Kevin Norton

Evidence for secular trends in children’s physical activity behaviour

It is not clear whether the global increase in weight problems in children is the result of excessive energy intake or decreasing energy expenditure. Methodological limitations have made it difficult to analyse. There is evidence that at least part of the problem may lie with increasing energy consumption, but it is important to examine the other side of the energy equation also. However, it is not possible to conclusively describe physical activity trends because of the absence of suitable baseline data. One solution is to summate all available evidence in as many areas of daily activities as possible and then draw tentative conclusions. This review summarises available trend data on direct representations of physical activity in a range of contexts, together with indirect measures such as sedentariness, fitness, and attitudes. The conclusions drawn are: physical activity in clearly defined contexts such as active transport, school physical education, and organised sports is declining in many countries; young people would like to be active but are often constrained by external factors such as school policy or curricula, parental rules in relation to safety and convenience, and physical environmental factors.

Position statement on physical activity and exercise intensity terminology.

The terminology used for monitoring and promoting physical activity and exercise among health and fitness professionals varies considerably. There is a large array of descriptor terms reported in the literature and used in day-to-day practice and this inconsistency can be confusing for clients and practitioners alike. The variation in terminology also makes it difficult to track changes in activity patterns over time and across studies. There are also a range of objective and relative intensity cut-offs used to describe the same intensity descriptors. This position statement addresses the question of standardisation of physical activity and exercise intensity terminology and makes recommendations that should assist those undertaking research and prescribing physical activity/exercise as well as those clients who are receiving professional guidance.

Morphological evolution of athletes over the 20th century: causes and consequences.

AbstractOver the course of the past century it has become increasingly difficult to find athletes of the size and shape required to compete successfully at the highest level. Sport is Darwinian in that only the ‘fittest’ reach the highest level of participation. Not every physical characteristic could be expected to play a role in this selection process, but two that are important and for which substantial data assemblies exist, are height and mass. Measurements of elite athlete sizes were obtained from a variety of sources as far back as records allowed. We charted the shift in these anthropometric characteristics of elite sportspeople over time, against a backdrop of secular changes in the general population. Athletes in many sports have been getting taller and more massive over time; the rates of rise outstripping those of the secular trend. In open-ended sports, more massive players have an advantage. Larger players average longer careers and obtain greater financial rewards. In some sports it is equally difficult to find athletes small enough to compete. In contrast, there are sports that demand a narrow range of morphological characteristics. In these sports the size of the most successful athletes over the century has remained constant, despite the drift in the population characteristics from which they are drawn. A number of social factors both drive and are driven by the search for athletes of increasingly rare morphology. These include globalisation and international recruitment, greater financial and social incentives, and the use of special training methods and artificial growth stimuli. In many sports the demand for a specific range in body size reinforces the need to adopt questionable and illegal behaviours to reach the required size and shape to compete at the top level. Future scenarios also include ‘gene-farming’ through assortative mating and athlete gamete banks.

Characteristics of Track Cycling

Track cycling events range from a 200m flying sprint (lasting 10 to 11 seconds) to the 50km points race (lasting ⊄ 1 hour).Unlike road cycling competitions where most racing is undertaken at submaximal power outputs, the shorter track events require the cyclist to tax maximally both the aerobic and anaerobic (oxygen independent) metabolic pathways. Elite track cyclists possess key physical and physiological attributes which are matched to the specific requirements of their events: these cyclists must have the appropriate genetic predisposition which is then maximised through effective training interventions. With advances in technology it is now possible to accurately measure both power supply and demand variables under competitive conditions. This information provides better resolution of factors that are important for training programme design and skill development.

Ken and Barbie at life size

There has been considerable discussion in both the scientific literature and general media concerning the appropriateness of the body shape and proportions of the Ken and Barbie dolls, the most popular dolls in modern history. The greatest concern has been of the possible influence that these, and other “cultural ideals” for body shape, may have on young children. However, these concerns have been based entirely on the subjective interpretation of how one perceives the body dimensions of the dolls relative to an adult size. We therefore used our skills in anthropometry and the rules of allometry to scale the dolls to an adult height to determine the dimensions that these dolls would assume at this adjusted size. These were compared to actual proportions of several representative adult groups of predominantly Anglo-Australian males and females. The critics have been justified in their opinions since both Barbie and Ken are thin relative to the reference samples. Barbies mean girth z-score relative to a reference cross-section of the young adult population was −4.2. This indicates that the probability for such a body shape is less than 1 in 100,000. Ken is more realistic at about 1 in 50.

Descriptive epidemiology of childhood overweight and obesity in Australia: 1901–2003

AIMS The overweight and obesity epidemic among children in Australia has attracted considerable attention as intervention strategies and public policy are debated. However, more information on the overweight prevalence trend is required to help understand its aetiology. In order to assist this public health crisis, we gathered every available raw dataset and other descriptive reports on the heights and weights of children over the last century. METHODS The raw datasets and datasets recreated using reported descriptive data were used to calculate the prevalence rates of overweight children aged 5 to 15 years. RESULTS Overweight prevalence among children was relatively low and relatively constant throughout most of the century but appears to have accelerated from about the early 1970s. DISCUSSION The prevalence rate for overweight and obesity among children in Australia continues to climb and we predict it will approach adult rates within the next 30 years.

