A strength training expert, who runs the 'hardest workout in NYC,' shares 3 moves to build muscle fast

• James McMillian is the president of Tone House, a strength training facility in New York City.
• McMillian shared a few tips for building muscle fast, especially if you don't have a lot of time.
• Compound exercises work multiple muscle groups simultaneously, while explosive movements develop power and speed.

Since childhood, James McMillian has learned the value of slowly getting stronger.

McMillian said he was diagnosed with asthma when he was born, and doctors advised his parents against letting him play sports like youth tackle football. "It made me tell myself that I need to train harder," McMillian told Business Insider.

Before and after practice, McMillian recalled running up the stadium steps six times. He'd also run to practice or run home with his sports equipment. Even though his asthma wasn't induced by sports, he noticed that the extra training kept him from being as winded.

McMillian is now the president and a trainer at Tone House, a strength training and conditioning-focused training facility deemed by Business Insider as "the hardest workout in New York City." He applies that same mentality from his upbringing to Tone House workouts that he coaches.

"You're going to be exposed for your weaknesses, but then you should always turn your weaknesses into your strengths," he said.

McMillian believes progressively overloading — slowly adding weight, reps, or intensity — is the best way to build strength.

"I always tell people, 'If you don't use it, you'll lose it," he said, particularly since we lose muscle mass as we age. "You're going to want to pick up your kid. You're going to want to hold those groceries. You're going to want to hold your Louis Vuitton bag a little bit longer at an event. You have to be strong to do that."

McMillian shared a few of his favorite quick movements to build muscle, whether you're a complete beginner, pressed for time at the gym, or wanting to speed up your progress.

Raise a glass to goblet squats

McMillian's favorite movement for beginners is the goblet squat, or squatting while holding a heavy kettlebell or dumbbell.

"When you're going into that squat, as you allow those knees to go out, you're working that lower body, your glutes, your hamstrings," he said. At the same time, you're also engaging your lats, triceps, forearms, and upper back from holding the weight.

To make the goblet squat more challenging, he said, you can elevate your heels to focus on building quad strength. McMillian also said it's easy to start with a lighter weight, say 10 pounds, and gradually work your way up.

Save time with compound exercises

Some of the best time-savers are compound exercises, which target multiple parts of the body at once and "allow you to shorten your time at the gym," McMillian said.

A favorite of McMillian's is transitioning from a squat to an overhead press, thus targeting both the upper and lower body.

He also likes to string together multiple consecutive movements. He opts for two rounds of 20 shoulder presses, 20 hammer curls, and 20 bent-over rows, all right after each other to activate different parts of his upper body.

"It's intense, it burns, but it's something that people can do with a single dumbbell," he said, thus also saving time on swapping out equipment.

It's also customizable, he said: You can use lighter weights and do fewer reps, but increase the number of rounds, for example.

Play with tempo

Explosive exercises — deliberately slowing down your tempo and "exploding" at the end of the movement — are also great for improving your strength, McMillian said.

He's a fan of slowing down his back squats: lowering slowly for five seconds, pausing for another five at the bottom, and then quickly pushing up.

"When you do things a little bit slower, controlled, it builds strength," he said, noting there's more than one way to challenge yourself.