Take a look around your gym, and you’ll probably see people who are doing the same cardio routines, day after day, without gaining noticeable improvements in their body shape or composition. Maybe you’re one of them. When, every once in a while, someone shows up with an enviously sculpted body, you may wonder: What is she doing differently?

The answer is: She’s probably training the right way for her body type — something 70 percent of people are not doing, according to Phil Catudal, a celebrated National Academy of Sports Medicine (NASM)–certified personal trainer in the Los Angeles area.

“Each of us has a genetic and physiological design that determines our body type, or somatotype, and different body types have different responses to certain fitness programs,” says Catudal, a global health coach and the author of Just Your Type: The Ultimate Guide to Eating and Training Right for Your Body Type. (Full disclosure: I wrote the book with him from which the following tips come.) So it could be that you or the men and women you see at the gym are performing the right exercises the right way — but they’re optimal for someone else’s body type, not yours.

It’s a common mistake, Catudal says, and it can be easily remedied by properly identifying your body type — whether you’re an ectomorph, a mesomorph, or an endomorph — then figuring out how to challenge your body with the right regimen. (To get the process started, take the body type quiz.) Here are nine other things you probably didn’t know about the optimal ways to train for your body type.

1. There’s a Good Chance You’re Misclassifying Your Body Type

“Very few people see themselves accurately — in my experience, about 50 percent of people misclassify their body type,” Catudal says. Some endomorphs (who generally have a larger bone structure with wider hips, narrower shoulders, and more pear-shaped bodies) may believe they’re mesomorphs (who have naturally muscular, athletic builds). Meanwhile, some ectomorphs (who tend to be lean and slender with a small to medium frame and relatively long limbs) may identify themselves as endomorphs, especially if they have a soft midsection.

The most common reasons for these cases of mistaken identity? People have general body insecurities, they have become deconditioned, or they’re excessively critical of their bodies. It’s easy to fall into these traps, Catudal says. “The ‘body ideals’ that are portrayed in the media are often digitally altered or enhanced with special filters or other forms of manipulation. Which means they’re not real!”

And that can leave the rest of us with potentially warped perceptions of what descriptors like “slender,” “lean,” “muscular,” and “big-boned” actually mean.

2. Most People Are Hybrids of Two Body Types Rather Than Pure Breeds

In most instances, body types lie on a spectrum, which means that you could have a dominant body type with a few characteristics of another one or a body type that has qualities that are evenly divided between two different ones, Catudal says.

It’s kind of like personality types. We sometimes group people into general categories, but the good news is that being a combination body type means you have the strengths of two different body types to work with — for instance, you may naturally have both the endurance of an ectomorph and the muscle strength of a mesomorph, which can lead to big training gains.

“The most common natural hybrids are ecto-mesomorphs, who have long, lean limbs and broader chests and shoulders, and endo-mesomorphs, who have thick but compact physiques that are muscular, not soft,” he says.

Endo-ectomorphs, on the other hand, tend to have thin legs but substantial fat storage in the midsection — which is usually because they’ve spent years consuming a poor-quality diet and being sedentary. “This body type is usually a result of behavior, not genetics,” Catudal says, which means it can be improved with a healthier diet and exercise regimen.

3. For All Body Types, Diet Determines Your Body’s Size or Volume, While Exercise Determines Your Shape

It’s that simple, Catudal says, so don’t even think about trying to out-train a bad diet. “At the end of the day, if you are taking in too much food or the wrong types of food, your body is going to grow in bad ways,” he says.

But paying attention to diet alone is unlikely to get you the body you want. “Exercise determines your muscle-to-fat ratio,” Catudal says. “It’s what’s going to sculpt and tone your muscles and give you definition.”

It’s when you eat well and train wisely that your body will become tighter and more toned in good ways.

4. If You’re an Ectomorph, You Don’t Need as Much Aerobic Exercise as Other Body Types to Stay Slim

Because they’re already lean by nature, ectomorphs don’t need much cardio. “If ectomorphs do too much cardio, their cortisol levels may increase, which signals their body to store fat because their body believes it’s under stress,” Catudal explains. “It’s why you often see runners who are skinny-fat — skinny in the legs with excess belly fat.”

What ectomorphs really need to get toned muscles and to prevent overuse injuries and common chronic problems like back pain and osteoporosis, he says, is to add muscle mass and strength through strength-training exercises.

