Regional Biceps Brachii Muscle Thickness, Muscle Cross‐Sectional Area, One-Repetition Maximum, and Maximum Isometric Strength: The Cross-Sectional Correlational Study

Ultrasonography (US) was used as an alternative to magnetic resonance imaging (MRI). However, the correlations between US-derived biceps brachii muscle thickness (BBMT) and MRI-derived muscle cross-sectional area (BBCSA) across regions have not been explored. This study aimed to investigate correlations between BBCSA and BBMT in the proximal, middle, and distal regions, and between muscle size and muscle strength. Twenty healthy active males were recruited. Three specific regions of biceps brachii were assessed for BBCSA via MRI and for BBMT via US. One-repetition maximum (1RM) of preacher curl and maximum isometric strength (MIS) of dominant elbow flexor were tested. The moderate to strong correlations between BBMT and BBCSA were observed in every corresponding region from proximal to distal regions (r = 0.45, r = 0.52, r = 0.77, respectively). The moderate correlations were also observed between 1RM and ∑BBMT (r = 0.59) and between 1RM and ∑BBCSA (r = 0.65). Similarly, ∑BBMT and ∑BBCSA also correlated with MIS (r = 0.45 and r = 0.59, respectively). Furthermore, a moderate correlation was found between MIS and 1RM (r = 0.67). In conclusion, BBMT was reliable for estimating BBCSA. Muscle size was an independent determinant of muscle strength. Besides, dynamic and isometric strength measures correlated.