Load Dependency of Postural Control - Kinematic and Neuromuscular Changes in Response to over and under Load Conditions

Abstract

IntroductionLoad variation is associated with changes in joint torque and compensatory reflex activation and thus, has a considerable impact on balance control. Previous studies dealing with over (OL) and under loading (UL) used water buoyancy or additional weight with the side effects of increased friction and inertia, resulting in substantially modified test paradigms. The purpose of this study was to identify gravity-induced load dependency of postural control in comparable experimental conditions and to determine the underlying neuromuscular mechanisms.MethodsBalance performance was recorded under normal loading (NL, 1g), UL (0.16g; 0.38g) and OL (1.8g) in monopedal stance. Center of pressure (COP) displacement and frequency distribution (low 0.15-0.5Hz (LF), medium 0.5-2Hz (MF), high 2-6Hz (HF)) as well as ankle, knee and hip joint kinematics were assessed. Soleus spinal excitability was determined by H/M-recruitment curves (H/M-ratios).ResultsCompared to NL, OL caused an increase in ankle joint excursion, COP HF domain and H/M-ratio. Concomitantly, hip joint excursion and COP LF decreased. Compared to NL, UL caused modulations in the opposite direction: UL decreased ankle joint excursions, COP HF and H/M-ratio. Collaterally, hip joint excursion and COP LF increased. COP was augmented both in UL and in OL compared to NL.ConclusionSubjects achieved postural stability in OL and UL with greater difficulty compared to NL. Reduced postural control was accompanied by modified balance strategies and compensatory reflex activation. With increasing load, a shift from hip to ankle strategy was observed. Accompanying, COP frequency distribution shifted from LF to HF and spinal excitability was enhanced. It is suggested that in OL, augmented ankle joint torques are compensated by quick reflex-induced postural reactions in distal muscles. Contrarily, UL is associated with diminished joint torques and thus, postural equilibrium may be controlled by the proximal segments to adjust the center of gravity above the base of support.

Bouncing on Mars and the Moon—the role of gravity on neuromuscular control: correlation of muscle activity and rate of force development

“…For that purpose, we assessed the ground reaction force (GRF), joint goniometry, and neuromuscular activity of relevant muscle groups involved in a bouncing movement as well as interrelations between the muscles' preactivation and reflex components and force output. Experiments were conducted during parabolic flights aboard an aircraft undergoing hypogravity flight profiles (44,46).…”

Kinetics and Muscle Activity Patterns during Unweighting and Reloading Transition Phases in Running

“…As gravity plays an essential role in terrestrial locomotion, several studies since the early works on weightlessness [1–3] have investigated the effects of reduced gravity on locomotion [4], balance control [5] and proprioceptive information [6]. The recent development of reduced gravity simulators [4] provides the opportunity to study the neuromechanical adjustments to partial unweighting over repeated running cycles.…”

The Effects of Different Force Directions and Resistance Levels during Unilateral Resistive Static Contraction of the Lower Trunk Muscles on the Ipsilateral Soleus H-reflex in the Side-lying Position

“…Elucidating load-dependent adaptations in monopedal stance, an increase in loading revealed a significant increase in the H/Mmax ratio; thereby, a reduction of the loading level led to a decrease of the H/Mmax ratio [14]. These receptor signals might arise from Golgi tendon organs and be conducted via type Ib afferents to the spinal locomotor generator [13], indicating that the strength of SCs of the lower trunk muscles, such as RSCPD, may influence the muscles of the lower extremity via Ib afferents.…”