Evolution of World Cup soccer final games 1966–2010: Game structure, speed and play patterns

OBJECTIVES There are relatively few performance analysis studies on field sports investigating how they evolve from a structural or tactical viewpoint. Field sports like soccer involve complex, non-linear dynamical systems yet consistent patterns of play are recognisable over time and among different sports. This study on soccer trends helps build a framework of potential causative mechanisms for these patterns. DESIGN Retrospective correlational study. METHODS Broadcast footage of World Cup finals between 1966 and 2010 was used to assess patterns of play and stop periods, type and duration of game stoppages, ball speed, player density (congestion) and passing rates. This involved computer-based ball tracking and other notational analyses. These results were analysed using linear regression to track changes across time. RESULTS Almost every variable assessed changed significantly over time. Play duration decreased while stoppage duration increased, both affecting the work: recovery ratios. Ball (game) speed increased by 15% over the 44-year period. Play structure changed towards a higher player density with a 35% greater passing rate. CONCLUSIONS Increases in soccer ball speed and player density show similarities with other field sports and suggest common evolutionary pressures may be driving play structures. The increased intensity of play is paralleled by longer stoppage breaks which allow greater player recovery and subsequently more intense play. Defensive strategies dominate over time as demonstrated by increased player density and congestion. The long-term pattern formations demonstrate successful coordinated states within team structures are predictable and may have universal causative mechanisms.

Olympic lightweight and open-class rowers possess distinctive physical and proportionality characteristics

Abstract Rowers competing at the 2000 Olympic Games were measured for 38 anthropometric dimensions. The aim was to identify common physical characteristics that could provide a competitive advantage. The participants included 140 male open-class rowers, 69 female open-class rowers, 50 male lightweight rowers, and 14 female lightweight rowers. Body mass, stature, and sitting height were different (P < 0.01) between the open-class and lightweight rowers, as well as a comparison group of healthy young adults (“non-rowers”, 42 males, 71 females), for both sexes. After scaling for stature, the open-class rowers remained proportionally heavier than the non-rowers, with greater proportional chest, waist, and thigh dimensions (P < 0.01). Rowers across all categories possessed a proportionally smaller hip girth than the non-rowers (P < 0.01), which suggested the equipment places some constraints on this dimension. Top-ranked male open-class rowers were significantly taller and heavier and had a greater sitting height (P < 0.01) than their lower-ranked counterparts. They were also more muscular in the upper body, as indicated by a larger relaxed arm girth and forearm girth (P < 0.01). For the male lightweight rowers, only proportional thigh length was greater in the best competitors (P < 0.01). In the female open-class rowers, skinfold thicknesses were lower in the more highly placed competitors (P < 0.01). In conclusion, the rowers in this sample demonstrated distinctive physical characteristics that distinguish them from non-rowers and other sports performers.

A comparison of two short-term intensive physical activity interventions: methodological considerations

BackgroundIncreases in chronic illness due to sedentary lifestyles and poor metabolic fitness have led to numerous intervention strategies to promote physical activity (PA). This paper describes the methodological strategies of two short-term PA interventions. Outcome measures reported are PA adherence and compliance rates during the intervention and at 3, 6 and 12-month follow-up.MethodsThe 40-day interventions were: a pedometer-based walking program (n = 251) and a group-based intensive program (n = 148). There was also an active control group (n = 135). Intervention subjects were prescribed PA each day and required to record all activity sessions (pedometer steps or energy expenditure from heart rate monitors).ResultsCompliance (≥ 150 min/wk PA) was highest post-intervention (81.1% and 64.5% for the group and pedometer subjects, respectively) and then progressively decreased across the 12-month follow-up period (final compliance rates were 53.5% and 46.6%, respectively) although they remained significantly higher than pre-intervention rates (zero %). There was significantly higher adherence to 6 months (75.0% and 64.9%), and compliance to 3 months (64.9% and 51.0%), for group versus pedometer subjects. The active control group maintained the highest adherence and compliance rates across the study.ConclusionsThe group-based program resulted in higher adherence and compliance rates post-intervention although both types of interventions showed long-term effectiveness to increase activity patterns.

Movement profiles of elite women soccer players during international matches and the effect of opposition’s team ranking

Abstract Movement patterns in elite men’s soccer have been reported in depth, but less research exists for women’s soccer. Aims of the study were to identify the movement profiles of elite women soccer players in international competition and examine the effect the level of opposition, based on Federation Internationale de Football Association (FIFA) rankings, had on the physical demands of the game. MinimaxX athlete tracking devices were used by 15 players during 13 international matches against opponent teams of varying ability. Total distance covered averaged 9292 ± 175 m. There was a decrease in high-intensity running (HIR) in the 60- to 75-min and 75- to 90-min periods compared to the 0- to 15-min period of 22.4% and 26.1%, respectively (P = 0.022, P = 0.004) although sprint distances remained unchanged across game periods. HIR distances covered were significantly greater for midfielders versus defenders, while defenders had lower sprinting compared to both midfielders and attackers. Stronger opponents elicited less HIR and greater low-speed activity (LSA) compared to playing teams of similar or lower ranking. These results are important to coaches to prepare players for international competition and show the differing demands required depending on the ability of the opponents.