Why do my veins pop out when I lift heavy weights?

This is a re-post of our most searched and read article ever! Enjoy!


I just got home from the gym. It was a hard muscle day, and I’ve done a lot of bicep, tricep, and chest work. Lots of push-ups, some dips, and some push jerks. Very dynamic, and helpful movements for building upper body strength. As I walk in the door, my wife looks at me and goes “oh my God, look at your arms!”

Now, all I know is that my arms are sore, and they’re going to be more sore tomorrow. So I look at her and I ask her what she’s talking about. She takes my arm, pulls it out in front of me, and says “look at your veins; they’re popping out all over the place!”

Looking down at my arms, I see that she’s absolutely right. All the veins in my arm, from the back of my hand all way up my forearm, are bulging out noticeably. I look like what one might call a “phlebotomist’s dream”. Looking at my other arm, I see the exact same thing, but I notice it’s only happening on the muscle groups where I spent the most time. It’s also only happening on my arms, but that’s more my personal physiology than anything else.

So, has this ever happened to you?

Now that I know to look for it, I see that it happens to me basically every time I work out, especially whenever I’m going hard on my arms. You see, your body responds very specifically to different kinds of stress. The reaction you see in your veins, i.e. when they bulge out like that, is one of those physiological reactions. It’s a response to the muscular need for oxygenated blood in support of energy needs during stressing activities.

When you exercise, your body moves through several stages of energy production. In order from strongest/shortest to weakest/longest they go:

Stage 1: Phosphogen

This initial stage lasts about 10 seconds and is the first one to provide energy to any given muscle in response to a strong stimulus. A molecule stored in your muscles, called phosphocreatine (PC), breaks down and releases a ton of energy, powering something quick like a 100m sprint or a challenging power lift.

This part of the energy system is very quick. If you were to run 100m, you would basically use all the PC stored in your leg muscles by the end of it. You would then need recovery time to build it back up.

This system is useful because it lets us output a huge amount of power at a very short notice. It is necessary for quick, powerful movements to occur.

Stage 2: Anaerobic Glycolysis

I know, those are some SAT words up there, but it’s simple. “Anaerobic” just means you don’t need oxygen to be present to obtain energy from this part of the system. The “glycolysis” part means that we are breaking down “glucose” – ya know, sugar! – to meet our energy needs.

Now in this system, the breakdown of sugar isn’t all neat and clean. The sugar is partially broken down to provide energy, and the main leftover is called Lactic Acid. This is the gunk that builds up in your muscles and causes some of that soreness over time.

This part of the system is responsible for any muscular work that lasts between 11 seconds and 2 minutes. It’s also important because it lets us power any activity that takes 1-3 minutes, such as long distance sprints, or that last little “oomph!” at the end of a 1500m run.

Stage 3: Aerobic

If “anaerobic” means “without oxygen” you can probably guess that “aerobic” means we’re now using oxygen. This is a complicated system that uses oxygen to breakdown glucose, which goes through a multi-stage process to produce a ton of ATP (adenosine triphosphate), which is the energy for your muscles.

This part of the energy system dominates after the 5 minute mark of exercising, where it will account for about 50% of all the energy going into your muscles. With extreme long term exercise, like a marathon, the aerobic system will account for more like 95-98% of all energy being produced.

“Holy Crap, I just want to know why my veins are gigantic?!”

I know, I know! Stick with me, we’re almost there!

So, you’re doing a ton of arm exercises: bicep curls, push-ups, tricep kick-backs, handstands, chest presses, and whatever else you can move with your arms at the gym.

For those first few movements, your body kicks in the phosphogen system and energy explodes out. Man, this is easy! One, two, three, four, five…you rep through fifteen good reps at a great pace. It’s like you’re not even lifting, bro!

You set the weight down, take a shot of water, and then go back to set number two. Ok, little harder this time; the phosphogen system is used up and anaerobic glycolysis has kicked in. You rep out the next two sets with some muscle fatigue kicking in, but you’re still pretty strong.

You get through 4 good sets of your workout, with a little rest in between. You notice that your heart is pumping a little heavy. Your breathing is a little quicker. You keep on with each rep, each set, and your blood pumps hard. You look down and your veins are popping out of your arms!

You’re in full-blown aerobic energy mode, son. You’re demanding that your muscles keep going, so they’re demanding more energy. They can’t get that energy from phosphocreatine anymore and the lactic acid system is spent. They need oxygen and the only way that’s getting there is, you guessed it, by the bloodstream!

You breathe hard, filling your lungs with huge amounts of air, and your lungs work with your heart, arteries, veins, and everything in between to get that oxygen into that blood, and get that blood to those muscles.

Your blood pressure goes up, and you can see the strain that your vascular system is under by the way your blood vessels are standing out. You’re in Beast Mode, man, and your arms know it!

So, yeah, that’s why your veins/arteries stand out when you lift. Thanks for stopping by. Go lift something heavy!