Yuki et al.
Journal of Physiological Anthropology(2023) 42:4
https://doi.org/10.1186/s40101-023-00321-8

Journal of
Physiological Anthropology

Open Access

SHORT REPORT

Association between decreased
grip strength in preschool children
and the COVID‑19 pandemic: an observational
study from 2015 to 2021
Atsumu Yuki1,2* , Yumi Tamase1 and Mika Nakayama3

Abstract
Background Coronavirus disease 2019 (COVID-19) has reduced people’s physical activity. It is essential to accumulate knowledge regarding the influence of COVID-19 on the stimulation of physical fitness and physical functions.
Several studies have reported the effects of COVID-19 on physical fitness; however, there are very few reports regarding preschoolers. This study aimed to compare the physical fitness of preschoolers before and during the COVID-19
pandemic to clarify the effects of curtailment of outings implemented to control the pandemic on physical fitness
among preschoolers.
Methods The subjects were 593 Japanese preschool children enrolled at a kindergarten during 2015–2019 and in
2021 who received a physical fitness test. Children enrolled in 2020 who did not receive a physical fitness test becauseof the COVID-19 pandemic were excluded. The physical fitness test included grip strength, standing long jump, and a
25-m run. The relationship between physical fitness level and survey year was analyzed using a general linear model,
with grip strength and standing long jump as dependent variables, year of study as the independent variable, andsex and age in months as adjusted variables. Kruskal–Wallis test was used to analyze data for the 25-m run. Multiple
comparisons were used to compare fitness levels between 2021 (during the COVID-19 pandemic) with levels in previous years.
Results Significant relationships were found between survey year and each of grip strength (p < 0.001), standing longjump (p < 0.05), and 25-m run (p < 0.001) among the overall subjects. Grip strength was significantly lower in 2021
compared with the 2016–2019 period. Similarly, sub-stratification analysis by sex showed that grip strength was lower
in 2021 than in previous survey years, in both sexes. However, there was no difference in standing long jump or 25-m
run times between before and during the pandemic among the overall subjects or according to sex.
Conclusions These findings indicate that the COVID-19 pandemic has had a negative effect on the development ofmuscle strength in preschoolers, and suggest the need to develop strategies that could promote the developmentof muscle strength of preschool children when limitations are placed on activity during prolonged infectious disease
pandemics.
Keywords Muscle strength, Development of physical fitness, SARS-CoV-2*Correspondence:
Atsumu Yuki
ats.yuki.73@gmail.com
Full list of author information is available at the end of the article© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​
mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Yuki et al. Journal of Physiological Anthropology(2023) 42:4

Page 2 of 6

Background
Coronavirus disease (COVID-19) caused by severe
acute respiratory syndrome-associated coronavirus-2(SARS-CoV-2), of which the first outbreak was in 2019 in
Wuhan, China, severely impacted people’s wellbeing. Its
impacts on physical fitness include a decrease in physical activity resulting from lockdowns and the refrainingof the general population from non-essential outings [1],and an associated increase in obesity and decline in physical fitness [2, 3]. Impairments of physical function andfitness following SARS-CoV-2 infection have also beenreported [4]. In view of the after-effects of COVID-19,
it is essential to accumulate knowledge concerning thestimulation of physical fitness and physical functions.
Several reports have indicated a decline in physical fitness and physical function in school-aged children following the COVID-19 pandemic [5–9]. According to the
National Survey on Physical Fitness, Exercise Ability andExercise Habits in Japan in 2021 [10], the total physicalfitness scores of both elementary and junior high school
students were lower in 2021 compared to the resultsof the 2019 survey. Effects of existing risk factors suchas decreased exercise time and increased screen time,
as well as those of activity limitation due to COVID19, have been suggested as reasons for the decline inphysical fitness. Knowledge of the effects of COVID-19
behavioral restrictions on children’s fitness is accumulating; however, there are very few reports regarding preschoolers [11]. The aim of this study was to compare thephysical fitness of preschool children before and during
the COVID-19 pandemic to clarify the effects of curtailment of outings implemented to control the pandemic onphysical fitness among preschoolers.

