being, psychological well-being, parental relationships and autonomy, social support and peers, and school environment. T scores of each dimension were calculated according to the manual, using a mean of 50 and a standard deviation (SD) of 10, to establish normality for children [17] and in this way to obtain a single total score or global index of HRQoL from the means of the five dimensions, where a higher score represents better HRQoL.

Mother’s education was measured by using a validated questionnaire about the maximum level of education achieved by parents [18]. Responses were categorised into four levels: “no studies or primary studies”, “secondary studies”, “high school”, and “university studies”.

Before proceeding with the analysis, the normality of the distribution of the continuous variables was checked using statistical methods (Kolmogorov‒Smirnov) and graphs (normal probability plots). Differences in basic characteristics between girls and boys were tested using Student´s t tests for continuous variables and chi-square tests for categorical variables. Homogeneity of variances was assessed with the Levene test.

Partial correlation coefficients adjusted by sex, age, and mother’s education level (considered the familial socioeconomic indicator more closely related to HRQoL and lifestyle behavior [19, 20]) were calculated to examine the relationship between steps per day, CRF, and HRQoL.

A multivariable linear regression model was used to estimate the linear association between 1000 steps/day increment and CRF, adjusting for sex, age, and mother’s education level. Furthermore, to explore the relation between steps per day and CRF, a locally weighted scatterplot smoothing (LOESS) regression was used. According to the shape of the LOESS regression, steps per day were categorised into 3 categories: <9,000 steps/day, 9,000–12,000 steps/day and > 12,000 steps/day. Analysis of covariance (ANCOVA) models were used to test the mean differences in CRF and HRQoL global score by steps per day categories (model 0), controlling for sex, age, and mother’s education level (model 1) and CRF (only when HRQoL global score was the dependent variable, model 2). Differences in the mean scores of each HRQoL by steps per day categories were examined using a multivariate analysis of covariance (MANCOVA), controlling for the above-described potential confounders. Second- and third-order interaction terms were evaluated in ANCOVA and MANCOVA. Pairwise post hoc hypotheses were tested using the Bonferroni correction for multiple comparisons.

Mediation analyses adjusted by sex, age, and mother’s education level were conducted to examine whether CRF mediates the association between steps per day and HRQoL (domains and global score) using the PROCESS SPSS Macro, version 3.5, selecting Model 4 and 5000 bias-corrected bootstrap samples [21]. In these analyses, the first equation (path a) corresponded to the regression coefficients of the mediating variable (CRF) on the independent variable (steps per day), and the second equation (path c, total effect) was the regression coefficient of the outcome (HRQoL) on the independent variable. Path b represents the regression coefficient of the outcome controlling for the independent variable. The relationship of the independent variable with the outcome and the mediator simultaneously was estimated in the third equation (path c’, direct effect). To test the statistical significance of the mediation effect in the parametric approach, we used the indirect effect (path a * path b), which indicates the change in HRQoL per unit change in steps per day that is mediated by CRF. Following the Hayes recommendation [22], the complete and partial mediation concepts were not used in this study.

All statistical analyses were performed using IBM SPSS Statistics software (Version 28.0; IBM Corp., Armonk, NY, USA), and p < 0.05 was considered to indicate significance.

Our study included 501 schoolchildren (mean age = 10.61 ± 0.04), of whom 237 (47.3%) were girls. Table 1 describes the main characteristics of the sample by sex. Compared to girls, boys showed a higher mean in steps per day and CRF, as well as in physical well-being and HRQoL global score (p < 0.05).

Partial correlation coefficients among steps per day, CRF, and HRQoL domains, controlling for. sex, age and mother’s education level, are presented in Table 2. Overall, the physical well-being domain and HRQoL global score were significantly correlated with steps per day and CRF. Similarly, psychological well-being and autonomy and parent relation domains were also correlated with steps per day but not with CRF.

A daily increment of 1,000 steps was associated with better CRF (β = 0.350, 95% CI: 0.192 to 0.508, p < 0.001). Figure 1 depicts the trend of the association between steps per day and CRF using LOESS regression, which indicates that from approximately 9,000 steps/day onwards, a higher number of steps per day is nonlinearly related to a higher level of CRF, stabilising at approximately 12,000 steps/day.

Table 3 shows the mean differences in CRF and HRQoL global score by steps per day categories. Schoolchildren with > 12,000 steps/day had higher levels of CRF than their peers with a lower number of steps per day (model 0). These differences remained significant after controlling for sex, age, and mother’s education level (model 1). Regarding HRQoL global score, better scores were shown in children who achieved more than 9,000 steps per day, even after adjusting for sex, age, and mother’s education level (model 1), although there were no significant differences in these HRQoL dimensions between achieving 9,000-12,000 steps/day or >12,000 steps/day (Model 0 and 1). When the model was adjusted by CRF, the significance disappeared.

