Associations among strength, steadiness, and hand function across the adult life span

Impact of manual dexterity on toothbrushing efficacy in typically developing children: A cross-sectional study

BACKGROUND

Manual dexterity includes gross motor skills (GMS) and fine motor skills (FMS). Literature reports manual dexterity as a contributing factor for improved oral hygiene and that the required dexterity for toothbrushing develops above 8 years of age. Research suggests grip force, movement speed, and motor coordination should be assessed to improve knowledge on kinetics of brushing teeth.

AIM

To assess the impact of manual dexterity on toothbrushing efficacy in 7 to 12 year old children.

DESIGN

The cross-sectional study included 150 typically developing 7-12 year old children. Oral health status was recorded using the Decayed, Missing, and Filled Teeth index. GMS and FMS were evaluated using the MInnesota Manual Dexterity Test (MMDT) and Archimedes spiral test (AST), respectively. Toothbrushing efficacy was determined by Turesky modification of Quigley-Hein Plaque Index- difference in mean scores from before and after toothbrushing.

RESULTS

Assessment of GMS, FMS, and toothbrushing efficacy using ANOVA showed a significant increase with age (p value: 0.000); unpaired t-test showed an association of toothbrushing efficacy with GMS and FMS irrespective of age (p value: 0.000).

CONCLUSION

Manual dexterity was significantly associated with toothbrushing efficacy in typically developing children. AST, a simple test to determine FMS, may help paediatric dentists to guide parents on the supervision of toothbrushing for their child.

Relationship Between Force Steadiness and Functionality in Older Adults: A Systematic Review With Meta-Analysis

The relevance of force steadiness (FS) in relation to task performance remains unclear. This systematic review with meta-analysis examines the strength of the relationship between FS and the physical task performance aspect of functionality in older adults, focusing on both upper and lower limbs. We conducted a comprehensive search across databases, including MEDLINE, Ovid, CINAHL, Scopus, and Web of Science, up to February 2024. We included correlations from observational or longitudinal studies that provided objective measures of task performance in both healthy and unhealthy older adults. A meta-analysis with robust variance estimation was performed to account for dependencies among effect sizes. Of 1293 studies screened, 21 met the inclusion criteria and 15 contributed data to the meta-analysis. Our findings revealed a moderate, statistically significant relationship between FS and task performance in the upper limbs (r = 0.58, 95% CI [0.49-0.65], p < 0.01) with negligible heterogeneity (I2 = 0%). For the lower limbs, the relationship was also moderate (r = 0.45, 95% CI [0.27-0.58], p < 0.01) but with moderate heterogeneity (I2 = 50.66%). These results highlight a notable association between FS and physical function in both upper and lower limbs. However, caution is warranted due to the moderate to high risk of bias in 13 studies and evidence of publication bias in studies focused on the upper limbs. Despite these limitations, our study emphasizes the importance of FS in clinical practice and underscores the need for improved methods in measuring FS and its link to physical function. PROSPERO Registration: CRD42021247720.

Preservation of Temporal Organisation of Tennis Service Following Ageing in Recreational Players

Background: Ageing leads to functional changes in body systems. Purpose: This study sought to examine the age-based differences in temporal patterning, temporal variability and temporal regularity of tennis service in older adults. Research design: cross-sectional study. Study sample: Participants of this study were volunteers from young (n = 10) and older (n = 11) adults who were self-defined as non-competitive, participating in tennis at a recreational (sub-elite) level for 2-3 days per week regularly. Data collection: They were asked to perform 20 trials of the same serves (flat, slice or top-spin) on a regular size court. The timing (duration) of the serve action was recorded and analysed, using a high-speed digital camera. Participants performed the tennis serves during their routine training sessions on a tennis court. They undertook a structured general (10min) and a specific warm-up routine (10min) before performing services. There was a 30-second rest period between trials. Results: Findings showed that there were no statistically significant differences between the two groups in temporal patterning, whereas the younger group performed the serves with higher variability and regularity/consistency than the older adults in some phases of the action. Conclusion: Older adults who participate recreationally in sports are able to preserve some functional organisation of perceptual-motor capacities, such as timing, due to long-term practice effects. The findings illustrate how sport participation may help maintain functional movement organisation following ageing to mitigate age-related declines in perception and action in late adulthood.

Influence of the variability in motor unit discharge times and neural drive on force steadiness during submaximal contractions with a hand muscle

Our purpose was to compare the influence of the spectral content of motor unit recordings on the calculation of electromechanical delay and on the prediction of force fluctuations from measures of the variability in discharge times and neural drive during steady isometric contractions with the first dorsal interosseus muscle. Participants (n = 42; 60 ± 13 yr) performed contractions at 5% and 20% MVC. After satisfying the inclusion criteria, high-density surface EMG recordings from a subset of 23 participants were decomposed into the discharge times of 530 motor units. The force and cumulative spike train (CST) signals were cross-correlated with a novel filtering approach to determine the electromechanical delay. Force and CST signals were bandpass filtered with three bandwidths (0.75-5 Hz, 0.75-2 Hz, and 2-5 Hz) to determine the influence of spectral content on the precision of the electromechanical delay measurement. Subsequently, the variability in the discharge times of motor units was quantified as the coefficient of variation for interspike interval (CVISI), and the variability in neural drive was represented as the standard deviation of the cumulative spike train (SDCST). The main findings were that all frequencies (0.75-5 Hz) were needed to determine the electromechanical delay and that the force fluctuations were best explained by measures of variability in both discharge times and neural drive (CVISI and SDCST) at 5% MVC force but only the variability in neural drive (SDCST) at 20% MVC force. These findings indicate that the source of the force fluctuations during the steady submaximal contractions with the hand muscle differed for the two target forces.NEW & NOTEWORTHY The fluctuations in force during steady submaximal contractions can be caused by either or both the variability in discharge times of individual motor units and in the neural drive. After careful alignment of the force and discharge times within an optimal bandwidth (0.75-5 Hz), the fluctuations in force at the lower target force were strongly correlated with both measures of variability, whereas those at the higher target force were best explained by the variability in neural drive.

Age-related differences in eye movements and the association with Archimedes spiral tracing performance in young and older adults

Age-related hand motor impairments may critically depend on visual information though few studies have examined eye movements during tasks of hand function in older adults. The purpose of this study was to assess eye movements and their association with performance while tracing on a touchscreen in young and older adults. Eye movements of 21 young (age 20-38 years; 12 females, 9 males) and 20 older (65-85 years; 10 females, 10 males) adults were recorded while performing an Archimedes spiral tracing task, a common clinical assessment sensitive to age-associated impairments in hand function. Participants traced an Archimedes spiral template on a touchscreen as accurately as possible under three conditions, using (1) a stylus, (2) the index finger, and (3) the index finger while performing a visuospatial dual task. Older adults made fewer total fixations than young adults, and participants made fewer fixations when tracing parts of the spiral where vision of the spiral template was likely more obstructed by the hand. Inter-fixation distance and inter-fixation distance variability were greater in older compared to young adults. A relationship between increased inter-fixation distance and increased spiral tracing error demonstrates the association between age-related changes in eye movements and spiral tracing performance in older adults. Results contribute novel findings of age-associated changes in ocuomotor behavior during a common clinical assessment and offer insight into motor control in older adults.

Preliminary report: Reduced hand sensory and motor function in persons living with heart failure

Despite the growing evidence highlighting reduced functional independence in persons living with heart failure (PwHF), the underlying mechanisms that lead to reduced functional independence in this patient population are unknown. Given the association between functional independence and fine motor skills, which are functionally related to hand sensory and motor functions, we hypothesized that PwHF exhibit reduced sensory and motor function of hands compared to healthy individuals. We recruited a total of 10 PwHF (age: 57.6 ± 12.5 years old, four females) and a total of age- & sex-matched healthy control individuals (age: 58.2 ± 12.2 years old, four females). Participants performed a wide range of tests assessing the level of independence, fitness, cognitive function, and hand sensorimotor function. While the level of independence was comparable between two groups, PwHF exhibited reduced sensory and motor function. Compared to healthy participants, the ability to identify an object via tactile and proprioceptive inputs was reduced in PwHF, though the tactile mechanoreceptor function showed normal integrity. Similarly, PwHF exhibited a decline in manipulating small objects and steady grip force production. Heart failure seems to have repercussions that extend to the sensorimotor control of hand actions in advance to a decline in functional independence. These results underscore the need of further investigation as to the underlying mechanisms of reduced sensorimotor function, potential intervention targets, and determine whether assessments of hand sensorimotor function can serve as a vehicle to quantify restoration of self-care functionality.

