![]() One leg was trained concentrically (5 sets × 30 repetitions at 90 deg/s), whereas the contralateral limb was trained both concentrically (2 sets × 30 repetitions at 90 deg/s) and eccentrically (3 sets × 30 repetitions at 90 deg/s). Each participant underwent 12 weeks of unilateral RT performing maximal knee extensions on a Cybex® isokinetic dynamometer. Nine recreationally active, young, healthy males (age = 24 ± 2 years, BMI = 24.1 ± 2.8 kg/m 2) volunteered for this study. Participant characteristics and study design The second hypothesis was that the RT‐induced change in VL MT would be positively correlated to changes in VL ACSA and VOL.Ģ.1. It was hypothesized that vastus lateralis (VL) MT assessed at a single time point using ultrasound would be positively correlated with quantification of VL ACSA and VOL using MRI at the same time point. Hence, the aim of this study was to examine whether muscle thickness measurements from ultrasound could be used to accurately estimate changes in muscle size and volume (assessed with MRI) following a RT protocol. However, as far as we are aware, no study has reported the utility of MT measurements for detecting changes in muscle size or volume induced by resistance exercise training (RT). 7, 8, 9, 10 Previous studies report a positive relationship between muscle thickness (MT) and lean mass (measured by DXA), 11, 12 MT and anatomical cross‐sectional area (ACSA, measured by MRI), 13 and between MT and muscle volume (VOL, measured by MRI) 14, 15, 16 at a single time point. Over the last 20 years, the use of ultrasound has been advocated as a potentially reliable tool for the quantification of skeletal muscle mass in young and older healthy volunteers 4, 5, 6 and in clinical populations, such as intensive care patients. 1 Nonetheless, repeated DXA scanning in longitudinal studies does raise ethical concerns because of the stochastic risk posed by repeated radiation exposure. DXA, for example, can provide estimates of regional and total lean masses at a lower cost than MRI and involves minimal radiation exposure compared to CT. 2, 3 However, besides its accuracy, estimation of whole‐body muscle mass is not as cheap and accessible as with other techniques. MRI is regarded as the gold standard for clinical and research imaging of skeletal muscle, allowing investigators to accurately assess muscle mass at an individual time point and its changes over time. 1 These techniques have been used in a variety of settings, yet can be expensive, often inaccessible and, in the case of CT and DXA, involve ionizing radiation. Over the last four decades, the quantification of skeletal muscle mass has been revolutionized by the introduction of imaging techniques such as computer tomography (CT), magnetic resonance imaging (MRI) and dual‐energy X‐ray absorptiometry (DXA), which facilitate the accurate quantification of whole‐body and regional muscle masses. Skeletal muscle is the largest adipose tissue‐free mass in humans, constituting a substantial portion of the whole‐body mass, and it is crucial for locomotion and metabolic health. MT changes following RT are associated with parallel changes in muscle ACSA mid but not with the changes in VOL, highlighting the impact of RT on regional hypertrophy. ![]() These data support evidence that MT is a reliable index of muscle ACSA mid and VOL at a single time point. ![]() The relationships between MRI and ultrasound measurements were tested by Pearson's correlation. ![]() Differences between baseline and post‐training were assessed by Student's paired t test. Measurements were taken at baseline and after 12 weeks of isokinetic RT. ![]() Nine healthy, young, male volunteers (24 ± 2 y.o., BMI 24.1 ± 2.8 kg/m 2) had vastus lateralis ( VL) muscle volume ( VOL) and ACSA mid (at 50% of femur length, FL) assessed by MRI, and VL MT measured by ultrasound at 50% FL. We tested whether MT could be used as a valid marker of MRI determined muscle anatomical cross‐sectional area ( ACSA) and volume changes following resistance training ( RT). Muscle thickness ( MT) measured by ultrasound has been used to estimate cross‐sectional area (measured by CT and MRI) at a single time point. ![]()
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