Even if you've been active and a frequent exerciser most of your adult life, your workout should reflect your age as well as your experience. If you're in your 40s, you shouldn't be doing the exact same routines you did in your 20s.

Nagging injuries can prevent you from executing proper form, and your body is more susceptible to problems associated with age. Here is a look at seven exercises people over 40 should avoid.

1. Crunches

Ab-targeted exercises alone won't shave off belly fat. A well-rounded workout combined with a healthy diet will help you lose weight overall. Even if you do 1,000 crunches a day, you can't get rid of that spare tire without working your entire body. Ab exercises are good for toning muscles that are already trim and lacking fat.

When you're middle aged, crunches, situps and other ab exercises can cause spinal problems. In extreme cases, you can sustain a spinal fracture. Crunches can also strain your neck and cause poor posture. Unless you keep your back 100 percent straight when doing crunches, you can injure yourself.

As a substitute, try planks instead.

2. Intense cardio

Women in particular love cardio, but it can be strenuous on a middle-aged person who is not used to extreme exercise. If your body is working too hard under stress, it produces the hormone cortisol, which will actually make you gain weight. That's the exact opposite of what you want to achieve!

Cardio includes jumping jacks. While they are an excellent full-body exercise, they can also be tough on your ligaments. High knees are also strenuous for the joints, tendons and ligaments. They can hurt the knees and hip flexors.

In moderation, cardio is great for your cardiovascular system. But if you're over 40 and frequently engage in intense cardio routines, it can be difficult on your muscles. So, skip the 60-minute boot camp class and opt for a shorter, high-intensity workout instead.

3. Squats

Squats are one of the most basic and effective exercises for the legs and glutes. However, older bodies are more susceptible to injury, particularly if weights are involved. If done incorrectly, squats can cause lower back and knee injuries due to muscle strains, tears and pulls.

In addition, squats may add muscle to your hips, making them appear wider. Many people will mistake the added bulk for fat gain when it's actually muscle gain. It's one area that people usually want to slim down, not emphasize. And because your body’s metabolism slows down after age 40, this is one spot you probably want to keep trim.

Good alternatives to squats are lunges and step-ups.

4. Leg extensions

Leg extensions can be taxing on your knees, particularly as you age. And if heavy weights are involved, it can cause big problems.

Your knees are not built to fully extend while pushing out a heavy set of weights. Knee and ankle injuries are a common problem associated with the use of a leg extension machine. Even younger people should avoid the equipment because it could cause knee problems in the future.

Try dumbbell lunges instead.

5. Deadlifts

If done improperly, deadlifts can be damaging to your back. At the very least, you'll complain of lower back pain for a few days. At worst, you can suffer a spinal injury. In addition, if you drop the weights while doing a deadlift, you can severely injure your foot.

When you age, it becomes more difficult to maintain proper form because you may have other injuries and try to compensate for the problem. Bent-over rows are a good substitute for deadlifts as long as you use proper form.

6. Triceps dips

One area that people often target is their triceps. Nobody likes their arms to jiggle. However, if you don't position your arms properly when doing this floor exercise, it can be painful and cause injury. Your upper arms and rotator cuffs include tiny muscles that can be easily damaged.

As an alternative, try triceps pushups or single-arm triceps kickbacks.

7. Behind the neck lat pulldowns

This is a slightly awkward exercise when just using a little amount of weight, so when you start piling on the pounds it puts increasing pressure on your shoulders and rotator cuffs. Some people who perform this exercise sustain shoulder strains and tears.

Close-grip pulldowns in front of the body are a good substitute.