Work is defined as the product of force multiplied by distance:
Work = force X distance
The SI unit for force is Newtons (N), whereas the SI unit for distance is meters (m). Consider the following example to compute work during a weight-lifting exer-cise. If you lifted a 10-kilogram (Kg) weight upward over the distance of two meters (m), the work performed would be:
Work = 97.9 N x 2m = 195.8 Joules
In the above calculation, the computation of work in SI units required a conversion of Kg to N. To obtain the force in N, we converted the 10 Kg to N using the conversion factor contained in table 6.3 (i.e., I Kg 9.79 N so 10 Kg = 97.9 N). Therefore, the work performed was computed by multiplying the force (expressed in N) times the distance traveled (expressed in m) with the resulting work being expressed in Joules, which is the SI unit for work (where 1 Joule = l Nm; table 6.3).
It is often difficult to compute how much work is performed during an athletic event. For example, a shot-putter performs work when he/she throws the shot. That is, the shot has mass and is moved verti-cally. However, the exact amount of work performed is difficult to compute because the vertical displace-ment of the shot is hard to measure without sophisti-cated photographic equipment. In contrast, a weight lifter performing a clean and jerk is lifting a known weight (i.e., force) over a fixed vertical distance, which makes the calculation of work easy. Although the SI units are the preferred units for quantifying exercise performance and energy expen-diture, a number of traditional units can be used to express both work and energy. Table 6.3 contains a list of terms that are in common use today. For example, the energy content of commercial food products is often listed on the label in kilocalories. However, the SI unit for energy content and expenditure is Joules, where 1 kilocalorie is equal to 4,186 Joules.
Power is the term used to describe how much work is accomplished per unit of time. The SI unit for power is the watt (W) and is defined as 1joule per (table 6.4). Power can be calculated as:
Powor = Work/ time
The concept of power is important 1,)ecause it describ0, the rate at which work is being periormed (work rdio, II is the work rate or power output that describes 1110 intensity of exercise. Given enough time, any hedithy adult could perform a total work output of 20,000 joules, However, only a few highly trained athletes could per-form this amount of work in sixty seconds (s). Calcula-tion of power output using this example can be done as follows:
Power = 20,000 Joules/60 seconds
= 333.33 watts
Note that the Si unit for power is watt. Table 6.4 contains a list of both the Si and more traditional terms and units used to express power.