Study archive · page 20

Resistance training at longer versus shorter mean muscle lengths produced trivial differences in regional muscle growth across 12 studies in young adults, with no site differing by more than an estimated 1.88%. The conditions compared differed by an average of only 21.8% of muscle length.

⚠What it shows: Reassuringly consistent: results pooled from 12 studies, all in young adults, found tiny differences at every site along the muscle. But the long and short conditions differed by an average of only 21.8% of muscle length, so a full deep stretch against a tight partial has not really been tested.Meta-analysis · Int J Sports Med

A meta-analysis of 15 trials in healthy adults found eccentric training produced greater average muscle growth than concentric training, 10.0% versus 6.8%, but the difference did not reach statistical significance.

⚠What it shows: Fairly solid but not final: results pooled from 15 trials in healthy adults leaned towards eccentric reps, yet the gap was small enough that chance could still explain it. Both actions clearly grew muscle.Meta-analysis · J Strength Cond Res

In a meta-analysis of 84 randomised trials in 5065 people with high blood pressure, exercise cut systolic pressure by 7.52 mmHg and diastolic by 4.36 mmHg, and resistance training matched aerobic exercise.

⚠What it shows: Strong evidence: results pooled from 84 trials in which 5065 people with high blood pressure were assigned at random to exercise or not. The comparison was exercise versus no exercise, so it cannot tell any one person which type would suit them best.Meta-analysis · Hypertens Res

Regular aerobic exercise lowered resting blood pressure in healthy East Asian adults across 31 randomised trial groups totalling 1994 people, by an average of 4.7 mmHg systolic and 3.2 mmHg diastolic. Bigger systolic drops came from programmes meeting guideline volumes: moderate intensity for more than 150 minutes a week.

⚠What it shows: Strong evidence for a modest effect: results pooled from 31 trial groups covering 1994 healthy East Asian adults, so the averages describe healthy people rather than anyone already treating high blood pressure. The drops are real but modest, a few points on each number.Meta-analysis · Clin Exp Hypertens

Pooling 51 randomised trials with 3152 healthy adults aged 60 and over, structured exercise improved cardiorespiratory fitness and added an average 36.18 m to six-minute walk distance, whether the training was aerobic, resistance or a combination of both.

⚠What it shows: About as solid as exercise evidence gets: results pooled from 51 trials in 3152 healthy people aged 60 and over, with benefits holding across training types, programme lengths and both sexes. The trials used varied routines, so the ideal dose and mix of exercise remain open questions.Meta-analysis · Biol Res Nurs

Exercise training improved every measured heart rate variability parameter in adults with type 2 diabetes across pooled results from 21 studies of 523 patients, with the strongest evidence for endurance training and a suggestion that supervised programmes work best.

⚠What it shows: Encouraging rather than settled: results pooled from 21 studies of 523 people with type 2 diabetes, but fewer than half of those studies assigned people to exercise at random, so some of the benefit could come from who chose to train.Meta-analysis · PLoS One

Pooled results from 17 randomised trials suggest resistance training improved working memory and cognitive flexibility in adults aged 60 and over without cognitive impairment, compared with control conditions. It showed no advantage over other forms of exercise on any executive function measure.

⚠What it shows: Take this as promising rather than proven: results pooled from 17 randomised trials in adults aged 60 and over, but the programmes varied widely, many trials ran a high risk of bias and the authors rated the overall evidence low certainty.Review · J Am Med Dir Assoc

A systematic review identified eight studies of psilocybin therapy for major depressive disorder, including treatment-resistant cases, and found that one or two doses given with psychological support produced rapid improvements in depressive symptoms, with an increased sense of well-being lasting months.

⚠What it shows: Promising but early: a sweep of all the studies on this found just eight, some in people with treatment-resistant depression and some in people facing cancer, so it is far from settled treatment. Every dose was paired with structured psychological support, which is part of the therapy rather than an optional extra.Review · Behav Sci (Basel)

In an analysis of 23,417 people across six population datasets, depression was linked to reduced grey matter volume and cortical surface area in the frontal cortex, anterior cingulate and insula, but showed no correlates in the subcortical regions long thought to shrink with depression, while unexpected correlates appeared in somatomotor and visual regions.

