Science

The research the BLOCKS assistant answers from: 1,590 studies and 99 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.

All Principles Guides Studies

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1,245 entries

Resistance-training volume in adults aged 60 and overAcross 151 randomised trials the lowest weekly volume ranked most effective for the timed up-and-go, 6-min walk, lean mass and leg muscle size, moderate and high volume for leg strength, and only…Main caveat: Read from the abstract only; heterogeneity, risk of bias, the network's consistency, the GRADE certainty (if any) and the weekly-volume cut-points for each…Radaelli 2025

Rise and fall of physical capacity in a general population followed from 16 to 63Every capacity peaked by 36 and fell 30-48% by 63, the yearly loss rising from under 1% to about 2%, while the spread between people grew 3- to 25-fold and being active at 16, or becoming active…Main caveat: Aerobic capacity is estimated from heart rate at a submaximal workload (Åstrand nomogram, age-corrected), and at 16 from a 9-min run converted by regression.Westerståhl 2025

I'm stuck in bed for two weeks — how much leg muscle will I lose?In 12 healthy young men kept in strict bed rest for 14 days, thigh muscle volume fell 5% on MRI (7.1 → 6.7 L), leg lean mass 5% on DXA (10.2 → 9.7 kg) and thigh cross-sectional area 6% on CT, with…Main caveat: Population: 12 healthy young men; training status not reported here; no women, no older adults, no athletes.Fuchs 2025

I can only train once a week — or once a fortnight — for 3 months. Will I keep what I built?Once a week, yes; once a fortnight, partly. The same full session every 7 days held leg strength, quadriceps size and aerobic power for 12 weeks; every 14 days, by week 12, about half the size and…Main caveat: Population: untrained young women in their first 12 weeks of structured training (Tier 0-1); neither athletes nor men.Mpampoulis 2024

I spent a week in bed — how long before I'm back to normal?Plan at least 2-4 weeks of progressive rebuilding with strength work in it — the authors' advice after up to 28 days in bed, possibly longer after illness or injury. No study has measured real…Main caveat: Zero studies met the criteria. Everything comes from Tier 2 men and, for strength, countermeasures and recovery, from Tier 0-1 people.Spiering 2023

I took 3 weeks off — how much did I lose?Some aerobic capacity, not most of it: in trained endurance athletes who stopped completely, VO2max was about 4-7% lower after 12-21 days, about 10% after 5 weeks and 13-20% after about 8 weeks…Main caveat: No appraisal and no pooling. The review used PRISMA for the search but assessed no risk of bias and calculated no effect sizes.Barbieri 2024

Sex differences in durability following heavy intensity cycling exercise in trained athletesAfter 90 min at 110% of GET on water only, power at the first threshold fell 16% in men and 2% in women, while peak power, VO2peak and neuromuscular function fell alikeMain caveat: One laboratory protocol: 90 min, heavy domain, water only. No time trial, race or field outcome.Pastorio 2026

Host-diet-gut microbiome interactions influence human energy balance: a randomized clinical trialMain caveat: n = 17 young healthy adults, mostly Black (11 of 17); no athletes; habitual fibre was low (7.6 g/1000 kcal/day), so the MBD was a large change for them.Corbin 2023

Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food IntakeMain caveat: n = 20, 2 weeks per diet, no run-in or washout; ward setting, food free and chosen for participants, so cost and convenience did not operate.Hall 2019

Postprandial energy expenditure in whole-food and processed-food meals: implications for daily energy expenditureMain caveat: n = 17 young, mostly female adults, one test meal per condition, morning only, after a fast.Barr & Wright 2010

Role of Nonexercise Activity Thermogenesis in Resistance to Fat Gain in HumansMain caveat: n = 16 nonobese volunteers, 8 weeks, no control group; untrained general population.Levine 1999

The Response to Long-Term Overfeeding in Identical TwinsMain caveat: Men only, young, n = 24; no women, no athletes.Bouchard 1990

Energy-balance studies reveal associations between gut microbes, caloric load, and nutrient absorption in humansMain caveat: 21 men only, white, non-athletic; 3 days per diet; the obese group was severely obese (BMI 40.4).Jumpertz 2011

Walnuts Consumed by Healthy Adults Provide Less Available Energy than Predicted by the Atwater FactorsMain caveat: n = 18 healthy, mostly overweight, middle-aged adults; no athletes.Baer 2016

Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human dietsMain caveat: n = 18 healthy, mostly overweight, middle-aged adults (BMI 27.4); no athletes and no high energy intakes.Novotny 2012

Carbohydrate ingestion during prolonged exercise and net skeletal muscle glycogen utilization: a meta-analysisMain caveat: Mostly young men (273 of 279); the authors state that effects in women cannot be determined.Rothschild 2026

