Inflammation and fatness in adolescents with and without Down syndrome: UP & DOWN study.

BACKGROUND: The main objective of this study was to describe the inflammatory status of adolescents with Down syndrome (DS) and their relationship with adiposity. METHODS: Ninety-five adolescents with DS (44.2% girls) and a control group of 113 adolescents (47.8% girls), aged between 11 and 18 years old, from the UP & DOWN study were included in this substudy. Serum C-reactive protein, C3 and C4 complement factors, total proteins, interleukin-6, tumour necrosis factor-α, insulin, cortisol, leptin, adiponectin, galactin-3 and visfatin were analysed; homeostatic model assessment index was calculated. In order to evaluate adiposity, we measured the following body fat variables: weight, height, waist circumference and skinfold thicknesses. Birth weight was obtained by questionnaire. In addition, body mass index, waist-to-height ratio (WHtR) and body fat percentage (BF%) were calculated. RESULTS: Down syndrome group showed higher levels of body mass index, WHtR, waist circumference, BF% and lower birth weight than controls (P < 0.001). In the general linear model in the total sample, WHtR was positively associated with C3 and C4 (P < 0.001) as well as with leptin levels (P = 0.015). BF% was positively associated with total proteins (P = 0.093) and leptin levels (P < 0.001). DS was positively associated with total proteins (P < 0.001), C3 (P = 0.047) and C4 (P = 0.019). Despite the higher levels of adiposity found in DS group, no direct association was found between BF% and leptin levels, comparing with the control group. CONCLUSIONS: These findings suggest that abdominal obesity should be controlled in adolescents because of its relationship with acute phase-inflammatory biomarkers but especially in DS adolescents who may show a peculiar metabolic status according to their relationship between adiposity and inflammatory biomarkers.

Muscle strength is associated with lower diastolic blood pressure in schoolchildren.

Cardiorespiratory fitness (CRF) provides protection against the elevated blood pressure in overweight youth. Less is known regarding any similar protective effect of muscular fitness. We investigated how handgrip strength, an easy to implement measure of muscular strength, interacted with CRF and BMI to determine blood pressure in youth. We measured systolic (SBP) and diastolic (DBP) blood pressure, handgrip strength (HG), CRF and body mass index (BMI) in n=7329 10-16year-olds (47% girls). We defined elevated blood pressure as >91st percentile and Good HG as >33rd percentile. Participants were classified as Fit or Unfit and as Normal or Overweight/Obese based on international standards. The prevalence of elevated SBP was 23%, and 44% of participants had elevated DBP. In unfit participants Good HG was associated with lower SBP (z=0.41 (95%CI: 0.20-0.61) and DBP (z=0.29 (95%CI: 0.12-0.47). In Overweight/Obese participants, DBP was z=0.24 (95%CI: 0.14-0.34) lower in the Good (versus Low) HG group. Overweight/Obese participants with Good HG also had a 32% lower risk of elevated DBP (OR: 0.68, 95%CI: 0.57-0.82). This association was attenuated but remained important after adjusting for BMI (20% risk reduction, OR: 0.80, 95%CI: 0.63-1.01). Muscular fitness appears to play some protective role against the risk of elevated blood pressure; particularly for the more prevalent measure: elevated DBP (44%). Effects may be restricted to Overweight / Obese or unfit youth, who have an increased risk of elevated BP and also may be less likely to engage in traditional cardiorespiratory fitness training. Research to determine the effects of muscular fitness training on blood pressure is warranted in these subgroups.

Physical fitness as a mediator between objectively measured physical activity and clustered metabolic syndrome in children and adolescents: The UP&DOWN study.

