Impact of COVID-19-Related Sports Activity Disruptions on the Physical Fitness of Japanese Adolescent Athletes

assessed whether the coronavirus disease 2019 (COVID-19) pandemic-related dis- ruptions impacted the physical tness of adolescent athletes. We reviewed the age-, sex-, and sports category-matched data of 78 adolescent athletes (divided into two groups: 2019 group = 37; 2020 group = 41) from the clinical database and investigated their height, weight, body composition, exibility muscle strength, and jump height. We also provided questionnaires to the teams' coaches to collect data on the duration of practice suspension due to the COVID-19 pandemic; the practice hours per week in August 2019, immediately after the suspension ended, and in August 2020; and the guidelines for the players after resuming their practice. For

height, weight, body composition, exibility muscle strength, and jump height. We also provided questionnaires to the teams' coaches to collect data on the duration of practice suspension due to the COVID-19 pandemic; the practice hours per week in August 2019, immediately after the suspension ended, and in August 2020; and the guidelines for the players after resuming their practice. For data analyses, we consideredp 0.05 as statistically signi cant. The strength of knee exion and extension was signi cantly lower in the 2020 group than in the 2019 group; there was no difference in the other physical tness parameters. The practice duration in August 2019 and August 2020 was the same. COVID-19-related interruptions did not alter the athletes' jump height, upper-limb strength, and exibility but reduced lower-limb muscle strength. We recommend that basic strength training protocols be followed to prevent sports-related injuries after such unexpected practice interruptions. Keywords:coronavirus disease-19; social forced interruption; physical check-up; youth athletes 1. Introduction The coronavirus disease 2019 (COVID-19) is an infectious viral disease caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that began to spread in December 2019 [1]. The disease rapidly spread worldwide throughout 2020 and was declared a pandemic by the World Health Organization (WHO) on 11 March 2020 [2]. In Japan, more than 3 million people have had positive test results as of February 2022, and about 20,000 deaths have been reported [3]. Following the WHO recommendations, countries across the globe have implemented safety measures to reduce human-to-human virus transmission, and governments have imposed restrictions on most public activities, which has impacted the lifestyles and routines of adolescents and adults alike. Currently, COVID-19 is associated with a low risk of serious illness in healthy adolescents [4]; however, they were still required to restrict their out-of-home activities to prevent the spread of the disease to chronically ill and older individuals. In a variety of individuals, physical activity has been reduced due to the limitation of activities associated with COVID-19. In healthy Italian adults, city-wide lockdown Adolescents2022,2, 140–149.

still required to restrict their out-of-home activities to prevent the spread of the disease to chronically ill and older individuals. In a variety of individuals, physical activity has been reduced due to the limitation of activities associated with COVID-19. In healthy Italian adults, city-wide lockdown Adolescents2022,2, 140–149.

Adolescents2022,2 141 associated with COVID-19 has been reported to predominantly reduce daily steps and mean heart rate [5]. In Spanish young adults, the walking time and number of steps measured using a smartphone accelerometer were reported to be predominantly low during lockdown [6]. In patients with heart failure, the average number of steps taken during lockdown was also measured using a wrist accelerometer, and the number of steps taken was reduced compared to normal conditions [7]. The same reports are available for children and adolescents. Moore et al. [8] reported that the COVID-19 pandemic resulted in less time spent out of the house and increased sedentary lifestyles, screen time, and sleep time. In Australian adolescents, the walking distance measured using smartphone sensors was also reported to have decreased signi cantly during the COVID-19 pandemic [9]. The decrease in physical activity in the months following the pandemic may further impact the physical tness of adolescents. Tsokos et al. [10] reported that a ve-month lockdown due to COVID-19 negatively in uenced the strength, power, and exibility of adolescent students, and notably, more in males than in females. Sunda et al. [11]. suggested that the COVID-19 lockdown negatively in uenced muscular tness status in adolescents, especially in boys. Due to concerns regarding such adverse effects, when trying to prevent COVID-19 infection or any other epidemic in the short term, it is recommended not to neglect its effects on the quality of life and healthy lifestyle behaviors of the general population in the long term [12]. Several sporting events, including the 2020 Tokyo Olympics and Paralympics, were canceled or postponed to follow physical distancing guidelines; most athletes have been forced to stop training due to restrictions on public gatherings. We hypothesized that the amount of physical activity in adolescent athletes has drastically reduced due to school closures, self-restraint, and suspension of practice. In elite athletes, signi cant total training volume and performance decreased during the lockdown [13]. Some experts have noted the decline in physical activity among young athletes in a socially distanced world [14] and have reported that prolonged restrictions may result in

