Factors influencing power hand tool fastening accuracy and reaction forces.

OBJECTIVE: A laboratory study investigated the relationship between power hand tool and task-related factors affecting threaded fastener torque accuracy and associated handle reaction force. BACKGROUND: We previously developed a biodynamic model to predict handle reaction forces. We hypothesized that torque accuracy was related to the same factors that affect operator capacity to react against impulsive tool forces, as predicted by the model. METHOD: The independent variables included tool (pistol grip on a vertical surface, right angle on a horizontal surface), fastener torque rate (hard, soft), horizontal distance (30 cm and 60 cm), and vertical distance (80 cm, 110 cm, and 140 cm). Ten participants (five male and five female) fastened 12 similar bolts for each experimental condition. RESULTS: Average torque error (audited - target torque) was affected by fastener torque rate and operator position. Torque error decreased 33% for soft torque rates, whereas handle forces greatly increased (170%). Torque error also decreased for the far horizontal distance 7% to 14%, when vertical distance was in the middle or high, but handle force decreased slightly 3% to 5%. CONCLUSION: The evidence suggests that although both tool and task factors affect fastening accuracy, they each influence handle reaction forces differently. We conclude that these differences are attributed to different parameters each factor influences affecting the dynamics of threaded faster tool operation. Fastener torque rate affects the tool dynamics, whereas posture affects the spring-mass-damping biodynamic properties of the human operator. APPLICATION: The prediction of handle reaction force using an operator biodynamic model may be useful for codifying complex and unobvious relationships between tool and task factors for minimizing torque error while controlling handle force.

Effect of sitting or standing on touch screen performance and touch characteristics.

OBJECTIVE: The aim of this study was to evaluate the effect of sitting and standing on performance and touch characteristics during a digit entry touch screen task in individuals with and without motor-control disabilities. BACKGROUND: Previously, researchers of touch screen design have not considered the effect of posture (sitting vs. standing) on touch screen performance (accuracy and timing) and touch characteristics (force and impulse). METHOD: Participants with motor-control disabilities (n = 15) and without (n = 15) completed a four-digit touch screen number entry task in both sitting and standing postures. Button sizes varied from 10 mm to 30 mm (5-mm increments), and button gap was 3 mm or 5 mm. RESULTS: Participants had more misses and took longer to complete the task during standing for smaller button sizes (< 20 mm). At larger button sizes, performance was similar for both sitting and standing. In general, misses, time to complete task, and touch characteristics were increased for standing. Although disability affected performance (misses and timing), similar trends were observed for both groups across posture and button size. CONCLUSION: Standing affects performance at smaller button sizes (< 20 mm). For participants with and without motor-control disabilities, standing led to greater exerted force and impulse. APPLICATION: Along with interface design considerations, environmental conditions should also be considered to improve touch screen accessibility and usability.

Relationships between biomechanics, tendon pathology, and function in individuals with lateral epicondylosis.

