One Year of Heavy Resistance Training Modifies Muscle Fiber Characteristics in the Elderly

Physical function declines with age, accelerating during the 6th decade of life, primarily due to loss in muscle mass and strength. The present study aimed to investigate the effect of one year of heavy resistance training in older adults (62-70 years) on muscle mass and strength. Further, we investigated muscle characteristics after the intervention by obtaining muscle biopsies from the vastus lateralis to compare muscle fiber characteristics between the heavy resistance training (HRT) (n=10) and the sedentary control group (CON) (n=10). We found that one year of resistance training increased isometric muscle strength (p<0.0001, ES: 2.43 (Hedges' g)) and lean body mass (p<0.05, ES: 0.96), whereas cross-sectional area of the vastus lateralis and lean leg mass were unaltered. At year 1, the percentage of type IIX muscle fibers was lower in HRT compared to CON (p<0.05, ES: 0.99), whereas the muscle fiber size did not differ between groups for the major fiber types (I and II). In conclusion, one year of resistance training in elderly improved muscle strength and lean body mass but not cross-sectional area and lean leg mass. This indicates that the increase in muscle strength may be caused by neuromuscular adaptations rather than morphological muscle tissue changes per se.