of physical activity in adolescent athletes has drastically reduced due to school closures, self-restraint, and suspension of practice. In elite athletes, signi cant total training volume and performance decreased during the lockdown [13]. Some experts have noted the decline in physical activity among young athletes in a socially distanced world [14] and have reported that prolonged restrictions may result in widespread attrition of youth from sport [15]. Unexpected and forced suspension of sports-related activities leads to increased sports injuries once athletes resume sports activities [16], which causes further deterioration in their general physical tness due to the periods of inactivity that are subsequently required for recovery. Therefore, the tness status of adolescent athletes should be assessed before they resume sports to prevent such injuries [17]. However, to date, no studies have described the association between COVID-19-related inactivity and physical tness in adolescent athletes. To address this knowledge gap, we aimed to investigate the in uence of COVID-19- related interruptions in sports training on the physical tness of adolescent athletes. Our report provides basic data on the tness status of adolescents after a period of inactivity due to pandemic-related restrictions on public gatherings. 2. Materials and Methods 2.1. Experimental Approach to the Problem In this retrospective study, to examine the effects of physical inactivity associated with COVID-19 on physical tness, we extracted the following data on adolescent athletes between 2019 and 2020 from our physical examination database: body type and composi- tion, muscle strength, exibility, and jump height. We also measured the data according to the prescribed procedures. Furthermore, we provided an internet questionnaire to the coaches to obtain additional data on the length of the suspension and the amount of time and content of practice before and after the suspension. 2.2. Participants This study was approved by the Ethics Committee of Hiroshima university hospital ( le number: E-941, approval period 1 February 2017, to 31 December 2023). Written informed consent was obtained from the athletes' parents/guardians, as per the Declaration of Helsinki and the guidelines in the American Psychological Association's Publications

2.2. Participants This study was approved by the Ethics Committee of Hiroshima university hospital ( le number: E-941, approval period 1 February 2017, to 31 December 2023). Written informed consent was obtained from the athletes' parents/guardians, as per the Declaration of Helsinki and the guidelines in the American Psychological Association's Publications

Adolescents2022,2 142 Manual, after both athletes and their parents/guardians received a thorough explanation of the bene ts and risks of the investigation. Adolescent athletes routinely undergo medical and physical check-ups at Hiroshima university hospital sports medicine center in August every year, and we retrospectively reviewed these data for our analysis. We investigated 41 adolescents who participated in 2020 (2020 group) and 37 athletes in 2019 (2019 group) and matched them according to their age, sex, and sports category. All the athletes played at the same competitive level (top-level in the prefecture) and in the same teams. The characteristics of both groups are shown in Table. Table 1.Pro le of participants. 2019 2020 pValue Sex Male 28 26 0.31 Female 9 14 Age (years) 13.6 13.8 0.41 Sports Rugby 7 15 Hockey 9 7 Handball 7 4 Table tennis 6 4 Kendo 8 3 We excluded participants with a body temperature of >37 C at the time of their medical check-up and those who had sustained a musculoskeletal injury 1 week before the check-up. Moreover, we encouraged the 2020 group to wear masks except when playing and requested a written con rmation indicating that they had no common cold symptoms or body temperature >37 C during the week before the experiment to prevent the spread of COVID-19. In the 2020 group, no history of COVID-19 infection before the measurement was observed. Vaccination had not been initiated in Japan at the time of the medical check-up [18], and all participants were unvaccinated. 2.3. Procedures We extracted the following data from the participants: body type and composition (height, weight, body fat amount, lean body weight, and muscle mass), muscle strength (isokinetic muscle strength during knee extension and exion, and grip power), exibility (straight-leg raising angle and heel-buttock distance), and jump height (squat jump height and counter-movement jump height). 2.3.1. Body Type and Composition We used an InBody S10 Body Water Analyzer (InBody Co., Seoul, Korea), a direct seg- mental multifrequency bioimpedance analysis (DSM-BIA) device, for our analysis. In this DSM-BIA method, we used an 8-point tactile electrode system that recorded30 impedance measurements at