⚠What it shows: A snapshot, not a cause: this links brain measures to depression in 23,417 people, so it shows what differs alongside depression, not what depression does to a brain. Its scale is the point, which is exactly why the missing deep-brain shrinkage is so notable.Study · Nat Ment Health

Across 72 studies of 3134 healthy people in 22 countries, a month of Ramadan daytime fasting produced only a tiny drop in fasting glucose and no meaningful change in insulin, insulin resistance, leptin or adiponectin.

⚠What it shows: Reassuring rather than revolutionary: results pooled from 72 studies of 3134 healthy non-athletes across 22 countries. Ramadan fasting bans food and drink in daylight hours only, so the findings may not transfer neatly to other intermittent fasting styles.Meta-analysis · Diabetes Res Clin Pract

In a network meta-analysis of 24 randomised trials with 1,694 people with overweight or obesity, adding aerobic exercise to calorie restriction lowered inflammatory markers including CRP, hs-CRP, TNF-α and IL-6 more than dieting alone. No exercise type produced a significant extra improvement in insulin resistance beyond the diet itself.

⚠What it shows: Reasonably solid on the headline result: findings pooled from 24 trials in 1,694 people with overweight or obesity, though several comparisons rested on only a few studies, so the ranking of exercise types is far from settled.Systematic review · Front Nutr

In a network meta-analysis of 158 trials with 17,059 people with type 2 diabetes, every form of exercise lowered HbA1c, with HIIT topping the ranking at a 0.61% reduction and even simple activity advice cutting 0.35%.

⚠What it shows: About as solid as exercise evidence gets: results pooled from 158 trials in 17,059 people with type 2 diabetes, all lasting at least 12 weeks. The rankings between exercise types rest partly on indirect comparisons, so the gap between HIIT and the rest is real but not ironclad.Meta-analysis · Diabetes Res Clin Pract

Acupressure improved sleep quality in older adults compared with controls across 11 randomised trials totalling 722 people. The benefit held even when participants were trained to apply the pressure themselves, though it looked smaller.

⚠What it shows: Promising rather than proven: results pooled from 11 small trials in 722 older people all pointed the same general way, but the studies disagreed with each other a great deal, so the size of the benefit is shaky.Meta-analysis · Explore (NY)

Digital psychosocial treatments for insomnia substantially reduced insomnia severity and improved sleep quality compared with no treatment across 37 randomised trials with 13,227 adults. They showed no significant difference from in-person treatment on insomnia severity, though face-to-face care kept an advantage on sleep quality, and guidance from trained human therapists improved results.

⚠What it shows: Strong evidence: results pooled from 37 trials covering 13,227 adults, with no sign that missing negative studies skewed the picture. The one clear gap is that face-to-face treatment still beat digital delivery on sleep quality, and programmes without a real therapist behind them did less well.Meta-analysis · J Med Internet Res

Omega-3 supplementation modestly raised adiponectin, a hormone released by fat tissue, across 52 trials with 4,568 participants, with the clearest gains at doses above 2000 mg daily taken for more than 10 weeks. Leptin, another fat-tissue hormone, did not budge.

⚠What it shows: Believable but small: results pooled from 52 trials in 4,568 people showed only a modest rise in adiponectin, and the trials disagreed with each other a lot, so the true size of the effect is uncertain. Leptin showed no effect at all.Meta-analysis · Crit Rev Food Sci Nutr

Across 69 randomised trials in 1937 adults, creatine plus resistance training improved bench or chest press strength by 1.43 kg and squat strength by 5.64 kg versus placebo, with gains in vertical jump and peak power too. Benefits were most consistent in younger adults and males, while handgrip and leg press showed no significant improvement.

