NEW YORK – The first weeks of a new exercise routine can be hard. Your muscles tremble, your lungs burn, your heart races.

But after a month or two, it gets easier: You are running faster and longer, or lifting weights with more ease. Then suddenly, progress slows or stalls. You have hit a workout plateau.

Such periods, when you stop seeing fitness improvements despite continuing to train, are common, said Mr Chris Perrin, a personal trainer and co-owner of Cut Seven, a gym in Washington, DC.

“I’ve yet to meet a fitness enthusiast who hasn’t hit (a workout plateau).”

Plateaus can happen once the body adapts to a new workout. After just a few training sessions, the brain can become more skilled at telling muscles to move. And, usually over the course of weeks or months, the body itself changes.

For example: “The heart gets stronger and better at pumping blood to the muscles,” said Mr Jeff Horowitz, an exercise physiologist at the University of Michigan.

But plateaus can also be caused by insufficient recovery, such as skimping on sleep or doing another intense workout too soon.

With your tank half-full, you may struggle to push yourself, making it likelier you will get stuck in a rut.

For those who are satisfied with an exercise routine that feels similar from one day to the next, a plateau is not necessarily a problem.

“I’m trying to maintain my fitness as I continue to get older,” Mr Horowitz said. “So to me, a plateau is a good thing.”

But for those who want to continue improving, the key is to challenge muscles in new ways while ensuring you rest properly.

Here are some strategies for moving beyond an unwelcome plateau.

Increase the stress

Exercising multiple muscles at once saves time, but it is not the best way to increase strength if your body has adapted to it, said Mr Jeremy Loenneke, an exercise scientist at the University of Mississippi.

A bicep curl with a lunge is great for overall fitness, but it short-changes your leg muscles, which can bear more weight than your arms.

Focus your workout with leg press machines or heavy squats, said Ms Fiona Judd, a personal trainer in Orem, Utah. Or add a few pulses to every squat – lifting and lowering an inch from the deepest part of the movement.

Another option is to wear a cuff around a muscle during exercise. This practice, known as blood restriction therapy, limits blood flow to mimic the effect lifting weights has on the muscle.

“It allows your muscles to work smarter, not harder”, gaining strength while lifting less weight, said Mr Brian Grawe, a sports medicine physician at the University of Cincinnati.

While the tool is safe, he recommended consulting a personal trainer or doctor before using one.

Go longer, not harder

For endurance training, such as cycling or running, athletes often encounter plateaus when they have too many intense workouts in a row, said Ms Elisabeth Scott, a marathoner and running coach with the coaching website Running Explained. It is difficult to add mileage if you are always going all-out.

Although it may be counterintuitive, throttle down the pace so that you can make your runs or rides longer or more frequent.

“The bulk of your training – 80 per cent, for example – should be at a conversational pace,” Ms Scott said. Round out your week with one to two faster workouts to develop power and speed.

Switch it up

Another way to challenge your body is to change the focus of your workouts every few weeks or months.

Ms Holly Roser, a personal trainer in San Francisco, suggested playing with variables such as weight, rest and the number of repetitions or sets.

For example, add 2 pounds (0.9kg) to each hand in your dumbbell chest press and switch from three sets of 15 repetitions to three sets of 10.

The waxing and waning of race seasons creates another way to mix things up. You can train for a half-marathon in one season, for example, and then focus on speed or strength in the next, Ms Scott said.

Do not forget to recover

While you are buckling down, do not neglect recovery time. Without it, you can plateau or even regress, Mr Perrin said. It is important to get enough sleep, rest for a day or two between especially hard workouts and eat a balanced diet.

But rest does not have to mean vegging out on the couch. Swop your bike for salsa dancing or ditch the dumbbells for a yoga class.

Switching gears like this gives your target muscles – and your mind – a break.

It is also important to quickly supply post-workout muscles with nutrients to rebuild. Research suggests this window of opportunity is longer than once thought – up to 24 hours after exercise.

“Spread your protein intake out over the course of a day to maximise the benefits,” said Mr Christoph Handschin, a muscle researcher at the University of Basel in Switzerland.

Workout plateaus are an inevitable part of any fitness journey, but they are also an opportunity to reflect, Mr Perrin said.

“It’s a chance to listen to your body, figure out what it needs to improve and reconnect to what you love about exercise.” NYTIMES