Abstract
Ultrasonography of the lower body typically encompasses supine rest due to fluid shifts affecting tissue size and composition. However, vastus lateralis (VL) examination is completed in the lateral recumbent position, and this positional change may influence morphology and its ability to predict function. This study aimed to examine the effect of position on VL morphology and its relationship with lower-body performance. Cross-sectional area (CSA), muscle thickness (MT), pennation angle (PA), echo intensity (UnCorEI), subcutaneous adipose tissue thickness (SFT), and echo intensity corrected for SFT (CorEI) were assessed in 31 resistance-trained males (23.0 ± 2.1 yrs; 1.79 ± 0.08 m; 87.4 ± 11.7 kg) immediately after transitioning from standing to supine (IP), after 15 min of standing (ST), and after 15 min of rest in three recumbent positions: supine (SUP), dominant lateral recumbent (DLR), non-dominant lateral recumbent (NDLR). Participants also completed unilateral vertical jumps, isometric/isokinetic tests, and a one-repetition maximum leg press. CSA, MT, PA, and SFT were greater in ST compared to NDLR, DLR, and SUP (p < 0.05). CSA, UnCorEI, and CorEI were different between recumbent positions; however no differences were observed for MT, PA, and SFT. Different magnitudes of relationships were observed between muscle morphological characteristics measured after rest in different positions and performance variables. Muscle morphology in IP generally appears to be the best predictor of performance for most variables, although utilizing the NDLR and DLR positions may provide comparable results, whereas morphology measured in ST and SUP provide weaker relationships with physical performance. IP also requires less time and fewer requirements on the technician and subject, thus researchers should consider this positioning for VL examination.
Highlights
The assessment of muscle morphology in vivo has been used to evaluate muscle function in response to various exercise and nutritional interventions, as well as in disease and other clinical conditions
The present study demonstrated that uncorrected echo intensity (UnCorEI) did not change after 15 min of rest in the recumbent position, which aligns with the findings of others [22,23] in the vastus lateralis (VL)
Of the three measurements taken in the recumbent positions after 15 min of rest (NDLR, SUP, and dominant lateral recumbent (DLR)), we reported that DLR exhibited the lowest UnCorEI and the greatest Cross-sectional area (CSA)
Summary
The assessment of muscle morphology in vivo has been used to evaluate muscle function in response to various exercise and nutritional interventions, as well as in disease and other clinical conditions. As muscle morphological characteristics obtained via ultrasonography appear to differ depending on whether they are obtained while standing or while recumbent [14,15,25], the ability of these characteristics to predict muscle function during upright activities may be compromised if ultrasound images are captured in the recumbent position. Changes in hydrostatic pressure and blood distribution may be induced with changes in recumbent positions [35,36], and a change in position (from rest in a supine position to examination in a lateral recumbent position) may alter muscle morphological characteristics, which may not reflect true changes in muscle function
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