Many individuals focus their strength-training workouts to be able to lift increasingly heavier weights. While improving absolute strength has its merits, improving your relative strength-- the ratio of muscle strength to the ability to accelerate these muscles--is more important in many sports and everyday activities. For example, a sprinter who drops from 165 to 150 pounds while maintaining his leg strength will be able to accelerate—and reach maximum sprint speed—faster. However, relative strength is beneficial to the non-athlete as well—for example, maintaining sufficient relative strength is necessary for independent walking and rising from a seated position in elderly adults.
You may find, after just two to three weeks of weight training that the exercises feel much easier, and you have increased the amount of weight you lift. Despite how muscular you feel you have gotten over the course of these couple of weeks, you have not gained significant muscle mass. You are, however, more efficient in a neuromuscular sense, meaning your nervous system is able to coordinate the muscle actions to make for a more efficient movement. Therefore, since the muscles have increased the amount of weight they can lift without increasing in mass, they have increased their relative strength.
Determining Relative Strength
The general quantification of relative strength, in terms of weightlifting, is the absolute muscular strength for a given exercise divided by body weight. For example, the world record for the clean-and-jerk is 168 kg for a 56 kg individual, so his relative strength would be 168 kg/56 kg= 3.0. However, you can apply relative strength to many situations—for example, the number of pull-ups one can do is a commonly-used rough measure of relative strength of the upper body.
Relative strength is important for activities such as running, cycling, and rowing, which require generation of power to move your body mass forward. An additional pound of muscle mass increases the absolute amount of power that muscle can generate. However, this pound of muscle is additional body mass you must carry through the movement, thus reducing the amount of net power improvements in the muscle. For example, a 130-pound and a 200-pound cyclist may be able to pedal at a maximum power of 400 watts; however, the 130-pound has less body mass to move and will go faster. Team rowing is another sport where relative strength is relevant—given equal power output capacities, it is advantageous to have the lighter rower on your team.
Aging and Functionality
Relative strength is also critical for older adults to maintain independence in everyday tasks, such as rising from a chair and climbing stairs. As you age, you tend to lose muscle mass, particularly the fast-acting fibers that play a big role in power movements, and gain fat mass. Even if your overall weight stays the same, losing the power-generating muscle mass will contribute to lower relative strength since fat mass does not contribute to movement. Therefore, resistance training using the muscles involved in everyday activities—such as step-ups or lunges to mimic stair-climbing—can help the older adult maintain a functional level of relative strength.