A lifetime of change: Measurements of total and basal energy in a large cohort of subjects at ages spanning from before birth to old age document distinct changes that occur during a human lifetime. Pontzer et al . report that energy expenditure (adjusted for weight) in neonates was like that of adults but increased substantially in the first year of life (see the Perspective by Rhoads and Anderson). It then gradually declined until young individuals reached adult characteristics, which were maintained from age 20 to 60 years. Older individuals showed reduced energy expenditure. Tissue metabolism thus appears not to be constant but rather to undergo transitions at critical junctures. —LBR

Data are lacking regarding the independent risk of injury related to intense single-sport training or growth rate in young athletes. To determine whether sports specialization, weekly training volumes, and growth rates are associated with increased risk for injury and serious overuse injury in young athletes. Case-control study; Level of evidence, 3. Injured athletes aged 7 to 18 years were recruited from 2 hospital-based sports medicine clinics and compared with healthy controls from affiliated primary care clinics undergoing sports physicals (2010-2013). Participants completed surveys reporting hours per week spent in organized sports, physical education class, and free play, as well as degree of sports specialization and Tanner stage. Heights and weights were measured. Injury details were obtained from athlete surveys and electronic medical records. Of 1214 athletes enrolled, 1190 (50.7% male) had data satisfactory for analysis. There were 822 injured participants (49.5% male; unique injuries, n = 846) and 368 uninjured participants (55% male). Injured athletes were older than uninjured athletes (14.1 ± 2.1 vs 12.9 ± 2.6 years; P < .001) and reported more total hours of physical activity (19.6 ± 9.2 vs 17.6 ± 8.9 h/wk; P < .001) and organized sports activity (11.2 ± 2.6 vs 9.1 ± 6.3 h/wk; P < .01). After accounting for age and hours in sports activity spent per week, sports-specialized training was an independent risk for injury (odds ratio [OR], 1.27; 95% CI, 1.07-1.52; P < .01) and serious overuse injury (OR, 1.36; 95% CI, 1.08-1.72; P < .01). Young athletes participating in more hours of sports per week than number of age in years (OR, 2.07; 95% CI, 1.40-3.05; P < .001) or whose ratio of organized sports to free play time was >2:1 hours/week had increased odds of having a serious overuse injury (OR, 1.87; 95% CI, 1.26-2.76; P < .01). Growth rates were similar between injured and uninjured athletes (4.8 cm/y for both groups; P = .96). Injured young athletes were older and spent more hours per week in organized sports. There is an independent risk of injury and serious overuse injury in young athletes who specialize in a single sport. Growth rate was not related to injury risk. The study data provide guidance for clinicians counseling young athletes and their parents regarding injury risks associated with sports specialization.

Context: Sports specialization is intense training in 1 sport while excluding others. Sports specialization in early to middle childhood has become increasingly common. While most experts agree that some degree of sports specialization is necessary to achieve elite levels, there is some debate as to whether such intense practice time must begin during early childhood and to the exclusion of other sports to maximize potential for success. There is a concern that sports specialization before adolescence may be deleterious to a young athlete. Evidence Acquisition: PubMed and OVID were searched for English-language articles from 1990 to 2011 discussing sports specialization, expert athletes, or elite versus novice athletes, including original research articles, consensus opinions, and position statements. Results: For most sports, there is no evidence that intense training and specialization before puberty are necessary to achieve elite status. Risks of early sports specialization include higher rates of injury, increased psychological stress, and quitting sports at a young age. Sports specialization occurs along a continuum. Survey tools are being developed to identify where athletes fall along the spectrum of specialization. Conclusion: Some degree of sports specialization is necessary to develop elite-level skill development. However, for most sports, such intense training in a single sport to the exclusion of others should be delayed until late adolescence to optimize success while minimizing injury, psychological stress, and burnout.

Compared to other apes, humans live longer, reproduce faster and have larger brains; here, total energy expenditure is studied in humans and all species of great ape, and is shown to be significantly higher in humans, demonstrating that the human lineage has experienced an energy-boosting acceleration in metabolic rate. Humans live longer than other apes, reproduce faster and have larger brains. This uniquely human portfolio of metabolically costly traits suggests that at some point in the hominin lineage there was a relaxation of energetic constraints, but the underlying mechanisms involved remain largely unknown. Here Herman Pontzer et al. study total energy expenditure in humans and all known species of great ape. They also revisit the archival data that seemed to have confused the issue somewhat. The authors conclude that total energy expenditure is significantly higher in humans, and that this is related to fat mass and particularly to brain mass. Thus human evolution owes much to an increased metabolic rate, along with changes in energy allocation, one result being our predisposition to deposit fat, whilst other hominoids remain relatively lean. Humans are distinguished from the other living apes in having larger brains and an unusual life history that combines high reproductive output with slow childhood growth and exceptional longevity1. This suite of derived traits suggests major changes in energy expenditure and allocation in the human lineage, but direct measures of human and ape metabolism are needed to compare evolved energy strategies among hominoids. Here we used doubly labelled water measurements of total energy expenditure (TEE; kcal day−1) in humans, chimpanzees, bonobos, gorillas and orangutans to test the hypothesis that the human lineage has experienced an acceleration in metabolic rate, providing energy for larger brains and faster reproduction without sacrificing maintenance and longevity. In multivariate regressions including body size and physical activity, human TEE exceeded that of chimpanzees and bonobos, gorillas and orangutans by approximately 400, 635 and 820 kcal day−1, respectively, readily accommodating the cost of humans’ greater brain size and reproductive output. Much of the increase in TEE is attributable to humans’ greater basal metabolic rate (kcal day−1), indicating increased organ metabolic activity. Humans also had the greatest body fat percentage. An increased metabolic rate, along with changes in energy allocation, was crucial in the evolution of human brain size and life history.

The relationship between microbiota, short chain fatty acids (SCFAs), and obesity remains enigmatic. We employ amplicon sequencing and targeted metabolomics in a large (n = 1904) African origin cohort from Ghana, South Africa, Jamaica, Seychelles, and the US. Microbiota diversity and fecal SCFAs are greatest in Ghanaians, and lowest in Americans, representing each end of the urbanization spectrum. Obesity is significantly associated with a reduction in SCFA concentration, microbial diversity, and SCFA synthesizing bacteria, with country of origin being the strongest explanatory factor. Diabetes, glucose state, hypertension, obesity, and sex can be accurately predicted from the global microbiota, but when analyzed at the level of country, predictive accuracy is only universally maintained for sex. Diabetes, glucose, and hypertension are only predictive in certain low-income countries. Our findings suggest that adiposity-related microbiota differences differ between low-to-middle-income compared to high-income countries. Further investigation is needed to determine the factors driving this association.