BACKGROUND AND AIMS: The extent to which physical fitness (PF) attenuates or modifies the association between physical activity (PA) and clustered metabolic syndrome risk factors (CMetSRF) is controversial. We aimed: i) To examine the independent and combined association of objectively measured PA and PF with CMetSRF in children and adolescents; ii) To test the mediating effect of PF in the association of PA with CMetSRF. METHODS AND RESULTS: A total of 226 children and 256 adolescents participated. Levels of PA (light, moderate, vigorous and moderate-to-vigorous [MVPA]) and PF were measured by accelerometry and ALPHA battery, respectively. Cardiorespiratory and muscular fitness values were combined in a global PF variable. A CMetSRF was computed by assessing the following variables: waist circumference, systolic blood pressure, high-density lipoprotein cholesterol, triglycerides and glucose. In children, the highest vigorous PA (ß = -0.193; P = 0.003) and MVPA (ß = -0.149; P = 0.025) were individually associated with lower CMetSRF, but these associations were not independent of global PF. In adolescents, the association of moderate (ß = -0.123; P = 0.046) and MVPA (ß = -0.147; P = 0.024) with CMetSRF was independent of PF. Among unfit adolescents, the higher time they spent in MVPA the lower CMetSRF levels were found (P = 0.032). CONCLUSIONS: The results are suggestive of a full mediation of global PF in the association of MVPA and vigorous PA with CMetSRF in children. In adolescents, the association of higher moderate and MVPA with lower CMetSRF was independent of levels of PF, and mediation analyses suggest only a partial mediation of global PF in the association of MVPA with CMetSRF.

Parental educational level and psychological positive health and health complaints in Spanish children and adolescents.

BACKGROUND: Interest on the impact of socioeconomic differences on youth's health is growing. The aim of the present study was to examine the association of parental educational level with psychological positive health and health complaints in Spanish children and adolescents. METHODS: Parental educational level, psychological positive health indicators (perceived health status, life satisfaction, quality of family relationships, quality of peer relationships and academic performance) and health complaint index (headache, stomach ache, backache, feeling low, irritability or bad temper, feeling nervous, difficulties getting to sleep, feeling dizzy) were self-reported using the Health Behavior in School-aged Children questionnaire in 685 (366 boys and 319 girls) children and adolescents. RESULTS: Children reporting parents with non-university studies (father, mother or both) had significantly higher odd ratio of having lower academic performance, lower life satisfaction, perceiving their health status as otherwise (vs. excellent) and having health complaints sometime than their counterparts reporting parents with university studies (father, mother or both). CONCLUSION: Current results provide evidence that children having parents with a university degree (father, mother or both) are more likely to have higher psychological positive health and lower health complaints than children reporting parents with non-university studies. This is particularly important for the welfare policy that must pay attention for implementing programs for helping population to access to university studies by their impact on youth health.

Reliability and feasibility of physical fitness tests in female fibromyalgia patients.

The aim of the present study was to determine the reliability and feasibility of physical fitness tests in female fibromyalgia patients. 100 female fibromyalgia patients (aged 50.6±8.6 years) performed the following tests twice (7 days interval test-retest): chair sit and reach, back scratch, handgrip strength, arm curl, chair stand, 8 feet up and go, and 6-min walk. Significant differences between test and retest were found in the arm curl (mean difference: 1.25±2.16 repetitions, Cohen d=0.251), chair stand (0.99±1.7 repetitions, Cohen d=0.254) and 8 feet up and go (-0.38±1.09 s, Cohen d=0.111) tests. Intraclass correlation coefficients (ICC) range from 0.92 in the arm curl test to 0.96 in the back scratch test. The feasibility of the tests (patients able to complete the test) ranged from 89% in the arm curl test to 100% in the handgrip strength test. Therefore, the reliability and feasibility of the physical fitness tests examined is acceptable for female fibromyalgia patients.

Muscular strength and markers of insulin resistance in European adolescents: the HELENA Study.

The aim of the study was to examine the association of muscular strength with markers of insulin resistance in European adolescents. The study comprised a total of 1,053 adolescents (499 males; 12.5-17.5 years) from ten European cities participating in the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA) Cross-Sectional Study. Muscular strength was measured by the handgrip strength and standing long jump tests. Cardiorespiratory fitness was measured by the 20-m shuttle run test. Fasting insulin and glucose were measured and the homeostasis model assessment (HOMA) and quantitative insulin sensitivity check index (QUICKI) indices were calculated. Weight, height, waist circumference and skinfold thickness were measured, and body mass index (BMI) was calculated. In males, the handgrip strength and standing long jump tests were negatively associated with fasting insulin and HOMA (all P < 0.05) after controlling for pubertal status, country and BMI or waist circumference. When skinfold thickness was included in the model, the association became non-significant. In females, the standing long jump test was negatively associated with fasting insulin and HOMA (all P < 0.001) after controlling for pubertal status, country and surrogate markers of total or central body fat (BMI, waist circumference or skinfold thickness). Findings were retained in males, but not in females after controlling for cardiorespiratory fitness. The findings of the present study suggest that preventive strategies should focus not only on decreasing fatness and increasing cardiorespiratory fitness but also on enhancing muscular strength.

