Effect of resistive knee extension training on postural control measures in middle aged and elderly persons.

The purpose of the present study was to determine whether knee extension strength gain in middle-aged and elderly persons is associated with improvement in the limits of stability when leaning his/her body in various directions. The resistance training group (EXT; 4 males, 17 females) completed two bilateral knee extension training sessions, consisting of one set of exercises, per week for 10 weeks. The non-training control group (CONT; 4 males, 3 females) were instructed not to train their legs during the 10-week control period. One set of exercises consisted of 8-12 repetitions of a dynamic resistance exercise until volitional fatigue for knee extension. The initial load for training was set at 70% of the one-repetition maximum (1-RM). The thickness of the rectus femoris (RF) and vastus lateralis (VL) muscles were measured using a B-mode ultrasound apparatus. The postural control measures, obtained using the Balance Master system, included the percentage limits-of-stability (%LOS) and path length (%Path). The 1-RM in EXT was increased significantly by resistance training (p < 0.001). In addition, significant differences were observed between the percentage increase of 1-RM in EXT and those in CONT at wk 5 and at wk 10 of resistance training (p < 0.001). However, no significant increase in muscle thickness of RF or VL was found in EXT. The %LOS to the rear target in EXT was increased significantly by resistance training (p < 0.05-0.01). In addition, the percentage change in %Path was decreased significantly by resistance training (p < 0.001). Therefore, strength gain in quadriceps femoris appears to be associated with improvement in the %LOS and %Path for the rear. In conclusion, strength gain in quadriceps femoris is thought to possibly enable accurate movement of the COG farther from the center target towards the rear, suggesting that strength gain has a positive influence on a person's perception of their ability to avoid falls.