Regular Follow-Up Increases Ground Reaction Forces During a Home-Based Exercise Intervention to Improve Bone Mass in Young Women

Abstract

Home-based exercises are convenient but do women follow the protocols they are given? PURPOSE: We compared ground reaction forces (GRFs) during a home-based jumping program for subjects receiving periodic follow-up with those who were not. METHODS: 205 women, 102 in cohort 1 (CH1) and 103 in cohort 2 (CH2) (aged 23.4±4.5y) were randomly assigned to one of three box jump height groups (4", 8", 12"). During the pretest visit, correct jumping technique was demonstrated for each subject. All were instructed to perform training at home from their prescribed box height adhering to this technique. CH1 subjects returned for posttest evaluation 9 months later, while CH2 subjects returned for evaluation at 3, 6, and 9 months. GRF evaluation consisted of 10 jumps on a Kistler force platform using the box height and technique practiced at home. Average peak GRF was determined for filtered peaks within each subject's mean ±1SD. RESULTS: Mean GRFs for CH1 and CH2 are shown in Table 1. GRFs for CH1 were not different across box heights, but were different for CH2 subjects using the 4" and 12" box. Subjects in CH2, 8" and 12" groups also achieved higher GRFs than those in CH1.Table 1: GRFs across three jump heightsCONCLUSIONS: We confirm the benefit of periodic follow-up to ensure that desired loads are being applied during home-based training. This has implications for programs to prevent bone loss in women who may unknowingly attenuate prescribed exercise-induced loading by altering kinematics during the landing phase of a box jump. Lab-based studies have shown GRFs of 6 times body weight for drop landings from 12-inches (Yeow et al, 2009), similar to our results at this height in CH2. We confirm that home-based training with follow-up can closely approximate GRFs during lab-based training. (NIH SC3 GM084705)