STUDY DESIGN: Single-cohort descriptive and correlational study. OBJECTIVES: To investigate the relationships between tendon pathology, biomechanical measures, and self-reported pain and function in individuals with chronic lateral epicondylosis. BACKGROUND: Lateral epicondylosis has a multifactorial etiology and its pathophysiology is not well understood. Consequently, treatment remains challenging, and lateral epicondylosis is prone to recurrence. While tendon pathology, pain system changes, and motor impairments due to lateral epicondylosis are considered related, their relationships have not been thoroughly investigated. METHODS: Twenty-six participants with either unilateral (n = 11) or bilateral (n = 15) chronic lateral epicondylosis participated in this study. Biomechanical measures (grip strength, rate of force development, and electromechanical delay) and measures of tendon pathology (magnetic resonance imaging and ultrasound) and self-reported pain and function (Patient-Rated Tennis Elbow Evaluation) were performed. Partial Spearman correlations, adjusting for covariates (age, gender, weight, and height), were used to evaluate the relationship between self-reported pain, function, and biomechanical and tendon pathology measures. RESULTS: Statistically significant correlations between biomechanical measures and the Patient-Rated Tennis Elbow Evaluation ranged in magnitude from 0.44 to 0.68 (P<.05); however, no significant correlation was observed between tendon pathology (magnetic resonance imaging and ultrasound) measures and the Patient-Rated Tennis Elbow Evaluation (r = -0.02 to 0.31, P>.05). Rate of force development had a stronger correlation (r = 0.54-0.68, P<.05) with self-reported function score than with grip strength (r = 0.35-0.47, P<.05) or electromechanical delay (r = 0.5, P<.05). CONCLUSION: Biomechanical measures (pain-free grip strength, rate of force development, electromechanical delay) have the potential to be used as outcome measures to monitor progress in lateral epicondylosis. In comparison, the imaging measures (magnetic resonance imaging and ultrasound) were useful for visualizing the pathophysiology of lateral epicondylosis. However, the severity of the pathophysiology was not related to pain and function, indicating that imaging measures may not provide the best clinical assessment.

Hypertonic dextrose and morrhuate sodium injections (prolotherapy) for lateral epicondylosis (tennis elbow): results of a single-blind, pilot-level, randomized controlled trial.

OBJECTIVE: Chronic lateral epicondylosis is common, debilitating, and often refractory. Prolotherapy (PrT) is an injection therapy for tendinopathy. The efficacy of two PrT solutions for chronic lateral epicondylosis was evaluated. DESIGN: This study is a three-arm randomized controlled trial. Twenty-six adults (32 elbows) with chronic lateral epicondylosis for 3 mos or longer were randomized to ultrasound-guided PrT with dextrose solution, ultrasound-guided PrT with dextrose-morrhuate sodium solution, or watchful waiting ("wait and see"). The primary outcome was the Patient-Rated Tennis Elbow Evaluation (100 points) at 4, 8, and 16 wks (all groups) and at 32 wks (PrT groups). The secondary outcomes included pain-free grip strength and magnetic resonance imaging severity score. RESULTS: The participants receiving PrT with dextrose and PrT with dextrose-morrhuate reported improved Patient-Rated Tennis Elbow Evaluation composite and subscale scores at 4, 8, and/or 16 wks compared with those in the wait-and-see group (P < 0.05). At 16 wks, compared with baseline, the PrT with dextrose and PrT with dextrose-morrhuate groups reported improved composite Patient-Rated Tennis Elbow Evaluation scores by a mean (SE) of 18.7 (9.6; 41.1%) and 17.5 (11.6; 53.5%) points, respectively. The grip strength of the participants receiving PrT with dextrose exceeded that of the PrT with dextrose-morrhuate and the wait and see at 8 and 16 wks (P < 0.05). There were no differences in magnetic resonance imaging scores. Satisfaction was high; there were no adverse events. CONCLUSIONS: PrT resulted in safe, significant improvement of elbow pain and function compared with baseline status and follow-up data and the wait-and-see control group. This pilot study suggests the need for a definitive trial.

Touch screen performance by individuals with and without motor control disabilities.

Touch technology is becoming more prevalent as functionality improves and cost decreases. Therefore, it is important that this technology is accessible to users with diverse abilities. The objective of this study was to investigate the effects of button and gap size on performance by individuals with varied motor abilities. Participants with (n = 38) and without (n = 15) a motor control disability completed a digit entry task. Button size ranged from 10 to 30 mm and gap size was either 1 or 3 mm. Results indicated that as button size increased, there was a decrease in misses, errors, and time to complete tasks. Performance for the non-disabled group plateaued at button size 20 mm, with minimal, if any gains observed with larger button sizes. In comparison, the disabled group's performance continued to improve as button size increased. Gap size did not affect user performance. These results may help to improve accessibility of touch technology.

Effect of touch screen button size and spacing on touch characteristics of users with and without disabilities.

