But going too hard, too fast is a recipe for disaster, as one teen found out. He was diagnosed with a dangerous condition called rhabdomyolysis after just one intense workout.
Jared Shamburger, a 17-year-old from Texas, had just acquired a gym membership and immediately got stuck into a 90-minute weight lifting session last week.
His dad and brother had been lifting weights for years, but he was only just starting out.
"I gotta catch up to them and get as big as them," Jared said to news station KTRK. "I have to go hard fast."
That was a mistake.
While it's normal to get some muscle soreness if you haven't been exercising for a while, after his intense workout session Jared complained of soreness and swelling that just wouldn't go away.
"Everything hurt. It hurt to the touch. It was swollen," Jared said.
His mum Judy, checked his symptoms online (which, by the way, is not recommended) and found information about rhabdomyolysis – a condition in which muscle breaks down extremely rapidly.
"The mama bear in me kind of took over and I called the pediatrician and said, 'I really think my son has rhabdo,'" Judy told KTRK.
Rhabdomyolysis - rhabdo for short - happens when skeletal muscle tissue gets damaged, swells up, and starts rapidly breaking down, leaking various molecules into the bloodstream.
Amongst these leaked substances is a protein called myoglobin, which normally sits in muscle tissue binding iron and oxygen. When it starts coursing through the bloodstream, it clogs up the kidneys, which is why rhabdo can lead to kidney failure if not treated.
On top of that, the destroyed muscles also leak several ions and enzymes, which can potentially disrupt heart rhythms and cause other troubles in the body, such as dangerously low calcium levels.
This type of muscle damage usually happens when people are injured through being crushed, but it can also happen due to strenuous exercise, or certain medications or drugs. Symptoms include muscle pains, vomiting, confusion, an irregular heartbeat and tea-coloured urine.
Treatment usually includes large quantities of intravenous fluids and rest. In worst cases, patients can also undergo dialysis.
"If he hadn't caught it, if he hadn't told me, if we had just gone out of town about our way," Judy said, "I can't even imagine. And I don't want to, about what could have happened."
Jared was in hospital for five days, but is expected to make a full recovery.
His story serves as a warning for potential gym junkies – the gym, or just getting some exercise in general is great for your health, but don't overdo it.
And if you've been crunching and notice tea-coloured pee or really, really sore muscles – maybe time to check in with the doctor.