A Brief Review of the Literature for Published Dual-Energy X-Ray Absorptiometry Protocols for Athletes

Abstract

Context:

Dual-energy x-ray absorptiometry (DXA) is widely known for its utility in diagnosing a patient with osteopenia or osteoporosis; however, its utility in evaluation of body composition and potential athletic performance was previously routinely overlooked. In recent years, athletic programs have begun employing this equipment during athlete screening. However, it is currently unknown how athletic programs are utilizing this information to guide an athlete’s training and health.

Objective:

To explore the literature to identify what is known regarding sports performance and athlete health based on body composition recordings.

Data Sources:

PubMed and Google Scholar databases were searched for this brief review.

Study Selection:

A focus was placed on articles within the past 10 years that discussed DXA protocols within athletic populations; 14 articles were included in this brief literature review.

Study Design:

Brief literature review.

Level of Evidence:

Level 5.

Data Extraction:

One member of the research team searched the literature and retrieved articles with the purpose of analyzing and/or explaining DXA imaging in body composition analysis of active persons (primarily athletes).

Results:

Quality assurance scans with a phantom calibration block as well as athlete prescreening condition and activity standardization was routinely recommended. However, only 1 study reported a specific DXA protocol for athletes, and only 1 study described guidelines for how to report DXA results in athletic populations, suggesting it is plausible yet difficult due to the small changes detectable.

Conclusion:

Due to the limited literature as well as a lack of reference values for specific athletic populations, the authors of this review recommend using the current Nana et al (Int J Sport Nutr Exerc Metab 2015;25:198-215) DXA protocol for performing DXA scans in the athletic population as well as current Hind et al (J Clin Densitom 2018;21:429-443) guidelines for distributing the information.

In 2020, the prevalence of low energy availability (described as inadequate energy intake relative to energy expenditure) in athletes was reported to range from 22% to 58%.^16,17 This finding is concerning due to the widely acknowledged fact that low energy availability is a significant factor triggering relative energy deficiency in sports’ unfavorable health outcomes and performance. ¹⁷ Among the unfavorable outcomes, weight-control behaviors due to the perceived vitality of low body weight for peak performance have been seen in athletes from a range of elite sports, especially leanness sports. ³⁰ Unfortunately, this may lead to gradual weight loss that can impact an athlete’s performance via increasing the athlete’s risk of slow glycogen resynthesis after training, loss of muscle protein, and experiencing stress fractures (caused by endocrinological disorders). ⁶ Additionally, athletes with a higher body weight due to a higher lean body mass, body weight and body mass index may lead to misclassification of the athlete as overweight or obese.” ⁹ Therefore, a new method for athlete body metrics characterization is needed.

One option is dual-energy x-ray absorptiometry (DXA). DXA scans have been utilized to determine bone composition and density as far back as the 1950s. ⁵ DXA employs x-ray technology to assess bone mineral density, fat mass, lean muscle mass, etc. For fat mass and lean muscle mass, photons at 2 different energies (eg, 40 and 70 keV) pass through soft tissue, allowing for the identification of a ratio of energy attenuation. ²⁹ This ratio is inserted into a predetermined algebraic equation for body composition calculation. ²⁹ Bone density measurements differ due to the requirement for comparing bone density to a sex-based reference population. ²⁸ As this technology has continued to develop, it has not only become the gold standard for measuring bone health^23,28 but also one of the methods of choice for measurement of body composition in athletes. ⁸ With this said, the International Society for Clinical Densitometry routinely publishes official positions regarding DXA body composition techniques in various populations, including HIV, bariatric surgery, sarcopenic, and obese patients; however, the International Society for Clinical Densitometry has not announced positions regarding body composition screening in athletes. ¹² Furthermore, the most recent studies investigating athlete body composition often include patient demographics, measuring instruments, time of the season, and country, but fail to include exact DXA positioning, calibration, and body tracking parameters. ²⁵ Therefore, the purpose of this review is to summarize the available literature for DXA protocols for measuring athlete body composition as well as the guidelines for utilizing DXA results for athlete safety, injury prevention, and training.

