Science

The research the BLOCKS assistant answers from: 1,544 studies and 96 guides, each graded for how strong the evidence is and who it was measured on, with a link to the original paper.

Three kinds of entry: a principle is how the body works, agreed across reviews; a study is what one experiment measured; a guide is what to do.

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Youth sport went with more bone and lean mass in young men and less fat in young women: in the Iowa Bone Development Study (328 people measured by DXA and CT at 23), men who played organised sport throughout childhood and adolescence had 377 g more bone mineral, 1.6 kg/m² more lean mass index and stiffer shin bones than men who never did, and those who dropped out still had much of the difference, while women with consistent sport had 1.4 kg/m² less fat mass index (p = 0.04, above the authors' corrected threshold of 0.01). Read in fullMain caveat: Observational: families and children who choose sport may differ in ways not measured (calcium and protein intake, stress and others named by the authors).Kwon 2025

Childhood aerobic fitness says little about aerobic fitness in mid-life: in 748 schoolchildren followed for 34 years, childhood cardiorespiratory fitness correlated r = 0.30 with young-adult and r = 0.16 with mid-adult fitness; a three-sentence abstract with no methods. From the abstractMain caveat: Three-sentence abstract: no test, ages, retention, adjustment or intervals.Guo 2024

Fitness carries over partly from youth into adulthood: in 21 prospective studies (6197 people at follow-up, mean 20.8 years) the correlation between youth and adult values was 0.38 for cardiorespiratory fitness, about 0.5 for muscular strength and endurance and 0.69 for sit-and-reach flexibility, slightly stronger in women and from adolescence, with very high heterogeneity. From the abstractMain caveat: Abstract only; risk-of-bias results not seen.García-Hermoso 2022

A sporty childhood goes with only a slightly higher chance of an active adulthood: across 38 studies (63,158 people, mean follow-up 20.9 years) physical activity tracked weakly from youth into adulthood (r = 0.14) and youth sport participation a little more (r = 0.26), both more strongly into the twenties than later and fading slightly with longer follow-up; mostly self-report and unadjusted correlations. Read in fullMain caveat: Mostly self-reported activity, much of it retrospective, open to recall bias over long follow-ups.García-Hermoso 2025

In Danish sports decided by centimetres, grams or seconds, athletes who reached elite level had specialised later and trained less as children than near-elite peers but stepped up their training more in late adolescence, while how much they did other sports neither differed nor predicted elite status; 243 athletes, a retrospective survey, with no numbers in the abstract. From the abstractMain caveat: Abstract only, with no numbers.Moesch 2011

Adult world-class athletes had done more coached practice in other sports as children and teenagers, started their main sport later, accumulated less main-sport practice over their careers and progressed more slowly than national-class peers, the reverse of what went with junior success; peer-led play had only negligible links with either, in a meta-analysis of 71 reports (9241 athletes, GRADE moderate to high for these predictors) built on retrospective sport histories. Read in fullMain caveat: Retrospective, self-reported sport histories; confounding and survivor bias cannot be excluded (the authors).Barth 2022

By topic

Physiology basics47 principles Endurance physiology2 guides · 201 studies Intervals & intensity134 studies Periodization, taper & overtraining106 studies Strength & power1 guide · 166 studies Nutrition & fuelling2 guides · 207 studies Heat, altitude & travel63 studies Sleep, recovery & monitoring3 guides · 135 studies Warm-up, pacing & the mind81 studies Running, injury & shoes136 studies Cycling, bike fit & indoor50 studies Women's health46 studies Masters, youth & para49 studies Health, longevity & sports medicine27 studies Other sports1 guide · 120 studies Frameworks & athlete types87 guides · 23 studies

Guides

A guide pulls the studies on one question into a decision: what to do by default, for whom, and what the evidence cannot yet say. All 96 guides →