Finding the motivation and energy to do all your weight lifting sets can sometimes be a challenge.
BUILDING ENDURANCE FIRST
Part of the problem is endurance. Many people who get into weight lifting at the beginning are trying to lift as much as they can, at the max, but after lifting 5 to 10 times need to take a break. After their break they lift another 10 times... then another break. They're lifting so much that they end up taking really long breaks in-between sets. Over a period of 60 minutes they might do this 10 times total (if the have the stamina for that), lifting the weight 100 times total, before giving up.
Trying to lift such large amounts is the first part of their problem. They see other (bigger) men at the gym lifting large amounts and they're trying to prove they can do it. This is more an ego problem for men than for women. Women might still try to prove they can do it, but they won't be so worried about it as the male ego will be.
What should be doing instead is a smaller amount of weight, but lifting it 50 times before taking a break. (Knowing math helps with this.)
Lets pretend for example that in 60 minutes you lift 10 sets of 10, of 300 lbs. Total 10 x 10 x 300 = 30,000 lbs. So at 30 minutes that is averaging 500 lbs per minute.
Instead what a person should be doing is 10 sets of 50, of 120 lbs. Total 10 x 50 x 120 = 60,000 lbs. So that is lifting an average of 1,000 lbs per minute.
Who do you think got the better workout? Who do you think will gain more muscle and/or more endurance?
During a strength training program there is a lot of benefits to building endurance first. If you're planning to be at the gym for an hour every day, but spend most of that time catching your breath and you run out of steam easily then you're not really lifting much weights, are you?
By building endurance first so you can workout the entire hour with minimal breaks, and then gradually increase the amount of weight you are lifting on a weekly or bi-weekly basis then you will be maximizing both your endurance and your weightlifting.
Tip! Having smaller free weights and dumbbells can help you to build endurance/strength faster because you can do a greater variety of exercises using free weights than you would with exercise machines.
SELF CONTROL + JOURNAL
When doing a strength training program, and trying to get beyond the level of absolute beginner, adding more than one set per muscle group is ideal. Doing multiple sets is a necessity. If you only do 1 set of 5, you aren't really challenging yourself. You need to give yourself a specific number of sets, a known number for each set, and a specific weight you want to lift for each set. For best results keep a JOURNAL of the total number of sets you did, how many repetitions, what weight you did, and you can even track how much rest time you gave yourself between sets. A good thing to track is also how well you were feeling when you got to the gym (eg. hungry, tired, upset, etc) because your mood and emotions can often effect your stamina and self control.
With longer sets and multiple sets there is an increase of blood flow to the muscle, and it stimulates better growth/development and therefore, strength building. The reason for this is because your body responds better to endurance strength building methods, building muscle faster than it would if you were just trying to lift larger amounts with only 1 set.
You also want to alternate which body parts you are focused on. A good technique is to alternate upper and lower body exercises on a daily basis. You also want to use a variety of different exercises that target different muscles. Only targeting 1 set of muscles (eg. biceps) won't really help you that much. You need to be thinking of muscle groups like dominoes. If you want to grow your biceps, then you also need to exercise all the other muscles surrounding the biceps if you want to get better results.
Only focusing on one specific muscle is also extremely boring. To maintain motivation and increase self control it helps to do a variety of different exercises. You get bored less and you will get better results.
In your journal make a list of exercise machines or free weight exercises you like doing. Then start tracking how many you do during an hour at the gym. Track your rest times too if possible.
Once you know what exercises you enjoy, try to make a routine or a circuit you can do every time you go to the gym. Track everything in your journal.
When bored, add extra exercises and try new things to spice up your weight lifting workout. Having the journal will help you keep focused and having a list of "chores" to do at the gym will help keep you on track with your goals.