Impact of a physical activity program on cerebral vasoreactivity in sedentary elderly people.

AIM: The aim of the present study was to determine the effect of a physical activity program on the hemodynamic response of the brain (vasoreactivity) in elderly people. METHODS: Eighteen men and 25 women (aged 62-67 years) were randomly assigned to an experimental (EXP, N.=22, 12 women) and a control (CON, N.=21, 13 women) group. Subjects in EXP group were required to complete a 7-month program based on aerobic training (3-4 sessions/weekd, 50 min/session, 3-4 sessions/week, at 70% maximum heart rate). Transcranial Doppler ultrasound was used to examine the cerebral blood flow response to hypercapnic and hypocapnic stimuli. We also determined blood pressure, total serum cholesterol, HDL and LDL cholesterol, and triglycerides, and conducted an aerobic capacity test (the 2.4-Km walking test). RESULTS.Brain vasomotor reactivity improved in the EXP group, reflected by a higher blood flow velocity in the middle cerebral artery (MCA) in both cerebral hemispheres in response to hypercapnia (induced by breath holding) (P<0.05). Subjects in EXP group also improved the cardiovascular profile aerobic physical condition (P<0.001) in terms of reduced arterial pressure, total cholesterol and triglyceride levels. CONCLUSION: Our findings indicate that cerebral vasoreactivity in elderly may be improved by undertaking an aerobic exercise program.

Criterion-related validity of field-based muscular fitness tests in youth.

AIM: The purpose of the present study was to analyze the association between isokinetic strength and field-based muscular fitness tests in youth. METHODS: One hundred twenty-six adolescents (14.4±1.7 y) participated in the study. Upper and lower body isokinetic strength were measured at preset angular velocities of 90 º/s and 60 º/s, respectively. Muscular fitness was also assessed by means of field-based tests: handgrip strength, bent and extended arm hang tests, standing long jump, squat jump, countermovement jump and Abalakov jump. Height, weight and skinfold thickness were used to estimate body composition. RESULTS: All field-based tests were significantly associated with isokinetic peak torque and power (P<0.001 in all cases). Handgrip strength and standing long jump showed the highest associations with the isokinetic parameters (0.61≤r≤0.87; 0.39≤R2≤0.76). Weight-bearing field tests increased on average 20 % their association (R2) with isokinetic parameters when standardized by individual's body weight (test score × weight), while the average increase was 16 % when standardized by fat-free mass (test score × fat-free mass). CONCLUSION: Handgrip strength and standing long jump tests seem to be the most valid field-based muscular fitness tests when compared to isokinetic strength. These tests can be useful to assess muscular fitness in young people when laboratory methods are not feasible.

Reliability of field-based fitness tests in youth.

The objective of this systematic review was to study the reliability of the existing field-based fitness tests intended for use with children and adolescents. The medical electronic databases MEDLINE, SCOPUS and SPORTS DISCUS were screened for papers published from January 1990 to December 2009. Each study was classified as high, low or very low quality according to the description of the participants, the time interval between measurements, the description of the results and the appropriateness of statistics. 3 levels of evidence were constructed according to the number of studies and the consistency of the findings. 32 studies were finally included in the present review. The reliability of tests assessing cardiorespiratory fitness (9 studies), musculoskeletal fitness (12 studies), motor fitness (3 studies), and body composition (10 studies) was investigated. Although some fitness components warrant further investigation, this review provides an evidence-based proposal for most reliable field-based fitness tests for use with children and adolescents: 20-m shuttle run test to measure cardiorespiratory fitness; handgrip strength and standing broad jump tests to measure musculoskeletal fitness; 4×10 m shuttle run test for motor fitness; and height, weight, BMI, skinfolds, circumferences and percentage body fat estimated from skinfold thickness to measure body composition.

Criterion-related validity of field-based fitness tests in youth: a systematic review.