raising angle and heel-buttock distance), and jump height (squat jump height and counter-movement jump height). 2.3.1. Body Type and Composition We used an InBody S10 Body Water Analyzer (InBody Co., Seoul, Korea), a direct seg- mental multifrequency bioimpedance analysis (DSM-BIA) device, for our analysis. In this DSM-BIA method, we used an 8-point tactile electrode system that recorded30 impedance measurements at six frequencies (1, 5, 50, 250, 500, and 1000 kHz) of ve body segments (right upper limb, left upper limb, trunk, right lower limb, and left lower limb). We also ensured that the measurements in children were accurate [19]. From the measured data, we derived the body fat amount, lean body weight, and muscle mass and included these values in our analyses. After waking up, the participants were asked to remain in a fasting state until their measurements were taken at 9:00 AM. All participants fasted for at least 9 h, and drinking water was prohibited 30 min before the test. The participants' height and weight were measured and entered into the device before starting BIA. The measurements were taken with the participants in the supine position with no limbs in contact with each other. Electrically conductive accessories, such as glasses, necklaces, watches, and bracelets, were removed. After pre-treating the skin with electrolytic tissues (InBody tissue, InBody Co.,

Adolescents2022,2 143 Seoul, Korea), the electrodes were placed on the rst and third ngers and both ankles. The participants were instructed to lie still while the measurements were being recorded. 2.3.2. Muscle Strength Measurements The Biodex System 4 Dynamometer (Biodex Medical Systems, New York, NY, USA) was used to measure the isometric muscle strength of the knee. The participants exed and extended their knees ve times while they were in the sitting position at an angular velocity of 60 per second. We noted the peak torque during each repetition and evaluated the highest peak torque in the ve repetitions (we did not consider the average peak value). The weight ratio of the measured peak torque was used as the measured value in this study. We used a Smedley-style digital grip dynamometer (Grip-D, Takei Scienti c Instru- ments Co. Ltd., Nigata, Japan) to assess grip power. The participants made a maximal gripping effort twice in the standing position, and we recorded the peak value from the two measurements as the grip power. 2.3.3. Flexibility Measurements The exibility measurements were obtained by two physical therapists. For the straight-leg raising angle (SLR), the athlete was placed in a supine position. One physio- therapist grasped the distal lower leg, raised it passively with the knee in full extension, and stopped the elevation as soon as some resistance was noted. At this position, the other physiotherapist measured the angle between the midline of the trunk and the long axis of the thigh in 5 increments using a goniometer. For the heel-buttock distance (HBD), the athlete was placed in the prone position. One physiotherapist grasped the distal lower leg and exed the knee passively, stopping the exion on encountering resistance. At this position, the other physiotherapist applied a scale vertically from the heel to the buttock and measured the distance between the two points. 2.3.4. Jump Height Measurements We used Opto Jump Next (Microgate co., Bozen, Italy) to measure two jump motions: the counter-movement jump (CMJ) and squat jump (SJ). The reliability of the jump height measurement with this device has been previously established [20]. For

applied a scale vertically from the heel to the buttock and measured the distance between the two points. 2.3.4. Jump Height Measurements We used Opto Jump Next (Microgate co., Bozen, Italy) to measure two jump motions: the counter-movement jump (CMJ) and squat jump (SJ). The reliability of the jump height measurement with this device has been previously established [20]. For the CMJ, we instructed the participants to stand upright with their hands on their hips, bend their knees, and jump straight up. For the SJ, we instructed them to follow the same steps, except that they had to stand still for a moment after bending the knees and before jumping up. We asked them not to use rebounding motions, such as swinging their head or squatting down further, after standing still. The participants performed maximal-effort CMJs and SJs three times. We recorded the highest jump heights of the three trials (we did not consider the average peak value of the three trials). 2.4. Internet Questionnaire As an additional survey, from September 2020 to October 2020, we sent an internet questionnaire to the coaches of the teams to which the athletes belonged. The questionnaire was administered using Google Forms. A questionnaire survey was conducted from the coaches who gave an explanation of the study on a Google form and gave their consent. The content of the questionnaire was as follows: (1) the start date of team practice suspension; (2) the end date of team practice suspension; (3) team practice time per day on weekdays and holidays in August 2019; (4) team practice time per day on weekdays and holidays immediately after suspension of practice; (5) team practice time per day on weekdays and holidays in August 2020; and (6) points to remember when practicing after the suspension (free description). The number of days of suspension was calculated from the answers to questions (1) and (2).

