Leg day is usually about the stairs, the hike or the squat you want to finish strong. A study that followed twin sisters for ten years found that the sister with more leg power also kept more of her thinking scores, and that link is worth reading closely.
The study comes from the twin research team at King's College London.1 In 1999 they tested 324 healthy female twins, aged 43 to 73 with an average of 55. A research nurse measured each woman's leg power on a machine built for the job, taking the best of three pushes with her dominant leg. Leg power is strength and speed together, so it shows how quickly your legs can produce force.
On the same visit each woman did seven short computer tests of memory and processing speed, which is how quickly the brain takes something in and responds. Ten years later, in 2009, they did the same tests again. The researchers then looked at whose scores had held up best.
The women with more leg power in 1999 showed less decline in their combined test score over the decade. That held after the team accounted for a long list of other factors measured at the start. Grip strength, lung function and the lean mass of the leg did not predict the change in the same way, and how active the women said they were had only a weak effect of its own.1
Twins let researchers ask a sharper question. Sisters share a family and a childhood, and identical twins share their genes too. In 42 pairs where one sister had clearly more leg power than the other, the stronger sister showed less decline. The result held in non-identical twins and fell short of significance in identical twins, where the authors note the numbers were small.1
About twelve years after the first visit, 20 pairs of identical twins had brain scans. More leg power at the start went with more total grey matter, the tissue where the brain does its thinking. In the nine pairs whose leg power differed most, the stronger sisters had more grey matter, and the weaker sisters had fluid-filled spaces inside the brain, called ventricles, that were 26% larger.1
This was a small group, and nobody had a scan at the start, so the scans show a difference at one moment rather than a change over time.
This was an observational study, which means the researchers measured people and watched what happened, without asking anyone to change how they trained. A study like that can show that two things travel together. It cannot show which one drives the other.
The authors say so themselves. They write that the imaging part of the study "cannot prove causality", and they raise the possibility that differences in how the brain controls movement could have given some women more leg power in the first place. They also suggest leg power may be a marker of how physically active someone is over the years, and that the activity is what matters. They call for confirmatory studies.1
There are other limits they list. The women were relatively well educated and in better health than the general population, there were no men, the tests covered memory and speed but not language, and there were only two time points. That is why we say linked.
A randomised trial is the stronger test, because people are assigned to training or to a comparison by chance. In Vancouver, 155 women aged 65 to 75 were assigned to strength training once a week, strength training twice a week, or balance and toning classes twice a week, for a year.2 The main measure was the Stroop test, where you name the colour of the ink a word is printed in while the word itself spells a different colour. It measures focus and the ability to ignore a distraction. Scores improved by 12.6% with once-a-week training and 10.9% with twice a week, and fell by 0.5% in the comparison group. One result went the other way: both strength groups lost more whole-brain volume over the year than the comparison group.2
In a second trial, 100 adults aged 55 and over with mild cognitive impairment, a measurable dip in memory or thinking, did high-intensity strength training or a sham exercise programme two to three days a week for six months.3 Strength training improved their thinking scores, and the gain in lower-body strength statistically accounted for that improvement, while the gain in aerobic fitness did not. These were people who already had some difficulty, so the result applies to people in that position.
A review that pooled 36 trials in adults over 50 found that exercise gave a modest improvement in thinking scores, and strength training was one of the types that showed a benefit. Across all types, sessions of 45 to 60 minutes at moderate intensity or more were linked to benefit.4 The authors rated the evidence as moderate quality, and noted that people in an exercise trial cannot be kept from knowing which group they are in.
Put together, the trials suggest strength training can improve some measures of thinking in the groups they tested. They do not show that it protects memory over decades, and the twin study is still the only one here that ran for ten years.
Whatever the brain link turns out to be, stronger legs carry you through the day. At the gym, squats, Bulgarian split squats, Romanian deadlifts and hip thrusts all work the legs, and two or three of them make a good session. Going a little heavier each time, 2 kg next week and 5 kg the week after, lets you see how far you can go. At home, taking the stairs over the lift, step-ups on a sturdy chair and lunges do the job.
Food is the other half. A review of 49 randomised trials with 1,863 people found that adding protein to strength training gave an extra 2.49 kg on the heaviest weight people could lift once, and an extra 0.30 kg of fat-free mass, which is everything in the body except fat.5
Carbs matter too. Your muscles store carbohydrate as glycogen, their fuel for hard work, and long, hard sessions draw it down. The International Society of Sports Nutrition notes that carbohydrate with protein around training may support strength and body composition, and that good-quality protein in the two hours after a session strongly switches on muscle rebuilding.6 So easy carbs before you train, a banana or toast with jam, and a high-protein meal with carbs on the plate afterwards cover both: protein to build the muscle and carbs to refuel it.
In a ten-year study of 324 twin sisters, more leg power was linked to less decline in memory and thinking scores, though the study cannot prove cause. Whatever the link between leg strength and the brain turns out to be, stronger legs carry you through the day. Eighty Thirty works out your daily protein and keeps count for you, so your training has what it needs, day after day. Start with our free macro calculator.
One ten-year study points that way. Among 324 twin sisters, those with more leg power, which is strength and speed together, showed less decline in memory and thinking scores. Grip strength and the lean mass of the leg did not predict the change in the same way.1
In some tests, yes. In a year-long Vancouver trial of 155 women aged 65 to 75, scores on the Stroop test, a measure of focus, improved by 12.6% with once-weekly strength training and 10.9% with twice weekly, and fell by 0.5% in the comparison group.2
Leg power is strength and speed together, so it shows how quickly your legs can produce force. In the twin study, a research nurse measured it on a machine built for the job, taking the best of three pushes with each woman's dominant leg.1
Because researchers measure people and watch what happens, without asking anyone to change. That can show two things travel together but cannot show which drives the other. The twin study authors suggest leg power may be a marker of how active someone is over the years.1
Yes, in a small group. Twenty pairs of identical twins were scanned about twelve years after the first visit. In the nine pairs whose leg power differed most, the stronger sisters had more grey matter and the weaker sisters had ventricles 26% larger.1
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