When you choose a gym, make sure to pick one that you feel comfortable in. Take your time - walk around, look at the machines, see how packed the place is and what type of people go there. Also check so that it is within reasonable driving distance. If you have to drive 30 minutes each way, chances are you'll start looking for excuses not to go.
Get the gear you need. A clean, loose T-shirt, knee-length shorts and indoor-only sneakers are a good start for clothing. You also want to bring a padlock, a bottle of water and a small sweat-towel. If you intend to shower at the gym, don't forget a full-size towel, fresh underwear and shampoo. You can also get optional things like gloves and lifting straps or hooks, but you may want to start without to assess what your needs are.
If you're unsure about the exercises, hire a personal trainer to make sure you get started on the right foot. The key to progress and avoiding injuries is getting the grooves right, and you might as well learn everything right from the start so you don't have to "unlearn" later. Many gyms offer a couple of free sessions with a trainer when you sign up - take advantage of it!
Learn the gym etiquette. Let others use your machine between your sets, wipe off your sweat from machines and pads, unload the plates when you're done and don't start yakking with people in the middle of their sets. Leave the pager and cell phone in the locker. And check your personal hygiene - nobody likes the guy who smells like a donkey.
Make sure to get plenty of sleep. You do most of your growing in bed, not in the gym, so don't rob yourself of growth by skimping on the Z's. Another obvious advantage of getting sufficient rest is that you're more energized and can train harder, which in turn improves the result of your workouts. A sleep-deprived person, on the other hand, is worn out even before stepping into the gym. Such a person can even get himself injured because of the lack of mental focus.
If your gym is too crowded, consider a different workout schedule. Since everybody is in the gym at 5 PM on Mondays, perhaps it is better to schedule your workout for 8 PM - or 7 AM, before work. Or better yet, go on Sunday afternoon when the weekend warriors are busy drinking beer and watching sports and make Monday a rest day.
Remember, your body couldn't care less what day of the week it is, so adjust your schedule to what's most convenient. One caveat: Try to get your weight lifting in when you're feeling the most energized. Morning people usually have no problems with early workouts, but night owls probably benefit more from a late evening workout, and vice versa.
Safety Pointers
As a beginner, your goal is to learn to lift right, not lift a lot. In addition to getting the basic movements right, there are some universal safety pointers you should keep in mind to decrease the odds of injuries now and later.
Hire a personal trainer or get a regular workout buddy to spot you for exercises that make you vulnerable to injuries. Examples of such injuries are bench presses, squats (will be introduced in the Intermediate section) and most types of overhead shoulder presses.
There are several advantages; a person who knows you can judge when you need and do not need a helping hand, he knows how strong you are and how much help to apply, and last but not least, you don't have to grab any bozo off the floor that could have the attention span of a French poodle.
Avoid overstretching joints like the plague. Getting a full range of motion during a set is good, pushing a joint beyond its natural limitation is asking for trouble. In most cases it's not even a conscious action.
A classic example is seated leg curls, where you regularly see people push through their set only to remain seated for a few seconds afterward. Their hamstrings are on fire, so they relax the muscles and take a few breaths before getting up. No harm in that, right? Wrong - the entire workload is putting brutal pressure on their knee joints without virtually any muscular support whatsoever.
Of course, it doesn't cause any direct pain so people don't recognize this as a problem until the day when they've worked themselves up to a weight when something snaps. Then you have plenty of pain to go around. This applies to elbows, wrists, shoulders and practically any joint you have.
If you do calf presses in a classic leg-press machine, always leave the safety stops engaged. They won't interfere with your calf presses, but if your soles slip off the plate you'll be very, very glad you did. Otherwise you'd have a few hundred pounds of plates with a sharp metal edge and a one-way ticket to your kneecaps.
Learn to flex your abs and maintain a tense midsection at will. This helps stabilize your torso and can do wonders in avoiding undue strain on your back. Remember, avoiding injuries is a key step to long-term bodybuilding success. Make it a habit to always tense up your abs while curling, pressing or pushing weights, especially for overhead exercises such as military presses.
Don't forget to employ proper lifting technique (straight back, knees bent and abs tense) when loading and unloading weight plates. Just because it's not a regular exercise doesn't mean you can ignore safety when dealing with 45-pound plates. Also check your grip. If you get sweat on your hands you have potential toe-crusher going if you try to unload the plates without wiping your hands first.
Some people like to use overhand "monkey grip," i.e. hold the bar with the thumb on the same side as the other fingers rather than grasp around the bar. This is a bad idea for two reasons. When bench pressing, you're forced to tilt your hand back all the way to avoid having the bar roll out of your palm and decapitate you.
Unfortunately, this means you'll have bone pressing against bone in your hand/upper arm, which can become quite painful if you make it a habit. Secondly, there's that tiny detail of having a 200something pound barbell suddenly coming down to get more closely acquainted with your front teeth. This is a pretty memorable event that could leave a deep impression in you.
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