Graded carbohydrate ingestion up to 120 g·h−1 attenuates the reduction in critical power following 3 h of moderate-intensity exercise in a dose-dependent mannerMain caveat: One trial, n = 16, 15 of them men; one 3-h moderate preload at 95% GET in a laboratory (ambient conditions not reported).Norte 2026

Accelerating endogenous carbohydrate oxidation impairs durability of the moderate-to-heavy intensity transitionMain caveat: n = 11 trained cyclists, laboratory, one 2-h moderate ride at 90% of VT1.Maunder 2026

RCT in 320 novice runners: 2 weeks of gait retraining with real-time visual feedback aimed at lowering impact loading cut loading rates (d > 0.99) and was followed by 16% vs 38% running injury over 12 months (HR 0.38, 95% CI 0.25-0.59, 62% lower risk) versus treadmill running without feedbackMain caveat: Single club, novice runners; transfer to experienced runners is untested here.Chan 2018

550 injured recreational runners on an instrumented treadmill: strike pattern and peak vertical force were the only biomechanical variables that set one injury location apartMidfoot strike went with Achilles tendon injuries (OR 2.27), forefoot strike with posterior lower-leg injuries (OR 2.59), peak vGRF weakly with hip injuries (OR 1.14); loading rate and cadence did…Main caveat: Injured runners only: shows which pattern goes with which location, not who gets injured.Hollander 2021

827 US Military Academy cadets followed through 9 weeks of basic training: the longest ground contact times (>0.42 s) went with 2.15× the risk of overuse lower-extremity injury after adjustment, the shortest stride length with 45% more overuse injury (univariate), and foot strike pattern and cadence were not associated with injuryMain caveat: 9-week follow-up in military basic training (Inference: marching, mixed loads); transfer to recreational runners is uncertain.Helton 2025

Systematic review of 13 studies on foot strike technique and running-related injury: low evidence for any relationship; 3 of 6 categorical studies found more retrospective injury in rearfoot strikers and 1 found more risk with mid/forefoot strike, but these were very low quality; only 1 of 7 continuous-measure studies found a relationshipMain caveat: Only 13 studies, mostly retrospective and small; English-language only.Burke 2021

In 52 collegiate cross-country runners, about 74% had a moderate or severe injury each year; habitual rearfoot strikers had about twice the rate of repetitive stress injuries of habitual forefoot strikers, while traumatic injury rates did not differ significantlyThe abstract names no Achilles, calf or metatarsal resultsMain caveat: Retrospective injury history; one team; 16 forefoot strikers.Daoud 2012

Meta-analysis of 16 studies in adult distance runners: forefoot strikers land with a plantar-flexed ankle and a more flexed knee, and rearfoot strikers have higher vertical loading rates; the abstract reports kinematics and loading rate onlyRunning economy was not an outcome, and no knee-versus-Achilles load comparison is reportedMain caveat: Total participants and pooled effect sizes not given in the abstract.Almeida 2015

Natural forefoot-striking women (n=19) had lower patellofemoral contact force (4.3 vs 5.1 body weights) and stress (11.1 vs 13.0 MPa) and a lower knee frontal-plane moment than matched rearfoot strikers (n=19) at 4 m/s, but a higher ankle plantarflexor moment (3.12 vs 2.54 N·m/kg) and Achilles tendon force (6.3 vs 5.1 body weights)Main caveat: Women only; training level not specified in the abstract.Kulmala 2013

Habitual rearfoot and forefoot strikers at 4.5 m/s did the same total lower-limb work and average power; the load sat at the knee in rearfoot and at the ankle in forefoot running, and rearfoot strikers switched to an imposed forefoot strike raised the ankle internal rotation moment by 33%, kept knee abduction moments 48.5% above habitual forefoot strikers and raised total positive limb power by 17%Main caveat: Sample size, sex and training level not given in the abstract.Stearne 2014

Habitual rearfoot (n=19) and forefoot (n=18) runners on a treadmill at 3.0, 3.5 and 4.0 m/s: with their own pattern the groups did not differ in oxygen cost or carbohydrate use; switching to forefoot raised both in rearfoot runners at 3.0 and 3.5 m/s, switching to rearfoot changed nothing in forefoot runners, and at 4.0 m/s the forefoot pattern cost more oxygen with no difference in carbohydrate shareMain caveat: Acute, single-session treadmill test; no retraining period.Gruber 2013

2017 IAAF World Championship men's 10,000 m final (top 12 finishers, filmed on six laps): no rearfoot strikes at all, forefoot and midfoot strikers in similar numbers with similar finishing times, and no change in pattern even when speed fell and contact time rose mid-raceMain caveat: Twelve men in one race; no women, no slower finishers.Hanley 2024

