Adaptive force control in grasping as a function of level of developmental disability

Association of Drug Burden Index with grip strength, timed up and go and Barthel index activities of daily living in older adults with intellectual disabilities: an observational cross-sectional study

BACKGROUND

Drug Burden Index (DBI), a measure of exposure to medications with anticholinergic and sedative activity, has been associated with poorer physical function in older adults in the general population. While extensive study has been conducted on associations between DBI and physical function in older adults in the general population, little is known about associations in older adults with intellectual disabilities (ID). This is the first study which aims to examine the association between DBI score and its two sub-scores, anticholinergic and sedative burden, with two objective measures of physical performance, grip strength and timed up and go, and a measure of dependency, Barthel Index activities of daily living, in older adults with ID.

METHODS

Data from Wave 2 (2013/2014) of the Intellectual Disability Supplement to the Irish Longitudinal Study on Ageing (IDS-TILDA) was analysed. Analysis of Covariance (ANCOVA) was used to detect associations and produce adjusted means for the physical function and dependency measures with respect to categorical DBI scores and the anticholinergic and sedative sub-scores (DBA and DBS).

RESULTS

After adjusting for confounders (age, level of ID, history of falls, comorbidities and number of non-DBI medications, Down syndrome (grip strength only) and gender (timed up and go and Barthel Index)), neither grip strength nor timed up and go were significantly associated with DBI, DBA or DBS score > 0 (p > 0.05). Higher dependency in Barthel Index was associated with DBS exposure (p < 0.001).

CONCLUSIONS

DBI, DBA or DBS scores were not significantly associated with grip strength or timed up and go. This could be as a result of established limitations in physical function in this cohort, long-term exposure to these types of medications or lifelong sedentary lifestyles. Higher dependency in Barthel Index activities of daily living was associated with sedative drug burden, which is an area which can be examined further for review.

Children with heavy prenatal alcohol exposure exhibit deficits when regulating isometric force

BACKGROUND

Production of isometric (i.e., constant) force is an essential component of performing everyday functional tasks, yet no studies have investigated how this type of force is regulated in children with confirmed histories of heavy prenatal alcohol exposure.

METHODS

Children 7 to 17 years old with heavy prenatal alcohol exposure (n = 25) and without exposure (n = 18) applied force to a load cell to generate an isometric force that matched a criterion target force displayed on a computer monitor. Two levels of target force were investigated in combination with 3 levels of visual feedback frequency that appeared on the computer monitor as a series of yellow dots. Force was maintained for 20 seconds and participants completed 6 trials per test condition.

RESULTS

Root-mean-square error, signal-to-noise ratio, and sample entropy indexed response accuracy, response variability, and signal complexity, respectively. The analyses revealed that in comparison with controls, children with gestational ethanol exposure were significantly less accurate and more variable in regulating their force output and generated a response signal with greater regularity and less complexity in the time domain.

CONCLUSIONS

Children with prenatal alcohol exposure experience significant deficits in isometric force production that may impede their ability to perform basic motor skills and activities in everyday tasks.

Force-independent distribution of correlated neural inputs to hand muscles during three-digit grasping

The ability to modulate digit forces during grasping relies on the coordination of multiple hand muscles. Because many muscles innervate each digit, the CNS can potentially choose from a large number of muscle coordination patterns to generate a given digit force. Studies of single-digit force production tasks have revealed that the electromyographic (EMG) activity scales uniformly across all muscles as a function of digit force. However, the extent to which this finding applies to the coordination of forces across multiple digits is unknown. We addressed this question by asking subjects (n = 8) to exert isometric forces using a three-digit grip (thumb, index, and middle fingers) that allowed for the quantification of hand muscle coordination within and across digits as a function of grasp force (5, 20, 40, 60, and 80% maximal voluntary force). We recorded EMG from 12 muscles (6 extrinsic and 6 intrinsic) of the three digits. Hand muscle coordination patterns were quantified in the amplitude and frequency domains (EMG-EMG coherence). EMG amplitude scaled uniformly across all hand muscles as a function of grasp force (muscle x force interaction: P = 0.997; cosines of angle between muscle activation pattern vector pairs: 0.897-0.997). Similarly, EMG-EMG coherence was not significantly affected by force (P = 0.324). However, coherence was stronger across extrinsic than that across intrinsic muscle pairs (P = 0.0039). These findings indicate that the distribution of neural drive to multiple hand muscles is force independent and may reflect the anatomical properties or functional roles of hand muscle groups.