Total and appendicular body composition comparisons between near-infrared reactance spectroscopy and dual energy X-ray absorptiometry.

Background: Near-infrared reactance spectroscopy (NIRS) has become increasingly popular in personal and professional settings now that it has been adapted to provide comprehensive body composition assessments. However, whether NIRS agrees with criterion methods remains unknown. Thus, this study aimed to determine the agreement between NIRS and DXA-derived body composition estimates.

Methods: Ninety-seven participants completed body composition assessments using DXA, and first-generation (NIRS_G1), second-generation (NIRS_G2), and muscle-specific NIRS (NIRS_FIT) devices. On a separate day, a subset of participants (n = 63) performed maximal voluntary contractions (MVC) on a handgrip dynamometer, which were used in conjunction with total appendicular lean mass (ALM) estimates to provide ratios (MVC/total ALM or MVC/ALM of the arms only) depicting muscle quality index (MQI).

Results: Fat mass, fat-free mass, body fat %, and ALM, from NIRS_G2, but not bone mineral content (BMC), and NIRS_FIT demonstrated equivalence (using equivalence tests) with DXA with R² from 0.83 to 0.97; though BMC revealed concordance coefficients of 0.83 and an R² of 0.88. MQI using total ALM from NIRS was not equivalent to DXA, but demonstrated low root mean squared error (0.08 kg/kg) and 95% limits of agreement (±0.21 kg/kg). Indices of visceral adipose tissue (iVAT) from NIRS_G1 and NIRS_G2 were significantly different (p < 0.001), but were both significantly associated with DXA VAT (NIRS_G1 R²: 0.53; NIRS_G2 R²: 0.62; both p < 0.001).

Conclusion: NIRS appears to demonstrate acceptable agreement with DXA and continual improvements could make NIRS a viable alternative for comprehensive body composition assessments.