Effectiveness of a home training program on improving pinch force perception in older adults

BACKGROUND

Hand function is reduced with aging which can lead to impairments in the performance of daily activities and eventually loss of independence. The ability to perceive the forces being applied to an object is an important component of hand control that also declines with age. However, the extent to which force perception can be improved through training remains largely unknown.

PURPOSE

This study evaluated the effectiveness of a home-training program focused on improving force perception in older adults.

STUDY DESIGN

Quasi-experimental - Uncontrolled trial.

METHODS

Eleven independent, healthy adults (mean age: 77.2 ± 6.8 years) participated in a home-based sensorimotor hand training program 6 days/week for 6 weeks. Force perception, the primary outcome variable, was measured as the ability to reproduce a pinch force equal to 25% maximum voluntary contraction in the absence of visual feedback using either the ipsilateral remembered or contralateral concurrent (CC) hand. We also measured hand strength, dexterity, tactile acuity, and cognition before and after training.

RESULTS

After the program was completed, participants showed a 35% reduction in absolute (p < 0.01, confidence interval (CI): [7.3, 33.2], effect sizes (ES): 0.87) and constant (p = 0.05, CI: [0.0, 34.9], ES: 0.79) force matching errors in the CC condition. Improvements in dominant hand dexterity (Purdue pegboard test) (p < 0.05, CI: [0.2, 2.4], ES: 0.60) and tactile sensitivity (JVP thresholds) (p < 0.05, CI: [-1.7, -0.1], ES: 0.94), as well as cognition (Trail Making Test B) (p < 0.05, CI: [-24,1. -1.6], ES: 0.30) were also observed post-training.

CONCLUSIONS

The results suggest that home-hand training can be an effective way to improve force perception among older adults.

Nerve conduction, latency, and its association with hand function in young men

INTRODUCTION

The median and ulnar nerves have been suggested to play a significant role in hand function; however, there are insufficient data to determine the strength of this association. This study aimed to investigate the correlation between hand function as measured with the Grooved pegboard test (GPT) and conduction velocity and latency of the median and ulnar nerves.

METHODS

We collected convenience samples in the College of Medicine, KSAU-HS. We used GPT to characterize hand function and performed measured nerve conduction velocity (NCV) and latency of the ulnar and median nerves of both hands. We used the Edinburgh handedness inventory (EHI) to determine hand dominance.

RESULTS

We recruited 28 healthy medical students aged 20-29 years (mean: 21.46 ± 1.62 years). Most were right-handed (n = 25, 89.3%), with a mean EHI score of 302 ± 210. The mean GPT time was significantly faster in the dominant (65.5 ± 6.4 s) than in the non-dominant (75.0 ± 9.6 s) hand. The NCV for the ulnar nerve of the dominant hand was significantly correlated with GPT (r = -0.52, p = 0.005) while median nerve was not correlated (0.24, p = 0.21). Regression analysis and collinearity test showed that the ulnar NCV explained 20% of the variance in GPT of the dominant hand (R2 = 0.203, p = 0.016).

CONCLUSION

The ulnar nerve conduction velocity, explained 20% of the variance in GPT times of the young men. Performance on this biomarker of neurological health seems to be more influenced by other factors in healthy young individuals.

Explaining the influence of practice on the grooved pegboard times of older adults: role of force steadiness

The purpose was to identify the variables that can explain the variance in the grooved pegboard times of older adults categorized as either fast or slow performers. Participants (n = 28; 60-83 years) completed two experimental sessions, before and after 6 practice sessions of the grooved pegboard test. The 2 groups were identified based on average pegboard times during the practice sessions. Average pegboard time during practice was 73 ± 11 s for the fast group and 85 ± 13 s for the slow group. Explanatory variables for the pegboard times before and after practice were the durations of 4 peg-manipulation phases and 12 measures of force steadiness (coefficient of variation [CV] for force) during isometric contractions with the index finger abductor and wrist extensor muscles. Time to complete the grooved pegboard test after practice decreased by 25 ± 11% for the fast group and by 28 ± 10% for the slow group. Multiple regression models explained more of the variance in the pegboard times for the fast group before practice (Adjusted R2 = 0.85) than after practice (R2 = 0.51), whereas the variance explained for the slow group was similar before (Adjusted R2 = 0.67) and after (Adjusted R2 = 0.64) practice. The explanatory variables differed between before and after practice for the fast group but only slightly for the slow group. These findings indicate that performance-based stratification of older adults can identify unique adjustments in motor function that are independent of chronological age.

Influence of visual feedback and cognitive challenge on the age-related changes in force steadiness

Force steadiness can be influenced by visual feedback as well as presence of a cognitive tasks and potentially differs with age and sex. This study determined the impact of altered visual feedback on force steadiness in the presence of a difficult cognitive challenge in young and older men and women. Forty-nine young (19-30 yr; 25 women, 24 men) and 25 older (60-85 yr; 15 women; 10 men) performed low force (5% of maximum) static contractions with the elbow flexor muscles in the presence and absence of a cognitive challenge (counting backwards by 13) either with low or high visual feedback gain. The cognitive challenge reduced force steadiness (increased force fluctuation amplitude) particularly in women (cognitive challenge × sex: P < 0.05) and older individuals (cognitive challenge × age: P < 0.05). Force steadiness improved with high-gain visual feedback compared with low-gain visual feedback (P < 0.01) for all groups (all interactions: P > 0.05). Manipulation of visual feedback had no influence on the reduced force steadiness in presence of the cognitive challenge for all groups (all P > 0.05). These findings indicate that older individuals and women have greater risk of impaired motor performance of the upper extremity if steadiness is required during a low-force static contraction. Manipulation of visual feedback had minimal effects on the reduced force steadiness in presence of a difficult cognitive challenge.

Short term effects of contralateral tendon vibration on motor unit discharge rate variability and force steadiness in people with Parkinson's disease

Background

Vibration of one limb affects motor performance of the contralateral limb, and this may have clinical implications for people with lateralized motor impairments through vibration-induced increase in cortical activation, descending neural drive, or spinal excitability.

Objective

The objective of this study was to evaluate the effects of acute biceps brachii tendon vibration on force steadiness and motor unit activity in the contralateral limb of persons with Parkinson's disease.

Methods

Ten participants with mild to moderate Parkinson's disease severity performed a ramp, hold and de-ramp isometric elbow flexion at 5% of maximum voluntary contraction with the more-affected arm while vibration was applied to the distal biceps brachii tendon on the contralateral, less-affected arm. Using intramuscular fine wire electrodes, 33 MUs in the biceps brachii were recorded across three conditions (baseline, vibration, and post-vibration). Motor unit recruitment & derecruitment thresholds, discharge rates & variability, and elbow flexion force steadiness were compared between conditions with and without vibration.

Results

Coefficient of variation of force and discharge rate variability decreased 37 and 17%, respectively in post-vibration compared with baseline and vibration conditions. Although the motor unit discharge rates did not differ between conditions the total number of motor units active at rest after de-ramp were fewer in the post-vibration condition.

Conclusion

Contralateral tendon vibration reduces MU discharge rate variability and enhances force control on the more affected side in persons with Parkinson's disease.

Increased velocity feedback gains in the presence of sensory noise can explain paradoxical changes in trunk motor control related to back pain

Literature reports paradoxical findings regarding effects of low-back pain (LBP) on trunk motor control. Compared to healthy individuals, patients with LBP, especially those with high pain-related anxiety, showed stronger trunk extensor reflexes and more resistance against perturbations. On the other hand, LBP patients and especially those with high pain-related anxiety showed decreased precision in unperturbed trunk movement and posture. These paradoxical effects might be explained by arousal potentially increasing average and variance of muscle spindle firing rates. Increased average firing rates could increase resistance against perturbations, but increased variance could decrease precision. We performed a simulation study to test this hypothesis. We modeled the trunk as a 2D inverted pendulum, stabilized by two antagonistic Hill-type muscles, based on their open-loop muscle activation dependent intrinsic stiffness and damping and through 25 ms-delayed, noisy contractile element length and velocity feedback. Reference feedback gains and sensory noise levels were tuned based on previously reported experimental data. We assessed the effect of increasing feedback gains on precision of trunk orientation at different perturbation magnitudes and assessed sensitivity of the effects to open-loop muscle stimulation and noise levels. At low perturbation magnitudes, increasing reflex gains consistently caused an increase in the variance of trunk orientation. At larger perturbation magnitudes, increasing reflex gains consistently caused a decrease in the variance of trunk orientation. Our results support the notion that LBP and related anxiety may increase reflex gains, resulting in an increase in the average and variance of spindle afference, which in turn increase resistance against perturbations and decrease movement precision.

