Training rewires your brain, and the rewiring appears to be what makes training work. When researchers silenced a small group of neurons was silenced, the same workouts produced almost no gain in endurance. A new study suggests the brain may be directing the endurance gains we usually credit to muscle. Researchers at the University of Pennsylvania, UT Southwestern, and the Jackson Laboratory studied neurons in the ventromedial hypothalamus that express a protein called SF1. The hypothalamus is a small brain region that helps control energy balance, blood sugar, and how your body uses fuel. These SF1 neurons were already known to matter for metabolism, but their role in exercise adaptation was unclear. The experiments were done in mice. The question: does the brain just reflect the benefits of exercise, or does it help produce them? This matters for aging because endurance capacity, the ability to keep producing energy over time, is tied to fitness, metabolic health, and resilience. If the brain helps drive those gains, then how it responds to exercise becomes part of the story. A few terms. Endurance capacity here means how far a mouse could run on a treadmill test that got faster until exhaustion. Excitability is how readily a neuron fires. Dendritic spines are tiny protrusions on a neuron that receive incoming signals, so more spines means more input. What the researchers found: • Silencing SF1 neurons left maximal oxygen uptake (VO2 max) unchanged but cut treadmill distance by more than half, and the animals burned through carbohydrate faster instead of using fat • After 3 weeks of training, control mice improved their endurance by roughly 900 meters. Mice with silenced SF1 neurons did not improve • The usual training-driven gene changes in leg muscle were nearly abolished in the silenced mice, including genes tied to mitochondria and fuel handling • A single run increased the share of SF1 neurons expressing Bdnf, an activity-linked gene, from 34.5% to 42.2% • Imaging 93 neurons across 4 mice showed that after a week of training, the share of neurons activated at the end of a run rose from 31.8% to 53.2% • Recordings from SF1 neurons showed firing rates of 6.8 Hz in trained mice versus 2.4 Hz in sedentary mice. Over a third of neurons from sedentary mice were silent, compared with none from trained mice • Training roughly doubled excitatory input to these neurons and doubled their dendritic spine density • Inhibiting SF1 neurons for just 15 minutes after each session cut the first-week endurance gain from about 600 meters to about 220 meters and blunted the post-exercise rise in blood glucose • Stimulating them for 60 minutes after each session roughly doubled the endurance gain by week 3 compared with controls, about 1,650 meters versus 800 meters One way to read this is that exercise leaves a memory in the hypothalamus. Each session strengthens the connections onto SF1 neurons, so they fire harder after the next one. Think of it like a path through a field that gets easier to follow each time you walk it. That post-exercise burst appears to help coordinate recovery and muscle remodeling. One possible route is raising blood glucose, which gives the body fuel to refill energy stores after a hard session. Another is switching on programs like PGC-1α, a master regulator that tells muscle to build more mitochondria and improve its capacity to use oxygen. This is consistent with the blunted glucose rise and the muted gene changes in muscle when the neurons were silenced. This seems to be a feed-forward loop between body and brain in which exercise strengthens the neurons, the stronger neurons help the body adapt, and a better-adapted body can then do more work in the next session, which strengthens the neurons further. Some important caveats, as always. The big one: This was done in mice, with small groups, and the recordings and imaging used only males. Switching neurons on or off with light and viruses is far more extreme than anything a person does. We don't know whether the same neurons play this role in humans, and the study didn't test whether other exercise benefits depend on them. For now, the practical takeaway is modest. The signal that follows a session may matter as much as the session itself, which fits the idea that consistent training is what builds the response. Each workout seems to make the next one more effective, including in the brain. Recovery, adequate fuel after hard sessions, and regularity are the sensible levers, though this study didn't test any of them in people.

Strength training doesn’t need to happen in one session! An 8-week RCT found that splitting 3 sets of squats across the day produced similar strength and endurance gains to one session—with greater enjoyment. Small study, short follow-up. sciencedirect.com/science/ar…

