BMI, Mechanical and Strength Relationships to Dynamic Balance

Background/Purpose: Evidence indicates that decreased physical fitness and a high BMI negatively influence activities of daily living such as balance. Variables such as lower body strength and ankle-complex joint mobility also create mechanical constraints on the sensori-motor system which could influence activity and postural control. Considering each variable in isolation may not be the defining factor. This study investigated the influence of select constraints as predictors of dynamic balance in college students.

Method: Twenty-three healthy male college students (20.1 ± 2.1 yrs, 170.3 ± 1.9 cm, 84.5 ± 12.7 kg) were measured for isokinetic ankle and leg strength, ankle-complex joint motion, dynamic balance and body weight and height. Strength measures included isokinetic peak torque /body weight values for ankle concentric  dorsiflexion  and concentric knee extension at 180°/sec. Ankle-complex joint inversion-eversion motion (degrees ROM) was measured using an instrumented ankle arthrometer which consisted of an adjustable plate fixed to the foot, a handle attached to a footplate through which a 4-Nm load was applied, and a tibial pad attached to the tibia which was connected to the footplate via a 6-degrees-of-freedom spatial-kinematic linkage system. The Biodex Balance System measured dynamic balance at stability level 2. The balance system is an instrumented circular tilt board that moves in a 360° horizontal plane. The degrees of tilt were measured and a stability index calculated based on deviations from horizontal. The average of 3 twenty-second trials was used as datum. Multiple regression was used for analyzing the data. The stability index was used as the criterion and the predictor variables were BMI, ankle and leg strength, and ankle-complex joint motion.

Analysis/Results: The linear combination of BMI, ankle and leg strength, and ankle-complex joint motion was significantly related to dynamic balance (R =.76, F_4,18 = 6.19, p = .003). The stability index (5.57 ± 2.91) was significantly associated with BMI (26.1 ± 3.6 kg⋅m^-2, t =3.98, p = .001), leg strength (68.7 ± 15.7 Nm/kg, t = 2.51, p = .022), and ankle strength (8.2 ± 2.6 Nm/kg, t = 2.01, p = .05), but not ankle-complex joint motion (33.11 ± 7.1 deg/ROM, t =.883, p = .389).

Conclusions: Results imply leg and ankle strength and BMI influence dynamic balance in healthy males more than ankle-complex joint range-of-motion. The novel finding of this study was a non-significant relationship between the mechanical variable of ankle-complex joint motion and dynamic balance.