Systematic review and meta-analysis of overground distance running (> 10 km, 12 studies): 79% of runners rearfoot strike early and 86% with increased distance; 11% change pattern, 84% of those from non-rearfoot to rearfoot; evidence for a performance advantage of non-rearfoot striking is inconclusive (5 studies for, 1 in women only, 4 no benefit, none favouring rearfoot)Main caveat: 12 observational studies; performance findings counted, not pooled.Bovalino & Kingsley 2021

At 8.1 km of a mid-size city marathon (1991 runners classified), 93.67% were heel strikers; foot-strike class differed with race position (Kruskal-Wallis P <.0001), with faster runners less likely to heel strike, and it did not differ by genderMain caveat: Single observation at 8.1 km; pattern later in the race not recorded.Kasmer 2013

2017 IAAF World Championship marathons (71 men, 78 women filmed at ~8.5, 19, 29.5 and 40 km): rearfoot striking was the most common pattern at every point (never below 54% of men or 67% of women), it did not separate top from bottom halves of the men's field, and more than 75% of athletes kept the same pattern across lapsMain caveat: Four filming points in one championship; heat, course and pacing of that race not described in the abstract.Hanley 2019

Filmed at 15 km of an elite-level half marathon (283 runners analysed): 74.9% rearfoot, 23.7% midfoot and 1.4% forefoot strikers; in the fastest group of 50 the split was 62.0 / 36.0 / 2.0%, so midfoot striking became more common with speed, and rearfoot contact time was longer than midfoot + forefoot (200.0 vs 183.0 ms)Main caveat: One camera point (15 km) in one race; only 283 of the four hundred fifteen filmed runners could be analysed.Hasegawa 2007

90, 120 and 150 g/h of glucose + fructose over 3 h of cycling in trained men: exogenous oxidation rose with the dose (1.23 → 1.48 → 1.62 g/min), whole-body carbohydrate oxidation did not rise from 120 to 150 g/h (2.6 g/min both), exercise capacity afterwards did not differ between 90, 120 and 150 g/h, and the modelled best dose was 107 g/h (95% CI 92-122) with wide individual variationMain caveat: n=8 trained males; no women, no untrained riders; competitive level not given in the abstract.Martyn 2026

A single run more than 10% longer than the longest run of the previous 30 days was associated with a higher rate of overuse running injury (HRR 1.64, 1.52 and 2.28 for runs >10-30%, >30-100% and >100% longer) in 5205 adult runners followed for up to 18 months with Garmin data; week-to-week change showed no relationMain caveat: Observational; injuries self-reported.Frandsen 2025

Recreational (half-)marathon runners (n=997): higher weekly volume and a longer longest run went with faster finish times; for the marathon a longest run under 25 km went with a slower finish (β 13.44, units not stated, likely minutes); no training characteristic was associated with injuryMain caveat: Observational and self-reported; fitter runners may train longer.Fokkema 2020

Elite cyclists, 7 weeks of intervals 3×/week in season with moderate-intensity volume cut by ~33% (~5 h/week) or kept: fresh ~20-min time trial improved (+3% and +2%), the time trial after a 120-min preload did not improve significantly overall (p = 0.19), and preload lactate fell only where volume was keptMain caveat: n=8 and 10, 7 weeks, in season; allocation not stated.Christensen 2024

Durability improved similarly after 10 weeks of low-intensity (6.8 h/week) or high-intensity (1.6 h/week) cycling in sedentary and recreationally active adults, measured over a 3-h ride at 48% VO2max; only high-intensity training raised VO2max, and the changes in drift were smallMain caveat: Untrained and recreational adults; 10 weeks; n=35 split into two groups.Matomäki 2023

Training twice every second day with low glycogen versus once daily for 3 weeks in well-trained cyclists (pair-matched, randomised): interval power was lower (297 vs 323 W), the time trial improved ~10% in both groups, and fat oxidation rose with the stacked scheduleMain caveat: n=14, 3 weeks; one time trial whose length is not given in the abstract.Hulston 2010

Twice every second day versus once daily for 3 weeks in trained cyclists: the same two sessions (100-min steady ride + 8 × 5 min) stacked 1-2 h apart went with higher fat oxidation and oxidative enzymes within that arm, a compromised interval session by the authors' conclusion, and ~10% on a 60-min time trial in both groups, no clear difference from training once a dayMain caveat: n=7 per group, 3 weeks, randomisation not stated.Yeo 2008

3 months of HIIT vs moderate-intensity continuous training (MICT) in obese adults: VO2peak +16% vs +6%; maximal fat oxidation rose only after HIIT; mitochondrial respiration rose in both (+36% vs +67%, no significant difference); after 4 months of follow-up only the HIIT group kept higher VO2peak and fat oxidationMain caveat: Obese, untrained adults; not athletes.Vaccari 2020