Effects of adiposity on postural control and cognition

Highlights

• We evaluated the relationship between postural control and measures of adiposity.

• Measures of adiposity included BMI and body fat percentages (via DEXA scan).

• Participants performed a working memory task and sensorimotor evaluations.

• Measures of motor function deteriorated as measures of adiposity increased.

• Percent body fat was a better predictor of postural control as compared to BMI.

Abstract

In the U.S., it is estimated that over one-third of adults are obese (Body Mass Index (BMI) > 30 kg/m²). Previous studies suggest that obesity may be associated with deficits in cognitive performance and postural control. Increased BMI may challenge cognitive and postural performance in a variety of populations; however, most relevant studies have classified participants based on BMI values, which cannot be used to accurately assess the effects of adiposity on cognitive performance and postural control. The objective of the current study was to examine motor and cognitive responses for overweight and obese adults compared to normal weight individuals by using both BMI and adiposity measures. Ten normal weight (BMI = 18–24.9 kg/m²), ten overweight (BMI = 25–29.9 kg/m²), and ten obese (BMI = 30–40 kg/m²) adults were evaluated (age: 24 ± 4 years). Participants were classified into three groups based on BMI values at the onset of the study, prior to body composition analysis. Participants performed (1) working memory task while maintaining upright stance, and (2) a battery of sensorimotor evaluations. Working memory reaction times, response accuracy, center-of-pressure (COP) path length, velocity, migration area, time to boundary values in anterior-posterior direction, and ankle-hip strategy-scores were calculated to evaluate cognitive-motor performance. No significant deficits in working memory performance were observed. Overall, measures of motor function deteriorated as BMI and body fat percentage increased. The relationship between deteriorating postural performance indices and body fat percentage were greater than those found between BMI and postural performance indices.

Introduction

The terms overweight and obesity are defined as abnormal/excessive fat accumulation with Body Mass Index (BMI) ≥ 25 kg/m² and 30 kg/m², respectively [1]. The World Health Organization (WHO) estimates that more than 1.9 billion adults are overweight worldwide; with 600 million obese adults in 2014 [1]. In the U.S., the situation is exacerbated with 78.6 million adults being classified as obese in 2012 [2].

Postural instability is defined as the inability to successfully respond to perturbations during upright stance [3] and is frequently associated with reduced sensorimotor function and increased fall risk [4], [5]. Impaired motor function due to an increase in adiposity may severely impact quality of life and increase the risk of reduced postural stability and injury by falls [6], [7]. Several studies have examined the relationship between obesity and postural control in adults. Hue et al. reported that increased body weight strongly correlated with decreased balance stability [8]. Similarly, increased body weight has been associated with increased anterior–posterior (AP) center of pressure (COP) movement [9]. Increased sway areas and an inability to modulate anticipatory actions suggests that obese participants use different postural strategies to maintain balance [10]. In contrast, Blaszczyk et al. suggested preserved postural control in obese adults [11], a notion later challenged in [12]. A primary limitation in these studies is that they used BMI as the primary classification method for identifying different weight groups; however, BMI only takes body mass and height into consideration. The exclusive use of BMI is flawed as a method to distinguish highly muscular persons from persons with high body fat percentages. Inconsistent outcomes from previous studies might have resulted from the use of BMI for classification. Using measures of fat amount may better illustrate the relationship between excessive adiposity and postural control.

Deficits in cognitive function have been reported as a powerful predictor of falls and correlate to dramatic increases in fall risks [13]. Recently, obesity has been linked with memory deficits and cognitive dysfunction in middle-aged and older adults [14], [15]. Increased adiposity, resulting in obesity, may require additional attention for controlling posture [16]. Cognitive-motor interference, defined as decrements in performance that occur when cognitive and motor tasks are performed simultaneously (dual-task conditions), has been linked with falls [15]. A priori, we did not expect to see cognitive deficits in this study due to the narrow age range of participants in the current study; however, these data are the first step in preparing a larger scale evaluation of cognitive-motor deficits with respect to adiposity, aging, and neurological disease. Examining postural control during cognitive tasks will provide valuable information regarding the relationship among motor function, cognitive distraction, and excessive adiposity.

The objective of the current study was to examine responses during cognitive-motor tasks using different assessments of adiposity. The correlations among BMI, body composition, postural control, and cognitive performance were examined to clarify and explore the impact of adiposity on postural stability. We hypothesized that: (1) measures of postural control will deteriorate as indices of adiposity increase; and (2) whole body fat percentage (%Fat_TOTAL) and trunk fat percentage (%Fat_TRUNK) will exhibit more consistent relationships with postural control as compared to BMI. The results of this study advance our understanding of the true relationship of adiposity, body mass, and body fat distribution on postural control and cognitive performance.