Longitudinal analysis of physical function in older adults: The effects of physical inactivity and exercise training.

Lack of exercise contributes to systemic inflammation and is a major cause of chronic disease. The long-term impact of initiating and sustaining exercise in late life, as opposed to sustaining a sedentary lifestyle, on whole-body health measures such as physical performance is not well known. This is an exploratory study to compare changes in physical performance among older adults initiating exercise late in life versus inactive older adults. Data from two observational cohorts were included in this analysis, representing two activity groups. The Active group cohort comprises older adults (n = 318; age 72.5 ± 7.2 years) enrolled in a supervised exercise program, "Gerofit." The inactive group comprises older adults (n = 146; age 74.5 ± 5.5 years) from the Italian study "Act on Ageing" (AOA) who self-reported being inactive. Participants in both groups completed physical performance battery at baseline and 1-year including: 6-min walk test, 30-s chair stand, and timed up-and-go. Two-sample t-tests measured differences between Gerofit and AOA at baseline and 1-year across all measures. Significant between-group effects were seen for all performance measures (ps = 0.001). The AOA group declined across all measures from baseline to 1 year (range -18% to -24% change). The Gerofit group experienced significant gains in function for all measures (range +10% to +31% change). Older adults who initiated routine, sustained exercise were protected from age-related declines in physical performance, while those who remained sedentary suffered cumulative deficits across strength, aerobic endurance, and mobility. Interventions to reduce sedentary behaviors and increase physical activity are both important to promote multi-system, whole-body health.

Resources and transversal competencies to reconcile child and parental responsibilities: A mini-review of the impact of COVID-19 on the Italian sandwich generation.

Longer life spans and the delayed economic and psychological independence of children mean that middle-aged parents find themselves caring for parents and children at the same period in their lives, at times this care may extend to grandchildren and grandparents. The type of care varies depending on each person's need but also on the gender of the individual who looks after their parents while taking care of their own children. Cultural factors can also come into play. Complications in the lives of those who are part of the Sandwich Generation (SG) may arise affecting the quality of their time, their psyche, physical and financial situation. Having the necessary skills and strategies to cope with these complications is extremely important.

Creativity and resilience: a mini-review on post-pandemic resources for adolescents and young adults.

Background: Two years after the outbreak of the pandemic, several studies look at the consequences for the well-being and mental health of young people. In particular, creativity and resilience are cited in the scientific literature as resources that promote this well-being in adolescents and young adults. Purpose: This mini-literature review was created with the aim of examining how many articles have explored the relationship between creativity and resilience in adolescents and young adults since the onset of the pandemic. Methods: Particular attention was paid to how many of the articles actually related to the consequences of the pandemic, in which country they were published, their target population, and the models, instruments and variables used to analyze them. Results: Only 4 articles emerged from the screening, of which only one was actually related to pandemic consequences. All articles were published in Asian countries with a target group of university students. Three of the articles used mediation models to examine the relationship between resilience as an independent variable and creativity as a dependent variable. All articles used self-assessment instruments for creativity and resilience, both at the individual and group level. Significance: This mini-review offers us the opportunity to reflect on the lack of studies that have addressed the issue of youth resources in the form of creativity and resilience since the beginning of the pandemic. The results show us a still underdeveloped interest in creativity in the scientific literature, in contrast to what the media reports on the promotion of creativity in daily life.

"Stay at Home" during the COVID-19 Pandemic: Effects on Physical Activity and Sedentary Behavior in an Italian Academic Community.

This study investigates changes in physical activity (PA) and sedentary behavior in an Italian university community during Phase 1 of SARS-CoV-2 lockdown ("stay at home" government decree, from March 8th to May 4th, 2020) compared to their habits prior to the COVID-19 pandemic. We also examine differences according to gender, university position, BMI categories, and sport participation. A total of 2596 people (median age 24, IQR 11 years; 70.8% women) filled out a survey after eight weeks of statutory confinement at home. The International Physical Activity Questionnaire measured PA and sedentary behavior in a typical week before and during lockdown. Physically inactive people passed from 10.9% to 35.0% before−during the lockdown. The total amount of PA decreased (median 2307 vs. 1367 MET-min/week; p < 0.001), while sedentary behavior increased (median 349 vs. 440 min/day; p < 0.001) between before and during the lockdown. The following categories showed a higher reduction in the total amount of PA: men when compared to women; people with normal weight when compared to pre-obese/obese people; and people who played sports when compared to those who did not play sports. There is a need to propose PA/exercise programs to counteract physical inactivity and sedentarism during a social emergency, with special attention to people who showed higher PA reduction.