“Focus on doing ‘compound lifts’ — ones that use multiple joints and muscle groups, such as deadlifts and squats with dumbbells — a few days per week, and you’ll get the toned, sculpted results you want,” Catudal recommends. If you’re not ready for exercises with weights, you could do a combination move of a push-up into a side plank (after you finish a push-up, lift one arm toward the ceiling and move into a side plank; return to a plank position and repeat on the opposite side).

Or replace some of your aerobic workouts with high-intensity interval training (HIIT) — alternating short bouts of vigorous exercise with brief periods at a slower pace. He suggests doing strength-training exercises at least twice a week to melt some body fat while retaining muscle. (Doing some type of strength or resistance exercise at least twice a week is also the recommendation of the latest physical activity guidelines for adults from the U.S. Department of Health and Human Services for general health.) Making small dietary changes, like swapping some of your carbs for protein, can also help build muscle.

5. For Maintenance, Low-Intensity, Steady-State Cardio Is Most Important for Mesomorphs

If you’re happy with your size and shape and want to stay that way, your best bet as a mesomorph is to focus the majority of your workouts on low- to moderate-intensity cardio. It can be as simple as brisk walking, performed at 65 to 75 percent of your maximum heart rate.

But be forewarned: “Because mesomorphs have fewer slow-twitch muscle fibers [which have a high aerobic capacity and are used in distance running, for example], they have lower endurance levels, which can lead to frustration or fitness plateaus if they don’t manage their training properly,” Catudal says. That’s why it’s wise for mesomorphs to change up their workout styles — with occasional sprints or HIIT, for example — on a regular basis. You might think of this as a way of tricking your muscles and cardiorespiratory system to get fitter faster because you’re specifically working on the types of activity that don’t come as naturally to you.

6. Shapely, Curvy Endomorphs Have the Potential to Be Super-Strong Athletes With Well-Defined Muscles

To get there, start with a low- to moderate-intensity cardio regimen to torch stubborn fat stores, then add a strength-training program once you’ve made progress. “The cardio is more important in terms of conditioning and fat loss,” Catudal says.

And once you get to the strength-building part of the equation, keep in mind that endomorphs are particularly responsive to isolation exercises (working one muscle at a time). So, targeting your quads with squats and lunges and targeting your biceps with biceps curls, for example, will likely be effective.

7. If You Become Sedentary, as You Get Older, You Have a Greater Chance of Slipping Into a Hybrid Ecto-Endomorph or Meso-Endomorph State

If you decrease physical activity and increase food intake, especially after age 50, your levels of testosterone and growth hormone are likely to decrease — which can make you susceptible to storing fat and losing muscle, Catudal says.

“It’s easier to keep something and maintain it than to try to reverse the process and get back on track,” he says — so try to avoid these slips. If they happen despite your best intentions, reduce your intake of starchy carbs and focus on doing compound strength-training movements.

8. Every Body Type Can Benefit From HIIT Workouts, but Endomorphs Do the Most

These days, high-intensity interval training (HIIT) is all the rage in the fitness world, and it’s easy to see why: With HIIT, you get a greater bang for your buck, especially because the workouts often last just 15 to 20 minutes. You’ll torch more calories, build muscle, and push your heart rate more than you can with steady-state exercise (like jogging or cycling at the same pace for the same amount of time).

Plus, you end up burning calories at a faster rate after the workout (called the afterburn effect) as your body recovers. “It’s a shock to the system, telling your body to burn more body fat, which is why it’s especially efficient for endomorphs, who tend to naturally store more fat than the other body types,” Catudal says.

9. You Don’t Have to Do Full-Body Strength-Training Workouts

For people under age 60, it’s actually more effective to train one or two body parts at a time and push yourself to the point of exhaustion and then focus on other muscle groups on alternate days, Catudal says. That means you might focus on strength-training moves for your chest and back one day, your legs and arms another day, and your core a third day. (Or, you could choose your own pairings.)

“If you hammer those specific muscles on those days with a greater volume — more reps or more sets — you’ll stimulate greater activation in your muscles, which will allow you to build more muscle in that area,” he explains. A hidden perk: Your workouts will continue to feel fresh as you rotate your efforts among body parts. It’s also a way to build in rest for the different muscle groups on the days when you’re focusing on other muscle groups, as you want to be sure to avoid working the same muscle groups two days in a row: Muscles need time to recover and rebuild in order to develop strength, and you don’t want to risk injuring yourself.

Stacey Colino and the personal trainer Phil Catudal are coauthors of the book Just Your Type: The Ultimate Guide to Eating and Training Right for Your Type.

9 Things You Didn’t Know About Training Right for Your Body Type