Can Thigh Girth Be Measured Accurately? A Preliminary Investigation

Transcription

1 Journal of Sport Rehabilitation, 1999,8,43-49 O 1999 Human Kinetics Publishers, Inc. Can Thigh Girth Be Measured Accurately? A Preliminary Investigation Eric Maylia, John A. Fairclough, Leonard D.M. Nokes, and Michael D. Jones Thigh girth is often used as an indicator of muscle hypertrophy or atrophy during the rehabilitation process following knee surgery. The measurement of thigh girth, using a conventional plastic tape measure, in an attempt to detect muscle hypertrophy or atrophy may be misleading. It is an inaccurate measure of thigh muscle bulk. Although the sample size is small, the results show that measurements are heavily biased by the expectations of observers, with the result that a considerable change in thigh girth is likely to be ignored. Key Words: thigh bulk, tape measure, hypertrophy, atrophy The measurement of thigh bulk, often termed quadriceps girth, has historically been used as an indicator of lower limb strength. Almost every practitioner and physiotherapist will at some time use a tape measure as an indicator of limb strength; for example, it is often used as an indicator of muscle hypertrophy or atrophy during the rehabilitation process following knee surgery. The assumption is made that a reduction in the bulk of the thigh muscle indicates a problem with the lower limb that has led to the decrease in thigh bulk. This measurement is often compared with that of the opposite limb. The circumferential measurements of thigh bulk are taken with a tape measure at a point on the thigh. The use of a tape measure for anthropometric measurements can provide a wealth of valuable information about a person's physique (3). Circumferences used alone or in combination with skinfold measurements at the same location are measures of growth and can provide indexes of nutritional status and levels of fat patterning (2). For example, head circumference is an index of brain growth for children under 6 years of age. Circumferences of the limbs, together with skinfold thickness measurements, can provide a value for the amount of adipose tissue or the amount of underlying muscle Eric Maylia, Leonard D.M. Nokes, and Michael D. Jones are with the Medical Engineering Research Unit, Cardiff School of Engineering, University of Wales Cardiff, P.O. Box 917, Cardiff, Wales, CF2 IXH, UK. John A. Fairclough is with the Department of Orthopaedics and Trauma, Cardiff Royal Infirmary, Cardiff, Wales, CF2 lxh, UK.

2 44 Maylia, Fairclough, Nokes, and Jones plus bone. When the appropriate formulas are used, these results can be used to monitor changes in the amount of adipose tissue and muscle during nutritional therapy or physical rehabilitation. The position at which such measurements should be taken has been investigated previously, and the reliability of certain measurements assessed. Lohman et al. (3) suggest that the error in taking the thigh girth measurement, between observers, is 0.5 cm, whereas Katch and Katch (2) suggest the error is as little as 0.2 cm. It was our experience from clinical practice that there was a lack of consistency that appeared to be related to the positioning of the tape and the tension applied to it on the thigh. This was highlighted previously by Fairclough et al. (I), who showed that observers failed to notice an increase of 3 cm, which was artificially introduced by altering the tape measure, when measuring the abdominal girth. In 1996 Soderberg et al. (4) looked at the reliability of lower extremity girth measurements after anterior cruciate ligament (ACL) reconstruction. This was carried out using a device specially designed to make circumferential measurements around the knee. The authors concluded that using this device gave sufficiently reliable results to justify its use both within and between examiners for subjects recovering from surgery of the ACL. However, in common practice a tape measure is the usual assessment tool used to monitor this sort of recovery, so research was required to see if it is a reliable tool. An initial study was devised to examine observer and intraobserver variability when measuring the thigh girth. Methods Two investigations were undertaken. In the first, measurements were taken from 3 subjects by seven observers (due to time constraints and availability, not all observers took part in measuring all the subjects). All subjects used in the study where healthy, with no history of recent injury to the lower limbs. The thigh was marked 10 cm above the top of the patella. None of the observers used in Investigation 1 had any previous experience using a tape measure. Therefore, they were shown how to correctly measure the thigh girth with a conventional plastic tape measure, using the technique described by Lohman et al. (3). The observers were asked to take sets of measurements of the thigh girth at the marked site on four consecutive occasions. This included taking the thigh girth measurement three times (consecutively) at the marked site on the right leg. To ensure that the observer was not recalling the previous measurement from memory, the observer was asked to measure the thigh girth by taking the reading from the other end of the tape-not the zero end. For the third and fourth measurements the tape was replaced with one that had 1 cm or 3 cm removed from a hidden portion, thus simulating an unexpected increase in thigh girth. The order of these four measurements was altered between measurers. To investigate the repeatability of the thigh girth measurements, Subject 2 was measured twice in the same day, 2 hr apart.