Visual feedback and declines in attention are associated with altered visual strategy during a force-steadiness task in older adults

Greater heterogeneity exists in older adults relative to young adults when performing highly skilled manual tasks. The purpose of this study was to assess the influence of visual feedback and attentional demand on visual strategy during a submaximal force-steadiness task in young and older adults. Eye movements of 21 young (age 20-38 yr; 11 females, 10 males) and 21 older (age 65-90 yr; 11 females, 10 males) adults were recorded during a pinch force-steadiness task while viewing feedback with higher and lower gain and while performing a visuospatial task. For the visuospatial task, participants imagined a star moving around four boxes and reported the final location after a series of directions. Performance on standardized tests of attention was measured. All participants gazed near the target line and made left-to-right saccadic eye movements during the force-steadiness tasks without the visuospatial task. Older adults made fewer saccades than young adults (21.0 ± 2.9 and 23.6 ± 4.4 saccades, respectively) and with higher versus lower gain (20.9 ± 4.0 and 23.7 ± 3.5 saccades, respectively). Most participants used the same visual strategy when performing the visuospatial task though seven older adults used an altered strategy; gaze did not stay near the target line nor travel exclusively left to right. Performance on standardized measures of attention was impaired in this subset compared with older adults who did not use the altered visual strategy. Results indicate that visual feedback influences visual strategy and reveals unique eye movements in some older adults when allocating attention across tasks.NEW & NOTEWORTHY This study contributes novel findings of age-related changes in visual strategy and associations with attentional deficits during hand motor tasks. Older adults used fewer saccades than young adults and with higher versus lower gain visual feedback during a force-steadiness task. A subset of older adults used an altered visual strategy when allocating attention across multiple tasks. Given that this subset demonstrated attentional deficits, the altered visual strategy could serve to indicate motor and/or cognitive impairments.

Practice-Induced Changes in Manual Dexterity of Older Adults Depend on Initial Pegboard Time

INTRODUCTION

The purpose of our study was to determine the influence of practice on the pegboard times and peg-manipulation phases of older adults who were classified as having either slow or fast initial pegboard times.

METHODS

Participants ( n = 26, 70 ± 6.6 yr) completed two evaluation sessions and six practice sessions in which they performed 25 trials (5 blocks of 5 trials) of the grooved pegboard test. All practice sessions were supervised, and the time to complete each trial was recorded. In each evaluation session, the pegboard was mounted on a force transducer so that the downward force applied to the board could be measured.

RESULTS

Participants were stratified into two groups based on the initial time to complete the grooved pegboard test: a fast group (68.1 ± 6.0 s) and a slow group (89.6 ± 9.2 s). Both groups exhibited the classic two-phase profile (acquisition + consolidation) for learning a de novo motor skill. Despite the similar learning profile for the two groups, there were differences between groups in the phases of the peg-manipulation cycle that became faster with practice. The fast group seemed to reduce trajectory variability when transporting the peg, whereas the slow group seemed to exhibit both a decrease in trajectory variability and greater precision when inserting pegs into the holes.

CONCLUSIONS

The changes underlying practice-induced decreases in grooved pegboard time differed for older adults who initially had either a fast or a slow pegboard time.

Cognitive challenge as a probe to expose sex- and age-related differences during static contractions

Despite activities of daily living being frequently performed simultaneously with a cognitive task, motor function is often investigated in isolation, which can hinder the applicability of findings. This brief review presents evidence that 1) performing a cognitive challenge simultaneously with a motor task can negatively impact force steadiness and fatigability of limb muscles during a static contraction, 2) the negative impact on old adults (>65 years old), particularly older women is greater than young when a cognitive challenge is simultaneously performed with a static motor task, 3) age-related mechanisms potentially explain impairments in motor performance in the presence of a cognitive challenge, and 4) the mechanisms for the age-related decrements in motor performance can be distinct between men and women. These observations are highly relevant to the older adults, given the increased risk of accidents and injury when a motor task is performed with a high cognitive-demand task, especially in light of the expanding reliance on an aging workforce.

Age-related differences in upper limb motor performance and intrinsic motivation during a virtual reality task

BACKGROUND

In recent years, virtual reality (VR) has evolved from an alternative to a necessity in older adults for health, medical care, and social interaction. Upper limb (UL) motor skill, is an important ability in manipulating VR systems and represents the brain's regulation of movements using the UL muscles. In this study, we used a haptic-feedback Virtual Box and Block Test (VBBT) system and an Intrinsic Motivation Inventory (IMI) to examine age-related differences in UL motor performance and intrinsic motivation in VR use. The findings will be helpful for the development of VR applications for older adults.

METHODS

In total, 48 young and 47 older volunteers participated in our study. The parameters including VBBT score, number of velocity peaks, velocity, grasping force and trajectory length were calculated to represent the task performance, manual dexterity, coordination, perceptive ability and cognitive ability in this study.

RESULTS

Age-related differences could be found in all the parameters (all p <  0.05) in VR use. Regression analysis revealed that the task performance of young adults was predicted by the velocity and trajectory length (R² = 64.0%), while that of older adults was predicted by the number of velocity peaks (R² = 65.6%). Additionally, the scores of understandability, relaxation and tiredness were significantly different between the two groups (all p <  0.05). In older adults, the understandability score showed large correlation with the IMI score (|r| = 0.576, p <  0.001). In young adults, the correlation was medium (|r| = 0.342, p = 0.017). No significant correlation was found between the IMI score and VBBT score (|r| = 0.142, p = 0.342) in older adults, while a medium correlation (|r| = 0.342, p = 0.017) was found in young adults.

CONCLUSIONS

The findings demonstrated that decreased smoothness in motor skills dominated the poor VR manipulation in older adults. The experience of understandability is important for older adults' intrinsic motivation in VR use.

Decreased nerve conduction velocity may be a predictor of fingertip dexterity and subjective complaints

We examined the causes of decreased fingertip dexterity in elderly individuals with an aim to improve their quality of life by improving their activities of daily living. We calculated nerve conduction velocity, absolute error during force adjustment tasks, and fingertip dexterity test scores for 30 young (21-34 years old) and 30 elderly (60-74 years old) participants to identify age-related changes. We also assessed subjective complaints of pain, motor function, and numbness. Motor nerve (young: 55.8 ± 3.7 m/s; elderly: 52.2 ± 5.0 m/s) and sensory nerve (young: 59.4 ± 3.4 m/s; elderly: 55.5 ± 5.3 m/s) conduction velocities decreased in an age-dependent manner. Moreover, the decrease of motor nerve conduction velocity was associated with decreased fingertip dexterity (objective index), while the decrease of sensory nerve conduction velocity was associated with subjective complaints of pain and motor function (subjective index).

Plantarflexor neuromuscular performance in Insertional Achilles tendinopathy

BACKGROUND

Insertional Achilles tendinopathy (IAT) is a common and painful musculoskeletal condition. The management of IAT commonly involves strengthening of the plantarflexors, although there is currently a paucity of research investigating plantarflexor neuromuscular performance specific to people with IAT.

OBJECTIVES

To compare plantarflexor neuromuscular performance between men with IAT and controls, and to investigate the relationship between plantarflexor neuromuscular performance and patient reported outcome measures for men with IAT.

DESIGN

Case control.

METHOD

34 men with IAT (age 43.7 years [SD 10.02], weight 89.6 kg [16.3]) were matched with 34 healthy men (age 42.8 years [SD 8.9], weight 87.2 kg [9.7]). Participants underwent a plantarflexion maximal voluntary isometric contraction (MVIC) task, and a target force matching task. Neuromuscular variables from these tasks include; MVIC, rate of torque development (RTD), electromechanical delay (EMD), and muscle force steadiness. Participants also completed questionnaires regarding; pain and function, and psychological factors.