⚠What it shows: About as good as supplement evidence gets: results pooled from 69 trials in 1937 adults. The weaker showing in women and older adults may reflect too few studies rather than no effect, and one author has advised companies that sell creatine.Meta-analysis · Nutrients

GLP-1 drugs were associated with a 40% higher risk of non-scarring hair loss in pooled data covering 1,091,743 patient-exposures, driven by telogen effluvium and pattern hair loss. Safety-report signals were strongest for semaglutide and tirzepatide.

⚠What it shows: A strong signal, not proof of cause: results pooled from 17 studies covering over a million patients' worth of drug use, most of which followed people rather than testing the drugs against a control. Rapid weight loss and the nutrient shortfalls it brings, rather than the drug itself, may be what triggers the shedding.Review · Skin Appendage Disord

Pooled data from 18 studies show no association between sunscreen use and melanoma, with earlier alarming findings explained by failure to adjust for sun sensitivity. There was no dose-response pattern with frequency or years of use.

⚠What it shows: Reassuring and consistent: results pooled from 18 studies found no link, and the supposed harm vanished once studies accounted for sun-sensitive skin. All of the studies followed people rather than testing sunscreen directly, and the authors note it may take decades to detect any protective effect of newer formulations, so the benefit side stays open.Meta-analysis · Ann Intern Med

Pooled results from 11 randomised trials lasting 8 to 24 weeks found intermittent energy restriction, including 5:2 regimens, produced essentially the same weight loss as continuous everyday dieting, with only a slight extra drop in fasting insulin of uncertain clinical relevance.

⚠What it shows: A trustworthy null: results pooled from 11 trials where people were assigned at random to fasting-style or standard calorie cutting, and weight loss came out the same. All the trials ran 24 weeks or less, so longer-term differences remain untested.Meta-analysis · J Transl Med

Resistance training improved sit-to-stand times and physical performance scores in frail and pre-frail adults over 65 across 10 randomised trials, with two weekly sessions the minimum and three appearing optimal; higher training volumes per session actually reduced the gains.

⚠What it shows: Solid for the headline finding: results pooled from 10 trials in 1303 frail and pre-frail adults aged 65 and over. Only a handful of studies measured each outcome, so the ideal training dose is a best estimate rather than a rule.Meta-analysis · Ageing Res Rev

A meta-analysis of 15 randomised trials found probiotics cut whole-gut transit time by 13.75 hours and added about one bowel movement per week in adults with functional constipation, with multi-strain products delivering benefits that single strains did not.

⚠What it shows: Among the better evidence you will find on this topic: results pooled from 15 trials in adults with functional constipation. But the trials were often poorly reported and participants usually knew what they were taking, so the true benefits may be smaller than these numbers suggest.Meta-analysis · Clin Nutr

On the hottest days in 12 Chinese cities, stroke death risk was 1.63 times higher for ischaemic stroke and 1.36 times higher for haemorrhagic stroke than on typical warm days. Women, older people and those with less education were hit hardest.

⚠What it shows: A clear pattern rather than proof: researchers compared death records with temperatures across 12 cities, following what happened rather than testing anything, so other hot-day factors could play a part. The link held after accounting for air pollution, humidity and season.Meta-analysis · Sci Total Environ

Across seven randomised trials in 423 women with PCOS, high-intensity interval training at 90 to 95% of maximum heart rate, three times a week for at least 10 weeks, reduced insulin resistance and BMI.

⚠What it shows: Credible for the headline result: results pooled from seven trials in 423 women with PCOS, and the certainty was rated moderate to high. Most trials were small and ran 10 to 16 weeks, so effects beyond insulin resistance and BMI are still unclear.Meta-analysis · PLoS One

In pooled trials of 939 adults aged 65 and over, accelerometer-based activity trackers significantly increased physical activity while simple pedometers did not.

⚠What it shows: Promising but wobbly: pooled results from nine trials in 939 people aged 65 and over, and most of those trials had a high risk of bias. Many bundled the tracker with coaching or other support, so the device's solo effect was never cleanly isolated.Meta-analysis · Exp Gerontol