3 Measuring Thigh Girth 45 In the second investigation, a single observer, familiar in taking thigh gnth measurements, measured a subject's thigh 50 times using an unaltered plastic tape measure. The measurements were taken 10 cm above the top of the patella over the course of 1 hr. In both investigations, the observers measured only the right thigh. The aim of the project was to investigate the measurement errors that occur when measuring thigh bulk. It was not the intention to compare measurements between thighs. Results Tables 1-4 list the measurements grouped under Investigation 1 for Subjects 1-3. They include normal conditions (Experiment I), using the other end of the tape (Experiment 2), and a simulated girth increase brought about by the removal of 1 - cm and 3-cm segments from the measuring tape without the knowledge of the observers (Experiments 3 and 4, respectively). Investigation 1 As shown in Table 1, the individual mean error for Subject 1 varied from 0.5 cm for Observer B to 3 cm for Observer D. Only one observer (B) was consistent in detecting an increase in thigh girth throughout all his measurements when measuring Subject 1. Three observers (A, D, and E) actually detected a decrease in thigh girth when the tape measure with 1 cm removed was used, whereas they should have noticed a I-cm increase. Four of the five observers detected an increase in thigh girth when the tape measure with 3 cm removed from it was used. The mean Table 1 Thigh Girth Measurements Made by 5 Observers, Subject 1 Observer Meana Range % errorb A B C D E Mean Range % error Wean error = Z observers' errorln, where n = number of observers taking measurements. b% error = rangelmean x 100.

4 46 Maylia, Fairclough, Nokes, and Jones error between observers varied from 3 to 3.5 cm, and the mean overall error between observers and between experiments was 4 cm, or 8.1 %. The individual mean error in the first measurement of the thigh girth of Subject 2, as shown in Table 2, varied between 1.5 and 2.5 cm. The mean error between observers ranged from 2.0 to 3.0 cm, and the overall mean error between observers and experiments was 3 cm (7.47%). As shown in Table 3, the individual mean error for the second measurement on Subject 2 varied from 2 to 2.5 cm. The largest mean error (2.5 cm) between observers occurred when the other end of the tape measure was used and also when 1 cm was removed from a hidden portion. The smallest error (1.0 cm) was when the unaltered tape measure and the one with 3 cm removed from it were used. The overall mean error between observers and experiments was 3.5 cm, or 7.63%. Table 2 Thigh Girth Measurements Made by 3 Observers, Subject 2 (1st measurement) Observer Mean Range % error Mean Range % error Table 3 Thigh Girth Measurements Made by 3 Observers, Subject 2 (2nd measurement) Observer Mean Range %error Mean Range 1.O O % error

5 Measuring Thigh Girth 47 Table 4 Thigh Girth Measurements Made by 6 Observers, Subject 3 observer Mean Range % error Mean Range % error As shown in Table 4, the individual mean error for Subject 3 varied from 1 cm for Observers A and E to 1.5 cm for Observers C, D, F, and G (Observer B did not take part in this test). The mean error between observers ranged from 2.5 cm (Experiment 1) to 4 cm (Experiments 2 and 3), and the overall mean error between observers and experiments was 4 cm, or 7.88%. From the results, the overall mean error was calculated to be 4 cm, or 8.27%. As mentioned previously, the thigh girth of Subject 2 was taken on two occasions during the same day. Looking at the measurements taken by Observers A, D, and E (Tables 2 and 3), it is seen that Observer E measured the thigh girth for Experiment 1 as 47.5 cm the first time and 45 cm the second time-a difference of 2.5 cm. Only Observer D was consistent throughout the experiments, between the two tests, in measuring the thigh girth, even though the accuracy of the measurements decreased by approximately 1 %. Investigation 2 Fifty measurements were taken from one subject, by an observer familiar with using a tape measure, throughout a 1-hr period. The mean value of the measurements was found to be cm, and the range was calculated to be 1.7 cm, or 3.35%. Discussion The measurement of thigh girth should be reasonably accurate, reproducible, and free from observer bias. However, from our results, estimates of thigh girth vary widely between observers, as evidenced in Tables 1-4, which show an error of up to 8.27%, or 4 cm. These results are at variance with the work of Lohman et al. (3)

