• adaptation;
  • exercise;
  • magnetic resonance imaging;
  • skeletal muscle physiology;
  • strength


The aim of this study was to determine morphological and functional changes of the elbow extensor muscles in response to a 12-week self-perceived maximal resistance training (MRT). Twenty-one healthy sedentary young men were engaged in elbow extensor training using isoacceleration dynamometry for 12 weeks with a frequency of five sessions per week (five sets of ten maximal voluntarily contractions, 1-min rest period between each set). Prior to, at 6 weeks and after the training, a series of cross-sectional magnetic resonance images of the upper arm were obtained and muscle volumes were calculated. Maximal and endurance strength increased (P<0·01) by 15% and 45% at 6 weeks, and by 29% and 70% after 12 weeks compared with baseline values, while fatigue rate of the elbow extensors decreased by 67%. The volume of triceps brachii increased in both arms (P<0·01) by 4% at 6 weeks, and by 8% after 12 weeks compared with baseline values (right arm – from 487·4 ± 72·8 cm3 to 505·8 ± 72·3 cm3 after 6 weeks and 525·3 ± 73·7 cm3 after 12 weeks; left arm – from 475·3 ± 79·1 cm3 to 493·2 ± 72·7 cm3 after 6 weeks and 511·3 ± 77·0 cm3 after 12 weeks). A high correlation was found between maximal muscle strength and muscle volume prior (r2 = 0·62) and after (r2 = 0·69) the training (P≤0·05). A self-perceived MRT resulted in an increase in maximal and endurance strength. Morphological adaptation changes of triceps brachii as a result of 12-week specific strength training can explain only up to 26% of strength gain.