How to build leg muscle without joint pain, according to a personal trainer

• You don't have to suffer through pain to get a good leg workout if squats or deadlifts hurt your body. 
• A personal trainer said there are way to modify exercise to protect your knees, back, and hips. 
• Start by assessing the problem, then use strategies like eccentrics or machine exercise to build strength. 

Don't let sore knees derail your next leg day — you can build muscle and strength in your lower body and avoid joint pain with the proper routine, according to a personal trainer. 

"Many trainers will tell you to squat and deadlift. They're fantastic exercises, but if someone is having joint pain during them, it's possible they don't have stability through the full range of motion," Darlene Marshall, certified wellness coach with the National Academy of Sports Medicine, told Insider. 

To make progress while avoiding aches and injury, prep your body appropriately for your workout, choice the right exercises and (ideally) work with a professional to find the source of the problem for your long-term health and fitness, she said. 

Get a movement assessment 

Even if you plan to work out on your own, it's always a good idea to invest in a few good sessions with a personal trainer first, Marshall said. Working with a professional can help you identify the source of any problems and come up with a plan to safely work out. This can be particularly helpful because, in some cases, the joint or area that hurts is actually just a side effect of tightness or imbalance somewhere else, according to Marshall. 

"It's called the 'bad neighbor theory.' A lot of times pain in the knee, for instance, is because you don't have proper hip or ankle range of motion. You feel it in the knee because it's the workhorse of the lower body, taking up the movement," she said. 

Warm up correctly

Skipping your warm-up is a common workout mistake. Starting with dynamic exercise and soft tissue work, like foam-rolling or using a massage gun, can help get your blood flowing so you'll have a better session, Marshall said. 

For best results, avoid just holding a few stretches as a warm-up. Instead, practice movements similar to what you'll be doing in the workout, such as glute bridges, clam shells, or calf raises for a lower body day, she said. 

"Static stretching is not a particularly effective way to repattern movements," Marshall said.

Try eccentric exercise for more gains without pain

If your main goal is to build muscle and strength safely, Marshall said a great technique is eccentric exercise, in which muscles contract while lengthening. 

Research suggests eccentric exercises is ideal for gains because it keeps the muscles under tension, prompting them to grow back bigger and stronger. 

To use this technique on leg day, emphasize slowly lowering the weight with control as you return to the start position in movements like a rack pull deadlift or dumbbell Romanian deadlift. 

Use exercise machines to build up strength and muscle

Exercise machines sometimes get a bad reputation because they focus on isolating certain muscles, rather than requiring the whole body to stabilize, as with free weights like barbells, dumbbells, and kettlebells.

"There's this impression in the fitness industry that using machines means you're not serious enough," Marshall said. 

But that's exactly what makes exercise machines helpful for beginners as well as people with pain or joint issues, since they require less mobility and you can find a range of motion that works for you, she said. To build muscle, try machine movements like eccentric hamstring curls or quad extensions. 

Stick to moderate weights to prioritize good form 

Finally, a key to avoiding injury is choosing a weight that is challenging, but one you can control. Marshall recommends starting light and working your way up — and not to worry if you don't feel completely exhausted after. 

"A lot of people think being too sore to move two days later is a sign of victory, but it means you over-damaged the muscles," she said. "I would rather have a moderate amount of stimulus that builds connection with that muscle group."