2021. Of these, all children enrolled in 2020 (n = 93),
who did not receive a physical fitness test due to the
COVID-19 pandemic, and those with missing variables
for the analysis (n = 22) were excluded from the study.
The final number of subjects included in the analysis was
593. The number of participants in each year from 2015
to 2021 (excluding 2020) was 107, 103, 104, 106, 90, and83 respectively; 301 boys and 292 girls. The median andinterquartile range of age in months and distribution ofsubjects by grade and sex are shown in Table 1.
Physical fitness test

The physical fitness tests included grip strength, standing
long jump, and a 25-m run. Grip strength was measured
twice each, alternating left and right, using an infant grip
dynamometer (T.K.K.5825; Takei Scientific Instruments,
Niigata, Japan) and the average value was calculated
from the maximum values for each of the left and rightsides. The standing long jump was performed using asheet with lines drawn at 1 cm intervals (KH-164, Kaneya
Industry, Osaka, Japan). The distance of the jump was
measured from the take-off line to the nearest point ofcontact during landing, and was performed twice, withthe higher recorded distance used for analysis. The 25-m
run was measured using a runway set at 30 m and thechildren were instructed to run through the 30 m line at
the highest speed possible. The test was performed onceand recorded to the nearest 0.1 s (SVAJ001; Seiko Watch
Corporation, Tokyo, Japan).
Statistical analysis

Statistical analysis was performed using EZR ver. 1.60
(Saitama Medical Center, Jichi Medical University,
Saitama, Japan), which is a graphical user interface
for R 4.2.1 (The R Foundation for Statistical Computing, Vienna, Austria), and SAS ver. 9.4 (SAS Institute,Inc., Cary, NC, USA). Normality of the data was tested
using the Shapiro–Wilk test. Analysis of the relationshipbetween physical fitness and survey year was performed

Methods
Subjects

The subjects were 708 preschool children enrolled inkindergartens affiliated with the Faculty of Education of
the National University in Kochi city between 2015 andTable 1 Distribution of subjects by year of survey

Age, months
Grade, nSex, n2015(n = 107)2016(n = 103)2017(n = 104)2018(n = 106)2019(n = 90)2021(n = 83)

χ2

p

1.11

0.953

8.05

0.624

4.22

0.518

63, 53–70

59, 53–71

62, 57–68

62, 53–71

61, 56–70

61, 51–68

First (age 3 years)

25

27

20

27

20

26

Second (age 4 years)

41

38

46

33

37

25

Third (age 5 years)

41

38

38

46

33

32

Boys

56

58

52

46

44

45

Girls

51

45

52

60

46

38

Age data are presented as the median and interquartile range
p values were obtained using Kruskal–Wallis test or χ-square testYuki et al. Journal of Physiological Anthropology(2023) 42:4

using a general linear model with grip strength andstanding long jump as dependent variables, year of survey
as an independent variable, and sex and age in months
as adjusted variables. Multiple comparisons were madeusing the Dunnett–Hsu method with the year 2021 as thecontrol group. For analysis of the 25-m run data, whichwere not normally distributed, the Kruskal–Wallis test
was used with the year of the survey as the independent
variable. Multiple comparisons were compared between
2021 and earlier years using the Dwass–Steele–Critchlow–Fligner test. Partial η2 was calculated for the effectsize of the main effect with general linear model and r forthe effect size of multiple comparisons.

Results
Table 2 shows the relationship between the results of thephysical fitness test and survey year. In the overall subjects, there was a significant association between grip
strength, standing long jump, 25-m run, and survey year.
Multiple comparisons revealed that grip strength was
lower in 2021 than in 2016–2019. However, there was nodifference in standing long jump and 25-m run in 2021
compared to earlier years. The sex-stratified analysis
showed a significant association between grip strengthand 25-m run and survey year among the boys. Multiple

Page 3 of 6

comparisons revealed that grip strength was lower in
2021 than in 2016–2018. There was no difference in 25-m
run in 2021 compared to earlier years. Among the girls,
there was a significant association between grip strength,
standing long jump, 25-m run, and survey year. Multiple comparisons revealed that grip strength was lower
in 2021 than in 2015–2019. The standing long jump was
lower in 2021 than in 2016.