PE-Iv (Panorama Education-Italian version): the adaptation/validation of 5 scales, a step towards a SEL approach in Italian schools.

Implementing a Social and Emotional Learning (SEL) approach in school requires monitoring certain skills. As awareness of SEL increases in Italy, it is necessary to provide instruments to monitor these skills within a systemic approach. This study presents the cultural adaptation/validation of 5 scales from Panorama Education, which are widely used in school districts in the United States, to the Italian middle/high school context: Grit, Sense of Belonging, Self-Management, Social Awareness, and Self-Efficacy. After cultural adaptation, 709 middle/high school students answered an online questionnaire (2021). Psychometric properties showed good internal consistency and confirmatory factor analysis showed a good fit index. The differences in gender and grade level support the validity of the instrument.

School closures and mental health, wellbeing and health behaviours among children and adolescents during the second COVID-19 wave: a systematic review of the literature.

OBJECTIVES: to evaluate the impact of school closures, as a measure to contain the transmission of SARS-CoV-2 infection, on the psychological well-being of students of all levels starting from the 2020-2021 school year. DESIGN: a systematic literature review was conducted according to the PRISMA 2020 Guidelines. The literature search was conducted on 4 different databases: MedLine, Embase, PsycINFO, and L.OVE Platform. Quantitative observational studies published until 10.01.2022 were included. Studies conducted during the first pandemic wave, i.e., during the 2019-2020 school year and/or during the mandatory lockdown or confinement period, were excluded. The methodological quality of the studies was assessed with validated scales. Study selection, data extraction, and quality assessment were carried out independently by two authors. SETTING AND PARTICIPANTS: children, adolescents, and young people attending all levels of education (including universities) and, for reasons related to COVID-19, having a suspension of "in presence" school or attending classes remotely. MAIN OUTCOME MEASURES: a. outcomes directly related to mental health: suicides, emergency department visits, and hospitalizations for psychiatric problems; anxiety and depression, emotional difficulties, feelings of loneliness and isolation; b. well-being outcomes: sleep quality, perceived well-being (by child/adolescent/youth or referred by parents); c. health-related behaviours: tobacco smoking, alcohol, drug use. Outcomes related to school/academic performance, physical health, and those related to parents were not considered. RESULTS: after having removed duplicate articles, 2,830 records were retrieved with the bibliographic search. Twelve studies (2 uncontrolled before-after studies and 10 cross sectional surveys) were included, involving a total of 27,787 participants. Three studies involved university students, 2 involved high school students, and the remaining involved a mixed population of students attending primary and middle schools. The studies were conducted between September 2020 and April 2021. The methodological quality was rated as high in five studies and intermediate in the remaining studies. Due to the high heterogeneity of outcome measures and statistical analyses performed among the included studies, it was not possible to conduct a meta-analysis of the results of the considered publications. Nevertheless, the present review showed a clear signal of increase in mental health problems in relation to school closure or virtual instruction. In particular, results suggest evidence of association between school closure and risk of suicidal attempts or thoughts, mental health symptoms such as anxiety, depression, emotional disorders, psychological stress. Sleeping problems, drug and alcohol addiction were poorly studied. CONCLUSIONS: despite the limitations of the included studies and possible residual confounding and contamination due to restrictive measures and social isolation implemented during the pandemic, the available evidence confirms the negative impact on students' mental health associated with school closures and distance learning. Given the availability of vaccination also for young children, a long period of school closure should be avoided also in the case of the emergence of new pandemic waves.

Effects of a Multicomponent Exercise Program on Prevalence and Severity of the Frailty Syndrome in a Sample of Italian Community-Dwelling Older Adults.