Methods

PubMed and Google Scholar databases was searched for this brief review. A focus was placed on articles within the past 10 years (2012-2022) that discussed DXA protocols within athletic populations. Specifically, the following search terms were used: dual-energy x-ray absorptiometry, DXA, protocol, athlete, sports, and body composition. One member of the research team searched the literature and retrieved articles with the purpose of analyzing and/or explaining DXA imaging in body composition analysis of active people (primarily athletes). Ultimately, the first 50 manuscripts for PubMed and Google Scholar databases were included in the initial analysis (100 total), as described in Figure 1. Articles were excluded if they were duplicated between databases; not in the English language; did not include DXA scan analysis; and did not discuss sports, athletes, and/or body composition. Once the articles were gathered, basic study information, research study participant demographics, DXA protocols, body composition tracking information, and pertinent conclusions were recorded. The studies were included only if they discussed body composition and/or fat and muscle mass analysis.

Figure 1.

Inclusion and exclusion flowchart.

Results

After searching the literature, 14 articles were incorporated in this brief review. Of these 14 articles, 6 were written in the form of a review and 3 incorporated position statements on DXA body composition analyses. The remaining papers were cross-sectional cohort-type studies where the subject acted as their own control. The included studies had a level of evidence between 3 and 5 (Table 1).

Table 1.

Study information

	Year of Publication	Level of Study	Study Description
Ackland et al 1	2012	5	Review and position statement
Colyer et al 2	2016	3	Cohort
Dunne et al 4	2022	4	Systematic review
Hind et al 8	2018	4	Systematic review
Kasper et al 11	2021	4	Scoping review
Kerr et al 14	2016	3	Cohort
Kerr et al 13	2017	3	Cohort
Larson-Meyer et al 15	2017	5	Review and position statement
Martin et al 18	2019	5	Position report
Nana et al 20	2012	3	Cohort
Nana et al 21	2013	3	Cohort
Nana et al 22	2015	4	Systematic review
Vargas-Molina et al 27	2020	3	Cohort
Zemski et al 31	2018	3	Cohort

Study participant demographics were limited in the majority of the review studies (Table 2). The remaining studies analyzed primarily various athletic populations, and 12 of the 14 studies utilized or recommended the use of quality assurance scans with a phantom calibration block, in accordance with guidelines from the DXA manufacturer. Additional standardization such as adequate rest, hydration, and fasting remain as consistent protocols to follow for accurate DXA measurement as well as other body composition methods.

Table 2.

Study participant demographics

	Women	Men	Mean Age, years	Athletes	Sport	Quality Control Scan
Ackland et al 1	–	–	–	–	–	–
Colyer et al 2	19	34	23 ± 4	Yes	Rugby, bob skeleton, swimming, athletics	Yes
Dunne et al 4	–	–	–	–	–	Recommends
Hind et al 8	–	–	–	–	–	Recommends
Kasper et al 11	–	–	–	–	–	Recommends
Kerr et al 14	16	14	36 ± 11	No	–	Yes
Kerr et al 13	0	32	31 ± 7	Yes	Resistance trained (> 2 years)	Yes
Larson-Meyer et al 15	–	–	–	–	–	–
Martin et al 18	–	–	–	Yes	–	Recommends
Nana et al 20	15	16	28 ± 6	Yes	Physically active at least 28 hours per week	Yes
Nana et al 21	41	14	28.3	Yes	Cycling, strength training	Yes
Nana et al 22	–	–	–	–	–	Recommends
Vargas-Molina et al 27	21	0	27.6 ± 4.0	Yes	Resistance trained (> 2 years)	Yes
Zemski et al 31	11	10	30.6 ± 0.2	Yes	Resistance trained	Yes

Lastly, as the research team gathered data from the articles, it was determined that considerable overlap in DXA scan protocol was occurring (Table 3). With this said, many studies also identified and reported the importance of standardizing DXA prescan and scan protocols in producing reliable, repeatable results, more so when tracking longitudinal changes in body composition. In most instances, athletes see little to no significant change over repeated DXA scans, which challenges any indication of the onset of injury, overtraining, etc. Only 1 study, Nana et al, ²² reported a specific DXA protocol for athletes, and only 1 study, Hind et al, ⁸ described guidelines for how to report DXA results in athletic populations (Table 4), suggesting it is plausible yet difficult due to the small changes detectible.