The objective of this systematic review was to comprehensively study the criterion-related validity of the existing field-based fitness tests used in children and adolescents. The studies were scored according to the number of subjects, description of the study population and statistical analysis. Each study was classified as high, low and very low quality. Three levels of evidence were constructed: strong evidence, when consistent findings were observed in three or more high quality studies; moderate evidence, when consistent findings were observed in two high quality studies; and limited evidence when consistency of findings and/or the number of studies did not achieve the criteria for moderate. The results of 73 studies (50 of high quality) addressing the criterion-related validity of field-based fitness tests in children and adolescents indicate the following: that there is strong evidence indicating that the 20 m shuttle run test is a valid test to estimate cardiorespiratory fitness, that the hand-grip strength test is a valid measure of musculoskeletal fitness, that skin fold thickness and body mass index are good estimates of body composition, and that waist circumference is a valid measure to estimate central body fat. Moderate evidence was found that the 1-mile run/walk test is a valid test to estimate cardiorespiratory fitness. A large number of other field-based fitness tests presented limited evidence, mainly due to a limited number of studies (one for each test). The results of the present systematic review should be interpreted with caution due to the substantial lack of consistency in reporting and designing the existing validity studies.

Assessing health-related fitness tests in the school setting: reliability, feasibility and safety; the ALPHA Study.

The aim of this study was to determine the reliability, feasibility and safety of a health-related fitness test battery administered by Physical Education (PE) teachers in the school setting. Six PE teachers, from three primary schools and three secondary schools, assessed twice (7 days apart) the 20 m shuttle run, handgrip and standing long jump tests, as well as weight, stature, triceps and subscapular thickness and waist circumference in 58 children (age: 6-11 yr) and 80 adolescents (age: 12-18 yr). Feasibility and safety were assessed by researches by means of direct observation. Significant inter-trial differences were found for the standing long jump test (3.8+/-12.7 cm, P<0.05) and for stature (0.73+/-0.8 cm, P<0.001) in children, and for waist circumference in both children and adolescents (-0.82+/-1.2 cm and -0.35+/-0.8 cm respectively, P=0.001). The feasibility and safety items assessed presented a successful answer. Therefore, the results indicate that health-related fitness tests administered by PE teachers are reliable, feasible and safe to be performed in the school setting.

[Health behaviour of school children at the province of Cádiz]. / Conductas de salud en escolares de la provincia de Cádiz.

OBJECTIVE: The aim of this study was to analyze some characteristics of health-related behaviour in school children at the province of Cadiz, centering on engagement in sports and physical activity, and on dietary habits. METHODOLOGY: Participants were 738 students, mean age 12.2 years, from primary school o high school. 50.9% were boys and 49.1% girls, who responded a Spanish adaptation of the Health Behavior in Schoolchildren Inventory. RESULTS: Sex differences were observed in the percentage of subjects not engaged in sports, which was higher in girls. Boys practiced sports and physical activity at a higher intensity and more time than girls. A large number of subjects considered good or normal their physical fitness, with only and small percentage describing it as regular. More than half of participants felt a support by parents, and to a smaller extent by brothers and friends. An important part of the subjects did not have breakfast every day, and some even never. A high percentage of the sample ate candies 1 to 3 days per week, being also high the intake of chips, nuts, hamburgers and sausages. Near a quarter of subjects reported not to consume vegetables. CONCLUSIONS: Results obtained confirm the necessity of an adequate lifestyle habits education and the development of intervention programs in children and youth, counseling on diet and physical activity and targeting on girls, who are less physically active and on risk of serious disorders.

Predictive validity of health-related fitness in youth: a systematic review.

The objective of the present systematic review was to investigate whether physical fitness in childhood and adolescence is a predictor of cardiovascular disease (CVD) risk factors, events and syndromes, quality of life and low back pain later in life. Physical fitness-related components were: cardiorespiratory fitness, musculoskeletal fitness, motor fitness and body composition. Adiposity was considered as both exposure and outcome. The results of 42 studies reporting the predictive validity of health-related physical fitness for CVD risk factors, events and syndromes as well as the results of five studies reporting the predictive validity of physical fitness for low back pain in children and adolescents were summarised. Strong evidence was found indicating that higher levels of cardiorespiratory fitness in childhood and adolescence are associated with a healthier cardiovascular profile later in life. Muscular strength improvements from childhood to adolescence are negatively associated with changes in overall adiposity. A healthier body composition in childhood and adolescence is associated with a healthier cardiovascular profile later in life and with a lower risk of death. The evidence was moderate for the association between changes in cardiorespiratory fitness and CVD risk factors, and between cardiorespiratory fitness and the risk of developing the metabolic syndrome and arterial stiffness. Moderate evidence on the lack of a relationship between body composition and low back pain was found. Due to a limited number of studies, inconclusive evidence emerged for a relationship between muscular strength or motor fitness and CVD risk factors, and between flexibility and low back pain.

