Strength is defined as how much force a muscle can exert against a given resistance. For example, how much weight one can bench press in a single attempt. Everything we do requires some level of strength. However, everyday general activity will not do much to increase strength, since our muscles have become accustomed to these levels of resistance.
Strength is developed by working against a resistance. Generally speaking, the greater the resistance the greater the strength gains that one will develop. Without a great enough resistance there will be no improvement in strength.
Studies have shown that exercising a muscle group 2-3 times per week, doing approximately 3-4 sets with about 8-10 repetitions in each set, is best for causing strength improvements.
A set is a group of movements. For example, doing 8 arm curls in a row is called 1 set. A repetition is a single movement.
Generally speaking if you can do more than 10 repetitions then the resistance is too low to cause any significant strength gains. However, if you are just starting out don't worry too much about this number, just use a weight that is easy to lift until you become comfortable with the movement and the resistance. You may also hear of other techniques that heavy body builders may use, however this formula is more than adequate for the average person.
Keep in mind that what you want to do is to force the muscle to work harder than what it is accustomed to. By doing this you cause microscopic muscle filament damage which the body is forced to repair. And through this repair process the muscle will become stronger than before. Make sure you allow adequate time between workouts for this repairing process to take place, usually about 48 hours.
Types of Contractions
Concentric contraction (also called positive contraction) is defined as when a muscle is contracting (getting shorter) during the movement. For example, the quadriceps (upper leg muscles) shorten during leg extensions. For most people, this method is quite adequate for general fitness.
Eccentric contraction (also called negative contraction) is defined as allowing the major muscles to lengthen but under resistance. It is a method where the resistance is greater than what the lifter can lift, so they need some assistance. But then the lifter will attempt to lower the weight as slow as possible to the original position. For example, with arm curls, a spotter will help lift the bar up, then the lifter will return it to the original position as slowly as possible. Some experts believe this is excellent for strength development.
Isometric contraction is a method where the muscle group is neither shortening or lengthening during the exercise. This method is excellent while recovering during an injury because there is very little movement. For example holding a push-up position while half way up and staying there for several seconds.
Isokinetic contraction is where the speed and resistance remains the same throughout the entire movement. This can not be done with a regular dumbbell, as the resistance will change pending on the angle of the joint. Special equipment is required to achieve isometric contractions, and for the average person it is not required to achieve strength gains.
Isotonic refers to a movement that moves the muscle through a complete range of motion.
Circuit training refers to having stations of different exercises and moving from one to the other with little rest between each one.
Plyometric exercises involve a rapid muscle stretching under stress followed immediately by a rapid concentric contraction. For example, jumping of a 1-foot high bench then jumping up as soon as you land.
Additional Strength Training Information
Speed is not a factor when developing only strength. In fact all movements should be in a controlled manner in order to reduce the risk of injury.
Working a muscle group too often, e.g. more than 3 times per week, may not allow enough time for the muscle to repair and to grow. In effect, this is counterproductive and for the most part should be avoided.
Measuring strength gains is quite easy. For example, put as much weight as you can and do 1 single bench press. As you get stronger you will be able to put more weight. Be careful though not to push too hard and cause an injury.
Other factors that may influence strength gains can include genetics, diet, rest, age, gender, etc.
Make sure you exercise opposite muscles groups, e.g. chest and upper back. If you don't do this you will have one group of muscles over powering the other. This can sometimes lead to injuries as things will not be aligned properly.
Strength is something that can be improved regardless of age. obviously a 20 year old will have a greater increase than a 60 year old, but everyone can benefit. And strength is an important factor as you get older in terms of being able to move, walk, climb stairs, etc. Without enough strength a person can not move easily.
Strength training does not cause one to become fat. And women, because they lack male hormones, will not become big and bulky. In fact, most men will also not become big and bulky because of the same reason. However, strength gains can be made without noticing a significant increase in size. After saying all this you should be cautioned however that some people, instead of becoming lean with strength training, may notice some weight gain and may feel bulky. This may occur because of water retention, increase in fat levels from an increase in eating. The best cure for this is to make sure you are doing plenty of cardio, and to cut back on heavy weights.
Muscle cells do not reproduce. This is a bit difficult to swallow but it's true. Whatever number of muscle cells you had shortly after you were born is all you will ever have. However, what does occur with growth and exercise is an increase in number of muscle filaments within each muscle cell. This causes the muscle to get bigger without an actual increase in muscle cells.
Of all the physical attributes strength gains will stay around the longest once someone stops exercising.
Children should not be involved in strength training for two simple reasons. They lack the hormones to achieve any significant strength gains so there is no real benefit, and the risk of injury, usually to the growth plates of bones, is very high.
Every 4-6 weeks the routine should be changed. E.g. instead of doing push-ups do some tricep extensions. Or alter the speed of the movements, or change the weight but do more reps. By changing things around it prevents the muscles from becoming too comfortable with an exercise and will continue to stimulate to continue growth.
Split routines are where weight lifting is done every day, but muscle groups are alternated. E.g. chest on day one, and upper back on day two. Most people don't need to do this. But it works well for people who are more advanced and can not do all muscle groups in a single workout. However, it takes more time as you have to workout almost every day.
Measuring strength is simple. Since strength is defined as how much force a muscle can exert against a given resistance use this to test it. Pick about 3-4 exercises and see, using only one repetition, how much weight you can lift, push, or pull.
Make sure you are rested so you are measuring strength and nothing else. And since you are going all out it's recommended that you have someone spot you. also, make sure you have warmed up well to avoid the risk of injury.