Table 3.

DXA protocol, body composition tracking, and study conclusions

	Performing DXA Scan Protocol	Body Composition Tracking	Study Conclusions
Ackland et al 1	No specific protocol discussed	Does not discuss tracking training and/or body composition changes	No gold standard methodology is available for body composition assessment currently Small, large, and/or lean athletes may experience higher errors The soft tissue of people who are very obese may move beyond the width of the scanning area Persons taller than 192 cm may be too tall for the scanning bed
Colyer et al 2	Two whole-body DXA scans, typically within 48 hours Supine position on the scanning bed enabled body regions to be easily partitioned Immediately after the supine position scan, the technician identified anatomic landmarks within the software that allowed the system to make its calculations The sum of all region masses was utilized to calculate the whole-body measurements	DXA scan can detect meaningful body composition changes in response to emphases on specific training The changes measured include and give the ability to: measure physical performance; confirm influence of body composition on strength and power ; inform training progress	Fat mass error was larger than the total mass and lean mass error measurements of the same body region No apparent sex differences in error measurements Total fat mass error measurements were higher in leaner athletes May have the ability to identify unfavorable body composition changes during a competitive season May be utilized to guide diet and training interventions in athletes
Dunne et al 4	No specific protocol discussed	Does not discuss tracking training and/or body composition changes	Fat and lean athletes may not receive reliable measurements
Hind et al 8	No specific protocol discussed	In highly trained athletes with minimal body composition changes over a period of time, it should be noted that reducing the precision error will also decrease the least significant change as well as the time required to detect significant changes	Standardize practice and reporting of longitudinal DXA measurements of body composition in athletes is needed Proposes a guide to support utilization of DXA scans in the sports science and medicine fields
Kasper et al 11	No specific protocol discussed	To date, no equation for body composition tracking has been validated for athletes due to wide variation across athlete body types pending specific sport If the goal is to track body fat changes, skinfold measurements may be the superior method of measurement when reported as a sum of millimeters rather than a relative percentage value	DXA is the best method to measure lean mass changes and/or if bone density measurements are required DXA utilization for body composition analysis has proven to be reliable and fast; however, it is not the most affordable or accessible form of body composition assessment available
Kerr et al 14	Nana et al 20 protocol was utilized NHANES protocol was also utilized, which described 2 scans being performed The patient was centrally aligned on the densitometer table with the feet internally rotated and Velcro strapped at the ankles The hands were laterally positioned against the hips	Does not discuss tracking training and/or body composition changes	Nana et al 20 positioning protocol on a single-beam DXA scanner reduces technical variability for regional fat mass and body mass composition Substantial differences noted between the Nana et al 20 and NHANES protocol with regional assessment highlighted the importance of exclusivity and that scans should not be interchanged
Kerr et al 13	Nana et al 20 and Kerr et al 14 protocols were utilized	Regression equations for DXA scans to track body fat were not validated	Biological error will be significantly increased for any DXA body composition measurements undertaken with nonstandardized presentation of subjects Subject presentation standardization (example below) should be mandatory for all DXA body composition analyses Overnight fasting, well-rested, and specific hydration regimen
Larson-Meyer et al 15	No specific protocol discussed	Over a period of time, DXA has limited ability to detect small body composition	Calibration algorithms have not been developed on athletes and are mostly unpublished and differ between manufacturers Protocols need to be standardized to increase reliability and monitor body composition changes over time Positioning and clothing should be standardized When performing DXA scans in athletes, the participant should be hydrated, fasted, measured after voiding and defecating, and having not exercised that day Fat and lean athletes may not receive reliable measurements