Criterion related validity of 1/2 mile run-walk test for estimating VO2peak in children aged 6-17 years.

We assessed the criterion related validity of 1/2 mile run/walk (1/2MRW) test for estimating VO2peak in children aged 6-17 years. The criterion related validity of the Fernhall's equation in a sub-group of children aged 10-17 years was also examined. A total of 86 children completed a maximal graded treadmill test and the 1/2MRW test. The cohort was randomly divided into either validation (n=47) or a cross-validation (n=39) group. A regression equation was computed and assessed through several error measures, and the Bland and Altman method. There was no systematic bias in the validation group nor in the cross-validation group (P > 0.1). The root mean sum of squared errors (RMSE), and the percentage error were 6.5 ml/kg/min, and 13.9%, respectively. These figures were very similar in the cross-validation group. The new equation had a lower RMSE and percentage error than the Fernhall's Equation (6.2 vs. 19.7 ml/kg/min, and 16% vs. 50.4%, respectively, P<0.001). The Fernhall's equation showed a significant underestimation of VO2peak (18.1 ml/kg/min, P<0.001). In conclusion, the new regression equation is valid for estimating VO2peak from the 1/2MRW time, sex, and body mass index in healthy children aged 6-17 years, and is more accurate than Fernhall's equation in the sample studied.

Criterion-related validity of sit-and-reach and modified sit-and-reach test for estimating hamstring flexibility in children and adolescents aged 6-17 years.

The purpose of the present study was to examine the criterion-related validity of the sit-and-reach test (SRT) and the modified sit-and-reach test (MSRT) for estimating hamstring flexibility in children and adolescents as well as to determine whether the MSRT is more valid than the SRT. A total of 87 (45 boys and 42 girls) children (6-12 years old) and adolescents (13-17 years old) performed the SRT and the MSRT. Hamstring flexibility was measured with goniometry through the passive straight-leg raise test. Regression analysis was performed to study the association of SRT and MSRT with hamstring flexibility (criterion measure). The SRT was associated with hamstring flexibility in both children (beta=1.089, R (2)=0.281, p=0.001) and adolescents (beta=0.690, R (2)=0.333, p=0.004). The MSRT was also associated with hamstring flexibility in both children (beta=1.296, R (2)=0.298, p<0.001) and adolescents (beta=0.588, R (2)=0.243, p=0.027). It is concluded that the criterion-related validity of the SRT and the MSRT for estimating hamstring flexibility is weak. The present data do not support that the MSRT is a more valid method than the SRT in children and adolescents.

The association of total and central body fat with pain, fatigue and the impact of fibromyalgia in women; role of physical fitness.

BACKGROUND: The relationship between estimates of total and central body fat with fibromyalgia pain, fatigue and overall impact has not been fully described. We aimed to assess the individual and combined association of body fat (total and central) with pain, fatigue and the overall impact in fibromyalgia women; and to study the possible mediation role of physical fitness in these associations. METHODS: A total of 486 fibromyalgia women with a mean (standard deviation) age of 52.2 (8.0) years participated. Pain was measured with self-reported measures and algometry, whereas fatigue with the Multidimensional Fatigue Inventory. The impact of fibromyalgia was measured with the Revised Fibromyalgia Impact Questionnaire (FIQR) total score. Total and central body fat were assessed by means of bioelectrical impedance and waist circumference, respectively. The Functional Senior Fitness Test battery and the handgrip strength test were used to assess physical fitness. RESULTS: Total and central body fat were positively associated with pain- and fatigue-related measures and the FIQR total score (ß from 0.10 to 0.25; all, p < 0.05). A combined effect of total and central body fat was observed on pain (FIQR and 36-item Short-Form Health Survey), general and physical-related fatigue and FIQR total score (all, overall p < 0.05), so that the group with no total and central obesity had more favourable results than those with total and central obesity. Cardiorespiratory fitness partially mediated (between 22-40% of the total effect) the associations between total and central body fat with pain, general fatigue, physical fatigue and reduced activity, and largely mediated (80%) the association of central body fat with the FIQR total score. CONCLUSIONS: Physical fitness might potentially explain the association between obesity and fibromyalgia symptoms.

