Your body has changed

I turned 40 and noticed something my mirror had been hinting at for a while. The shoulders that used to recover from a bad night's sleep took a week. The post-curry lethargy lasted into the next afternoon. The same workout that left me sore for a day at 28 left me sore for three.

This is not a complaint. It's an inventory.

Your body at 40 is not a broken version of your body at 25. It's a different machine running on a different operating system. The sooner you read the new manual, the sooner you stop fighting it.

The hormonal story

Testosterone in men begins a slow decline from around age 30, falling roughly 1% a year on average. That number sounds small. Compounded over fifteen years, it isn't. Lower testosterone tracks with reduced lean mass, slower recovery, and a flatter motivational baseline (the thing that used to get you out of bed at 6am for no reason).

Growth hormone and IGF-1 follow a similar curve. Cortisol tends to creep up, partly from life (mortgage, kids, work) and partly from worse sleep. Insulin sensitivity often drifts in the wrong direction, especially around the midsection.

You can influence almost all of this through training, sleep, and food. You cannot reverse the calendar. The goal isn't to be 25 again. The goal is to be the strongest, leanest, most mobile version of the man you actually are.

Sarcopenia is the quiet thief

Sarcopenia is the age-related loss of muscle mass and strength. It starts around 30 and accelerates after 50. Most men don't notice it because the loss is gradual and the bathroom scale stays roughly the same (muscle leaves, fat arrives, the number lies).

Here's what the evidence suggests: untrained adults lose somewhere between 3-8% of muscle mass per decade after 30, and the rate accelerates with each subsequent decade. Strength tends to fall faster than mass. Power (the ability to produce force quickly) falls fastest of all, which is why older people trip on stairs they used to bound up.

The intervention is not mysterious. Resistance training. Adequate protein. Repeated, week after week, year after year. The men in their 60s lifting heavy at my gym look like men in their 40s. The men in their 40s who stopped lifting in their 30s look 60.

Recovery is the new bottleneck

In your 20s the constraint on training was usually motivation or time. In your 40s the constraint is recovery. You can still hit the same workout. You just can't hit it as often.

Things that take longer at 40:

• Muscle protein synthesis after a hard session
• Tendon and connective tissue repair
• Glycogen replenishment after high-intensity work
• Central nervous system recovery from heavy lifting
• Sleep debt (one bad night used to be a free pass / now it's a tax)

This isn't a reason to train less. It's a reason to train smarter. Two heavy sessions a week with full recovery beats four sessions where you're always slightly broken. Consistency beats intensity over a year.

What's actually happening to your tissues

The collagen in your tendons turns over slower. Cartilage repair is less efficient. Your fascia gets stiffer if you don't move through full ranges. Your joints don't hate you. They hate being underused.

Bone density peaks in your late 20s and starts a slow decline. Resistance training (heavy enough to matter) is one of the few interventions that meaningfully slows it. Walking is good. Lifting is better. Both is best.

The cardiovascular system is doing its own thing. Max heart rate drops by roughly one beat per year. VO2 max declines around 10% per decade in untrained adults. In trained adults the decline is roughly half that. You don't get to opt out of ageing. You do get to opt out of accelerated ageing.

The mental shift

The hardest change at 40 isn't physical. It's the ego.

You used to be able to skip warm-ups, lift through soreness, drink on Saturday and run on Sunday. You can't anymore. Pretending you can is how 40-year-old men end up with shoulder impingements, lower back flares, and Achilles tendinopathy that lasts six months.

The men who do this well at 40+ share a posture: they take warm-ups seriously, they leave one rep in the tank, they sleep like it's part of the programme (it is), and they treat soreness as information, not a badge.

You're not training to peak at the next CrossFit Open. You're training so you can carry your kid up stairs at 60, hike a coastline at 70, get off the floor unassisted at 80. The horizon is longer. The volume is lower. The patience is higher.

What this series will cover

The next five modules walk through the levers that matter most at 40+:

• Strength as the foundation (heavy lifting > running for this age)
• Protein, sleep, recovery (the inputs that make the training count)
• Cardio that works (Zone 2, intervals, VO2 max)
• Mobility and injury prevention (the 10 minutes that prevent the 6 months out)
• A 12-week plan you can actually run

If you take one thing from this module, take this. The body you have at 40 is the most adaptive object you'll ever own. It still responds to training, food, and sleep with the same biology it had at 25. The dose is different. The direction is the same.

Train for the next forty years. Not the last forty.

Further watching

• Why Strength Is KEY for a Long, Healthy Life — Peter Attia (11:32)
• Testosterone & TRT — Peter Attia & Andrew Huberman (16:51)