Restoring one lipid in the muscle of mice that were dying young rebuilt their mitochondria, began reversing muscle loss, and fully rescued their lifespan. A new study shows how a lipid in the mitochondrial membrane, cardiolipin, seems to be a driver of muscle aging. The study asks a question the field has struggled with for years. As we age, muscle loses mitochondrial function. Yet the muscle that remains shifts toward fibers that depend more on mitochondria. If mitochondria are failing, why would muscle lean on them harder? And is the decline in mitochondrial function a cause of muscle aging, or just a bystander? The fiber shift matters for how you age. Your muscle is a mix of fiber types. Slow-twitch fibers are packed with mitochondria and burn fuel with oxygen, which suits endurance and posture. Fast-twitch glycolytic fibers rely more on breaking down sugar quickly, which suits power, like standing up from a chair fast or catching yourself when you trip. With age, the fast glycolytic fibers shrink first. You lose power before you lose endurance, and that loss tracks closely with falls and frailty. What drives that loss of power may start inside the mitochondria, with a lipid called cardiolipin. It makes up less than 2% of the fats in muscle, but it sits almost entirely in the inner mitochondrial membrane, where it shapes the folds that house the energy machinery. One enzyme, cardiolipin synthase 1 (Crls1), controls its production. Cardiolipin loss is already tied to disease, including Barth syndrome, a rare genetic condition that causes muscle weakness. What the researchers found: • Cardiolipin falls with age in muscle. It declined in 2-year-old mice compared with 9-week-old mice, and in people aged 53 to 69 compared with those aged 22 to 35. Crls1 activity dropped too. The human groups were small (4 young, 5 older), so treat that part as a signal, not a verdict • Cutting cardiolipin was enough to mimic aging. Deleting Crls1 in the muscle of young mice reproduced key features of aging: smaller muscles, weaker mitochondria, and the shift from glycolytic to oxidative fibers. Mice that lost it from early life also failed to grow normally after weaning • The fiber shift was a signal, not random damage. Low cardiolipin sent a message from the mitochondria to the cell nucleus through a receptor called estrogen-related receptor γ (ERRγ). That message made muscle cells take up more glucose and route it into pathways that produce antioxidants. Mitochondria make reactive oxygen species, the reactive byproducts of energy production, and damaged mitochondria make more of them • The damage was reversible in mice. Turning Crls1 back on in adult mice rebuilt cardiolipin levels, began reversing muscle atrophy, and fully rescued the early death seen in these animals One way to read this: the fiber shift may be muscle adapting, not just breaking down. When mitochondrial membranes falter, the cell leans on glucose to protect itself from oxidative stress. That protective response may come at the cost of the fast fibers that generate power. It would explain the paradox, because the cell is compensating for weaker mitochondria, not strengthening them. The limits matter. The mice lost cardiolipin through genetic deletion, which is far more abrupt than the slow decline in people. The human data show that cardiolipin falls with age, but not that the loss causes muscle decline in humans. And no supplement or drug was tested, so there is nothing here to take yet. What this means if you follow longevity science closely: most of the mitochondrial strategies people discuss, such as boosting NAD+ or clearing damaged mitochondria, work on how many mitochondria you have or how well they run. This study points to a different layer, the lipid makeup of the membrane they run in. That is a reason to be careful about treating mitochondrial health as one number. It also means you can't test for this yet. Cardiolipin isn't part of any standard panel, so the measures you can actually track are functional ones: grip strength, how quickly you can stand from a chair, and muscle power, not just muscle size. Still, the findings point to mitochondrial membrane health as an upstream target in muscle aging, and one that appears reversible, at least in mice. For now, the practical levers are the ones already known to support mitochondria. Resistance training protects the fast fibers that generate power. Aerobic training builds mitochondrial capacity. Adequate protein supports both.

Damn, when music was music 📷… two people, a guitar, a piano…. Miss these days James Taylor & Carole King - You've Got A Friend (BBC In Concert, 11/13/71)

Building muscle takes less training than you think. 💪 Meta-analyses show that a few hard sets per week can stimulate hypertrophy. The key? Train close to failure to maximize the stimulus per set. Less volume, more effort. Quality beats quantity. tandfonline.com/doi/full/10.…

👀 THE BEST SURGEONS DON’T JUST READ THE CASE. THEY READ THE ROOM. A hesitant resident. A subtle shift in tone. An unspoken concern. 🏈 Like an elite quarterback reading a defense, great surgeons anticipate problems before they unfold. 🎯 READ THE ROOM. LEAD THE TEAM. PROTECT THE PATIENT. #TheDailySurgeon #SurgicalLeadership

🥤 Diet drinks vs water for weight loss? In a 2-year RCT, non-nutritive sweetened läsk produced similar weight outcomes to water (−4.8 vs −3.7 kg; no significant difference) Diet drinks aren’t magic—but they don’t appear to sabotage weight loss either pubmed.ncbi.nlm.nih.gov/4254…