Reprogramming of gene expression contributes to structural and functional 
adaptation of muscle tissue in response to altered use. The aim of this study 
was to investigate mechanisms for observed improvements in leg extension 
strength, gain in relative thigh muscle mass and loss of body and thigh fat 
content in response to eccentric and conventional strength training in elderly 
men (n = 14) and women (n = 14; average age of the men and women: 80.1 ± 3.7 
years) by means of structural and molecular analyses. Biopsies were collected 
from m. vastus lateralis in the resting state before and after 12 weeks of 
training with two weekly resistance exercise sessions (RET) or eccentric 
ergometer sessions (EET). Gene expression was analyzed using custom-designed 
low-density PCR arrays. Muscle ultrastructure was evaluated using EM 
morphometry. Gain in thigh muscle mass was paralleled by an increase in muscle 
fiber cross-sectional area (hypertrophy) with RET but not with EET, where muscle 
growth is likely occurring by the addition of sarcomeres in series or by 
hyperplasia. The expression of transcripts encoding factors involved in muscle 
growth, repair and remodeling (e.g., IGF-1, HGF, MYOG, MYH3) was increased to a 
larger extent after EET than RET. MicroRNA 1 expression was decreased 
independent of the training modality, and was paralleled by an increased 
expression of IGF-1 representing a potential target. IGF-1 is a potent promoter 
of muscle growth, and its regulation by microRNA 1 may have contributed to the 
gain of muscle mass observed in our subjects. EET depressed genes encoding 
mitochondrial and metabolic transcripts. The changes of several metabolic and 
mitochondrial transcripts correlated significantly with changes in mitochondrial 
volume density. Intramyocellular lipid content was decreased after EET 
concomitantly with total body fat. Changes in intramyocellular lipid content 
correlated with changes in body fat content with both RET and EET. In the 
elderly, RET and EET lead to distinct molecular and structural adaptations which 
might contribute to the observed small quantitative differences in functional 
tests and body composition parameters. EET seems to be particularly convenient 
for the elderly with regard to improvements in body composition and strength but 
at the expense of reducing muscular oxidative capacity.