Measuring Children’s Vertical Ground Reaction Forces with Accelerometry during Walking, Running, and Jumping: The Iowa Bone Development Study

Abstract

Ground reaction forces (GRF) are associated with bone hypertrophy; therefore, they are important to understanding physical activity’s role in children’s bone health. In this study, we examined the ability of accelerometry to predict vertical GRF in 40 children (mean age 8.6 yr) during slow walking, brisk walking, running, and jumping. Correlation coefficients between accelerometry-derived movement counts and GRF were moderate to high and significant during walking and running, but not during jumping. Given a large proportion of children’s daily physical activity involves ambulation, accelerometry should be useful as a research method in bone-related research. However, this method underestimates GRF during jumping, an important physical activity for bone modeling and remodeling.

Accelerometer counts and raw acceleration output in relation to mechanical loading

“…ActiGraph GT1M output had a strong relationship with GRF and followed a similar pattern across activities as average resultant force and peak loading rate. This is consistent with previous research with children (Janz et al, 2003;Garcia et al, 2004). Activities eliciting a mean GRF of three body weights have positive associations with bone health (Bassey et al, 1998); a peak GRF of three body weights related to an ActiGraph output of 274 757 counts/s (16,46573391 counts/min) in the current study.…”

“…Eston et al, 1998;Janz et al, 2003;Swartz et al, 2000), this study consisted of a series of structured activities. This is a limitation as activities tend to be sporadic and unstructured during daily life.…”

Weight-bearing bones are more sensitive to physical exercise in boys than in girls during pre- and early puberty: a cross-sectional study

“…There is a need to validate the motion sensors for impact loading of the bone. From a biomechanical viewpoint and some evidence from the literature [29,30], it makes sense to assume that the counts as expression of the vertical displacement of the body are somehow correlated to the amount of ground reaction forces, at least in a semiquantitative way. Motion sensors poorly capture PA performed in low motion or when the body is carried by a vehicle.…”

“…A cut-off of 4,200±840 cpm has been found for jumping activities eliciting ground reaction forces of about 3.5 times body weight for 6-to 10-year-old children [29]. Considering the standard deviation of 840 cpm and an intraclass coefficient of correlation of 0.91 in their reliability measurements, we set a cut-off of 3,000 cpm to elicit ground reaction forces that have been shown to be efficient at increasing femur BMD in premenopausal women [30].…”

Acceleration slope of exercise-induced impacts is a determinant of changes in bone density

“…High acceleration levels exceeding a threshold of about 4g (g ¼ acceleration of gravity, 9.81 m/s 2 ) were found to significantly correlate with bone mineral density (BMD) changes. Accelerations caused by impacts during exercise have been shown to be related to loading forces (Janz et al, 2003;Servais et al, 1984). For a rigid body undergoing an impact, the applied force F induces acceleration according to the effective mass m (F ¼ ma).…”