CORRELACIÓN EXISTENTE ENTRE RENTABILIDAD ABSOLUTA Y

Upper arm anthropometry provides additional information to BMI (kg/m²) and WC (cm) by allowing a determination of body composition through the prediction of fat mass (FM) from tricep skinfold thickness (TSF) and fat free mass (FFM) from mid arm muscle circumference. The prediction of FFM in particular is important in older people as this is likely to influence functional status and thus influence a person’s ability to perform activities of daily living (ADL). As there is growing concern about the health risks associated with the loss of FFM with ageing it is important to measure this within the study population. Protocols published by ISAK were also used for upper arm anthropometry (Norton & Olds, 1999) and measurements were standardised to the right side of the body (Norton & Olds, 1999). Comparisons between the left and right sides of the body have shown that there is either no significant difference in skinfold thickness (Womersley & Durnin, 1973) or that the differences, although statistically significant, are of no clinical significance (Martorell et al., 1988). Standardising the measurements to the right side of the body will therefore not affect the results of the study.

2.3.2.1 Mid upper arm circumference (MUAC) (cm)

As the arm contains both subcutaneous fat and muscle, mid upper arm circumference (MUAC) (cm) can be used to indirectly estimate FM and FFM together (Heyward & Wagner, 2004). MUAC (cm) was measured using a flexible Lufkin W606PM steel tape measure. The point of measurement for MUAC is the midpoint equidistant from the acromiale and radiale. Participants were asked to stand and assume a relaxed position, arms hanging freely by their sides. Their palms faced their thighs and their shoulder girdle was in a mid position in order to allow identification of the acromiale and the radiale.

The acromiale is the point at the superior and external border of the acromion process of the scapula. This was located by the researcher positioning themselves behind the right side of the participant. The spine of the scapula to the corner of the acromion was palpated and the straight edge of a pencil was then applied to the lateral external border of the scapula to identify the most lateral part of the border of the acromion process. The most superior, lateral margin was located with the side of the thumb and marked with a hypoallergenic pencil.

The radiale is the point at the proximal and lateral border of the head of the radius.

This was located by the researcher again being positioned at the right side of the participant. The right thumb was used to palpate downward in the lower portion of the lateral dimple of the right elbow. If necessary, participants were asked to pronate or supinate their forearm to produce a rotary movement of the head of the radius. The position was then marked with a hypoallergenic pencil. Once identified the linear distance was measured between the acromiale and radiale landmarks with the arm relaxed and extended at the side, avoiding any curvature surface of the arm. A horizontal mark using a hypoallergenic pencil was placed at the midpoint

between these two landmarks. The mark was then projected around to the posterior surface of the arm as a horizontal line (to allow the measurement of the tricep skinfold).

In order to obtain the MUAC, participants continued to assume a relaxed position with arms hanging by their sides. The participants arm was abducted slightly to allow the steel tape measure to be passed around the arm. The tape was placed perpendicular to the long axis of the arm when the subject was standing erect. The circumference was measured at the marked level of the mid acromiale - radiale line.

The MUAC was measured to the nearest 0.1 cm.

MUAC (cm) measures both FM and FFM and so to determine FM, the TSF (mm) can be measured which in combination with the MUAC allows for the calculation of mid arm muscle circumference (MAMC (cm)) which is an indirect measure of FFM.

2.3.2.2 Tricep skinfold thickness (TSF) (mm)

Tricep skinfold thickness was measured to 0.2 mm using Harpenden skinfold calipers. The Harpenden calipers were calibrated by Harpenden prior to commencing the study and again at the end of the study. The tricep skinfold site is the most widely used single skinfold site for estimating total fat mass stores operating on the assumption that subcutaneous fat stores at this point are representative of whole body fat stores (Brodie & Hutcheon 1998).

The participant was asked to assume a relaxed position with the right arm hanging by the side but this time with the shoulder joint slightly externally rotated and the elbow extended at the side of the body. The skinfold was raised parallel to the long axis of the arm at the site of the posterior mid acromiale - radiale line. The skinfold

was grasped and raised at the marked line so that a double fold of skin plus the underlying subcutaneous adipose tissue was held between the thumb and index finger of the left hand. The nearest edge of the contact faces of the calipers were applied 1 cm away from the edge of the thumb and finger. The measurement was recorded two seconds after the full pressure of the calipers was applied (Kramer &

Ulmer, 1981). This approach was used as adipose tissue is compressible and a constant recording time enables test/retest comparisons to be made while controlling for this known compressibility (Martin et al., 1985). Two measurements were taken and the mean value recorded.

2.3.2.3 Mid arm muscle circumference (MAMC) (cm)

Mid arm muscle circumference (MAMC) is considered to be an estimate of fat free mass (FFM) and is commonly used to reflect whole body FFM stores (Jackson &

Pollock, 1976). It represents the circumference of the inner circle of muscle mass surrounding a small central core of bone (Gurney & Jelliffe, 1973). It does have some limitations in that it does not take into account inter-subject variation in the diameter of the humerus relative to the MAMC (Frisancho, 1981). Despite this, it is widely used as a marker of FFM as it is considered an accurate reflection of this body compartment. MAMC is derived from the measurements of MAC and TSF as described above using the following equation:

MAMC (cm) = MUAC (cm) - (л x TSF (mm)) (Frisancho, 1990)