Background: Frailty is a well-known condition that leads to a lack of resilience, with a reduced homeostatic capacity and a consequent higher risk of suffering adverse health outcomes. This study investigated the effectiveness of an exercise program to improve and reverse physical frailty amongst Italian older adults. Methods: One hundred and twenty-three community dwelling older adults (mean age 74 years, SD = 6; 64% women) were involved in an experimental (EG; n = 62) and a control (CG; n = 61) group. Frailty was assessed at baseline and after the intervention using an adapted version of the frailty phenotype. The EG took part in a 16-week exercise program, consisting of endurance, strength, balance and flexibility exercises, while the CG maintained the same routine. Results: After the exercise program, the EG was more robust than the CG (F = 43.51, p < 0.001). Within the EG, 46% of pre-frail and 50% of frail people reached the robust and pre-frail levels, respectively. Effects of training were higher in frail and pre-frail people (reduction of frailty of 0.67 and 0.76 points, respectively) compared to robust ones (who frailty levels increased by 0.23 points; F = 11.32, p < 0.001). Conclusions: A multicomponent exercise program may be effective at improving and reverting frailty, specifically for frail and pre-frail people.

Health promoting schools and COVID-19: preparing for the future.

We face an unprecedented period of history during which COVID-19 is clustered with other global conditions, such as obesity, undernutrition, an infodemic, and climate change. This syndemic (synergy of epidemics) calls for the development of children's and youth's health literacy and socioemotional skills, support for behavioural hygiene (e.g. washing hands, wearing masks), and adults' responsibility and caring. Moreover, it calls for creating conditions for healthy living and learning for all and paying extra attention to inequalities that have increased during the pandemic. Today, more than ever, there is an essential demand for schools to create environments that maintain and promote health for all. Within this commentary, we argue that whole-school approaches, such as the health promoting school, are essential to fight against the pandemic and to prepare schools for future challenges.

A Balancing Act During Covid-19: Teachers' Self-Efficacy, Perception of Stress in the Distance Learning Experience.

One of the many drastic changes caused by Covid-19 was the quick implementation of distance learning which represented a great technological challenge to many teachers and students. In fact, Italy ranks 24th amongst the 27-EU member countries in digital competitiveness which testifies to the significant delays and gaps in basic digital skills amongst the population. Based on the difficulties encountered in organizing distance learning, we assumed that teachers' perceived stress increased. Given that transversal skills can be associated with this relationship, we hypothesized that among these skills, self-efficacy mediated the relationship between the difficulties in organizing distance learning and perceived stress. Since we targeted teachers from Italy and other European countries, we also hypothesized that this mediator effect would be different for both samples. Our sample was composed of a total of 366 primary/middle school teachers of which 86% female. After doing a mediation analyses with Process, Hayes' Model 4, we confirmed H1 but not H2: resulting in a partial mediation effect of self-efficacy for each individual group of teachers. Since difficulties of distance learning can affect the perception of stress, we believe that the promotion of transversal skills, such as self-efficacy, can better equip teachers when facing stressful situations.

Relation among Perceived Weight Change, Sedentary Activities and Sleep Quality during COVID-19 Lockdown: A Study in an Academic Community in Northern Italy.

In Italy, COVID-19 lockdown was imposed from 8 March until 3 May 2020 with negative consequences on the lifestyles and health of people. Within this context, the paper aims: (i) to analyse the impact of COVID-19 lockdown on perceived weight changes; (ii) to evaluate factors associated with the perception of weight changes (Body Mass Index (BMI), sleep quality, time spent in sedentary activities), in an Italian academic community of students and workers. A total of 3666 participants took part in this cross-sectional study (2838 students and 828 workers, of whom 73.0% were female). T-test, Chi-square test and the two-way ANOVA were used. Results showed that 43.3% of participants perceived a weight gain. Workers experienced a more substantial increase in body weight (0.7 kg) compared to students (0.3 kg; p = 0.013). A significant difference between preobese/obese workers (0.9 kg) and students (-0.3 kg; p < 0.001) was found. Overall, 57.0% of the sample was characterized by high levels of sedentary activities. Sedentary people noticed a higher weight gain (0.4 kg) compared to less sedentary people (0.3 kg; p = 0.048). More than 45% of participants reported a worsening of sleep quality and showed a perceived increase in body weight (0.5 kg) in comparison to those who improved their sleep quality (no weight change; p = 0.001). Designing tailored interventions to promote health-related behaviours during lockdown periods is essential.

The Role of Working Memory on Dual-Task Cost During Walking Performance in Childhood.

