Since their inception, exercise machines were designed to provide a safe alternative to free-weights. But some could actually injure you, putting your body through unnatural positions and move your joints through harmful motions. So which machines should you stay clear of? Below are some suggestions by Men’s Fitness for what to avoid and what to use instead for safer, more results-oriented training.

1. Seated Twist Machine

These ab machines have been known to rotate your lower back beyond the 13 degrees considered safe. Exceeding that limit and adding the machine’s resistance to the movement can severely strain your vertebrae. These loaded twisting moves can quickly become more than your back can bear. To enhance your rotational strength, perform core exercises like the side-plank that keep your spine stable and your core rigid.

2. Seated Sit-Up Machine

Avoid this one, especially if you sit in an office all day. Many people yank their neck forward, round their shoulders, and flex their spine to unsafe levels. A study in Clinical Biomechanics found that sit ups ”whether bent knee or straight leg” increased compressive loads on the lower back. A safer alternative is to avoid flexion/extension and staying stable with an ab rollout bodysaw.

3. Smith Machine

Avoid squats, bench presses and deadlifts on the Smith machine. Its bar moves in a fixed path, forcing your shoulders and elbows into awkward positions. And since it balances the weight for you, it reduces the muscle tension you need to build strength, stability, and bulk. Aaron Brooks, a biomechanics expert and owner of Perfect Postures in Auburndale, Mass notes in SHAPE that Smith machines don’t account for differences in strength or arm length when doing a bench press. You may actually overwork and exacerbate a pre-existing dysfunction, since the weight’s fixed path forces the joint to move in a way that it may not want to move. This, warns Brooks, can lead to major muscle injury. It’s better to do squats and bench presses (with a spotter) using free-weights.

4. Seated Hip Abductor/Adductor Machine

These so-called leg-toning machines are supposed to work the inner and outer thigh, but they do more harm than good. In an article in TNATION, Dr. John Rusin, internationally recognized performance and fitness expert specializing in injury prevention and rehabilitation, notes that hip abductor can over activate your tensor fascia lata, the muscle that directly attaches to your IT-band (the tendonous and fascial band that originates on your hipbone). Similarly, the hip adductor places the targeted hip adductors and medial hamstring group at a biomechanical disadvantage.

5. Seated Military Press Machine

People with fragile bones or who are at risk for fractures are advised to stay away from this machine, notes the Colorado Center for Bone Research. These machines deny you the freedom to twist your arms and shift your body to accommodate the weight, straining your joints as you reach overhead. If both handles are connected, one arm will work harder than the other. It’s better to do (L-shaped) pike pushups.

Seated Leg Extension Machine. (Image: GettyImages)

6. Seated Leg Extension Machine

These machines may look intuitively safe, but they impart too much torque on your knee joints, pulling your shins back as you lower the weight. They also create an imbalance between your quads and hamstrings, which can lead to knee problems. When you normally move, your quads are not isolated, but consistently work with your other muscles. Brooks warns of this machine as well, saying that since the load is only on one end and not centered, it places too much strain on the knee. Making matters worse is that fact that people often incorrectly sit in the chair as they attempt to generate more force by moving their pelvis. To strengthen your quads, involve your entire lower-body using a barbell and front squats or simply doing forward lunges.

7. Leg Curl Machine

Whether they’re seated or prone, leg curl machines won’t work your gluten. You may pull a hamstring or even injure your knee. Why you isolate your hamstrings (as these machines do), they can tighten and become overactive. It’s better to extend your hips and keep those glutes active with a glute-ham raise using an exercise ball.

Machines Disappearing From Gyms

In response to the many warnings about exercise machines, gyms and health clubs have started to eliminate them from their workout venues. As noted by Eric Stevens, a certified personal trainer with the National Strength and Conditioning Association (NSCA), Universal machines may have been the rave in the 1980s, but it’s now back to basics with bodyweight exercises and old-school movements and lifts. Today, the shift is toward function fitness, driven by training knowledge and changes in the social interaction of exercise. So rather than a room full of machines, you’re seeing roomfuls of people doing more exercises using free weights or even movements without weights. Check out Body-Weight Moves You Can Do Anywhere and the 30-Minute Bodyweight-Only Cardio Sweat Fest.

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