RESULTS

The IAT group had reduced MVIC (p < 0.01) and RTD, (p < 0.01) compared to controls, however no significant difference in plantarflexor force steadiness (p = 0.08), or EMD (p = 0.71) was observed. Low strength correlations were detected between the VISA-A and RTD (r = 0.37, p = 0.04), kinesiophobia and EMD (r = 0.45, p = 0.03).

CONCLUSIONS

This study established impairments in plantarflexor strength and RTD among people with IAT. Plantarflexor force steadiness and EMD is not altered in IAT, which is in contrast to evidence from mid-portion Achilles tendinopathy. Plantarflexor RTD was the only neuromuscular outcome measure linked to symptom severity, which may indicate it is an important rehabilitation finding.

Ageing and skeletal muscle force control: current perspectives and future directions

During voluntary muscle contractions, force output is characterized by constant inherent fluctuations, which can be quantified either according to their magnitude or temporal structure, that is, complexity. The presence of such fluctuations when targeting a set force indicates that control of force is not perfectly accurate, which can have significant implications for task performance. Compared to young adults, older adults demonstrate a greater magnitude and lower complexity in force fluctuations, indicative of decreased steadiness, and adaptability of force output, respectively. The nature of this loss‐of‐force control depends not only on the age of the individual but also on the muscle group performing the task, the intensity and type of contraction and whether the task is performed with additional cognitive load. Importantly, this age‐associated loss‐of‐force control is correlated with decreased performance in a range of activities of daily living and is speculated to be of greater importance for functional capacity than age‐associated decreases in maximal strength. Fortunately, there is evidence that acute physical activity interventions can reverse the loss‐of‐force control in older individuals, though whether this translates to improved functional performance and whether lifelong physical activity can protect against the changes have yet to be established. A number of mechanisms, related to both motor unit properties and the behavior of motor unit populations, have been proposed for the age‐associated changes in force fluctuations. It is likely, though, that age‐associated changes in force control are related to increased common fluctuations in the discharge times of motor units.

Alterations in Muscle Force Control With Aging: Is There a Modulatory Effect of Lifelong Physical Activity?

Recent technological developments have enabled significant advances in our understanding of the ability to voluntarily control muscle force output. The fluctuations inherent to muscle force output can be quantified according to both their magnitude and temporal structure (or "complexity"), with such quantification facilitating comparison of force control between distinct populations. In comparison to young adults, older adults exhibit an increase in the magnitude (i.e., decreased steadiness) and a decrease in the complexity (i.e., decreased adaptability) of force fluctuations, both of which are indicative of a loss of force control. There remain, however, key gaps in knowledge that limit our interpretation of this age-related loss of force control. One such gap relates to the effect of lifelong physical activity on force control. To date, research on aging and force control has largely been conducted on inactive or moderately active older adults. However, high levels of lifelong physical activity, such as that exhibited by Masters athletes, have been shown to have protective effects on the function and morphology of the neuromuscular system. Some of these effects (e.g., on impaired inhibitory transmission in the motor cortex and on motor unit discharge rates) have the potential to attenuate the age-related loss of force control, while others (e.g., greater motor unit remodeling capacity) have the potential to worsen it. We therefore propose that, in order to progress our knowledge of the effects of aging on force control, future studies must consider the potential modulatory effect of lifelong physical activity.

The Precision of the Human Hand: Variability in Pinch Strength and Manual Dexterity

Changes in hand morphology throughout human evolution have facilitated the use of forceful pad-to-pad precision grips, contributing to the development of fine motor movement and dexterous manipulation typical of modern humans. Today, variation in human hand function may be affected by demographic and/or lifestyle factors, but these remain largely unexplored. We measured pinch grip strength and dexterity in a heterogeneous cross-sectional sample of human participants (n = 556) to test for the potential effects of sex, age, hand asymmetries, hand morphology, and frequently practiced manual activities across the lifespan. We found a significant effect of sex on pinch strength, dexterity, and different directional asymmetries, with the practice of manual musical instruments, significantly increasing female dexterity for both hands. Males and females with wider hands were also stronger, but not more precise, than those with longer hands, while the thumb-index ratio had no effect. Hand dominance asymmetry further had a significant effect on dexterity but not on pinch strength. These results indicate that different patterns of hand asymmetries and hand function are influenced in part by life experiences, improving our understanding of the link between hand form and function and offering a referential context for interpreting the evolution of human dexterity.

Patterns of Movement Performance and Consistency From Childhood to Old Age

It is widely accepted that the general process of aging can be reflected by changes in motor function. Typically, optimal performance of a given motor task is observed for healthy young adults with declines being observed for individuals at either end of the lifespan. This study was designed to examine differences in the average and variability (i.e., intraindividual variability) of chewing, simple reaction time, postural control, and walking responses. For this study, 15 healthy children, 15 young adults, and 15 older adults participated. Our results indicated the movement performance for the reaction time and postural sway followed a U shape with young adults having faster reaction times and decreased postural sway compared to the children and older adults. However, this pattern was not preserved across all motor tasks with no age differences emerging for (normalized) gait speed, while chewing rates followed a U-shaped curve with older adults and children chewing at faster rates. Taken together, these findings would indicate that the descriptive changes in motor function with aging are heavily influenced by the nature of the task being performed and are unlikely to follow a singular pattern.

Measuring hand sensory function and force control in older adults: Are current hand assessment tools enough?

BACKGROUND

The ability to grasp and manipulate objects is essential for performing activities of daily living. However, there is limited information regarding age-related behavioral differences in hand sensorimotor function due, in part, to the lack of assessment tools capable of measuring subtle but important differences in hand function. The purpose of this study was to demonstrate performance differences in submaximal force control and tactile pattern recognition in healthy older adults using two custom-designed sensorimotor assessment tools.

METHODS

Sensorimotor function was assessed in 13 healthy older adults (mean age 72.2 ±5.5y, range: 65-84y) and 13 young adults (mean age 20 ±1.4y, range: 19-23y). Clinical assessments included the Montreal Cognitive Assessment (MoCA), monofilament testing, maximum voluntary contraction (MVC), and Grooved Pegboard Test. Sensorimotor assessments included submaximal (5, 20% MVC) grip force step-tracking and tactile pattern recognition tasks.

RESULTS

Clinical assessments revealed no or minimal group differences in MVC, monofilament thresholds, and MoCA. However, sensorimotor assessments showed that older adults took longer to discriminate tactile patterns and had poorer accuracy than young adults. Older adults also produced submaximal forces less smoothly than young adults at the 20% force level while greater variability in force maintenance was seen at 5% but not 20% MVC.

CONCLUSIONS

These results demonstrate the ability to integrate higher-order tactile information and control low grip forces is impaired in older adults despite no differences in grip strength or cognition. These findings underscore the need for more sensitive evaluation methods that focus on sensorimotor ability reflective of daily activities.

The role of eye movements, attention, and hand movements on age-related differences in pegboard tests

Well-documented manual dexterity impairments in older adults may critically depend on the processing of visual information. The purpose of this study was to determine age-related changes in eye and hand movements during commonly used pegboard tests and the association with manual dexterity impairments in older adults. The relationship between attentional deficits and manual dexterity was also assessed. Eye movements and hand kinematics of 20 young (20-38 yr) and 20 older (65-85 yr) adults were recorded during 9-Hole Pegboard, Grooved Pegboard, and a visuospatial dual test. Results were compared with standardized tests of attention (The Test of Everyday Attention and Trail Making Test) that assess visual selective attention, sustained attention, attentional switching, and divided attention. Hand movement variability was 34% greater in older versus young adults when placing the pegs into the pegboard and this was associated with decreased pegboard performance, providing further evidence that increased movement variability plays a role in dexterity impairments in older adults. Older adults made more corrective saccades and spent less time gazing at the pegboard than young adults, suggesting altered visual strategies in older compared with young adults. The relationship between pegboard completion time and Trail Making Test B demonstrates an association between attentional deficits and age-related pegboard impairments. Results contribute novel findings of age-associated changes in eye movements during a commonly used manual dexterity task and offer insight into potential mechanisms underlying hand motor impairments in older adults.NEW & NOTEWORTHY This eye tracking study contributes novel findings of age-associated changes in eye movements during the commonly used pegboard tests of manual dexterity, including a greater number of corrective saccades and lesser time gazing at the pegboard holes in older compared with young adults. An association between attentional deficits and dexterity impairments in older adults is also highlighted. Results shed light on potential mechanisms underlying well-documented motor deficits in older adults.

