Original Article

European Journal of Applied Physiology

, Volume 89, Issue 6, pp 555-563

First online:

Muscle hypertrophy, hormonal adaptations and strength development during strength training in strength-trained and untrained men

  • Juha P. AhtiainenAffiliated withNeuromuscular Research Center and Department of Biology of Physical Activity, University of Jyväskylä Email author 
  • , Arto PakarinenAffiliated withDepartment of Clinical Chemistry, University of Oulu
  • , Markku AlenAffiliated withPeurunka-Medical Rehabilitation Center
  • , William J. KraemerAffiliated withThe Human Performance Laboratory, Department of Kinesiology and Department of Physiology and Neurobiology, The University of Connecticut
  • , Keijo HäkkinenAffiliated withNeuromuscular Research Center and Department of Biology of Physical Activity, University of Jyväskylä

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Hormonal and neuromuscular adaptations to strength training were studied in eight male strength athletes (SA) and eight non-strength athletes (NA). The experimental design comprised a 21-week strength-training period. Basal hormonal concentrations of serum total testosterone (T), free testosterone (FT) and cortisol (C) and maximal isometric strength, right leg 1 repetition maximum (RM) of the leg extensors were measured at weeks 0, 7, 14 and 21. Muscle cross-sectional area (CSA) of the quadriceps femoris was measured by magnetic resonance imaging (MRI) at weeks 0 and 21. In addition, the acute heavy resistance exercises (AHRE) (bilateral leg extension, five sets of ten RM, with a 2-min rest between sets) including blood samples for the determination of serum T, FT, C, and GH concentrations were assessed before and after the 21-week training. Significant increases of 20.9% in maximal force and of 5.6% in muscle CSA in NA during the 21-week strength training period were greater than those of 3.9% and −1.8% in SA, respectively. There were no significant changes in serum basal hormone concentrations during the 21-week experiment. AHRE led to significant acute decreases in isometric force and acute increases in serum hormones both at weeks 0 and 21. Basal T concentrations (mean of 0, 7, 14 and 21 weeks) and changes in isometric force after the 21-week period correlated with each other (r=0.84, P<0.01) in SA. The individual changes in the acute T responses between weeks 0 and 21 and the changes in muscle CSA during the 21-week training correlated with each other (r=0.76, P<0.05) in NA. The correlations between T and the changes in isometric strength and in muscle CSA suggest that both serum basal testosterone concentrations and training-induced changes in acute testosterone responses may be important factors for strength development and muscle hypertrophy.


Basal hormones Hormonal responses Magnetic resonance imaging Resistance exercise