Discussion
The present study investigated whether the COVID-19
pandemic caused a decline in physical fitness among preschool children in Japan by comparing physical fitness
tests of preschoolers before and during the COVID-19
pandemic. The results showed that grip strength was
lower during the COVID-19 pandemic than before thepandemic.
This study appears to be the first to report a reduction in grip strength in preschool children due to the
COVID-19 pandemic. Several studies have evaluatedthe association between the COVID-19 pandemic
and grip strength in children and adolescents. A studyof adolescents reported an association between the
COVID-19 pandemic and decreased grip strength inmale students [3]. However, studies of school-aged

Table 2 Relationship between physical fitness and the COVID-19 pandemic
Year of survey
2015
Overall (n = 593)

n = 1072016
n = 1032017
n = 104n = 1062019
n = 902021
n = 83F or χ2ppartial η2

Grip strength, kg

7.7 ± 0.2
(0.13)

8.9 ± 0.2***(0.40)

8.9 ± 0.2***(0.41)

8.6 ± 0.2***(0.34)

8.3 ± 0.2***(0.29)

7.2 ± 0.2

12.14

< 0.001

0.09

Standing long jump, cm

90.8 ± 1.4(0.04)

94.0 ± 1.5(0.15)

89.5 ± 1.5(< 0.00)

87.3 ± 1.5(0.08)

92.9 ± 1.6(0.11)

89.6 ± 1.6

2.72

0.019

0.02

25-m run, s

6.6, 5.9–7.4(– 0.11)

6.8, 6.0–7.5(– 0.03)6.6, 6.1–7.3(– 0.07)6.6, 6.2–7.5(– 0.04)

7.2, 6.7–8.1(0.19)

6.6, 6.3–7.6

22.23< 0.001–n = 56n = 58n = 52n = 46n = 44n = 45

Boys (n = 301)

Grip strength, kg

7.8 ± 0.3
(0.01)

9.1 ± 0.3**(0.32)

9.4 ± 0.3***(0.36)

9.1 ± 0.3**(0.32)

8.6 ± 0.3
(0.20)

7.8 ± 0.3

6.15

< 0.001

0.09

Standing long jump, cm

94.5 ± 2.1(0.01)

94.2 ± 2.1(0.01)

95.4 ± 2.2(0.03)

90.4 ± 2.3(0.13)

96.8 ± 2.4(0.08)

94.5 ± 2.3

0.85

0.517

0.01

25-m run, s

6.6, 5.8–7.4(– 0.11)

6.8, 6.3–7.5(0.04)

6.3, 5.9–6.9(– 0.19)

6.6, 6.2–7.2(– 0.04)

7.0, 6.3–7.9(0.14)

6.6, 6.2–7.6

14.15

0.015

–

Girls (n = 292)

n = 51n = 45n = 52n = 60n = 46n = 38

Grip strength, kg

7.6 ± 0.3*
(0.27)

8.6 ± 0.3***(0.50)

8.4 ± 0.3***(0.46)

8.0 ± 0.2***(0.37)

8.0 ± 0.3***(0.39)

6.5 ± 0.3

6.91

< 0.001

0.11

Standing long jump, cm

87.1 ± 2.0(0.08)

94.9 ± 2.1**(0.34)

83.3 ± 1.9(0.05)

84.3 ± 1.8(0.02)

88.9 ± 2.1(0.15)

84.8 ± 2.3

4.40< 0.001

0.07

25-m run, s

6.5, 6.0–7.5(– 0.11)

6.9, 6.0–7.5(– 0.09)

6.9, 6.3–7.7(0.03)

