Instrumentation in Human Bioscience - Essay Example

A discussion of the methods reveals that all have their advantages as well as their disadvantages. The Skinfold Caliper is the most widely used method to determine the amount of body fat. It uses a set of mechanical calipers to measure skinfold thickness at key points on the body. The measurements are then referenced to a chart, which infers the percent of body fat. Though the tools are simple, inexpensive, and relatively non-invasive, the procedure requires a high degree of training to obtain reliable results.

The typical accuracy of a correctly administered Skinfold measurement is plus or minus 3 percent (Doyle 1998). This is a marked increase over the universal Body Mass Index (BMI), which compares height to weight and results in an accuracy of 5 to 6 percent. (FitnessGram 2003). A more recent addition to the available methods is the use of the Bioelectrical Impedance Analyser (BIA). This instrument operates on the principle that fat retains less water than muscle. The increased percentage of water in muscle makes it a better electrical conductor and by measuring a body's resistance to current flow, we can measure the body's fat content.

This non-invasive technique is well suited for a wide range of subjects including elderly and disabled. The measurement is fast, easy to use, and is able to be used with a minimum of training due to a direct electronic readout. The cost is comparable to the Skinfold calipers and the accuracy obtained is similar to the Skinfold method. However, to attain this accuracy care must be taken to void the subject of alcohol, urine and other liquids for up to 48 hours prior to administering the test (Doyle 1998).

These variables all have the potential to impact the accuracy negatively. A more recent method to measure body fat is Dual Energy X-ray Absorpitometry (DEXA). DEXA is a low-level x-ray that measures not only muscle and fat, but also uses bone mineral content as a factor in body composition (Doyle 1998). The technique uses a safe level of x-ray radiation, is non-invasive, and the subject requires no preparation. Though DEXA is costly and requires a high degree of training, it's accuracy exceeds both the Skinfold and BIA methods (Doyle 1998).

In measuring the potential for good or diseased health one must also consider and analyse the expired air of the subject. Through measurement of the CO2 and O2 components of expired air, calculations can indicate a healthy metabolic function or detect areas of concern with respect to the subject's overall fitness and health (Jacobs, Mintz, and Nash 1999). The method of assessment most commonly used is known as Indirect Calorimetry (Measuring Energy Expenditure). The method involves the collection of expired air over a given time period and the subsequent analysis of the CO2 and O2 components.

The method has some variations in the collection apparatus as well as the means used to analyse the gases. The Douglas Bag is a direct method used to collect expired air. It is considered to be clumsy, due to it's 200-litre bag size, and interferes with the subject's activity while under test. Air is sampled for approximately 10 minutes and then the gas is measured in a dry gas analyser (Messer, Pelto, and Pelto 1989). A less bulky apparatus used to collect expired air is the K.M Respirometer.

Smaller and more portable than the Douglas bag, it has gained popularity and is a more widely used method. The technique of