1. Myth: Always do high rep ranges when cutting
Fact: Higher rep ranges will improve your muscular endurance. However, high rep ranges are no better then low rep ranges when it comes down to cutting.
People believe higher rep ranges will burn more kcals resulting in fat loss. However, Most fat burning occurs after exercise and not during, due to the calories required for recovery and altered hormone levels caused by exercise of appropriate intensity. So surely that means the harder you work your muscles and the more 'DOMS' (Delayed Onset Muscle Soreness) you have the more kcals you will burn...? I would recommend using different reps ranges for different exercises and not just one. For example, use lower reps (3-8) for compound movements and higher reps (10-12) for isolation movements. As It can sometimes be hard to contract the specific muscle you are trying to work when performing certain isolation exercises. The most important thing to think about is the total number of reps you do during the workout. 24-32 is a good total of reps you can aim for during a workout. This can be achieved by performing 5r x 5s, 10r x 3s, 12r x 2s etc...
2. Myth: The longer you work out the better
Fact: 5 hours in the gym won't make your biceps look 5x bigger
Cortisol is a hormone produced when the body is put under too much stress and can cause the body to go into a catabolic state leading to 'reversibility' (the brake down of muscle tissue) when produced at high concentrations. So Cortisol is the last thing we want when building muscle. A result of continuously elevated cortisol levels could be a condition commonly refereed to as 'overtraining'. So I would recommend not working out for more then 1 hour 15 mins if you are working to failure on each set.
3. Myth: Weights will make a girl look bulky
Fact: Women will find it very hard to look bulky from weight training
Women will find it near to impossible to gain huge amounts of muscle by merely touching weights. This is because women cannot naturally produce as much testosterone (main bodybuilding hormone) as males do. The image that seems to come into women's minds is that of a professional bodybuilder. However, these women will most probably have perfect genetics when it comes down to building muscle and they will be on a strict diet/routine to reach their specific goals. Not to mention the Anabolic steroids they are most probably taking.Women shouldn't be training any differently to men to get the physique their looking for. Whether that means upping the weight and training low rep ranges/high sets.
4. Myth: You can re-shape your muscles with isometric exercises
Fact: You can not change the structure or shape of your muscles.
Yes, you can change the mass, size and strength of your muscles however, the shape of your muscles is determined by genetics. Loosing body fat will help show their shape and will make them look more defined but unfortunately there is no way to change the shape of the muscles.
5. Myth: Loads of sit-ups will give you six pack abs
Fact: Getting the six pack abs you're looking for is determined by your body fat percentage.
You can do all the sit-ups you want but you will never see your abs if your body fat percentage is above 11-13% for men and about 15-18% for women, depending on your genetics. You might be building the muscle and strength however, It will be covered by a layer fat preventing you to see your abs clearly. So if you can't see your abs and you want to look cut I recommend working your abs at least twice a week and most importantly being in a 200-600kcals deficit. Being in a deficit will result in fat loss over time and will help you see the abs you want. However, be careful as being in a deficit for a long time or dropping your kcals too low can lead to loss of muscles mass and strength.