According to the results of MANOVA models presented in Table 4, those children who achieved a higher number of steps per day scored better in physical and psychological well-being than those who did not achieve this figure, although with no significant differences between 9,000-12,000 steps/day and >12,000 steps/day (Model 0 and 1). Similar results were identified for autonomy and parent relation domain when adjusted for sex, age, and mother’s education level (model 1). When the MANCOVA models were also adjusted for CRF (model 2), the differences disappeared for physical well-being and autonomy and parent relations, while for psychological well-being, they remained.

Considering the preceding results, physical and psychological well-being, and HRQoL global score were analysed in the mediation models presented in Fig. 2. In the first regression equation (direct effect, path a), steps per day were positively related to CRF (p < 0.001). In the second equation, the total effect (path c) showed that steps per day were positively associated with physical well-being (p < 0.001), psychological well-being, and HRQoL global score (p < 0.05). Finally, the relationship between steps per day and these domains of HRQoL and global score became weaker, although significant, when CRF was included in the models (path c’). The percentage of the total effect mediated by CRF was 20% for physical and psychological well-being and 25% for HRQoL global score.

After testing mediation hypotheses using the indirect effect and bootstrapping method, the significant paths were steps per day→CRF→HRQoL (physical and psychological well-being, and global score). Thus, an increase in steps per day resulted in a higher CRF level, which was positively related to better physical and psychological well-being and HRQoL global score.

This study is the first to analyse the relationships of physical activity, measured as steps per day, with CRF and HRQoL in children and to examine whether the relationship between steps per day and HRQoL is mediated by CRF in this population. Our data support that children with a higher number of steps per day have higher CRF levels, physical and psychological well-being and HRQoL global score than their peers with fewer steps per day, being greater when they accumulate more than 9,000 steps/day. Furthermore, our study results suggested that the association between steps per day and HRQoL is mediated by CRF in schoolchildren.

Reducing sedentary time and increasing physical activity levels have shown benefits for children's physical and psychosocial health [23], improving HRQoL [24]. In addition, increased physical activity indirectly involves spending more time outdoors and in natural environments, which potentially improves mood and affective states, leading to a greater effect on physical and mental well-being [25]. This is in line with our findings, which support that increasing the number of steps per day would enhance physical and psychological well-being in schoolchildren, suggesting that step counting in children is a correct objective measure of physical activity [26].

In light of the current evidence, it is not easy to answer two main questions: what the minimum number of steps is to meet the current recommendations of 60 minutes of MVPA for schoolchildren, and what is the cut-off point of steps per day, if any, beyond which the benefits are negligible. The answer to the first question is not possible because there is no consensus regarding the boundaries between light and moderate physical activity (for children, as many as 3 and 4 METS have been proposed [26]). Therefore, it might be more practical to define the cut-off point of physical activity associated with a self-perception of physical and psychological well-being rated as good (this could be the equivalent of patient-reported outcomes for sick populations). For this concern, our data suggest that 9,000 steps per day could be associated with the minimal volume of physical activity associated with an acceptable level of HRQoL. For the second question, 12,000 steps per day has been suggested as a useful single cut point for both gender children and adolescents [27]. Our data are in accordance with this recommendation because, although higher number of steps per day is associated with better HRQoL, substantive improvements above 12,000 steps would not be found.

The use of wearable activity trackers provides ongoing support and motivation, increasing steps per day by up to 10%, probably because these devices raise children's awareness of their physical activity volume, thus facilitating more active behaviours and promoting long-term adherence to physical activity [26]. Moreover, the steps are intuitively understood and therefore easy to translate into clinical counselling, wellness programmes and public health recommendations [28]. HRQoL may be affected by motivation, as high expectations lead to positive behaviors and increased health-related well-being [29]; therefore, the use of these tools could be an effective method for improving children's HRQoL.

It has been shown that increased physical activity, through a greater number of steps per day, also increases CRF [30]. According to our observations, walking at least 9,000 steps/day is associated with improvements in CRF, with higher values at 12,000 steps/day, and for every 1,000-step increase per day, the CRF level is associated with an increase of 0.35 ml/kg/min. It is well established that increased CRF is positively related to HRQoL [31], so the influence of steps per day on HRQoL could be transmitted through improvements in CRF, as confirmed by our results, which support that part of the effect of the steps per day on the improvement of HRQoL, in particular on physical and psychological well-being, is mediated by the improvement of CRF.

