Reviews: Rapid! Rapid! Rapid! …and systematic

Systematic reviews can help practitioners keep abreast of the medical literature by summarizing large bodies of evidence and helping to explain differences among studies on the same question. A systematic review involves the application of scientific strategies, in ways that limit bias, to the assembly, critical appraisal, and synthesis of all relevant studies that address a specific clinical question. A meta-analysis is a type of systematic review that uses statistical methods to combine and summarize the results of several primary studies. Because the review process itself (like any other type of research) is subject to bias, a useful review requires clear reporting of information obtained using rigorous methods. Used increasingly to inform medical decision making, plan future research agendas, and establish clinical policy, systematic reviews may strengthen the link between best research evidence and optimal health care.

Physical activity in adolescence may contribute to the development of healthy adult lifestyles, helping reduce chronic disease incidence. However, definition of the optimal amount of physical activity in adolescence requires addressing a number of scientific challenges. This article reviews the evidence on short- and long-term health effects of adolescent physical activity. Systematic reviews of the literature were undertaken using a reference period between 2000 and 2004, based primarily on the MEDLINE/PubMed database. Relevant studies were identified by examination of titles, abstracts and full papers, according to inclusion criteria defined a priori. A conceptual framework is proposed to outline how adolescent physical activity may contribute to adult health, including the following pathways: (i) pathway A--tracking of physical activity from adolescence to adulthood; (ii) pathway B--direct influence of adolescent physical activity on adult morbidity; (iii) pathway C--role of physical activity in treating adolescent morbidity; and (iv) pathway D - short-term benefits of physical activity in adolescence on health. The literature reviews showed consistent evidence supporting pathway 'A', although the magnitude of the association appears to be moderate. Thus, there is an indirect effect on all health benefits resulting from adult physical activity. Regarding pathway 'B', adolescent physical activity seems to provide long-term benefits on bone health, breast cancer and sedentary behaviours. In terms of pathway 'C', water physical activities in adolescence are effective in the treatment of asthma, and exercise is recommended in the treatment of cystic fibrosis. Self-esteem is also positively affected by adolescent physical activity. Regarding pathway 'D', adolescent physical activity provides short-term benefits; the strongest evidence refers to bone and mental health. Appreciation of different mechanisms through which adolescent physical activity may influence adult health is essential for drawing recommendations; however, the amount of exercise needed for achieving different benefits may vary. Physical activity promotion must start in early life; although the 'how much' remains unknown and needs further research, the lifelong benefits of adolescent physical activity on adult health are unequivocal.

Fifty reviews published during June 1985 to June 1986 in four major medical journals were assessed in a study of the methods of current review articles. Assessments were based on eight explicit criteria adapted from published guidelines for information syntheses. Of the 50 articles, 17 satisfied three of the eight criteria; 32 satisfied four or five criteria; and 1 satisfied six criteria. Most reviews had clearly specified purposes (n = 40) and conclusions (n = 37). Only one had clearly specified methods of identifying, selecting, and validating included information. Qualitative synthesis was often used to integrate information included in the review (n = 43); quantitative synthesis was rarely used (n = 3). Future research directives were mentioned in 21. These results indicate that current medical reviews do not routinely use scientific methods to identify, assess, and synthesize information. The methods used in this systematic assessment of reviews are proposed to improve the quality of future review articles.