You're crossing a street when your toe catches the edge of a curb. For a half second, your body has to decide what to do. A younger version of you would have caught it without noticing: one quick step, a snap of the hips, back to walking. This time the step comes a beat late. You get there, but it's a stumble, and your heart is pounding afterward. You tell yourself it was nothing.

It might have been nothing. It might also have been your first real encounter with a quality of muscle that almost nobody measures and almost nobody trains: power.

Strength and power are not the same thing

Strength is how much force a muscle can produce. Power is how quickly it can produce that force. Physiologists define it as force multiplied by velocity. Standing up from a chair slowly, using every bit of your effort, is strength. Springing up, catching a stumble, or taking the stairs two at a time without thinking is power.

The distinction matters because the two don't decline together. In the research on aging muscle, including a widely cited review by Reid and Fielding on power training in older adults, power tends to fall faster than strength. Part of the reason is that fast-twitch (type II) muscle fibers, the ones built for quick, forceful movement, are the ones that shrink most readily with age and disuse. Your slow-twitch fibers hang on. Your fast ones are the first to go.

That's the quiet reason power is a better early warning than most of the numbers you probably track. You can still lift a decent weight slowly and yet find that your reflexes with your own body weight have dulled.

Why a GLP-1 can put this under pressure

People on Ozempic or Mounjaro are in a calorie deficit, often a large one, with a smaller appetite and, for many, less protein than their muscles want. A deficit with low protein and no heavy or fast loading is exactly the setup in which the body sheds lean tissue along with fat. Clinical trials of semaglutide and tirzepatide have found that a meaningful share of the weight lost can be lean mass, though how much varies between people and studies, and lean mass on a scan isn't identical to muscle.

I'll be careful here: I'm not aware of good evidence showing that GLP-1 drugs specifically erode muscle power more than other weight loss. What we can say is that the conditions that threaten fast-twitch fibers (an energy deficit, less protein, and a tendency to move less) are common on these medications. And power is the capacity most people never deliberately train in the first place.

There's a second effect that has nothing to do with muscle. If you carry less weight, the same muscle moves a lighter body. Day to day you may feel lighter and spry. But the margin you have for the unexpected, the stumble, the slip on wet tile, the missed stair, depends on how much quick force you can summon in a split second. It's worth knowing whether that capacity is keeping pace.

What power training actually looks like

The word "power" suggests jumping and Olympic lifts, and that scares off exactly the people who need it. It doesn't have to look like that. In the trials on older adults, power training typically means ordinary exercises (leg press, chair stands, step-ups, presses) done with one change: you move the weight up fast and lower it slowly.

The principle is intent. Moderate loads, moved with the intention of speed, recruit more of the fast-twitch fibers than slow grinding does. You aren't trying to heave. You're trying to be crisp.

A reasonable template, adapted from how this is usually done in research settings:

  • Choose a load you could lift for many more reps than you'll do, often described as a moderate or fairly light weight rather than your maximum.
  • Do 3 to 6 reps per set, which keeps every rep fast. The moment a rep slows to a grind, the set is over.
  • Push up or out as fast as you can with control, then take two to three seconds to lower.
  • Rest properly between sets, around a minute or two, so each set stays sharp rather than turning into cardio.

This doesn't replace heavier strength work. It sits next to it. The heavy sets build the engine, and the fast ones train it to deliver.

Fuel and recovery still decide whether it works

Fast training is neurologically demanding, and it's done best when you're fed and rested. If you're under-eating protein, your muscle has little to build with, and the training signal goes to waste. Most guidance for people losing weight suggests aiming for a higher protein intake than the standard minimum, and your doctor or a dietitian can help you set a number that suits your kidneys, your medications, and your goals.

Spacing matters too. Because these sessions are short and low in volume, many people can fit them into existing strength days rather than adding new ones. And if the dose of your medication just went up and your energy is low, a crisp set of five is far better than skipping the session because you don't feel up to a hard one.

A note on safety

Speed adds risk if your form is sloppy. Start lighter than you think you need to. Use machines or a sturdy chair before free weights. Keep jumping or hopping out of it until you've built a base, and skip it entirely if you have joint problems, osteoporosis, or a heart condition without clearing it with your clinician first. The aim is quickness you can control, not a dramatic display.

Your next moves

  • Run a chair-rise speed test today. Sit in a sturdy chair with your arms crossed. Time how long it takes to stand up and sit down five times as fast as you safely can. Write the number down. Retest in four weeks. A time that's rising is information worth having.
  • Add one fast exercise to your next strength day. Take a lift you already do, like a leg press, goblet squat to a box, or a push press, and do 3 sets of 5 reps at a lighter load, driving up quickly and lowering for three seconds.
  • Stop each set when speed drops. If the bar slows noticeably, end the set. Quality of movement is the signal here, not exhaustion.
  • Check your protein before you train. Have a real serving of protein, such as Greek yogurt, a shake, or eggs, within a few hours of the session so the effort has something to build from.
  • Practice one balance-recovery habit daily. Stand on one leg while you brush your teeth, near a counter you can touch, for 30 seconds per side. It's small, and it trains the quick corrective reflex you want when a curb catches your toe.

What it comes down to

Weight loss is easy to see: the scale moves, the jeans loosen. Power is invisible until the moment you need it, and by then it's too late to wonder whether you built it. The people who come through a big weight loss feeling capable are usually the ones who kept asking their bodies for something quick and demanding while the pounds came off.

That's the thread Lean is built around: protein targets that keep your muscle fed, and strength tracking that shows whether your body is keeping up with your weight loss, not just shrinking. If you'd like a simple place to keep your protein, your lifts, and your trends together, you can take a look at Lean. Either way, go time your five chair rises today. Whatever you find, you'll know where you're starting from.