Effects of Rest Position on Morphology of the Vastus Lateralis and Its Relationship with Lower-Body Strength and Power

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.

Muscle Quality, Measured by Ultrasound-Derived Corrected Echo Intensity, Does not Affect Changes in Cross-sectional Area of the Vastus Lateralis Following Recumbent Rest

“…Therefore, several of the methods presented here have been previously described by the authors. 6 Briefly, participants were recruited and reported to the Human Performance Laboratory on two occasions. During the first visit, participants were informed of all study procedures, risks, and benefits and completed a written informed consent form.…”

“…27,39 Therefore, EI corrected for SFT may better reflect true muscle quality than raw EI values. In accordance, CSA, SFT, uncorrected EI, and EI corrected for SFT (EI Cor ) were assessed using the following procedures, which have been previously described 6 :…”

“…17,20,26 The gray-scale values for each individual pixel were projected on a histogram. EI was quantified as the mean of all gray-scale values 5–7,17–20,27,31,39–41 and was reported in AU.…”

“…Intraday reliability values of the sonographer in the quantification of CSA, EI, SFT, and EI Cor of the VL for the three images taken at T0 and T15, corresponding to immediately post recumbency (“IP”) and 15 minutes after rest in the non-dominant lateral recumbent position (“NDLR”) in our previous study, respectively, have been reported. 6 In addition, interday reliability values of the sonographer in the quantification of CSA and EI of the VL have previously been completed on a separate sample of participants with at least 24 hours between examinations. 19 These values demonstrate high to excellent precision and reliability of the sonographer for all variables measured.…”

“…Resistance training is purported to increase the ratio of intramuscular contractile to noncontractile tissue 36 ; however, large discrepancies in muscle quality and composition can exist even between resistance-trained individuals. The authors have previously reported that 15 minutes of recumbent rest results in significant decreases in CSA of the vastus lateralis (VL) in resistance-trained males 6 , but the effects of muscle quality on the extent of decrease in muscle CSA were not examined. Thus, the research objective was to determine whether muscle quality, as determined via ultrasound-derived EI corrected for subcutaneous fat thickness (SFT), is related to the extent of change in CSA of the VL following 15 minutes of recumbent rest.…”