Martin et al 18	No specific protocol discussed	It is possible DXA scans could be a reliable tool to assess body composition changes over time; however, more research must be performed to validate this theory	Studies looking at DXA analysis for athletes have shown practicality advantages but no accuracy advantages for this assessment modality Seasonal body composition variability may be possible with newer DXA models; however, insufficient data are currently available Newer DXA models have not been adequately tested for accuracy and reproducibility against alternative measurements at this time
Nana et al 20	Five whole-body DXA scans were performed during a 2-day period on each participant In the morning after an overnight fast 5 minutes later after repositioning on the scanning bed 8 hours later after usual daily activities The following morning before breakfast 30 minutes after breakfast The participants were aligned in the center of the scanning area with their feet and hands placed in custom foam blocks with 15 cm between the feet and 3 cm between the hands and trunk The custom-made blocks were made of Styrofoam and were transparent under DXA Scans were automatically analyzed by the software and were confirmed by the technician	Does not discuss tracking training and/or body composition changes	Daily activities, including fluid and food intake, will increase the value of body composition estimates via DXA Future studies need to report their scanning and analysis protocols Changes in the mean of repeated measurements (immediate) and between-day biological variation (am to am) for total and regional mass estimates, for total lean mass, and for total and regional body mass composition was less than the smallest worthwhile effect No substantial changes in the mean of total and regional fat mass was identified depending upon the conditions (immediate, am to pm, am to am, and am to meal) Within an hour of eating a meal, effects were seen primarily in terms of total and trunk estimate increases of mass and lean mass
Nana et al 21	Nana et al 20 protocol was utilized	Does not discuss tracking training and/or body composition changes	Utilizing fasted and rested subjects with a standardized scanning protocol is the easiest and most practical way to minimize biological noise 1 hour of strength training depicted trivial changes in total and most regional mass estimates Trivial changes were identified in immediate reassessment for total and regional lean and fat mass estimates for strength-trained and cyclist-trained subjects After cycling, an identifiable, yet small, change between male and female cyclists in total and regional body composition estimates was identified
Nana et al 22	Prescanning Minimal clothing worn Fasted with no fluid No exercise Optimize hydration Bladder voided Scanning Perform routine quality control and quality assurance system in place Standardize positioning with positioning aids as needed Analysis Check the regional analysis software Have standardized regional composition analysis protocol One technician to perform and analyze the scan over time	Does not discuss tracking training and/or body composition changes	Until future work and further refinements are made, the Best Practice Protocol should be considered the standard of care
Vargas-Molina et al 27	Both pre- and postintervention, DXA scans were performed 7 days postmenstruation Trunk tissue (area defined below) was included in the body composition analysis The upper horizontal border of the stomach was located at half the distance between the external end of iliac crests and the acromion process, while a lower border was identified by lateral borders extending to the edge of the abdominal soft tissue and the external end of the iliac crests Result reliability was obtained by having 2 separate observers select the measured area for each participant	Does not discuss tracking training and/or body composition changes	The stated purpose and methods of the study could be a source of measurement error due to prestudy body composition scans being performed when glycogen levels are high versus poststudy scans being performed during a glycogen deplete state
Zemski et al 31	Participants had 2 consecutive DXA scans performed on the first day of testing A third scan was completed either the day before or after The Nana et al 22 protocol was utilized	Precision error and least significant change values should be calculated from a consecutive day analysis and utilized when tracking changes in body composition Technical error and biological variation accounted for in this manner which is important to interpreting longitudinal change	The least significant change should be calculated for body composition before quantitative statement of changes are made for fat mass and/or lean mass measurements The majority of regional body composition measures, and whole-body mass composition, fat mass, and lean mass measurements depicted significant sex-specific differences When DXA scans were performed on the same day, excellent precision was obtained Regional precision for consecutive day measurements was similar to same day measurements for body mass composition in all areas