A new visual feedback-based system for the assessment of pinch force, endurance, accuracy and precision. A test-retest reliability study

Introduction

Given that pinch is a precision grip involved in sustained submaximal activities, a Sustained Contraction (SC) task could be associated to Maximal Voluntary Contraction (MVC). To better evaluate the thumb-index system, the test-retest reliability of pinch MVC and SC, measured by a visual feedback-based pinch gauge was assessed.

Methods

26 healthy participants performed MVC and SC in two separate sessions. SC required to maintain 40%MVC as long as possible and it was evaluated in terms of time, accuracy (Mean Distance between force trace and target force, MD), precision (Coefficient of Variability of force trace, CV). MD and CV analyses were conducted dividing the SC task into three equivalent time stages (beginning, middle, exhaustion). Relative Reliability (RR) was measured by Intraclass Correlation Coefficient, and Absolute Reliability (AR) was measured by Standard Error of Measurement and by Bland-Altman plot.

Results

MVC and Time showed high RR and AR in both hands. RR of MD and CV in right hand was excellent in the beginning and middle stages, and fair in the exhaustion one, showing decreasing reliability as fatigue increases. In the left hand RR of MD and CV was generally lower. MD showed excellent reliability in the beginning stage and good reliability in the other stages. CV showed fair relative reliability at both beginning and middle stages, excellent in the last one. Conversely, it was observed high AR of MD and CV in all stages in both hands.

Conclusions

All indices are reliable to assess motor control of thumb-index pinch in both hands.

Time spent on the smartphone does not relate to manual dexterity in young adults

Background

The Grooved Pegboard Test (GPT) is widely adopted to evaluate manual dexterity, it presents normative data but the test is influenced by different factors. The influence of time spent on smartphones has not been considered before, for this reason, the objective of this study was to evaluate if smartphone use influences the time to complete the GPT. A total of 38 (21 women; 17 men) young adults 20.7 (1.5) years participated in the study. The time spent on the smartphones during the last seven days was recorded through the device itself and the GPT performance was measured. A correlation analysis between the time spent on the smartphone and GPT was performed while the t-test was adopted to evaluate gender differences.

Results

No statistically significant differences were detected between men and women in the time to complete the GPT (p = 0.20) and in the time spent on the smartphone (p = 0.87). The GPT and the time spent using the smartphone were not correlated (r = 0.044, p = 0.78).

Conclusion

The time spent on the smartphone by young adults does not influence the time to complete the GPT, indicating that smartphone use does not influence measures of manual dexterity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-021-00639-y.

Force Steadiness: From Motor Units to Voluntary Actions

Voluntary actions are controlled by the synaptic inputs that are shared by pools of spinal motor neurons. The slow common oscillations in the discharge times of motor units due to these synaptic inputs are strongly correlated with the fluctuations in force during submaximal isometric contractions (force steadiness) and moderately associated with performance scores on some tests of motor function. However, there are key gaps in knowledge that limit the interpretation of differences in force steadiness.

Motor control characteristics of upper limbs in response to assistive forces during bilateral tasks

Most research on power assist suits (PASs) that concerned PAS-human interactions has used human physical reactions as criteria to evaluate the mechanical function, however, with minimal emphasis on human reactions in response to PASs. In this study, we focused on the physiological responses of the upper limbs including muscle activity of the biceps brachii and the triceps brachii, co-activation, force steadiness (CV) and rated perceived exertion (RPE) to various patterns of bilateral assistive force, such as unilateral assistance (L0% & R67% [% = percentage of workload force, L = left arm, R = right arm], L67% & R0%, L0% & R33%, L33% & R0%), symmetrical (L0% & R0%, L33% & R33%, L67% & R67%) and asymmetrical bilateral assistance (L33% & R67%, L67% & R33%), during bilateral isometric force-matching tasks. The results showed a similar muscular response of the two arms to bilateral assistive conditions, and the muscle activity of the arm that was being observed decreased only when the assistive force that applied on itself increased, indicating that both arms may have adopted similar but independent motor control mechanisms to acclimate to the bilateral assistive forces. Comparison between the two unilateral assistances (L0% & R33% and L33% & R0%) and the two asymmetrical bilateral assistances (L33% & R67%, L67% & R33%) showed no significant differences in muscular responses, CV and RPE, indicating that bilateral assistances with bilateral interchanged assistive levels may be equally effective regardless of which arm the higher assistive force is applied to. Comparison between unilateral and symmetrical assistive conditions that have similar overall workloads (L67% & R0%, L33% & R33%, L0% & R67%) showed a lower CV and RPE score at symmetrical assistance compared with unilateral assistance, suggesting that assisting both arms with the same level simultaneously improves task performances compared with applying the assistive force to only one arm.

Reconstruction of net force fluctuations from surface EMGs of multiple muscles in steady isometric plantarflexion

The purposes of this study were to clarify if force fluctuations during steady multi-muscle contractions have a temporal correlation with a low-frequency component of rectified surface EMG (rEMG) in the involved muscles and collection of that component across muscles allows for the reconstruction of force fluctuations across a wide range of contraction intensities. Healthy young men (n = 15) exerted steady isometric plantarflexion force at 5-60% of maximal force. Surface EMG was recorded from the medial and lateral gastrocnemii, soleus, peroneus longus, abductor hallucis, and tibialis anterior muscles. The cross-correlation function (CCF) between plantarflexion force fluctuations and low-pass filtered rEMG in each muscle was calculated for 8 s. To reconstruct force fluctuations from rEMGs, the product of rEMG and an identified constant factor were summed across muscles with time-lag compensation for electro-mechanical delay. A distinct peak of the CCF was found between plantarflexion force fluctuations and rEMG in most cases except for the tibialis anterior. The CCF peak was greatest in the medial gastrocnemius and soleus. Reconstructed force from rEMGs was temporally correlated with measured force fluctuations across contraction intensities (average CCF peak: r = 0.65). The results indicate that individual surface rEMG has a low-frequency component that is temporally correlated with net force fluctuations during steady multi-muscle contractions and contributes to the reconstruction of force fluctuations across a wide range of contraction intensities. It suggests a potential applicability of individual surface EMGs for identifying the contributing muscles to controlling or disturbing isometric steady force in multi-muscle contractions.

Population based norms for the box and blocks test in healthy right-handed Taiwanese adults

BACKGROUND

This study establishes norms for the Box and Block Test (BBT) in healthy Taiwanese adults between 15 and 75 years of age.

METHODS

621 right-handed healthy adults (296 males and 325 females) completed the study. All participants performed the BBT following the standard protocol. An age by gender by testing hand analysis of variance (ANOVA) was performed to determine differences for the variables of interest.

RESULTS

On average, females performed better on the BBT than males by approximately 2 points (p < 0.001). Across all participants, dominant hand performance was 2.8 points higher than non-dominant hand performance (p < 0.001). Significant changes of BBT scores across life span were observed at the ages of 30, 45 and 60 years old. Average scores across all age groups are at least one standard deviation below the previously established American norms for each corresponding age group.

CONCLUSION

When using the BBT test with adult Taiwanese clients, clinical practitioners should strongly consider using right-handed normative data from Taiwanese individuals as the norms for this population differ from the previously established norms from American adult participants.

Can Resistance Training Improve Upper Limb Postural Tremor, Force Steadiness and Dexterity in Older Adults? A Systematic Review

BACKGROUND

The ageing process and several health conditions may increase tremor and reduce force steadiness and dexterity, which can severely impact on function and quality of life. Resistance training can evoke a range of neuromuscular adaptions that may significantly reduce tremor and/or increase force steadiness and/or dexterity in older adults, irrespective of their health condition.

OBJECTIVES

The objective of this study was to systematically review the literature to determine if a minimum of 4 weeks' resistance training can reduce postural tremor and improve force steadiness and/or dexterity in older adults, defined as aged 65 years and over.

