Exercise machines were invented to provide a safe alternative to free weights, but sometimes they’re anything but. They can put your body into unnatural positions and take your joints through dangerous ranges of motion. Over time, this can lead to injuries. Avoid the following machines at all costs, and use the alternative exercises we provide instead for safer, more effective training.1 Seated Twist MachineThese ab machines can create lower back problems because they rotate the area beyond a safe range of motion. Your lumbar spine can only twist 13 degrees—that’s less than one hour on a clock. Turning beyond that puts massive strain on your vertebrae, and, combined with the resistance of the machine, can quickly become more than your back can bear.Your lower back is actually designed to resist twisting, not generate it. To boost your rotational strength, pick core exercises that keep your spine stable and your core rigid.Use these instead:Side PlankPallof PressAnti-rotational Cable Chop 2 Back ExtensionThe back extension bench is a time-tested core builder, but its mechanical twin is the black sheep of back exercises. Repeatedly flexing your lower back under a load can cause injury to the lumbar discs, and the rigid position the machine holds you in doesn’t allow your core, glutes, and hamstrings to contract as they should to protect you.Instead, strengthen your lower back with exercises that force you to maintain the natural arch of your lumbar spine.Use these instead:Body-weight Back ExtensionBentover RowStiff-leg Deadlift3 Seated Situp MachineThink twice about doing any situp. The tendency to yank your neck forward, round your shoulders, and flex your spine is too dangerous for some people to bother with, especially if they sit at desks for long periods. A study in Clinical Biomechanics found that situps of any kind increased compressive loads on the lower back. The study author concluded that “the issue of using straight legs or bent knees [to perform a situp] is probably not as important as the issue of whether or not to prescribe situps at all.”To blast your core safely, use exercises that train it to resist flexion and extension and stay stable.Use these instead:Plank with arms on a stability ballAb RolloutBody Saw with Valslides or towels on a wood floor4 Smith MachineAvoid any exercise on the Smith machine, especially squats, bench presses, and deadlifts. Although its main benefit is that you can stop the bar whenever a set gets too heavy, the Smith's bar moves in a fixed path, and that forces your shoulders and elbows into awkward positions.The Smith machine also balances the weight for you, which reduces the tension in your muscles and robs you of strength, stability, and size gains. In separate studies in the Journal of Strength and Conditioning Research, researchers found that squats and bench presses done with free weights activated far more muscle than their Smith machine counterparts did.If safety is your concern, use safer variations of the squat, bench press, and deadlift that don't require a barbell or a spotter.Use these instead:Goblet SquatFloor PressBarbell Hip Thrust5 Pec Deck (or Chest Flye)Here’s the main problem with the pec deck: guys don’t need another exercise to pull their shoulders forward and twist their arms inward—we already spend too much time at our computers and target our chests often enough in the gym. Over time, this pulls our shoulders out of alignment and creates impingements in the joints.The pec deck yanks your arms backward as you approach the end of the range of motion, and when you relax at the end of the set, which can harm your shoulder joints. Rather than use a machine, stick to free-weight exercises that move in a safe range of motion.Use these instead:Dumbbell FlyeSlideboard FlyeSuspended Flye6 Seated Military PressYou never push overhead in a perfectly straight line—the movement drifts forward and backward, your arms twist, and your body shifts. Machines, however, eliminate that freedom.And although the seated military press can add muscle to your shoulders, it also spawns shoulder problems because it strains your joints as you reach overhead. If both handles are connected, you can even create imbalances where one arm works harder than the other. Use these instead:Dumbbell Overhead PressPush PressPike Pushup7 Seated Leg ExtensionMuch like the back extension, people mistakenly believe the leg extension prevents injuries. Instead, it places dangerous torque on your knee joints because it pulls your shins back as you lower the weight.Also, knee extensions develop an imbalance between your quads and hamstrings, which causes knee problems. As you move, your quads always work with other muscles, never in isolation—even when you kick a soccer ball, you flex your hips, twist your trunk, and stabilize through your other leg.The best way to strengthen your quads is to involve your entire lower body as well.Use these instead:Front SquatSplit SquatForward Lunge8 Leg CurlYour hamstrings are built to work with your glutes to create movement. Seated or prone leg curl machines, however, ignore your glutes, which increases your risk of hamstring pulls and knee injuries. By isolating the hamstrings alone, they become tight and overactive over time.The best exercises to build strong hamstrings also maintain hip extension and glute activation.Use these instead:Swiss-ball Leg Curl, or Leg Curl on a Suspension TrainerGlute-Ham RaiseRomanian Deadlift9 Seated Abductor and Adductor MachineJust because an exercise looks weird doesn’t mean it’s bad. (Barbell hip thrusts, for example, look like something you should never do in a gym.) In this case, however, the seated abductor and adductor machine is both weird and bad. By forcing your legs to open and close, you put a lot of stress on your hip capsules and IT bands.A better way to strengthen your abductors and adductors is to stand on one leg: not only are you activating those muscles to keep your leg stable, but you’re also activating your core.Use these instead:Lateral squatSingle-leg Romanian DeadliftSingle-leg Squat