Bioelectric impedance aactually determines the electrical impedance, or opposition to the flow of an electric current through body tissues which can then be used to calculate an estimate of total body water (TBW). This can then be used to estimate fat-free body mass and body fat. Recent technological improvements have made BIA a more reliable and therefore more acceptable way of measuring body composition. BIA is also considered a relatively cheap method of measuring body composition however accuracy and therefore validity of results in comparison with other methods are considered suspect.
Infrared Inheritance principally includes light absorption and reflection using near-infrared spectroscopy. A probe is placed on the skin above the site to be measured. The amount of energy that is reflected indicates the composition of the tissue directly under the probe.
The final of the four principal methods and one of the most important methods in terms of relevance to this experiment is skin fold thickness method. The skin fold method is the most widely used method due its ease of use and low cost completion. The skin fold method includes measuring skin fold with callipers at a variety of sites on the body, the choice of sites depend on which skin fold method is used. The values obtained are used to estimate body density, relative body fat, or fat-free mass using the correct calculation for the method chosen by the experimenter for example Durnin and womersley. This method relies heavily on the training and experience of technician and the correct identification of skin fold site.
Method
Participants in this experiment consisted of Year 2 Sports and Exercise science students from the University Of Derby, the experiment was laboratory based and took place at the University of Derby.
Bioelectric Impedance Procedure
As the bioelectric impedance the resistance of body tissue to the flow a small electric current, the participant should not be in contact with any other non conducting surface with legs and arms away from the body. The device is then connected to the hand and wrist and on the ankle and foot by electrodes.
Attach the electrodes as follows:
Wrist: Place on an imaginary line from the protruding bone of the wrist straight across to other side of wrist. Make sure the top of the electrode is toward the shoulder with
the tab facing away from the body.
Hand: Place on middle finger just above hand knuckle. Tab facing away from the body.
Ankle: Place on an imaginary line between the protruding ankle bones straight across to other side of ankle. Make sure that the top of the electrode is toward the thigh
with tab facing away from the body.
Foot: Place just behind the middle toes above the knuckles (about 1 cm) of the right
Foot.
When the measurements have stabilized, read and record the displayed Resistance (R), and Reactance (Xc). If the values fluctuate for either of the readings, use the lower value.
Skinfold Method procedure
The following method is the standardized description of skin fold sites and procedures for the Durnin and Womersley (1974) skin fold method using the Harpenden callipers.
Site 1 = Biceps: Vertical fold: on the anterior aspect of the arm over the belly of the biceps muscle, 1cm above the level used to mark the triceps site.
Site 2= Triceps: Vertical fold: midway between the acromin and olecranon process; with the arm freely held to the side of the body.
Site 3= Sub scapular: diagonal fold (at a 45 degree angle); 1 to 2 cm below the inferior angle of the scapular.
Site 4 = sacroiliac: diagonal fold ; in line with the natural angle of the iliac crest taken in the anterior axiallry line immediately superior to the iliac crest.
All sites should be marked and measurements should take place on the right hand side of the body. For increased accuracy at least two measures should be taken at each site, and if values vary by more than 1mm additional measurements are required. In terms of the actual reading the pinch should be maintained whilst the reading is taken and a 1 to 2 second wait is required before reading.
Results
Fig 1. Displaying group Statistics in Mean and Std Deviation format
Fig 2 Displaying an Independent t-test between gender differences during Skin folds
Fig 2. Displaying group statistics in Mean and Std Deviation format
Fig 3 Displaying independent t-test between gender differences during bioelectrical impedance test.
Discussion
In terms of examining the relationship between the two methods and concluding which method provides the more accurate results in this particular research it is important to assess the merits of each method. In terms of this particular experiment the bioelectrical impedance analysis the control of participant’s diet and therefore hydration may have had an impact on the accuracy of results. Using BIA to estimate body fat assumes that the body is within what would be deemed `normal` hydration ranges, if a participant was dehydrated the amount of fat tissue would be over estimated. Normal factors which affect hydration could have an affect on accuracy of results, therefore not drinking enough fluids, drinking to much caffeine or alcohol, exercising or eating just before measuring and certain prescription drugs could all have impacted on results as no conditions in terms of testing such as same time of day and hydration control were placed in this research.
The correct applications of the electrodes on the required sites on the body are also important to accuracy levels within this research. (Houtkooper, L. B., Lohman, T. G., Going, S. B. and Hall, M.C (1989) Validity of bioelectric impedance for body composition assessment in children. Journal of Applied Physiology, Vol 66, Issue 2 814-821.)
In terms of using the skin fold method for estimating body fat there are also a number of issues that must be considered particular within this particular research. The technician’s skill and experience is of vast importance to the results within this method, as the participants involved were novices results are impacted to a larger degree in theory. The correct location of the sites on the body also comes under experience and the technician’s ability.
The equation used to predict the body fat percentage is also an important factor, it has been suggested that some equations consistently show higher or lower results and therefore accuracy is affected.
The varying sample size in terms of gender may also have played a part in results as physiological there are gender differences in terms of body fat with females in the main having a higher body fat percentage which is shown in the results and an equal sample size may provide evidence for this point.
Having discussed the merits of each method and having looked at the results and significant differences in terms of this experiment I conclude that the Bioelectric Impedance analysis is more accurate measure of body fat percentage within this research. I feel the number number of potential errors within the skin fold method may well have affected the accuracy of results. The validity in terms of would the skin fold produce consistent results if this procedure was repeated would also be in question due to the number of potential mistakes.
References
Body composition accessed online 24/01/08 available at http://medical.webends.com/kw/Body20Composition
Bouchard, C. (Editor) (2000) Physical Activity and Obesity. Champaign, IL: Human Kinetics.
Houtkooper, L. B., Lohman, T. G., Going, S. B. and Hall, M.C (1989) Validity of bioelectric impedance for body composition assessment in children. Journal of Applied Physiology, Vol 66, Issue 2 814-821.
Wilmore, J. H. & Costill, D. L. (2008) (4th edition) Physiology of Sport and Exercise. Champaign, IL: Human Kinetics. PP. 382-397.
Body composition accessed online 24/01/08 available at http://medical.webends.com/kw/Body20Composition