METHODS

An electronic search using Ovid, CINAHL, SPORTDiscus and EMBASE was performed. Risk of bias was assessed using the Cochrane Risk of Bias Tool.

RESULTS

Fourteen studies met the eligibility criteria, including six randomised controlled trials and two quasi-randomised controlled trials. All eight studies that recruited healthy older adults reported significant reductions in postural tremor and/or improvements in force steadiness and dexterity. Five out of seven studies that examined older adults with a particular health condition reported some improvements in force steadiness and/or dexterity. Specifically, significant benefits were observed for older adults with chronic obstructive pulmonary disease and essential tremor; however, small or no changes were observed for individuals with osteoarthritis or stroke.

CONCLUSIONS

Resistance training is a non-pharmacological treatment that can reduce tremor and improve force steadiness and dexterity in a variety of older adult populations. Future research should employ randomised controlled trials with larger sample sizes, better describe training programme methods, and align exercise prescription to current recommendations for older adults.

Force control during submaximal isometric contractions is associated with walking performance in persons with multiple sclerosis

Individuals with multiple sclerosis (MS) experience progressive declines in movement capabilities, especially walking performance. The purpose of our study was to compare the amount of variance in walking performance that could be explained by the functional capabilities of lower leg muscles in persons with MS and a sex- and age-matched control group. Participants performed two walking tests (6-min walk and 25-ft walk), strength tests for the plantar flexor and dorsiflexor muscles, and steady submaximal (10% and 20% maximum) isometric contractions. High-density electromyography (EMG) was recorded during the steady contractions, and the signals were decomposed to identify the discharge times of concurrently active motor units. There were significant differences between the two groups in the force fluctuations during the steady contractions (force steadiness), the strength of the plantar flexor and dorsiflexor muscles, and the discharge characteristics during the steady contractions. Performance on the two walking tests by the MS group was moderately associated with force steadiness of the plantar flexor and dorsiflexor muscles; worse force steadiness was associated with poorer walking performance. In contrast, the performance of the control group was associated with muscle strength (25-ft test) and force steadiness of the dorsiflexors and variance in common input of motor units to the plantar flexors (6-min test). These findings indicate that a reduction in the ability to maintain a steady force during submaximal isometric contractions is moderately associated with walking performance of persons with MS.NEW & NOTEWORTHY The variance in walking endurance and walking speed was associated with force control of the lower leg muscles during submaximal isometric contractions in individuals with multiple sclerosis (MS). In contrast, the fast walking speed of a sex- and age-matched control group was associated with the strength of lower leg muscles. These findings indicate that moderate declines in the walking performance of persons with MS are more associated with impairments in force control rather than decreases in muscle strength.

Explaining Individual Differences in Fine Motor Performance and Learning in Older Adults: The Contribution of Muscle Strength and Cardiovascular Fitness

It remains controversial whether aging influences motor learning and whether physiological factors, such as local strength or fitness, are associated with fine motor performance and learning in older adults (OA). OA (n = 51) and young adults (YA, n = 31) performed a short-term motor learning session using a precision grip force modulation task. The rate of improvement of OA compared with YA was steeper with respect to performance variability and temporal precision. Both age groups showed positive transfer during an unpracticed variant of the force modulation task. Local muscle strength (pinch and grip strength) and high cardiovascular fitness positively predicted fine motor performance, whereas initial performance, muscle strength, and motor fitness (heterogeneous motor test battery) negatively predicted rate of improvement. Analyses indicated potentials, but also limits of plasticity for OA.

Oscillations in neural drive and age-related reductions in force steadiness with a cognitive challenge

A cognitive challenge when imposed during a low-force isometric contraction will exacerbate sex- and age-related decreases in force steadiness, but the mechanism is not known. We determined the role of oscillations in the common synaptic input to motor units on force steadiness during a muscle contraction with a concurrent cognitive challenge. Forty-nine young adults (19-30 yr; 25 women, 24 men) and 36 old adults (60-85 yr; 19 women, 17 men) performed a cognitive challenge (counting backward by 13) during an isometric elbow flexion task at 5% of maximal voluntary contraction. Single-motor units were decomposed from high-density surface EMG recordings. For a subgroup of participants, motor units were matched during control and cognitive challenge trials, so the same motor unit was analyzed across conditions. Reduced force steadiness was associated with greater oscillations in the synaptic input to motor units during both control and cognitive challenge trials ( r = 0.45-0.47, P < 0.01). Old adults and young women showed greater oscillations in the common synaptic input to motor units and decreased force steadiness when the cognitive challenge was imposed, but young men showed no change across conditions (session × age × sex, P < 0.05). Oscillations in the common synaptic input to motor units is a potential mechanism for altered force steadiness when a cognitive challenge is imposed during low-force contractions in young women and old adults. NEW & NOTEWORTHY We found that oscillations in the common synaptic input to motor units were associated with a reduction in force steadiness when a cognitive challenge was imposed during low-force contractions of the elbow flexor muscles in young women and old men and women but not young men. Age- and sex-related muscle weakness was associated with these changes.

The effects of age and musculoskeletal pain on force variability among manual workers

The present study investigated the influence of age and musculoskeletal pain on force variability during a continuous isometric handgrip force task performed at 30% of maximal voluntary contraction carried out until failure. We recruited 96 male manual workers aged 51-72 years. The participants were stratified according to their age (50-59 and 60+ years) and by pain status (no pain, acute pain and chronic pain). The amplitude and structure of variability expressed as respectively standard deviation (SD) and coefficient of variation (CV), and sample entropy (SaEn) were calculated from the endurance task. The oldest group had an approximately 18% longer endurance time than the youngest group. No between-group differences were found in SD or CV, whereas a significant interaction between age and pain stage was found for SaEn. The youngest group showed lower SaEn than the oldest for both those with chronic pain and those without pain, indicating less force complexity, whereas a tendency for the opposite was found in the acute pain group. Within the pain stage groups, workers with acute pain had higher SaEn compared with both the no pain and chronic pain groups. These findings suggest that age and musculoskeletal pain differentially affects the structure of force variability in manual workers.

Poor estimates of motor variability are associated with longer grooved pegboard times for middle-aged and older adults

Goal-directed movements that involve greater motor variability are performed with an increased risk that the intended goal will not be achieved. The ability to estimate motor variability during such actions varies across individuals and influences how people decide to move about their environment. The purpose of our study was to identify the decision-making strategies used by middle-aged and older adults when performing two goal-directed motor tasks and to determine if these strategies were associated with the time to complete the grooved pegboard test. Twenty-one middle-aged (48 ± 6 yr; range 40-59 yr, 15 women) and 20 older adults (73 ± 4 yr; range 65-79 yr, 8 women) performed two targeted tasks, each with two normalized target options. Decision-making characteristics were not associated with time to complete the test of manual dexterity when the analysis included all participants, but slower pegboard times were associated with measures of greater movement variability during the target-directed actions. When the data were clustered on the basis of pegboard time rather than age, relatively longer times for the faster group were associated with greater motor variability during the prescribed tasks, whereas longer times for the slower group were associated with increased risk-seeking behavior (α) and greater variability in the targeted actions. NEW & NOTEWORTHY This study was the first to examine the association between decision-making choices and an NIH Toolbox test of manual dexterity (grooved pegboard test) performed by middle-aged and older adults. Significant associations were observed between decision-making choices and time to complete the test when the analyses were based on pegboard times rather than chronological age. This result indicates that decision-making choices of middle-aged and older adults, independent of age, were associated with time to complete a test of manual dexterity.

Hand strength and dexterity in patients with Prader-Willi syndrome: a pilot intervention study

OBJECTIVE

The study aim was to examine the hand function (hand strength and dexterity) and intervention effects of training in adults with Prader-Willi syndrome (PWS).

METHODS

Six adults with PWS (two females; mean age 26.14 years) underwent hand muscle strength and dexterity training for 3 months (2 hours per week). The following hand function tests were performed pre- and post-intervention: (1) hand grip, lateral pinch, and tip pinch hand strength tests, (2) the Box and Block test (BBT) for gross manual dexterity and (3) the Purdue Pegboard test for finger dexterity.

RESULTS

Before treatment, all subjects showed lower hand grip, lateral pinch, tip pinch strength, and poorer manual/finger dexterity relative to healthy adults. After training, hand function scores improved on many test items, but only the left hand tip pinch and the right hand BBT performance showed significant improvements.