This study examined the effect of a secondary motor task on walking ability, whether performance differed according to age and the possible relationship between cognitive abilities, specifically working memory, and dual-task costs in children with typical development. Fifty-three female children (mean age M = 10 ± 2 years), were divided into two different age groups: a young (7-9 years; n = 17) and an older group (10-13 years; n = 36). First, participants performed a Walking Test (WT) without additional tasks; afterward, they performed the same walking test while performing each of the following tasks: carrying (1) a glass of water, (2) a ball on a round tray and (3) the combination of both tasks (1) and (2). The Test of Memory and Learning were used to assess working memory. WTs under a dual-task condition generally produced worse results compared to a single-task condition [F(3,135) = 32.480, p < 0.001]. No age-related difference was observed [F(1,45) = 0.497, p = 0.485]. Age, digit forward and backward, facial memory, and paired recall accounted altogether for 28.6% of variance in dual-task ability during WT while carrying a glass of water and a ball on a round tray. Specifically, facial memory significantly accounted for the variance of DTC in WTWT (ß = -0.381, p = 0.016). Moreover, a trend toward a statistical significance was observed for digit forward (ß = -0.275, p = 0.085). Results underlined that regardless of the age, a dual-task performance might affect walking performance depending on the required secondary task. Moreover, our results showed the association between working memory skills and dual-task cost in walking ability.

Participation in a school-based walking intervention changes the motivation to undertake physical activity in middle-school students.

The motivation to perform physical activity is a crucial factor in achieving a persistent active lifestyle. However, motivation decreases with increasing age from childhood to adolescence. The promotion of physical activity in educational settings might be an important tool to increase motivation and, consequently, to decrease sedentary behavior. The aim of this study was to explore the effect of a 4-month school-based walking intervention on motivation to participate in physical activity among Italian middle-school students. This study included 276 students (mean age 13 ± 1 years, 41.3% female). A total of 138 students (intervention group) participated in a brief walking intervention that was added to their routine daily school activity, while a convenience sample of 138 students performed the routine daily school activity. The activity consisted of walking one kilometer outside of school buildings during the morning break. Motivation data were collected before and after the walking breaks using the Participation Motivation Questionnaire (PMQ). Controlling for age, significant interactions between group and time were observed in the "Social Status" [F(1,273) = 4.851; p = 0.028], "Team" [F(1,273) = 6.015; p = 0.015] and "Energy Release" components [F(1,273) = 8.527; p = 0.038]. Specifically, a significant decrease in the "Social Status" components of the PMQ and an increase in the "Team" and "Energy Release" components were observed in the intervention group. On the contrary. control group showed an increase in "Social Status" and a decrease in the "Team" and "Energy Release" components. Within this developmental context, incorporation of the walking activity helped to modify the motivational orientation towards physical activity to include more intrinsic factors, which were related to the possibility of remaining with classmates and peer groups and releasing a surplus of energy.

Dancing in the golden age: a study on physical function, quality of life, and social engagement.

The aim of this study was to determine the effects of dancing activity based on different dance styles, in groups as well as with a partner, on mobility performance, quality of life and social engagement in a sample of older adults. One hundred and sixty-three older adults (mean age, 70 years; SD = 4 years) participated in a supervised dancing activity programme for 16 weeks. The dancing activity included different dance routines and was progressive in terms of motor complexity. Data on mobility, health-related quality of life and social engagement were collected before and after a 16-week training period. Significant improvements in mobility, quality of life and social engagement were noted in single as well as dual-task performance after the intervention. Our results emphasise the benefit of a 16-week dance training on multidimensional features, including physical and psychosocial domains, which are important for successful ageing.

Fear of falling and activities of daily living function: mediation effect of dual-task ability.

OBJECTIVE: The aim of the study was to explore the association between fear of falling (FOF), dual-task ability during a mobility task, and the activities of daily living (ADL) in a sample of older adults. METHODS: Seventy-six older adults (mean age M = 70.87 ± 5.16 years) participated in the study. Data on FOF (using the Falls Self-Efficacy Scale-International), walking ability during both single- and dual-task performances and ADL were collected. RESULTS: Mediation analysis demonstrated the mediation effect of dual-task ability (ß = 0.238, p = 0.011) between FOF and ADL level (ß = 0.559, p < 0.001). Moreover, significantly lower performances were observed during dual-task condition [F (2, 73) = 7.386, p < 0.001], and lower ADL levels were also found in older adults with FOF [F (2, 73) = 13.734, p < 0.001]. CONCLUSION: The study underlines the relationship between FOF, dual-task ability and ADL level. These results could be used to develop specific intervention programmes for successful ageing.

