Considerable progress has been made in recent years in the development of non-invasive methods for the assessment of the skeleton. Among the numerous measuring alternatives, Dual Energy X-Ray Absorptiometry (DEXA) is unquestionably the method of choice for the assessment of bone mass and subsequently the risk of osteoporosis as well as monitoring the effects of therapy.

The rationale of the technique lies in the fact that all DEXA systems generate X-Rays at two different energies and make use of the differential attenuation of the X-Ray beam through the body. Two scanning modes i.e. pencil or fan beam have been developed.

Most DEXA instruments have been extensively validated for the quantitative assessment of bone mass in the clinically important skeletal sites particularly at risk of osteoporotic fracture i.e. the lumbar spine, the hip and the forearm. These measurements assess areal bone mineral density (BMD), which integrates the size of the bone and its thickness, as well as the true volumetric density. Areal density provides useful information relative to fracture risk, since there is a strong inverse relationship between incidence of osteoporotic fractures and BMD.

More specialized DEXA systems also perform whole-body scans and can be used to determine the bone and soft tissue composition of the whole body as well as of sub regions such as arms, legs, and trunk. Although several methods for measuring body composition are available, in the medical setting DEXA became the gold standard for everyday practice. Thus, the method is increasingly used to measure body composition in terms of fat and fat-free mass.

The effective dose incurred during DEXA scanning is very small, and, consequently, DEXA is a simple and safe technique: Studies of radiation dose to patient from DEXA confirm that patient dose is small (0.08-4.6 _Sv) compared to that given by many other modalities involving ionizing radiation. The accuracy of DEXA measurements, however, can be problematic: Marked systematic differences in bone and soft tissue values are found between the commercially available systems due to differences in calibration, bone edge detection and other factors, but results generally correlate well with ashed bone measurements. In addition, differences in reference data provided by each manufacturer can lead to an individual appearing normal on one machine but at risk of osteoporosis on another.

As far as body composition measurements, major sources of inaccuracy include inhomogeneous distributions of fat, hydration, software version, hardware and the subject population. Lack of absolute inter unit comparability may cause difficulties in clinical practice.

However, the potential for error in terms of both accuracy and precision for dua x-ray absorptiometry measurements emphasizes the need for meticulous attention to detail in data acquisition and data analysis, and a knowledge of the limitations of the particular technique, are the prerequisites for generating valid data, thus eliminating much of the contradictory conclusions among investigations, especially follow-ups.

Weightlifting training intergrates muscle training and a high-protein, low-fat diet in order to achieve maximal muscle mass and strength. A compromise with body weight exists: Since body weight is an important factor, every attempt to change it, may provoke alterations in body composition. It is evident that DEXA can be used as a valuable tool in the follow up during the training period of weightlifters. In contrast with other sports, there are very few data regarding this issue.

We and others studied by means of DEXA on several occasions competitive weightlifters and found that:

• Weightlifters had higher bone mass density and lean mass and lower fat mass than the controls.
• During the pre-competition training, weightlifters lost fat, while they exhibited a trend towards lean mass gain.
• Higher performance (Sinclair Index) was associated with lower off-season %fat, higher off season %lean mass and lower fat reduction during training for competition.

These results indicate that a good physical condition, when monitored by the off-season metabolically more optimal body composition profile as assessed by DEXA, is associated with higher scores in competition.

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