CONCLUSIONS

All subjects showed lower hand strength and poorer manual/finger dexterity compared with healthy adults; this should be considered during physical training programs. Owing to limitations in the intervention intensity and possible subject behavioral deficits, further research is needed to clarify the effects of this intervention on hand function in PWS patients.

Force Steadiness During a Cognitively Challenging Motor Task Is Predicted by Executive Function in Older Adults

Motor performance and cognitive function both decline with aging. Older adults for example are usually less steady for a constant-force task than young adults when performing low-intensity contractions with limb muscles. Healthy older adults can also show varying degrees of cognitive decline, particularly in executive function skills. It is not known, however, whether age-related changes in steadiness of low-force tasks and cognitive function are independent of one another. In this study, we determined if executive function skills in aging are associated with the steadiness during a low-force muscle contraction performed with and without the imposition of a cognitive challenge. We recruited 60 older adults (60–85 years old, 34 women, 26 men) and 48 young adults (19–30 years old, 24 women, 24 men) to perform elbow flexor muscle contractions at 5% of maximal voluntary contraction (MVC) force in the presence and absence of a difficult mental-math task (counting backward by 13 from a four-digit number). Force steadiness was quantified as the coefficient of variation (CV) of force and executive function was estimated with the Trail-making Test part A and B. The cognitive challenge increased the CV of force (i.e., decreased force steadiness) with greater changes in older adults than young adults (5.2 vs. 1.3%, respectively, cognitive challenge × age: P < 0.001). Older adults were 35% slower in both parts A and B of the Trail-making Test (P < 0.001), and to eliminate the effects of age and education on this variable, all further analyses were performed with the age-corrected z-scores for each individual using established normative values. Hierarchical regression models indicated that decreased force steadiness during a cognitive challenge trial was in part, explained by the performance in the Trail-making Test part A and B in older (r = 0.53 and 0.50, respectively, P < 0.05), but not in young adults (P > 0.05). Thus, healthy community-dwelling older adults, who have poorer executive function skills, exhibit reduced force steadiness during tasks when also required to perform a high cognitive demand task, and are likely at risk of reduced capacity to perform daily activities that involve cognitively challenging motor tasks.

Decomposing sensorimotor variability changes in ageing and their connection to falls in older people

The relationship between sensorimotor variability and falls in older people has not been well investigated. We developed a novel task having shared biomechanics of obstacle negotiation to quantify sensorimotor variability related to locomotion across age. We found that sensorimotor variability in foot placement increases continuously with age. We then applied sensory psychophysics to pinpoint the visual and somatosensory systems associated with sensorimotor variability. We showed increased sensory variability, specifically increased proprioceptive variability, the vital cause of more variable foot placement in older people (greater than 65 years). Notably, older participants relied more on the vision to judge their own foot’s height compared to the young, suggesting a shift in multisensory integration strategy to compensate for degenerated proprioception. We further modelled the probability of tripping-over based on the relationship between sensorimotor variability and age and found a correspondence between model prediction and community-based data. We reveal increased sensorimotor variability, modulated by sensation precision, a potentially vital mechanism of raised tripping-over and thus fall events in older people. Analysis of sensorimotor variability and its specific components may have the utility of fall risk and rehabilitation target evaluation.

Get a grip: individual variations in grip strength are a marker of brain health

Demonstrations that grip strength has predictive power in relation to a range of health conditions-even when these are assessed decades later-has motivated claims that hand-grip dynamometry has the potential to serve as a "vital sign" for middle-aged and older adults. Central to this belief has been the assumption that grip strength is a simple measure of physical performance that provides a marker of muscle status in general, and sarcopenia in particular. It is now evident that while differences in grip strength between individuals are influenced by musculoskeletal factors, "lifespan" changes in grip strength within individuals are exquisitely sensitive to integrity of neural systems that mediate the control of coordinated movement. The close and pervasive relationships between age-related declines in maximum grip strength and expressions of cognitive dysfunction can therefore be understood in terms of the convergent functional and structural mediation of cognitive and motor processes by the human brain. In the context of aging, maximum grip strength is a discriminating measure of neurological function and brain health.

Measuring dexterity in the podiatrist population: a cross-sectional comparison of novice students and experienced podiatrists

BACKGROUND

There is no 'gold-standard' for the evaluation of dexterity for the health professional or podiatrist populations. This has resulted in a broad array of generalised tests to evaluate dexterity. Thus, the aim was to determine which objective generalised dexterity tests are best suited to evaluating dexterity in a podiatry student population.

METHODS

A cohort of Novice podiatry students and Experienced podiatrists were recruited and evaluated on a battery of dexterity tests selected to evaluate a variety of different elements. Group differences were evaluated statistically and regression undertaken on significant test outcomes.

RESULTS

A total of 108 participants were recruited with 54 participants in each of the Novice and Experienced groups. Five of the eight tests were able to discriminate dexterous ability of participants in the Novice and Experienced groups. These included the Grip-lift task, GPT, P-MVC, G-MVC and the AsTex® sensory discrimination test. These tests comprised a total of 11 significant dependent variables (p <  0.05). From the test battery, outcomes were able to predict 79% of the group membership. Age and experience did not explain within-group variability for the Experienced group.

CONCLUSION

Whilst the Experienced group displayed superior performance in strength and speed, the Novice group showed superior coordination and sensory ability. From these findings, we would recommend that outcomes from the Grooved Pegboard Test, Grip-lift task, Grip Strength test and Pinch Grip strength test be used to evaluate elements of dexterity in this population.

Impaired Trunk Flexor Strength, Fatigability, and Steadiness in Postpartum Women

PURPOSE

To determine whether postpartum women (vaginal and cesarean delivery) have deficits in trunk flexor strength, fatigability and steadiness, compared with nulligravid women, up to 26 wk postpartum. We hypothesized that postpartum women would be weaker, more fatigable, and have greater torque fluctuations than controls, with cesarean delivery showing greater deficits than vaginal delivery.

METHODS

Twenty-two control women (nulligravid) and 29 postpartum women (20-40 yr, 19 who delivered via vaginal birth, 13 via Caesarian section) participated. Postpartum women were tested 8 to 10 wk and 24 to 26 wk postpartum. Control women were tested 16 to 18 wk apart. Maximal voluntary isometric contractions (MVC) were performed at multiple trunk positions with the trunk flexor muscles. To determine trunk flexor fatigability, subjects performed intermittent isometric contractions at 50% MVC (6-s contraction, 4-s rest) in upright sitting until task failure. An MVC was performed during the fatiguing task (one per minute) and at 10 and 20 min of recovery.

RESULTS

At 8 and 26 wk, postpartum women (groups pooled) were weaker at all trunk angles (38% and 44% respectively, P < 0.05) than controls despite no differences in handgrip strength. Postpartum women were more fatigable (71% and 52% respectively) and had greater torque fluctuations than controls (P < 0.05). At 8 wk postpartum, women who had a cesarean delivery, were 59% more fatigable (P = 0.004) than the vaginal delivery group, with no difference between delivery types at 26 wk postpartum.

CONCLUSIONS

Musculoskeletal recovery, including trunk flexor muscle strength and fatigability, is incomplete at 26 wk postpartum. These findings provide a rationale for future studies to address outcomes of rehabilitation programs specifically targeted at improving strength and fatigability of the trunk flexor muscles after pregnancy and childbirth.

Variability in common synaptic input to motor neurons modulates both force steadiness and pegboard time in young and older adults

KEY POINTS

The fluctuations in force during a steady isometric contraction (force steadiness) are associated with oscillations in common synaptic input to the involved motor neurons. Decreases in force steadiness are associated with increases in pegboard times in older adults, although a mechanism for this link has not been established. We used a state-space model to estimate the variability in common synaptic input to motor neurons during steady, isometric contractions. The estimate of common synaptic input was derived from the discharge times of motor units as recorded with high-density surface electrodes. We found that the variability in common synaptic input to motor neurons modulates force steadiness for young and older adults, as well as pegboard time for older adults.