Adolescents2022,2 144 2.5. Statistical Data Analysis All statistical analyses were performed using R v2.8.1 for Windows (R Founda- tion for Statistical Computing, Vienna, Austria). Each parameter is presented as the mean standard deviation (SDs). All data were tested for normality using the Shapiro– Wilk normality test. Physical tness data were compared between the 2019 and 2020 groups using Welch'st-test or Mann–Whitney U test.p-values < 0.05 were considered signi cant. We compared the practice times in August 2019, immediately after the suspension, and in August 2020 according to the internet questionnaire using a one-way analysis of variance or the Kruskal–Wallis rank-sum test. We carried out post hoc tests, Tukey–Kramer test, or Steel–Dwass test if the above analyses were signi cant. 3. Results 3.1. Physical Fitness Data The muscle strength during isokinetic knee exion and extension was signi cantly lower in the 2020 group than in the 2019 group. In contrast, there was no signi cant difference in the body type and composition, exibility data, jump parameter data, and grip power (Table) between the two groups. Table 2.Comparison of the physical tness data between 2019 group and 2020 group. 2019 2020 pValue Body type composition Height (cm) 160.8 10.2 (161.6) 162.5 7.7 (163.1) 0.40 weight (kg) 51.4 13.3 (58.5) 55.4 12.6 (59.7) 0.12 body fat amount (kg) 8.7 5.2 (7.5) 10.4 6.6 (8.3) 0.32 lean body weight (kg) 42.9 9.6 (41.3) 44.9 8.5 (44.6) 0.28 muscle mass (kg) 40.3 9.2 (39.0) 42.4 8.1 (42.2) 0.30 Muscle strength Rt KEM (Nm/Kg) 223.4 42.7 (221.4) 197.2 34.7 (221) <0.01 * Lt KEM (Nm/Kg) 218.7 41.5 (219.7) 193.1 34.3 (192.6) <0.01 * Rt KFM (Nm/Kg) 110.4 24.5 (111.2) 98.7 26.5 (99.8) 0.04 * Lr KFM (Nm/Kg) 107.1 25.7 (105.2) 93 25.4 (94.8) 0.02 * Rt GP (kg) 31.2 8.8 (29.7) 30 7.7 (28.6) 0.51 Lt GP (kg) 26.6 7.1 (26.7) 27.1 5.6 (26.8) 0.82 Flexibility Rt SLR (degree) 55.4 8.7 (55.0) 54.4 10.4 (51.0) 0.53 Lt SLR (degree) 55 9.1 (55.0) 51.1 10.5 (50.0) 0.21 Rt HBD (cm) 7.1 5.1 (8.0) 5.9 4.7 (5.7) 0.25 Lt HBD (cm) 7.3 5.4 (8.0) 5.4 4.1 (5.0) 0.12

GP (kg) 31.2 8.8 (29.7) 30 7.7 (28.6) 0.51 Lt GP (kg) 26.6 7.1 (26.7) 27.1 5.6 (26.8) 0.82 Flexibility Rt SLR (degree) 55.4 8.7 (55.0) 54.4 10.4 (51.0) 0.53 Lt SLR (degree) 55 9.1 (55.0) 51.1 10.5 (50.0) 0.21 Rt HBD (cm) 7.1 5.1 (8.0) 5.9 4.7 (5.7) 0.25 Lt HBD (cm) 7.3 5.4 (8.0) 5.4 4.1 (5.0) 0.12 Jump SJ (cm) 24.4 6.5 (23.9) 24.4 5.4 (24.5) 0.96 CMJ (cm) 26.6 7.1 (26.7) 27.1 5.6 (26.8) 0.82 Each parameter is shown as mean standard deviation (median). *p< 0.05. Abbreviations: KEM, knee extension muscle; KFM, knee exion muscle; GP, grip power; SLR, straight leg raise; HBD, heel-buttock distance; SJ, squat jump; CMJ, counter movement jump; Rt, right; and Lt, left. 3.2. Internet Questionnaire The 10 coaches of all the participants' teams responded to our survey with a 100% response rate. The average duration of suspension of practice was 82.5 days and varied widely from a maximum of 168 days to a minimum of 14 days, depending on the team. The coaches guided the training as per the new social distancing guidelines and the athletes' decreased physical tness following the period of inactivity (Table). There was no signi cant difference in the practice duration between August 2019, immediately after the suspension period, and in August 2020 (Table).

The study investigates the impact of COVID-19 disruptions on the physical fitness of adolescent athletes.