DXA, dual-energy x-ray absorptiometry.

Table 4.

Athlete DXA scan acquisition and distribution guidelines^8,22

Nana et al 22 DXA Protocol for Athletes

Hind et al 8 DXA Reporting for Athletes

• Prescanning ○ Athletes should wear minimal clothing which may include wire-free underwear or crop top with all jewelry removed ○ Athletes should be fasting with no fluid intake on the morning of the DXA ○ No exercise should take place on the morning of the DXA ○ The hydration status of the athlete should be optimized and checked by specific gravity analysis on a urine sample as soon as the athlete wakes up ○ The bladder should be completely voided before the scan • Scanning ○ DXA equipment should undergo frequent, routine, quality control checks as well as placement and maintenance of the quality assurance system ○ Positioning of the athlete should be standardized with positioning aids if possible • Analysis ○ Regional software analysis should be checked ○ Regional composition analysis protocol should be standardized ○ One technician should undertake and analyze all scans, if possible

• At baseline and follow-up, record the DXA system manufacturer, model, and software • If applicable, include scan mode information and reference population details ○ Include a statement regarding meaningful individual changes in body composition with least significant change (= 277 × precision error) • Fully describe the athlete’s prescan preparation, positioning (include whether athlete did not fit within DXA scan parameters), and use of any/all positioning aids ○ For special consideration subpopulations (disabilities, too broad, too tall), fully specify techniques and accommodations utilized • Analysis technique should be described for any reported regional composition • Any/all customized region of interest should be described in detail • In methods, include how precision error of measurements was calculated (eg, sample size, demographics, scanning protocol, scan mode, etc) ○ Also, state the precision error for each outcome of interest

DXA, dual-energy x-ray absorptiometry.

Discussion

DXA is an imaging strategy suitable for most athletes and provides the distinct advantage of providing regional body composition information in a short amount of time, utilizing low-dose radiation. ²² In comparison with magnetic resonance imaging (MRI), visceral adipose tissue measurements derived from DXA were larger and more significantly correlated with those derived from MRI across a wide range of values. ¹⁹ Therefore, utilizing DXA as the choice imaging modality is reasonable assuming the correct data are gathered per patient/athlete demographic; however, determining what data should be gathered for each athlete demographic may prove difficult due to lack of literature. Currently, no evidence exists for DXA body composition screening and tracking in pediatric athletes; however, for generalized pediatric osteoporosis diagnoses, it has been recommended to receive a total body less head and posterior-anterior (PA) spine, while the adult cohort should obtain PA spine, total hip, and femoral neck. ³ In adult populations, DXA protocols have been standardized across many devices and populations; however, there is not currently a universal, athlete-specific DXA protocol for institutions to reference for bone health and body composition considerations.

The literature has recently begun supplying DXA protocols for assessing body composition in athletes,^20,22 as well as how to utilize the interpretations ⁸ ; however, the literature is limited in this population. With this said, there is no shortage of hypotheses for how it may be useful. First, DXA can be utilized for the analysis of relative energy deficiency in sports diagnosis by recording data from a young athlete, including hip, spine, and total body assessment for osteopenia, low fat, and low muscle mass evaluation. ²⁶ DXA may also be utilized to evaluate recovery from injury and performance by looking at differences between contralateral limbs.^7,10,26 However, numerous challenges still exist within this field, such as the validation of DXA measurements.^13,18 Santos et al ²⁴ have begun the process of validation of DXA instrumentation in athletes, but much work must still be performed for this to be a reliable tool. Due to the limited literature as well as lack of reference values for specific athletic populations, the authors of this review recommend using the current Nana et al ²² DXA protocol for performing DXA scans in the athletic population as well as current Hind et al ⁸ guidelines for distributing the resulting information (Table 4).

Conclusion

Due to the limited nature of the protocols as well as standardized-reference population values, the authors of this review propose utilizing a cross-sectional survey gathering current DXA protocols from athletic programs as well as previously gathered athlete body composition and injury data. There is a documented need for standardized practice and reporting in athletic populations for the longitudinal measurement of body composition using DXA. ⁸ With such standardization in place, athletic programs will have a better understanding of how to utilize the metrics they gather. Until additional information is gathered, it is recommended athletic programs follow Nana et al ⁸ DXA protocol for athletes, which suggests that prescan clothing, food/drink, and exercise of the athlete, as well as DXA equipment maintenance, athlete positioning for DXA, and DXA analysis, be standardized. ²²