The mediator role of CRF in this association might be explained by a longer duration of MVPA improving overall fitness in children and adolescents [32]. Furthermore, fitness has been related to physical and mental functioning and HRQoL [31]. Children who spend more time in sedentary behaviors have significantly lower psychosocial health, whereas MVPA is related to better HRQoL [4]. The effect of physical activity on neuropeptides such as serotonin and endorphins, which positively influence mood, and changes in the brain structure and its function would support the positive relationship between CRF and mental health [33]. Higher CRF levels are also associated with better bone health and body composition, lower risk of cardiometabolic diseases and greater muscular endurance, which may be related to improved perceptions of physical well-being [34, 35].

LIMITATIONS

Some limitations of our study should be recognised. First, the main limitation was its cross-sectional design, which does not allow us to establish causal relationships because although a longitudinal effect of physical activity on both CRF and HRQoL has repeatedly been evidenced, these relationships have never been established using steps per day to estimate physical activity; therefore, the reported results should be prospectively confirmed. Second, the study sample included only Spanish children from 4th to 6th grade, so caution is necessary when extrapolating these data to another population, age range, or to children of non-Caucasian origins. Third, a self-report questionnaire was used to measure HRQoL, which is a dynamic process influenced by context and difficult to capture through verbal processes. Finally, as the mediation models are exploratory in nature, we cannot exclude additional mediators that might have influenced the association between steps per day and HRQoL and their domains of physical and psychological well-being.

Our data are relevant from a clinical perspective because they suggest that steps per day are a useful objective physical activity metric in children, suggesting that walking 9,000 steps/day or more is associated with improved CRF and physical and psychological well-being. Furthermore, this study shows that the effect of physical activity expressed in terms of steps per day could be partially conveyed in an improvement of CRF. Therefore, promoting physical activity in children by encouraging an increase in the number of steps per day could be a practical strategy of particular interest for improving the HRQoL of schoolchildren.

Funding: This work was supported by the Ministry of Economy and Competitiveness-Carlos III Health Institute and FEDER funds (PI19/01126).

Conflict of interest disclosures: None declared.

Eva Rodríguez Gutiérrez and Ana Torres Costoso participated in the design of the study and contributed to data collection and data reduction/analysis. Irene Martínez García, Maribel Lucerón Lucas-Torres and Sergio Núñez de Arenas Arroyo participated in the design of the study and contributed to data collection. Vicente Martínez Vizcaíno, Celia Álvarez Bueno and María Medrano Echeverría contributed to data reduction/analysis and interpretation of results.

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Table 1. Characteristics of the total study sample, and by sex.
	Total (n = 501)	Boys (n = 264)	Girls (n = 237)	p-value
Age (year)	10.61 ± 0.04	10.58 ± 0.06	10.64 ± 0.06	0.500
Weight (kg)	39.91 ± 0.43	39.69 ± 0.61	40.11 ± 0.62	0.630
Height (cm)	144.37 ± 0.38	143.93 ± 0.51	144.77 ± 0.55	0.268
BMI (kg/m²)	18.99 ± 0.16	19.01 ± 0.23	18.97 ± 0.2	0.904
Steps per day	10,820.02 ± 154.08	12,311.58 ± 235.82	9,518.81 ± 163.20	<0.001
CRF (VO₂ max; ml/kg/min)	46.20 ± 0.21	47.54 ± 0.33	44.98 ± 0.23	<0.001
Health-related quality of life
Physical well-being	52.40 ± 0.38	54.29 ± 0.55	50.71 ± 0.51	<0.001
Psychological well-being	53.82 ± 0.41	54.55 ± 0.56	53.18 ± 0.60	0.096
Autonomy and parent relation	52.24 ± 0.40	52.40 ± 0.57	52.08 ± 0.57	0.692
Social support & peers	55.21 ± 0.37	55.38 ± 0.54	55.07 ± 0.52	0.679
School environment	58.05 ± 0.42	57.81 ± 0.62	58.27 ± 0.57	0.591
Global score	54.91 ± 0.42	55.90 ± 0.62	54.02 ± 0.56	0.026
Mother’s education level (%)				0.010
No studies/Primary studies	4.1	1.9	5.9
Secondary studies	23.5	19.6	26.7
High school	29.3	30.4	28.3
University studies	43.2	48.1	39.0
Values are mean ± standard error, except for mother’s education level, which are shown as percentages (%). Abbreviations: BMI = body mass index; CRF = cardiorespiratory fitness; VO₂ max = maximal oxygen intake. CRF indicates VO₂ max (mL/kg/min) values calculated with the Leger formula (18). The values in bold indicate statistical significance at p < 0.05. P values are from parametric test as all variables are normally distributed.

Table 2. Partial correlation coefficients (r) between steps per day, cardiorespiratory fitness, and dimensions of health-related quality of life adjusted by sex, age, and mother’s education level.

