Mechanical efficiency is an exercise term that describes the ratio of work output to work input during physical activity. The more efficiently you move with the least amount of effort expended, the greater your mechanical efficiency. A measure of mechanical efficiency is especially important to athletes whose goal is to improve sports performance. Physical therapists and researchers may also use this term when measuring how well clients perform in studies. Stretching and continued exercise may improve mechanical efficiency.

## Gross Efficiency

There are three primary ways to describe mechanical efficiency during physical activity: gross efficiency, net efficiency and delta efficiency. Gross efficiency is the percentage ratio of external work achieved compared to the total energy expenditure. This means how much work you produce in relation to how much total energy you used. The formula for gross efficiency is 100 divided by the total energy expenditure multiplied by the external work.

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## Net Efficiency

Net efficiency is another way to measure mechanical efficiency. It measures how much energy you produced compared to the total energy expended, like gross efficiency, but also takes into account the energy you used to produce the external work. Net efficiency basically measures gross efficiency minus the extra energy you use when exercising compared to while you are not exercising. Your body uses energy just to keep you alive. Net efficiency subtracts the extra energy above that amount that exercise requires. The formula is the same as gross efficiency minus the extra energy expenditure during physical activity.

## Delta Efficiency

Delta is a term in geometry that denotes change. Delta efficiency measures mechanical efficiency with changing work loads. You compare the work output between different work loads with the difference in energy expenditure during the time you are exercising under each load. This could be, for example, the change in efficiency when cycling on a flat surface and up a hill. The formula is the change, or difference, in work output between two loads divided by the change in energy expenditure between the two loads, multiplied by 100.

## Improvement

More experienced athletes demonstrate greater mechanical efficiency than novice exercisers. The more you perform a particular action, the more efficient your body becomes. Stretching also improves mechanical efficiency. Stretching improves flexibility in the muscles and connective tissue that surround joints. This means that you use less energy when you exercise because your joints move more easily and through a wider range of motion. Stretching also decreases tension, enhances circulation, relieves muscle soreness and improves posture. Stretching reduces your risk of lower back pain by stretching the hip flexors and hamstrings that attach to the pelvis, which relieves stress on the lumbar spine.