We've all seen people make slip-ups at the gym (see-through white shorts come to mind). But if you think about it, the gym is a little like Sydney's Mardi Gras - pretty much anything goes. Some people run fast, some slow. Some do 15 reps, some eight. Some go with the iPod, some request Nickleback during spin class. The thinking: as long as we're doing some kind of exercise, it must be good. But the gym is a place where you can make mistakes - the kind that can lead to injury, and even derail all your exercise and body goals. Here, workout flaws to fix:

Married to the machines

Weight machines would have to be the lowest-maintenance pieces of workout equipment since the jump rope. Using machines means there's no searching for dumbbells or fighting for a free bench with the no-neck crowd. But don't rely solely on machines, because typically you can work more muscles and build greater practical strength with free weights or even no weights, says Jay Dawes, a personal trainer. For example, although a leg curl will strengthen your hamstrings, it isn't exactly a move you'll make in life. A lunge-and-press (see below), on the other hand, strengthens quadriceps, hamstrings, butt, calves, upper back and shoulders, and builds balance and coordination used in daily activities, like lifting kids and playing sports.

THE FIX To get the most from each workout, try performing a mix of exercises - using machines, body weight, free weights and dumbbells, says Dr Cedric Bryant, an exercise physiologist. Dawes suggests two to three sets of a move like the lunge-and-press several times a week. To do it, hold a dumbbell in each hand at shoulder height with arms bent close to your sides and palms in. Keep your feet hip-width apart, with one foot a stride ahead of the other and your back heel lifted. Hold abs in, bend your knees so the front knee aligns with your front ankle and the back knee points toward the ground. At the same time, press the dumbbells overhead. Straighten your legs and lower dumbbells to the starting position, then complete 12 to 15 repetitions.

Rushing your workouts

Speeding through your sets may help you make it back in time for MasterChef but it could also be a sign you're missing momentum, executing the exercise incorrectly, or using too much or too little weight. Many women tend to use momentum with crunches, potentially straining the neck, says Janet Huehls, a clinical exercise physiologist. Another momentum temptation: lunges. Speeding through them increases the risk of pulled muscles or joint strains and sprains.

THE FIX With any strength move, go at a slow, controlled pace in the lifting and lowering phases (two seconds up, two seconds down). There should be no point at which you pick up speed, says trainer Jay Blahnik, author of Full-Body Flexibility (amazon.com). With crunches, hold dumbbells or a medicine ball on your chest to slow you down. For lunges, hold a dumbbell in each hand as you perform your reps or try doing them with your front foot on a Bosu balance trainer (qpec.com.au/bosu). If you want to raise your heart rate during circuit training, decrease the time of rest between exercises rather than rushing through the exercise.

Using 2 for the price of 1

It's not a mistake, per se, to do leg extensions and biceps curls with both legs or arms at once, but it can lead to lopsided strength gains. We're asymmetrical by nature, with one dominant side, Dawes says. So, when working both legs, your stronger side will dominate and help you through those sticking points. Then you get more development on one side, setting you up for imbalances and injury.

THE FIX Do some unilateral exercises within each total-body workout to correct imbalances, using machines that let you work the arms or legs separately, or doing free weight exercises so you have that option. Start an exercise with the non-dominant side and do as many reps as you can, then do the dominant side, Dawes says. If you do three more reps with the dominant side, say, go back and do those last three with the non-dominant side to try to reduce that deficit.

Going at it hell for leather

High-intensity, high-impact aerobic activities can be great for kilojoule-burning, but not for joint-saving. Constantly pounding the body with high-intensity exercise often won't give your body an adequate amount of recovery time. That can result in you reaching a plateau or worse, an overuse injury, Dr Bryant says.

THE FIX "Limit anything that has a lot of jumping, bounding or repetitive stress (running, Body Attack class) to three times a week," says Ben Lucas, personal trainer and director of Vision Personal Training, North Sydney. Don't push your heart rate above 90 per cent of your maximum (estimated as 220 minus your age) more than two or three days a week, particularly if you're doing high-impact activities. Instead, sub in swimming, walking, cross trainers, resistance training or rest. "You need a mixture of training techniques, both high-impact and resistance, to both save your poor knees and also for the most effective weight loss," says Lucas. Signs you're overdoing it include muscle soreness lasting more than a day or two, fatigue lasting more than a few hours after a workout, frequent injury, loss of motivation, and increased or decreased appetite, Huehls says.

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