On the importance of the hip abductors during a clinical one legged balance test: A theoretical study

Abstract

Background The ability to balance on one foot for a certain time is a widely used clinical test to assess the effects of age and diseases like peripheral neuropathy on balance. While state-space methods have been used to explore the mechanical demands and achievable accelerations for balancing on two feet in the sagittal plane, less is known about the requirements for sustaining one legged balance (OLB) in the frontal plane. Research question While most studies have focused on ankle function in OLB, can age and/or disease-related decreases in maximum hip abduction strength also affect OLB ability? Methods A two-link frontal plane state space model was used to define and explore the ‘feasible balance region’ which helps reveal the requirements for maintaining and restoring OLB, given the adverse effects of age and peripheral neuropathy on maximum hip and ankle strengths. Results Maintaining quasistatic OLB required 50%-106% of the maximum hip abduction strength in young and older adults, and older patients with peripheral neuropathy. Effectiveness of a ‘hip strategy’ in recovering OLB was heavily dependent on the maximum hip abduction strength, and for healthy older women was as important as ankle strength. Natural reductions of strength due to healthy aging did not show a meaningful reduction in meeting the strength requirement of clinical OLB. However deficits in hip strength typical of patients with peripheral neuropathy did adversely affect both quasistatic OLB and recoverable OLB states. Significance The importance of hip muscle strength has been underappreciated in the clinical OLB test. This is partly because the passive tissues of the hip joint can mask moderate deficits in hip abduction strength until it is needed for recovering OLB. Adding a follow up OLB test with a slightly raised pelvis would be a simple way to check for adequate hip abductor muscle strength.

On the hip abduction moment required to balance on one leg: an experimental study

“…In so doing there is no doubt that the hip abduction demand to maintain OLB is strenuous: the calculated abduction intensity exceeded 50% of the adjusted maximum supine hip abduction strength in both the young and older adults ( Table 2 ). A strength is that this finding corroborates our earlier estimates [10] based on non-coherent published strength and anthropometric data. A second novel finding was that, despite the large calculated abduction intensity, our results still led to the rejection of the primary hypothesis: that neither the measured endurance time of the hip abductor muscles at half-maximum hip abduction MVS nor the hip abduction endurance time predicted from the intensity of the hip abduction moment demand predicted an upper limit for the UST.…”

“…For the calculation of ankle and hip moments during OLB we used a simple double inverted pendulum model to represent the subject in the frontal plane [10]. Full description of how the parameters and states of the double inverted pendulum model were calculated can be found in S1 Text Section 3.…”

“…To calculate the intensity of the OLB hip abduction moment demand, we divided the hip abduction moment demand by the maximum isometric strength at any time point thereby deriving a time-series for the intensity of the hip abduction moment demand (and expressed as a percentage). We accounted for the change in maximum isometric hip abduction strength with the hip abduction angle as described earlier [10].…”

“…In our earlier study [10] we calculated that lateral flexion of the trunk through half its maximum range of motion could reduce the intensity of the hip abduction moment demand during OLB by 37%. Should the participants have maintained their trunk lateral flexion, that effect would not have been captured by the inverse dynamic algorithm calculating the hip abduction moment because the double inverted pendulum model assumed, for simplicity, that the upper body and the non-stance leg were a single rigid body (M 2 ).…”

“…In an earlier paper we used a simple double inverted pendulum mass-link model to estimate the ankle and hip strength frontal plane requirements for OLB [10]. One link represented the stance leg while the other represented the rest of the body.…”