6.7, 6.1–7.5(–0.06)

7.5, 6.7–8.1(0.23)

6.8, 6.3–7.8

15.39

0.009

–

Values are mean ± standard error or median and interquartile range
Values in parentheses indicate effect size (r)

*

2018

p < 0.05; **p < 0.01; ***p < 0.001 vs. survey in 2021

Yuki et al. Journal of Physiological Anthropology(2023) 42:4

children close to the age of the present subjects havereported that the COVID-19 pandemic and related
lockdown were not associated with decreased grip
strength [5, 8, 9]. The inconsistency between the present results and the previous results of school-aged
children may be due to differences in the year in which
the fitness tests were performed during the COVID-19
pandemic, rather than to differences in school grades
between the studies. The World Health Organization(WHO) declared the COVID-19 outbreak as a global
pandemic on 11 March 2020 [12]. These previous studies began to assess grip strength within one year at thelatest after the pandemic declaration [5, 8, 9]. In contrast, the present study used fitness test data collected
approximately 18 months after the declaration of thepandemic. Consistent with studies that reported adecrease in physical activity in preschool children that
was associated with the COVID-19 pandemic [13–16],
the present subjects might have been exposed for a
relatively longer time to low levels of physical activity. Although the present study did not assess physicalactivity, some studies have reported that COVID-19
behavioral restriction has increased sedentary behavior in preschool children [15, 17]. Although there areno consistent results on whether sedentary behavior in preschool children inhibits the development ofgrip strength [18–20], if sedentary behavior caused by
COVID-19 behavioral restrictions had increased in
the present subjects, this could possibly be the reason
for the inhibition of grip strength development. Furthermore, Japan experienced repeated waves of the
COVID-19 pandemic during this 18-month period [21]during which restrictions on activities were ordered.
In addition, attendance at kindergarten and leaving thehome were prohibited for children infected with SARSCoV-2 or identified as close contacts of a SARS-CoV2-infected person. These environments might havebeen risk factors for increased sedentary behavior inpreschool children.
Decreased grip strength during the COVID-19 pandemic might have been caused by insufficiency of physical development resulting from measures taken against
COVID-19, including behavioral restrictions. However,as height and weight data were available only for thirdgrade children (aged 5 years), it was difficult to provide sufficient results. Therefore, to examine whether
there was any association of stunted growth due to the
COVID-19 pandemic with reduced grip strength, we performed additional analysis using the complete data forthird-grade children to examine differences in body massindex between the survey years. The results showed nodifferences in body mass index between the survey years(Supplementary Table S1). This finding indicates that inPage 4 of 6

the specific case of third-grade children, the decline ingrip strength in 2021 was not due to impairment of physical development.
Although the trend of lower grip strength during the
COVID-19 pandemic than before the pandemic wasgenerally consistent for both sexes, the effect size wasgreater in girls than in boys. Therefore, the impact of
the COVID-19 pandemic on grip strength might havebeen stronger in girls than in boys. No previous studies
have assessed the effects of the COVID-19 pandemic ongrip strength in preschool children. A study of US children aged 5–13 years reported that girls were exposed tolonger sitting times than boys in the early post-pandemic
period [22]. A study of Canadian children reported thatfewer girls aged 5–11 years were achieving sufficient levels of physical activity after the pandemic than boys ofthe same age group [23]. These reports suggest the interesting possibility that undesirable lifestyle habits may
have appeared in girls specifically. However, as studies
assessing muscle strength and physical activity in preschool children are limited, further research is essential
to clarify this issue.
The present study found no association of the
COVID-19 pandemic with reduced jump and sprint
performance. A previous study that compared fundamental motor skills such as standing long jump and25-m run before and after the COVID-19 pandemic in
608 Japanese preschool children reported no change inthe standing long jump before and after the pandemic,in all age groups. A decline in the 25-m running record
after the COVID-19 pandemic was reported only in the
5-year-old group [11]. The present results appear to
generally support the findings of this previous report[11]. It is well known that jumping and sprinting ability
are affected by coordinated motions as well as by lower
limb muscular strength. Coordination of these motions
occurs through play in early childhood. In addition,
moderate-to-vigorous physical activity (MVPA) is positively associated with the development of jumping andsprinting ability [18, 19]. A study of preschool children
aged 3–5 years in 14 countries found no significant
change in MVPA in preschool children between before
and during the COVID-19 pandemic [17]. In addition,a study of Japanese preschool children reported nochange in MVPA on weekends before and during the
COVID-19 pandemic [15]. We did not assess physical activity in the present study; however, it is possiblethat COVID-19 behavioral restrictions might not have
reduced MVPA in preschool children. Nevertheless, aminor discrepancy remains, as the results of the 25-m
run in the 5-year-old population differ between studies [11]. Among the present female subjects, there weredifferences between the standing long jump in 2016 andYuki et al. Journal of Physiological Anthropology(2023) 42:4

