title: The normal growth of the biceps brachii muscle in human fetuses.
abstract: BACKGROUND
  The biceps brachii muscle, the strongest flexor and supinator at the elbow joint, and an accessory flexor of the glenohumeral joint is characterized by the two heads, long and short.
  
  
  OBJECTIVE
  The purpose of this study was to examine the linear parameters (length and width) of the biceps brachii in human fetuses and to provide their mathematical growth models.
  
  
  METHODS
  Using methods of anatomical dissection, digital analysis (Multiscan v.14.02), and statistics (Student's t-test and regression analysis) the authors bilaterally measured the length (mm) and width (mm) of the biceps brachii muscle in 30 fetuses of both sexes (14♂,16♀), aged 17-30 weeks.
  
  
  RESULTS
  Neither sex nor laterality differences were found. All the parameters studied increased proportionally with age. Both the mean length (5.68 mm) and widths, measured at its mid-length (0.60 mm) and at the widest level (0.65 mm) of the long head's belly, were found to be statistically shorter (5.93 mm, 0.65 mm and 0.72 mm, respectively) when compared to its short head's belly. For these parameters, the following linear models were generated in relation to the long head's belly: y = -0.801 + 0.276 x Age (R2 = 0.591), y = -0.254 + 0.036 x Age (R2 = 0.201) and y = -0.238 + 0.038 x Age (R2 = 0.226), and in relation to the short head's belly: y = -0.134 + 0.258 x Age (R2 = 0.551), y = -0.227 + 0.038 x Age (R2 = 0.241) and y = -0.316 + 0.044 x Age (R2 = 0.333). The tendon length turned out to be the only significantly greater value for the long head (1.89 mm vs. 1.09 mm). The following linear models y = 1.024 + 0.037 x Age (R2 = 0.084) for the long and y = 0.177 + 0.039 x Age (R2 = 0.157) for the short heads were computed.
  
  
  CONCLUSIONS
  Neither sex differences nor laterality differences are observed in morphometric parameters of the biceps brachii muscle. The long head's belly is shorter and thinner than that of the short head's belly. The long head's tendon is longer than that of the short head. The developmental dynamics of the biceps brachii muscle follow proportionately.
authors.affiliation: Department of Normal Anatomy, Nicolaus Copernicus University of Toruń, Ludwik Rydygier Collegium Medicum in Bydgoszcz, Poland. kizanat@cm.umk.pl
authors.forename: Michał
authors.initials: M
authors.lastname: Szpinda
authors.forename: Monika
authors.initials: M
authors.lastname: Paruszewska-Achtel
authors.forename: Maria
authors.initials: M
authors.lastname: Dąbrowska
authors.forename: Mateusz
authors.initials: M
authors.lastname: Badura
authors.forename: Gabriela
authors.initials: G
authors.lastname: Elminowska-Wenda
authors.forename: Adrianna
authors.initials: A
authors.lastname: Sobolewska
authors.forename: Anna
authors.initials: A
authors.lastname: Szpinda
mesh_terms: D005260:Female; D005333:Fetus / Q000033:anatomy & histology / Q000196:embryology*; D005865:Gestational Age; D006801:Humans; D008297:Male; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000196:embryology*; D013710:Tendons / Q000033:anatomy & histology / Q000196:embryology