Segmented lateral compartmental analysis resulted in strong intrarater reliability for left and right leg measures of LM, FM, and total mass in the anterior and posterior compartments (Table 4). Intrarater CV values also demonstrated high reliability and precision for LM, FM, and total mass in the anterior and posterior compartments (Table 4). Segmented total (i.e., sum of anterior and posterior compartments) upper leg measurements resulted in slightly lower reliability, on average, and larger CV values than those obtained for compartmental (i.e., anterior/posterior) measurements across LM, FM, and total mass. All intrarater CV values for segmented total upper leg composition were ≤3.85% and for compartmental composition were ≤2.69% (Table 4).
This is the first study to assess lateral subject positioning using DXA to analyze ipsilateral upper leg compartmental (i.e., anterior/posterior) composition. The current study demonstrates that the segmented lateral DXA scanning method developed by our research group is both accurate and reliable in assessing LM, FM, and total tissue mass compared with traditional scanning methods. This study observed no significant differences between the total-body frontal and the segmented lateral DXA scan body composition measures in either leg of each participant. Inter- and intrarater reliability was high for the quantification and assessment of segmented lateral upper leg compartment-specific LM, FM, and total tissue mass.
To understand the context of our findings, current literature only reports the high reliability of contralateral regional comparisons of the upper leg (thigh) and lower leg (calf muscles) in the traditional total-body frontal view using manually generated ROIs and supine and prone subject positioning (5,13,18,23). As such, current literature does not report the accuracy nor the reliability of a lateral view DXA scan—a scanning method that would provide a more in-depth body composition analysis of ipsilateral symmetry and regional differences within a leg in athletic and clinical populations. The findings of this study therefore add to the current body of literature by providing initial accuracy and reliability support for using lateral subject positioning as an additional method to assess body composition, including LM, FM, and total tissue mass, using DXA—not only for contralateral comparisons, as previous research (5,13,23) has examined, but also for ipsilateral compartmental (anterior vs posterior) comparisons. Although the preceding measurements may be possible using CT and magnetic resonance imaging, the limitations associated with these two methods (i.e., cost, feasibility, accessibility, and CT radiation) make their use unlikely for assessing compartmental composition (1). In comparison, DXA’s increased feasibility and accessibility, lower cost, quick scan time, and minimal radiation make DXA a practical method to assess compartmental body composition.
Among athletes, current literature notes the utilization of DXA as a practical method to assess an athlete’s body composition in the total-body frontal plane as it relates to performance and nutritional intervention (1). Nana et al. (21) note the use of this assessment to describe athletes’ physical characteristics across sports or within the same sport (26,27), to examine an athlete’s suitability for a weight class in a weight division sport (e.g., wrestling) (6), and to examine athletes’ contralateral leg asymmetries—in the standard total-body frontal plane—for FM and LM measures (17). Therefore, a lateral scan analysis would not only provide information about athletes’ physical characteristics and contralateral symmetry but also ipsilateral symmetry in opposing upper leg compartments. Further, examination of opposing ipsilateral, compartmental differences in the lower limbs may be more beneficial in assessing injury risk, causes of injury, and the rehabilitation process, as changes in body composition affect elite athletes’ competitive performance (24). In fact, segmented lateral DXA scans would allow for longitudinal tracking of compositional changes (e.g., baseline/preinjury, postinjury, before returning to play, etc., or during multiple seasons) in opposing ipsilateral body compartments of athletes, as previous studies have made this assessment using the total-body frontal scanning method (2,25).
Clinically, precise and accurate body composition measurement is important in assessing certain medical conditions (e.g., sarcopenia), the aging process, and evaluating interventions (12). In addition, segmented DXA body composition assessment methods may be useful in populations where standard DXA positioning remains a significant challenge (e.g., musculoskeletal disorders). This segmented lateral scanning method could be used to assess and longitudinally monitor body composition changes in elderly, diseased, and disabled populations affected by muscle wasting; this is in addition to monitoring LM improvements (and prevention of LM loss) over time in response to individualized therapeutic interventions (e.g., pretherapy, midpoint, posttherapy). Therefore, the ability of this novel segmented lateral scanning method to evaluate opposing ipsilateral and contralateral regions of the body would provide greater insight into the injury, aging, and disease processes affecting LM and FM measures.
Major strengths of the current study include the study population's wide body composition variability (BMI range = 19.0–32.0 kg·m−2) and the type of statistical analyses performed (paired t-tests and ICC). The former allowed for reliability assessment across a broad BMI value range. A study population with a narrower BMI range may have resulted in lower variation in the standard deviation of the mean differences (i.e., greater accuracy) and smaller CV values (i.e., greater reliability)—biased results which, while desired, limit generalizability. Second, the within-subject statistical analyses chosen—for both accuracy and reliability examinations—controlled for differences between subjects.
Limitations of the current pilot study include its small sample size, the potential systematic measurement errors in the manual generation of ROIs, and the limited custom ROI box size due to the ankle foam pad. Specifically, the small sample size may have contributed to higher variation in the standard deviation of the mean differences comparing the two scanning methods and between and within raters reflected in higher CV values. Yet despite its small sample size, this study provides initial evidence for this segmented lateral scanning method’s accuracy and reliability. Second, although specific instructions detailed the manual production of ROI borders, slight differences in ROI box measurements may have occurred between the frontal and the lateral scans and for compartmental tissue quantification between and within raters. Third, the ankle foam pad limited the custom ROI box size in comparing the two scanning methods, as frontal and lateral scan ROI borders were drawn to avoid pad inclusion. Further, the postscan analysis of this segmented lateral scanning method may not be capable of fully separating muscle compartments—a limitation of the DXA scanner. Despite these limitations, no significant differences in body composition measures were observed between frontal and lateral scanning methods, and ICC and CV values were reliable between and within raters. A larger sample size and greater precision of custom ROI borders may demonstrate higher reliability.
In conclusion, we made the novel observation that lateral subject positioning using DXA is an accurate and reliable method to assess compartmental composition, allowing for the assessment of LM, FM, and total tissue mass in the anterior and posterior upper leg compartments. Future research should examine reliability measures using a larger sample size and a diverse array of populations across age, body size, body fatness, athletic status, and musculoskeletal development. Future studies may also evaluate the feasibility of examining upper extremity compartmental composition using this novel lateral DXA scanning method to assess potential imbalances. Limitations of examining the upper limbs, however, may include difficulty in upper extremity lateral positioning on the DXA scanner due to shoulder and forearm rotational differences across individuals, difficulty in delineating the upper arm’s anatomically smaller anterior/posterior compartments, and difficulty in obtaining a maximal visible area of soft tissue without head interference. Nonetheless, the ability to assess upper and lower extremity compartmental composition using this study's lateral DXA scanning method may provide a more in-depth analysis for rehabilitative, clinical, and performance purposes.
This study was funded by the Clinical and Translational Science Institute (CTSI) at the University of Minnesota (CTSA: NIH UL1TR000114).
There were no conflicts of interest in the current study. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.
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Keywords:© 2017 American College of Sports Medicine
DUAL X-RAY ABSORPTIOMETRY; SEGMENTATION; REGION OF INTEREST; LEAN MASS; FAT MASS