In premenopausal women a number of RCTs have reported positive effects of weight-bearing impact exercise
programs, such as vertical and multidirectional jumping, bounding, hopping, and bench stepping,which are associated with GRFs of approximately two to five times body weight, on hip and spine BMD [187,188,193,194]. Early work by Bassey and Ramsdale [187] showed a significant enhancement in trochanter BMD of 3.4% following 6 months of high-impact training which included a 60-minute aerobics class incorporating 3 to 6 minutes of jumping and skipping once per week and 50
double leg jumps performed 6 days per week. In a more extensive 18-month trial in which 98 healthy women
aged 35 to 45 years were randomized to a progressive high-impact program or a control group, Heninonen
et al. reported net gains in BMD at loaded sites of 1% to 2% in the impact loading group that was accompanied
by increased muscle performance, aerobic fitness,and dynamic balance [188]. Several other studies have included as few as 10 jumps per day [195] and 50 jumps [197] with positive effects on BMD of up to 2.6% at the lumbar spine and hip. A unilateral intervention in which premenopausal women were randomized to perform 50 hops (2.5 to 2.8 times body weight) on 2, 4, or 7 days per week for 6 months found that the change in femoral neck BMD in the exercise relative to control limb was greatest in those who exercised 7 days per week (net gain 1.8%) compared to twice a week or control subjects [196]. Interestingly, there was no significant difference between 7- and 4-days per week training, which suggests that short bouts of impact exercise conducted 4 days per week might be optimal. However, since the total load (volume)
of training was not controlled in this study it is difficult to ascertain whether this is the optimal training frequency or dose.