	CRF	Physical well-being	Psychological well-being	Autonomy and parent relation	Social support & peers	School environment	Global score
Steps per day	0.240**	0.197**	0.167*	0.120*	0.042	0.011	0.143**
CRF		0.250**	0.107	0.084	0.040	0.065	0.135*
Physical well-being			0.383**	0.325**	0.401**	0.394**	0.626**
Psychological well-being				0.440**	0.407**	0.421**	0.727**
Autonomy and parent relation					0.356**	0.349**	0.636**
Social support & peers						0.387**	0.509**
School environment							0.616**
Abbreviations: CRF = cardiorespiratory fitness. The values in bold indicate statistical significance. P value = * p < 0.05; ** p < 0.001.

Table 3. Analysis of covariance of cardiorespiratory fitness and health-related quality of life global score by steps per day categories.

		Steps per day categories
		Low (L) <9,000	Medium (M) 9,000-12,000	High (H) >12,000	p
	n	157	176	168
Cardiorespiratory fitness (ml/kg/min)	M₀	44.11 ± 0.35^M,H	46.33 ± 0.33^L,H	48.03± 0.34^L,M	<0.001
Cardiorespiratory fitness (ml/kg/min)	M₁	44.40 ± 0.42^M,H	46.93 ± 0.39^L,H	48.09 ± 0.41^L,M	<0.001
Health-related quality of life global score	M₀	52.92 ± 0.75^M,H	56.10 ± 0.71^L	55.54 ± 0.72^L	0.005
	M₁	52.60 ± 0.86^M,H	55.72 ± 0.81^L	55.61 ± 0.85^L	0.016
	M₂	52.94 ± 0.90	55.50 ± 0.81	55.03 ± 0.87	0.101
Data are presented as mean ± standard error (SE). The values in bold indicate statistical significance at p < 0.05. Model 0 (M₀): raw data analysis. Model 1 (M₁): controlling for sex, age and mother’s education level. Model 2 (M₂): model 1 + cardiorespiratory fitness. Superscript letter indicates statistical significance (p < 0.05) between categories for post-hoc tests using the Bonferroni comparisons.

Table 4. Multivariate analysis of covariance of health-related quality of life domains by steps per day categories.

		Steps per day categories
		Low (L) <9,000	Medium (M) 9,000-12,000	High (H) >12,000	P value
	n	157	176	168
Physical well-being	M₀	50.04 ± 0.68 ^M,H	52.77 ± 0.64^L	54.67 ± 0.65^L	<0.001
	M₁	50.23 ± 0.79^M,H	52.93 ± 0.72^L	54.20 ± 0.76^L	0.002
	M₂	51.18 ± 0.82	52.75 ± 0.72	51.18 ± 0.82	0.146
Psychological well-being	M₀	51.63 ± 0.74 ^M,H	55.10 ± 0.70 ^L	54.87 ± 0.71^L	<0.001
	M₁	51.31 ± 0.92^M,H	54.75 ±0.84 ^L	55.19 ± 0.89^L	0.006
	M₂	51.23 ± 0.97^M,H	54.50 ± 0.85^L	54.79 ± 0.91^L	0.019
Autonomy and parent relation	M₀	50.80 ± 0.74	53.18 ± 0.69	52.66 ± 0.70	0.050
	M₁	50.23 ± 0.89^M	52.53 ± 0.81	53.61 ± 0.86^L	0.027
	M₂	50.32 ± 0.93	52.44 ± 0.82	53.16 ± 0.88	0.096
Social support and peers	M₀	54.67 ± 0.69	55.58 ± 0.65	55.18 ± 0.66	0.631
	M₁	53.98 ± 0.85	55.83 ± 0.78	55.57 ± 0.82	0.245
	M₂	54.01 ± 0.91	55.62 ± 0.79	55.41 ± 0.85	0.387
School environment	M₀	58.54 ± 0.76	58.94 ± 0.72	57.33 ± 0.73	0.261
	M₁	57.99 ± 0.93	58.97 ± 0.85	58.28 ± 0.90	0.713
	M₂	58.07 ± 0.98	58.71 ± 0.86	57.86 ± 0.92	0.767
Data are presented as mean ± standard error. The values in bold indicate statistical significance at p < 0.05. Model 0 (M₀): raw data analysis. Model 1 (M₁): controlling for sex, age, and mother’s education level. Model 2 (M₂): model 1 + cardiorespiratory fitness. Superscript letter indicates statistical significance (p < 0.05) for post-hoc tests using the Bonferroni comparisons. Using Pillai’s trace: M₀: p < 0.001; M₁:p = 0.01, M₂:p = 0.193.

No competing interests reported.

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published 18 Nov, 2023

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Influence of steps per day on health-related quality of life in schoolchildren: the mediator role of cardiorespiratory fitness

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