in 2021. Furthermore, several studies of children aged
6 years and older have noted that standing long jump
ability was reduced following the COVID-19 pandemic[7, 8]. Further research is necessary to address theseconflicting findings.
This study has several limitations. First, the study
design did not follow individuals. Therefore, the effectof the COVID-19 pandemic on the development of thephysical fitness of preschool children is unknown. Second, as the study was based on one kindergarten in arural city, the results cannot be generalized. Third, dataon physical fitness for 2020 and on physical activity were
not obtained. These data might be necessary to further
elucidate the association between physical fitness of preschoolers and the COVID-19 pandemic. Furthermore,other background factors affecting physical fitness were
not adequately considered in the analysis. Play with physical movement is considered particularly important forthe physical development of preschool children. Theremight have been changes in play behavior, such as a shift
from outdoor play to indoor play and fewer opportunities
to play with friends.

Conclusion
This study examined the impact of the COVID-19 pandemic on physical fitness of preschool children by comparing physical fitness data obtained in 2015–2019 withthose in 2021. Grip strength was significantly lower in
2021 than in 2016–2019. These findings indicate that the
COVID-19 pandemic may have had a negative effect on
the development of muscle strength in preschool children, and suggest the need to develop strategies that
could promote the development of muscle strength inpreschool children when prolonged infectious disease
pandemics occur.
Abbreviations
COVID-19	Coronavirus disease 2019
SARS-CoV-2	Severe acute respiratory syndrome-related coronavirus-2

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40101-​023-​00321-8.
Additional file 1: SupplementalTable S1. Relationship between bodymass index and the COVID-19pandemic in five-year-old children.
Acknowledgements
We would like to express our gratitude to all our participants and their parents,
and the kindergarten staff for their contributions to this study.

Page 5 of 6

Authors’ contributions
AY and YT conceived and designed the study. YT and MN managed the survey. AY analyzed data and wrote the initial manuscript. All authors edited therevised manuscript and approved the final manuscript.
Funding
This study was partly supported by JSPS KAKENHI (Grant No. 17K13246) and
Unit-based bottom-up research project grants from Kochi University.
Availability of data and materials
The datasets generated during and/or analyzed during the current study areavailable from the corresponding author on reasonable request.

Declarations
Ethics approval and consent to participate
This study was approved by the Research Ethics Committee of the Education
Unit in Kochi University (H27-1, H30-1). The study objectives and methods
were explained to all children’s parents, who then gave their consent toparticipate in the study.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Faculty of Education, Kochi University, 2‑5‑1 Akebono, Kochi City, Kochi
780‑8520, Japan. 2 Kuroshio Science Program, Graduate School of Integrated
Arts and Sciences, Kochi University, 200 Monobe‑Otsu, Nankoku City, Kochi
783‑8502, Japan. 3 Kindergarten affiliated with the Faculty of Education, Kochi
University, 10‑26 Odu, Kochi City, Kochi 780‑0915, Japan.
Received: 30 November 2022 Accepted: 18 March 2023

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