Bilateral and unilateral strength training in post-menopausal women

The purpose of the study was to determine the effects of bilateral (BL) and unilateral (UL) strength training on the bilateral deficit and lean tissue mass in post-menopausal women. The bilateral deficit is a phenomenon seen in resistance training where the strength of two homologous limbs contracting simultaneously is less than the sum of the strength of each limb contracting unilaterally. The bilateral deficit was computed as a bilateral index: Bl(%) = 100[BL strength/(Left UL strength + Right UL strength)]-100. A negative BI indicates a bilateral deficit. There were two hypotheses for the study: 1) Changes in the bilateral deficit would be specific with training; BLD would be reduced with BL training (BI would move in the positive direction); and the BLD would increase with UL training (BI would move in the negative direction); and 2) It is expected that the UL training group would show a greater increase in muscle mass since there is a strength deficit during BL contractions (Seki and Ohtsuki, 1990). Post-menopausal women (n = 26) were randomly assigned to either BL (n= 14; age= 55.8 ± 8.2) or UL (n= 12; age= 54.8 ± 6.5) training groups. Pre and post one maximal repetitions (1-RM) of BL, left UL and right UL strengths were measured for the leg press (LP), lat pulldown (LAT) and knee extension (KE) exercises. Whole, lower and upper (arms and trunk) body lean tissue mass were assessed by dual energy x-ray absorptiometry. The participants trained three times per week for six months using a whole body program with eight-ten repetitions for two sets per exercise. A dependent (one-sample) t-test was used to assess baseline BI for all three exercises to determine if the BI was different from zero, which would indicate a BLD. A two-factor analysis of variance (ANOVA) with repeated measures on the second factor (time, pre/post training) was used to analyze changes in the BI for LP, LAT and KE, as well for changes in bone mineral free lean tissue mass for the whole, lower and upper body. Initially there was a BLD in the LP and LAT exercises (p < 0.05), however not for KE (p = 0.095). There was a significant time by group interaction for the BI for LP, LAT and KE (p < 0.05), with the BI increasing on average by 7.8% (moved in the positive direction) for the BL group and decreasing by 1.1% for the UL group (moved in the negative direction). Tukey post-hoc testing indicated that the BL training significantly increased the BI for LP and KE for the BL group (p < 0.05) and the BI was significantly different after training between the groups (p < 0.05) for all exercises. Strength training increased lean tissue to a similar extent in both groups for whole, lower and upper body measures (p < 0.05). All of the strength measures (1-RM) increased over time (p < 0.05), with no differences between groups. These results indicate that the BLD decreased with BL training for LP and KE and there is a trend for UL training to increase the BLD (n.s.). These results suggest that 1) specific BL training can decrease the BLD and; 2) UL and BL training are equally effective for increasing lean tissue mass in post-menopausal women