Television viewing, psychological positive health, health complaints and health risk behaviors in Spanish children and adolescents.

AIM: The aim of this study was to study the correlation of television viewing with positive and negative health in youth. METHODS: The present cross-sectional study comprised a total of 680 children and adolescents aged 6-17.9 (46% girls) representative of the province of Cádiz (south Spain). We used the Health Behavior in School-aged Children questionnaire to assess television viewing, positive and negative health. RESULTS: It was found that correlations between television viewing >2 hours and several outcomes were inconsistent. No effects were found for quality of family relationships, quality of peer relationships, perceived academic performance and health risk behaviors in children, or with perceived excellent health status, excellent life satisfaction, quality of peer relationships, perceived academic performance and health risk behaviors in adolescents. However viewing >2 hours of television was correlated with lower quality family relations in adolescents, and lower perceived excellent health status, lower life satisfaction and higher health complaints index in children. Correction for multiple comparisons would render all television relationships as non-significant. CONCLUSION: Our results suggest that negative television influences on children and adolescents are minimal. However excessive television viewing may be symptomatic of other underlying mental health problems for some children.

Independent and combined influence of neonatal and current body composition on academic performance in youth: The UP & DOWN Study.

BACKGROUNDS: Unhealthy body composition is a cause for concern across the lifespan. OBJECTIVE: The objective of this study was to examine the independent and combined associations between neonatal and current body composition with academic performance among youth. METHODS: This cross-sectional study was conducted with a total of 1557 youth (745 girls) aged 10.4 ± 3.4 years. Birth weight and length at birth were self-reported. Current body composition was assessed by body mass index (BMI), waist circumference (WC) and percentage of body fat (BF%). Academic performance was assessed through schools records. RESULTS: Birth weight was related to all academic variables in boys, independent of potential confounders, including BMI; whereas WC, BMI and BF% were related to all academic performance indicators in both boys and girls, independent of potential confounders, including birth weight (all P < 0.05). In addition, the combined adverse effects of low birth weight and current overweight on academic performance were observed in both boys and girls for grade point average (GPA) indicator. Boys in the group with none adverse effect had significantly higher scores in GPA (score +0.535; 95% confidence interval, 0.082-0.989) than boys in the group of both adverse effects (P < 0.007); among girls, GPA score was higher in the group with none adverse effect than in the groups with one or two adverse effects (P for trend = 0.029). CONCLUSIONS: Neonatal and current body composition, both independently and combined, may influence academic performance in youth.

Substance abuse and health self-perception in Spanish children and adolescents.

OBJECTIVE: The aim of this study was to analyze substance abuse and health self-perception in children and adolescents from the province of Cádiz (Spain). METHODOLOGY: Participants were 738 students, 50.9 boys and 49.1% girls, from elementary school to high school (1st to 12th grade, mean age 12.2. years), who responded a Spanish adaptation of the Health Behavior in School-aged Children Inventory. RESULTS: No difference was observed in percentage of boys and girls reporting to smoke or drink alcohol. Smoking and drinking habits increased with age, being higher in 11th and 12th grade students. Significant differences were observed among the percentage of smokers and non smokers recognizing to have parents, older brothers or friends who smoke. Rates of drug abuse were generally low, being cannabis the most frequently consumed illicit drug. Most respondents had a perception of excellent or good health, with no significant gender differences. About half of subjects considered that health exclusively depends on self behavior, but an important percentage also gave a relevant role to luck. Stomach-ache was the most frequent physical complaint, followed by headache. Psychological complaints mainly corresponded to nervousness and bad temper. Only a small percentage of subjects declared the use of medicines or tablets without prescription. No significant difference in the percentage of respondent who perceived an excellent or good health was observed among substance users and non users. CONCLUSIONS: Substance abuse and health self-perception in children and adolescents are the result of the interaction of a complex series of individual and social factors. Activities aimed to improve health focusing on partial aspects of adolescents' lifestyle most probably will have limited results, and global programs are required.