Taking more than 2 or 3 HIIT classes a week could stall your progress, according to personal trainer for a top studio

• High intensity interval training (HIIT) is a popular workout style for fitness and weight loss.
• But too much HIIT can cause injury and burnout and stall gains, according to a personal trainer.

Too many HIIT workouts a week can slow your fitness progress and lead to injury and burnout, according to a personal trainer for a national fitness studio.

High-intensity interval training (HIIT) is a popular workout style involving periods of max-effort exercise with short, limited rest periods to help elevate your heart rate, burn calories, and boost your endurance.

But many people struggle to meet their fitness goals by overdoing HIIT, according to Amanda Butler, a personal trainer with seven years of experience. Butler works for a well-known gym franchise famous for HIIT classes, but said she couldn't name the brand for PR reasons.

She posted in a popular TikTok video that many of her clients attend five or more HIIT classes a week, ending up with fatigue, burnout, or injuries instead of results.

She clarified that HIIT itself isn't the problem and can be a useful tool, but too much of it is detrimental to building strength and muscle or burning fat.

"Some clients, they look the same today as they did a year ago. They aren't able to build muscle or lose weight because there's no progressive overload and they're burning their bodies out," Butler said. "I want to make sure workouts are working for them, not against them."

Constant fatigue and soreness are red flags that you're exercising too much

For some fitness enthusiasts, exercise can turn into something akin to an addiction, chasing the endorphin rush of a high heart rate sometimes called a runner's high. The feel-good chemicals released during exercise aren't necessarily a bad thing, and can improve performance and motivate you to keep a consistent workout routine.

However, if you're unable to slow down or stop even when you're injured, it may be time to re-consider your workouts.

"It's so ingrained that doing more is better, sweating buckets and being in pain is a good workout and it's really hard to break that mindset," Butler said.

She said she personally suffered from overtraining, including burnout, fatigue, and hormone disruptions, and was recently diagnosed with an autoimmune disorder called Hashimoto's disease.

"I experienced first-hand the damage of this and I don't want people to go through it," she said.

It's possible to overdo any kind of exercise, but excessive, strenuous HIIT classes can be especially hard on the body, messing with your metabolism and blood sugar over time, research suggests.

Warning signs of overtraining include a lack of progress, constant fatigue, soreness that doesn't go away, and injuries — you shouldn't be starting your workout exhausted or trying to push through pain, according to Butler.

For best results, combine HIIT with strength training and good recovery

While some HIIT has benefits like revving up your metabolism and boosting mental health, it isn't the best option for everyone, and more isn't necessarily better. Butler said two classes a week is plenty, three at the most if you have fitness experience.

"Every body is different. Listen to your body. If you're feeling good, you're walking out feeling energized and strong, then you should do what works for you," Butler said.

To build muscle, prioritize heavy weight lifting and a technique called progressive overload, gradually increasing weight over time to get stronger, said Butler. Evidence suggests as few as two days a week of weight lifting can help you build strength and muscle.

If you're looking to lose weight, resistance training is still key, although you may want to add some HIIT or cardio at the end of your workouts, or spend less time resting between sets to keep your heart rate up, she said.