Dual-task training in older adults: The effect of additional motor tasks on mobility performance.

OBJECTIVES: Dual-task (DT) performance is common to most activities of daily living and difficulties in DT activities may reduce quality of life in older adults. This study investigated the effect of DT training in a sample of older adults. METHODS: Sixty older adults (mean=74.4±3.1years) participated in the study. Twenty-two older adults were included in the control (CG), 19 in the single-task (ST) training and 19 in DT training group. ST group received balance and walking training twice a week for16 weeks, while DT training group performed the same training with additional motor tasks. Data were gathered on 6m timed walk (6MTW), timed up and go test (TUG) and four square step test (FSST). DT conditions required participants to complete 6MTW, TUG and FSST, either (i) while carrying a glass of water or (ii) while carrying a ball on a round tray. RESULTS: A significant Group x Time interaction was found in TUG (F [2,57]=29.5; p<0.01; partial η2=0.51) and in FSST (F [2,57]=23.2; p<0.01; partial η2=0.44). After intervention DT showed better scores in overall TUG (mean difference=1.21s [95% CI, 0.82-1.60]; p<0.05) and FSST (mean difference=2.51s [95% CI, 1.67-3.35]; p<0.01), whereas CG and ST did not exhibit significant changes. CONCLUSION: Our results suggested that 16 weeks of motor DT training, using motor additional tasks as manipulation of common objects of everyday life, could improve mobility in older age.

Emotion experience and frailty in a sample of Italian community-dwelling older adults.

Frailty increases individual vulnerability to external stressors and involves high risk for adverse geriatric outcomes. To date, few studies have addressed the role of emotion perception and its association with frailty in aged populations. This cross-sectional study aimed to explore whether a significant association between frailty and emotional experience exists in a sample of Italian community-dwelling older adults. Our sample consisted of 104 older adults (age 76±8 years; 59.6% women) living in Piedmont, Italy. Frailty was measured using the Italian version of the Tilburg Frailty Indicator (TFI), and emotion perception was measured with the Positive and Negative Affect Schedule (PANAS). The Mini-Mental State Examination was used as a screening tool for cognitive functions (people with a score ≤20 points were excluded). One-way analysis of covariance (ANCOVA), adjusted for interesting variables, and post hoc tests were performed where appropriate. According to the TFI, 57.7% of participants resulted as frail. Analysis showed a significant greater severity of frailty in the low positive affect (PA) group compared to the high PA group. Similarly, those with high negative affect (NA) showed significantly higher levels of frailty than the low NA group. As expected, significant differences for frailty were also found among the groups composed of 1) people with high PA and low NA, 2) people with low PA or high NA, and 3) people with low PA and high NA. Post hoc tests showed a greater severity of frailty in the second and in the third groups compared to the first one. Lastly, robust participants aged >75 years showed higher levels of PA than the group aged between 60 and 75 years. These findings demonstrate that both PA and NA may influence frailty, giving new insights for the evaluation and prevention of frailty in older adults.

Age-related decrements in dual-task performance: Comparison of different mobility and cognitive tasks. A cross sectional study.

This cross-sectional study investigated the age-related differences in dual-task performance both in mobility and cognitive tasks and the additive dual-task costs in a sample of older, middle-aged and young adults. 74 older adults (M = 72.63±5.57 years), 58 middle-aged adults (M = 46.69±4.68 years) and 63 young adults (M = 25.34±3.00 years) participated in the study. Participants performed different mobility and subtraction tasks under both single- and dual-task conditions. Linear regressions, repeated-measures and one-way analyses of covariance were used, The results showed: significant effects of the age on the dual and mobility tasks (p<0.05) and differences among the age-groups in the combined dual-task costs (p<0.05); significant decreases in mobility performance under dual-task conditions in all groups (p<0.05) and a decrease in cognitive performance in the older group (p<0.05). Dual-task activity affected mobility and cognitive performance, especially in older adults who showed a higher dual-task cost, suggesting that dual-tasks activities are affected by the age and consequently also mobility and cognitive tasks are negatively influenced.