ABSTRACT

We investigated the associations between grooved pegboard times, force steadiness (coefficient of variation for force) and variability in an estimate of the common synaptic input to motor neurons innervating the wrist extensor muscles during steady contractions performed by young and older adults. The discharge times of motor units were derived from recordings obtained with high-density surface electrodes when participants performed steady isometric contractions at 10% and 20% of maximal voluntary contraction force. The steady contractions were performed with a pinch grip and wrist extension, both independently (single action) and concurrently (double action). The variance in common synaptic input to motor neurons was estimated with a state-space model of the latent common input dynamics. There was a statistically significant association between the coefficient of variation for force during the steady contractions and the estimated variance in common synaptic input in young (r2  = 0.31) and older (r2  = 0.39) adults, although not between either the mean or the coefficient of variation for interspike interval of single motor units with the coefficient of variation for force. Moreover, the estimated variance in common synaptic input during the double-action task with the wrist extensors at the 20% target was significantly associated with grooved pegboard time (r2  = 0.47) for older adults but not young adults. These findings indicate that longer pegboard times of older adults were associated with worse force steadiness and greater fluctuations in the estimated common synaptic input to motor neurons during steady contractions.

Expectation of movement generates contrasting changes in multifinger synergies in young and older adults

Anticipatory synergy adjustment (ASA) is a feed-forward control mechanism that describes a continuous decrease in the stability of the current motor state beginning about 150 ms prior to a state transition. Recently, we described an associated phenomenon in which the system stability was reduced solely in response to a cue that generates an expectation of a state change, independent of whether the state change actually occurs. Both phenomena are of the same kind (stability reduction), but evoked by distinct antecedent conditions. Since, logically, cuing for movement must occur before the initiation of that movement, we named this new phenomenon 'Stage-1 ASA' and rechristened the well-established version 'Stage-2 ASA'. Here, we used a four-finger, isometric force production task to explore (1) the effect of healthy aging on Stage-1 ASA, and (2) if Stage-1 ASA resulted in a more rapid state change. Young and older adult participants produced 10% of their maximal force when they did not expect to produce any change in the force, and when they expected to change their force in an unknown direction and at an unknown time. In the latter condition, the 10% constant-force phase was followed by a choice reaction time task, in which the participants rapidly changed their force to follow a moving target presented on a computer monitor. Both young and older adults displayed equivalent amount of Stage-1 ASA. This was driven by a 42% reduction in finger-force variability in young adults. In contrast, it was driven by a 38% increase in finger-force variability in older adults. We speculate that the reduction in finger force variability assists the young adults in rapid state changes via two mechanisms: (1) the finger forces occupy a restricted set of states that are optimal for quick state transitions, and (2) lower variability during steady state translates into lower self-motion during state transition. Self-motion is the covariation between finger forces that fails to change the total force. The older adults are unable to adopt this strategy, and the increase in finger-force variability arises from (1) the adoption of an alternative strategy of destabilizing the attractor associated with the current state to facilitate state transitions and (2) the inability to coordinate multiple finger forces. Finally, older adults displayed longer reaction times than young adults, but a clear relation between Stage-1 ASA and consequent behavioral benefit in terms of reduced reaction time remained elusive.

Peg-manipulation capabilities of middle-aged adults have a greater influence on pegboard times than those of young and old adults

Declines in manual dexterity are frequently quantified as the time it takes to complete the grooved pegboard test. The test requires individuals to manipulate 25 pegs, one at a time, by removing them from a well and inserting them into a prescribed hole. The manipulation of each peg involves four phases: selection, transport, insertion, and return. The purpose of our study was to compare the times to complete the four phases of peg manipulation and the forces applied to the pegboard during peg insertion as young, middle-aged, and old adults performed the grooved pegboard test. The relative significance of the peg-manipulation attributes for 30 young (24.0 ± 4.4 years), 15 middle-aged (46.5 ± 6.5 years), and 15 old (70.4 ± 4.0 years) adults was assessed with a multiple-regression analysis. The grooved pegboard test was performed on a force plate. Pegboard times for the old adults (81 ± 17 s) were longer than those for young (56 ± 7 s) and middle-aged (58 ± 11 s) adults. Regression analysis indicated that the explanatory variables for the pegboard times of young (R² = 0.33) and middle-aged (R² = 0.78) adults were the times for the peg insertion and return phases, whereas the predictors for old adults (R² = 0.49) were the times for the peg selection and transport phases. The relative influence of peg-manipulation capabilities on a pegboard test of manual dexterity was greater for middle-aged adults than for young and old adults.

Handgrip force steadiness in young and older adults: a reproducibility study

Background

Force steadiness is a quantitative measure of the ability to control muscle tonus. It is an independent predictor of functional performance and has shown to correlate well with different degrees of motor impairment following stroke. Despite being clinically relevant, few studies have assessed the validity of measuring force steadiness. The aim of this study was to explore the reproducibility of handgrip force steadiness, and to assess age difference in steadiness.

Method

Intrarater reproducibility (the degree to which a rating gives consistent result on separate occasions) was investigated in a test-retest design with seven days between sessions. Ten young and thirty older adults were recruited and handgrip steadiness was tested at 5%, 10% and 25% of maximum voluntary contraction (MVC) using Nintendo Wii Balance Board (WBB). Coefficients of variation were calculated from the mean force produced (CVM) and the target force (CVT). Area between the force curve and the target force line (Area) was also calculated. For the older adults we explored reliability using intraclass correlation coefficient (ICC) and agreement using standard error of measurement (SEM), limits of agreement (LOA) and smallest real difference (SRD).

Results

A systematic improvement in handgrip steadiness was found between sessions for all measures (CVM, CVT, Area). CVM and CVT at 5% of MVC showed good to high reliability, while Area had poor reliability for all percentages of MVC. Averaged ICC for CVM, CVT and Area was 0.815, 0.806 and 0.464, respectively. Averaged ICC on 5%, 10%, and 25% of MVC was 0.751, 0.667 and 0.668, respectively. Measures of agreement showed similar trends with better results for CVM and CVT than for Area. Young adults had better handgrip steadiness than older adults across all measures.

Conclusion

The CVM and CVT measures demonstrated good reproducibility at lower percentages of MVC using the WBB, and could become relevant measures in the clinical setting. The Area measure had poor reproducibility. Young adults have better handgrip steadiness than old adults.

Joint Moment-Angle Properties of the Hip Extensors in Subjects With and Without Patellofemoral Pain

Strength deficits of hip extension in individuals with patellofemoral syndrome are commonly reported in literature. No literature to date has examined these deficits with variable positions of the knee and hip; altering knee angle alters the length and therefore potentially the force produced by the biarticular muscles. Beyond strength, neuromuscular control can also be assessed through the analysis of isometric joint moment steadiness. Subjects consisted of a group of individuals with patellofemoral syndrome (n = 9), and a group of age- and size-matched controls with no symptoms (n = 9). Maximum isometric joint moments for hip extension were measured at 4 points within the joint's range of motion, at 2 different knee positions (0° and 90°) for each group. The joint moment signals were analyzed by computing signal Coefficient of Variation (CV). The results indicate that no significant differences were found between the groups of subjects for the hip extension moments when the knee was extended. However, there was a significant difference between the groups for the joint moments of hip extension with the knee flexed at all 4 hip positions. Results also showed hip extension CV values to be significantly higher in the patellofemoral group compared with the control group, indicating greater signal noise and therefore poorer neuromuscular control of the hip extensor musculature. This study demonstrated that individuals with patellofemoral syndrome have reduced hip extension strength and reduced neuromuscular control with the knee flexed compared with a control group. These results have implications for the etiology of patellofemoral syndrome and its rehabilitation.

Spiral tracing on a touchscreen is influenced by age, hand, implement, and friction

Dexterity impairments are well documented in older adults, though it is unclear how these influence touchscreen manipulation. This study examined age-related differences while tracing on high- and low-friction touchscreens using the finger or stylus. 26 young and 24 older adults completed an Archimedes spiral tracing task on a touchscreen mounted on a force sensor. Root mean square error was calculated to quantify performance. Root mean square error increased by 29.9% for older vs. young adults using the fingertip, but was similar to young adults when using the stylus. Although other variables (e.g., touchscreen usage, sensation, and reaction time) differed between age groups, these variables were not related to increased error in older adults while using their fingertip. Root mean square error also increased on the low-friction surface for all subjects. These findings suggest that utilizing a stylus and increasing surface friction may improve touchscreen use in older adults.