The locally expressed isoform of the Insulin-like Growth Factor-I (IGF-I) gene has been implicated in the response of skeletal muscle to high intensity resistance exercise. The interpretation of recent reports on the influence of age, of which we know little, is problematic due to the utilisation of different exercise protocols and sampling times (1,2,3). Using an isometric exercise protocol, we have previously shown that the upregulation of this growth factor (IGF-IEa) occurs in younger women (4). Here we aimed to apply our protocol in a study comparing the responses of groups of young and old women in their eighth decade and older. Sixteen healthy women (n=6 old, median age 81 y, range 76-82 y; n=10 young, median age 26 y, range 21-30 y) undertook 120 maximal voluntary isometric contractions of the knee extensors of one leg as 20 sets of 6 contractions over 90 minutes. Muscle samples were obtained from the lateral mass of the quadriceps at baseline and at 2.5h post-exercise using the needle biopsy technique. Quantification of mRNA for IGF-IEa was by real-time reverse-transcriptase polymerase chain reaction (qRT-PCR). Statistical analysis was by repeated measures ANOVA. Individual responses of IGF-IEa mRNA to exercise are shown in Fig1. Exercise elevated (geometric) mean (95% CI) mRNA values (relative amounts) for the IGF-IEa transcript in both the young (from 9.91 (5.64 to 17.4) to 21.7 (6.73 to 69.9)) and old (from 4.77 (1.84 to 12.4) to 16.5 (6.13 to 44.3)) women and this was statistically significant when the groups were analysed together (ANOVA F=5.24, p = 0.043). Although the magnitude of the IGF-IEa mRNA response was greater in the old women, (3.5-fold vs 2.2-fold), the effect of age was not statistically significant (ANOVA F=1.98, p = 0.19). This is the first study to report muscle specific IGF-IEa gene expression after voluntary isometric resistance exercise in young and old women. The IGF-IEa response to exercise appears to be maintained in old age. Furthermore our results suggest that it is not age per se which drives the variability of the growth factor response to resistance exercise.