Personal Values as a Mediator of Relations Between Perceived Parental Support and Control and Youth Substance Use.

BACKGROUND: Tobacco and marijuana smoking are very popular in adolescence and there is a high rate of comorbidity between them, even in young adulthood. Parental support and control may hinder involvement in the use of these substances by promoting conventional values among adolescents. OBJECTIVES: The present study investigates the relations between family functioning (parental support and control) and psychoactive substance use (tobacco and marijuana smoking) and determines whether these relationships are mediated by personal values (in terms of disapproval of deviance and beliefs about the importance of school, health and religion). METHODS: 175 Italian late adolescents (17 to 20 years old) participated in this two-wave longitudinal study. Data were collected at school through an anonymous questionnaire. RESULTS: Greater parental control and support were directly associated with lower adolescent tobacco and marijuana use; adolescent acceptance of conventional values mediated the association between parenting and adolescent marijuana use. CONCLUSION: Findings emphasize the influence of family relationships throughout adolescence. The transmission of conventional values to adolescents may be a critical mechanism through which parenting protects adolescents from substance use, especially marijuana use.

Mobility, balance and frailty in community-dwelling older adults: What is the best 1-year predictor of falls?

AIM: The present study aimed, first, to compare the ability to predict falls over 12 months for three measures - mobility, balance and frailty. Second, among the three domains of frailty - physical, psychological and social - we investigated what is the strongest predictor of falls. METHODS: A total of 192 community-dwelling older adults (age 73.0 ± 6.2 years; 62% women) were involved in this longitudinal study. The Timed Up and Go (TUG) test, One Leg Standing (OLS) test and the Tilburg Frailty Indicator (TFI) were respectively used to measure mobility, balance and frailty. The TFI is a questionnaire based on a multidimensional conceptualization of frailty consisting of 15 items in three domains (physical, psychological and social). Falls were self-reported during the 12-month follow up. Logistic regression models, adjusted for interesting variables, were carried out to predict the risk of falls. RESULTS: History of falls and chronic conditions were the indicators more strongly related with falls over 12 months. The TFI resulted as a stronger predictor of falls when compared with the TUG and OLS tests. The explained variance of the three models was 31.2%, 22.4% and 22.2%, respectively. The TFI was significantly associated with falls (P < 0.001), whereas the TUG and the OLS were not (P > 0.05). Among the three frailty domains, physical (P < 0.001) and psychological (P = 0.041) domains were significant predictors of falls. CONCLUSIONS: The findings showed that the TFI might be an effective tool for predicting falls at 12 months in aged populations, probably because it is able to capture the multifactorial facets that can lead to falls. Geriatr Gerontol Int 2017; 17: 1463-1469.

Age-related differences in dual task performance: A cross-sectional study on women.

AIM: Simultaneous performances of motor and attention-demanding tasks are common in activities of everyday life. The present cross-sectional study examined the changes and age-related differences on mobility performance with an additional cognitive or motor task, and evaluated the relative dual-task cost (DTC) on the motor performance in young, middle-aged and older women. METHODS: A total of 30 young (mean age 25.12 ± 3.00 years), 30 middle-aged (mean age 47.82 ± 5.06 years) and 30 older women (mean age 72.74 ± 5.95 years) were recruited. Participants carried out: (i) single task: Timed Up & Go Test; (ii) cognitive dual-task: Timed Up & Go Test while counting backwards by three; (iii) manual dual-task: Timed Up & Go Test while carrying a glass of water. A repeated measures anova with between-factor as age groups and within-factor as tasks was carried out to assess the effect of aging on the performance of mobility tasks. DTC was calculated as ([performance in single-task - performance in dual-task] / performance in single task) × 100%. One-way ancova were carried out to compare the DTC among the three age groups. RESULTS: A significant interaction between age groups and task (F4,172 = 6.716, P < 0.001, partial η2 = 0.135) was observed. Specifically, older women showed a worse mobility performance under dual-task condition compared with young and middle-aged groups. Furthermore, DTC differences in cognitive task were observed in older women compared with younger and middle-aged women (F2,86 = 7.649, P < 0.001, partial η2 = 0.151), but not in manual task. CONCLUSION: Dual-task conditions might affect mobility performance differently across the lifespan, and could be particularly challenging in older women. Geriatr Gerontol Int 2017; 17: 315-321.