Some of my thoughts/edits on the fitness myths from here and here.

MYTH: Cardio is the best way to burn fat.

High-intensity exercise such as interval training burns more fat calories on an absolute basis than lower intensity activities, making it better for fat loss. It also increases EPOC (Excess Post-exercise Oxygen Consumption) the amount of calories you burn after you work out. — which helps keep your metabolism elevated long after you’ve stopped working out.

MYTH: Sweat is a good indicator of exercise intensity. 

All sweating means is that your body is getting hot and it’s trying to regulate your temperature. Instead, try to focus on keeping yourself at what feels like an “8” or higher on a scale of 1 to 10 to work out intensely.

MYTH: If you stop lifting weights, your muscle will turn to fat. 

I think this myth is idiotic because I don’t think people believe it’s alchemy and their muscle turns to fat. It is true that if you become less fit and your body fat increases and you allow your muscle mass to atrophy, you will replace some of your muscle with fat. I think it’s obvious that if you’re a 200-lb bodybuilder you’re not just going to convert muscle to fat? Most likely you might increase your bodyfat which would mean you’d be bulky with the muscle and then might look “fatter” because you look less fat?

MYTH: Using the Stairmaster will give you a big butt. 

Again, dumb myth. If you put resistance on the Stairmaster, then yeah, it’ll build up your glutes. If you’re just paddling your legs quickly, it’s cardio.

MYTH: Women should train with very light weights so they won’t bulk up. 

Yes, this is bullshit, however that doesn’t mean that you should try to do a Tracy Anderson video with 15lb weights. In almost any workout that asks you to use 1-3lb, or 3-5lb or 5-7lb or whatever weights, use those - just keep in mind that it’s just cardio with some added pizzazz, not weightlifting just because you’ve got your 3 pounders.

MYTH: Lactic acid causes muscle soreness.

Any lactic acid that accumulates in muscle is rapidly cleared within an hour or two after exercise. Since delayed onset muscle soreness (DOMS) doesn’t manifest until about 24 hours after a training session, it therefore follows that lactic acid cannot play a role in its origin.

DOMS is a product of damage to muscle tissue. Intense exercise produces small microtears in the working muscle fibers, primarily as a result of eccentric activity (i.e. lengthening a muscle against tension). These microtears allow calcium to escape from the muscles, disrupting their intracellular balance. Metabolic waste is produced and that interacts with the free nerve endings surrounding the damaged fibers, resulting in localized pain and stiffness.

In response, white blood cells migrate to the site of injury, generating free radicals that further exacerbate the sensation of pain. The discomfort can last for several days or even up to a week, depending on the extent of muscle damage.

If you experience DOMS, the best thing you can do is to stay active, enhancing blood flow to the affected area. This will expedite nutrients to the muscles, accelerating the rate of their repair and consequently reducing associated discomfort.