Accurate, accessible imaging of skeletal muscle size is important for monitoring training adaptations and clinical conditions. The authors evaluated an extended field-of-view (EFOV) wireless palm-sized ultrasound device for quantifying quadriceps femoris cross-sectional area (CSA), using magnetic resonance imaging (MRI) as the reference standard. Prior work has examined EFOV ultrasound broadly, but validation of wireless palm-sized devices against MRI in a large cohort and testing sensitivity to training-related change had not been reported in the source.
The investigation comprised two linked experiments. Experiment 1 assessed validity and intra-rater reliability of midthigh CSA measurements by EFOV ultrasound compared with MRI in a cohort of 100 young adults (75 males, 25 females). Reliability metrics reported were intraclass correlation coefficient (ICC), standard error of measurement (SEM), coefficient of variation (CV), and smallest detectable change (SDC).
Experiment 2 evaluated sensitivity to muscle hypertrophy. Eleven males completed an 8-week resistance training program. Pre-to-post changes in CSA (ΔCSA) measured by EFOV ultrasound were compared with MRI-derived ΔCSA to determine whether the ultrasound device could detect training-induced hypertrophy and whether changes correlated between modalities.
Specific details about the ultrasound model, MRI protocols, exact scanning landmarks, operator training procedures, resistance training regimen, and participant inclusion/exclusion criteria were not reported in the abstract and therefore are not available from the source.
In the 100-subject sample, the EFOV wireless palm-sized ultrasound demonstrated excellent intra-rater reliability. For males the reported metrics were ICC = 0.996, SEM = 0.85 cm2, CV = 1.19%, and SDC = 2.35 cm2. For females the corresponding values were ICC = 0.993, SEM = 0.95 cm2, CV = 1.73%, and SDC = 2.63 cm2.
When compared with MRI, EFOV ultrasound measurements of midthigh CSA showed a strong correlation (r = 0.98, p < 0.001). The mean bias between modalities was reported as -1.23 ± 2.70 cm2, indicating a small systematic difference with ultrasound measurements on average lower by 1.23 cm2 relative to MRI in this cohort.
In the training intervention (n = 11 males), both EFOV ultrasound and MRI detected statistically significant increases in quadriceps CSA (p < 0.001). The mean pre-to-post change measured by ultrasound (ΔCSA) was 3.77 cm2, corresponding to a 5.98% increase. This mean ΔCSA exceeded the ultrasound SDC reported for males (2.35 cm2), indicating that the observed group-level change surpassed measurement noise for this device and operator.
ΔCSA values measured by ultrasound correlated strongly with MRI-derived changes (r = 0.92, p < 0.001), supporting the device’s sensitivity to detect true hypertrophic adaptations over the 8-week program.
Based on the reported results, the EFOV wireless palm-sized ultrasound device is presented as a valid, reliable, and sensitive tool for quantifying quadriceps femoris CSA and for monitoring training-induced muscle hypertrophy. The combination of high ICCs, low SEM/CV, close agreement with MRI, and the ability to detect pre-to-post changes that exceed the device’s SDC supports its potential use in athletic performance monitoring and clinical settings where MRI is impractical or unavailable.
The findings suggest clinicians and practitioners may use this class of handheld EFOV ultrasound to track muscle size longitudinally, provided operators use standardized scanning procedures and are trained to achieve similar measurement reliability.
The abstract does not provide some methodological specifics needed for full appraisal and replication, including:
Because these items were not reported in the abstract, they cannot be described here; they may be available in the full text of the published article.
In this study reported in European Journal of Sport Science (2026), an EFOV wireless palm-sized ultrasound device demonstrated excellent intra-rater reliability, strong correlation and small bias versus MRI for quadriceps CSA, and sufficient sensitivity to detect 8-week resistance training–induced hypertrophy. The device appears suitable for quantifying quadriceps CSA and monitoring muscle adaptations in athletic and clinical environments, with the caveat that full methodological details are provided in the primary article for implementation and replication.