6 48 Maylia, Fairclough, Nokes, and Jones and that of Katch and Katch (2). Because the experiment protocols used by those authors are not fully described in the relevant papers, it is not possible to explain why the percentage errors found in this study are considerably higher than those found by the other authors. Tables 14 also show that intraobserver percentage error for each experiment varied among subjects. For example, as shown in Table 1 the errors in Experiments 2, 3, and 4 were almost identical (7.01,7.13, and 7.10%, respectively), and the error in Experiment 1 was less, at 6.07%. As shown in Table 4, the percentage errors for Experiments 2 and 3 were identical (7.88%), with that for Experiment 4 less, at 5.98%, and for Experiment 1 even less, at 4.89%. It could be concluded that it is unlikely that any method of using a tape measure can be considered reliable. The intraobserver percentage error varied even when the same subject was used. For example, as shown in Table 2, the percentage errors for Experiments 1 and 3 were almost identical (4.3 and 4.29%, respectively), with that for Experiment 2 slightly higher (5.34%) and for Experiment 4 even higher (6.36%). In Table 3, the percentage errors for Experiments I and 4 were identical (2.2%) and for Experiments 2 and 3 were very similar (5.52 and 5.38%, respectively). This leads us to conclude that a tape measure, whatever method is used, is probably an unreliable assessment tool. Even when measuring the same subject twice during 1 day, a difference of 3.5 cm was noted (Tables 2 and 3). It was interesting to see that all observers showed a decrease in accuracy between measuring Subject 2 the first time and the second time. This demonstrates that the observers failed to obtain repeatability, even though there was only a 2-hr time period between measurements. The lack of repeatability between measurements was also noted when the same observer measured a thigh on 50 occasions in a 1-hr period, when a 3.35%, or 1.68-cm, difference was recorded. This decrease in error, compared with interobserver error, was not surprising. However, it was not expected that the error would be more than 8 times that reported by Katch and Katch (2) and almost 4 times greater than that suggested by Lohman et al. (3). As explained above, no explanation can be given for why the percentage error was considerably higher than those found by the other authors. From a practical point of view, it appears that thigh bulk measurements are not reproducible. This lack of reproducibility when tape measurements are used in clinical practice was highlighted by Fairclough et al. (I), who demonstrated that observers failed to notice an increase of 3 cm when measuring abdominal girth with a tape measure. Perhaps the most cogent reason for regarding this form of measurement with skepticism is the clear evidence that observers are capable of, and often demonstrate, sufficient bias to allow them to ignore differences in thigh girth of up to 3 cm. This is clearly seen in Tables 1-4. The ease of use and ready availability of tape measures have led their use in clinical practice to become standard, but this does not indicate the value of their use. In order for any measurement to be of value, it must have a degree of consis-

7 Measuring Thigh Girth 49 tency in order to allow an observer to recognize some change from normal, whether same-side or opposite-side measurements are used. This report, however, clearly shows that the degree of inaccuracy of tape measurements of the thigh is sufficient to indicate that it is of little value in the assessment of the lower limb. Conclusion Using a tape measure to measure thigh bulk, and using this measurement as an indicator of muscle hypertrophy or atrophy, is a common technique of medical practitioners and physiotherapists. Although the sample size is small, it has been shown in this study that the technique, used independently, is not a reliable method of monitoring the rehabilitation of a patient. Nonetheless, a larger trial needs to be undertaken to validate these findings. References 1. Fairclough, J.A., W.J. Mintowt-Czyz, I. Mackie, and L. Nokes. Abdominal girth: An unreliable measure of intra-abdominal bleeding. Injury 16:85-87, Katch, El., and V.L. Katch. Measurement and prediction error in body composition assessment and the search for the perfect prediction equation. Res. Q. Exerc. Sport 51: , Lohman, T.G., A.F. Roche, and R. Martorell (Eds.). Anthropometric Standardization Reference Manual (abridged ed.). Champaign, L: Human Kinetics, Soderberg, G.L., B.T. Ballantyne, and L.L. Kestel. Reliability of lower extremity girth measurements after anterior cruciate ligament reconstruction. Physiothel: Res. Int. 1:7-16, Acknowledgments Special thanks to Dr John Williams, Alison Maylia, and colleagues from the Medical Engineering Research Unit for their help during the preparation of this paper.