OBJECTIVE: The aim of this study was to investigate the effect of button size and spacing on touch characteristics (forces, impulses, and dwell times) during a digit entry touch screen task. A secondary objective was to investigate the effect of disability on touch characteristics. BACKGROUND: Touch screens are common in public settings and workplaces. Although research has examined the effect of button size and spacing on performance, the effect on touch characteristics is unknown. METHOD: A total of 52 participants (n = 23, fine motor control disability; n = 14, gross motor control disability; n = 15, no disability) completed a digit entry task. Button sizes varied from 10 mm to 30 mm, and button spacing was 1 mm or 3 mm. RESULTS: Touch characteristics were significantly affected by button size. The exerted peak forces increased 17% between the largest and the smallest buttons, whereas impulses decreased 28%. Compared with the fine motor and nondisabled groups, the gross motor group had greater impulses (98% and 167%, respectively) and dwell times (60% and 129%, respectively). Peak forces were similar for all groups. CONCLUSION: Button size but not spacing influenced touch characteristics during a digit entry task. The gross motor group had significantly greater dwell times and impulses than did the fine motor and nondisabled groups. APPLICATION: Research on touch characteristics, in conjunction with that on user performance, can be used to guide human computer interface design strategies to improve accessibility of touch screen interfaces. Further research is needed to evaluate the effect of the exerted peak forces and impulses on user performance and fatigue.

The effect of lateral epicondylosis on upper limb mechanical parameters.

BACKGROUND: Lateral epicondylosis is a prevalent and costly musculoskeletal disorder characterized by degeneration of the common extensor tendon origin at the lateral epicondyle. Grip strength is commonly affected due to lateral epicondylosis. However, less is known about the effect of lateral epicondylosis on other functional parameters such as ability to react to rapid loading. METHODS: Twenty-nine lateral epicondylosis participants and ten controls participated in a case-control study comparing mechanical parameters (mass, stiffness and damping), magnetic resonance imaging signal intensity and grip strength of injured and uninjured limbs. A mixed effects model was used to assess the effect of dominance and injury on mechanical parameters and grip strength. FINDINGS: Significant effect of injury and dominance was observed on stiffness, damping and grip strength. An injured upper limb had, on average, 18% less stiffness (P<0.01, 95% CI [9.8%, 26%]), 21% less damping (P<0.01, 95% CI [11%, 31%]) and 50% less grip strength (P<0.01, 95% CI [37%, 61%]) than an uninjured upper limb. The dominant limb had on average 15% more stiffness (P<0.01, 95% CI [8.0%, 23%], 33% more damping (P<0.01, 95% CI [22%, 45%]), and 24% more grip strength (P<0.01, 95% CI [6.6%, 44%]) than the non-dominant limb. INTERPRETATION: Lower mechanical parameters are indicative of a lower capacity to oppose rapidly rising forces and quantify an important aspect of upper limb function. For individuals engaged in manual or repetitive activities involving the upper limb, a reduction in ability to oppose these forces may result in increased risk for injury or recurrence.

Effect of lateral epicondylosis on grip force development.

STUDY DESIGN: Case-Control. INTRODUCTION: Although it is well known that grip strength is adversely affected by lateral epicondylosis (LE), the effect of LE on rapid grip force generation is unclear. PURPOSE OF THE STUDY: To evaluate the effect of LE on the ability to rapidly generate grip force. METHODS: Twenty-eight participants with LE (13 unilateral and 15 bilateral LE) and 13 healthy controls participated in this study. A multiaxis profile dynamometer was used to evaluate grip strength and rapid grip force generation. The ability to rapidly produce force is composed of the electromechanical delay and rate of force development. Electromechanical delay is defined as the time between the onset of electrical activity and the onset of muscle force production. The Patient-rated Tennis Elbow Evaluation (PRTEE) questionnaire was used to assess pain and functional disability. Magnetic resonance imaging was used to evaluate tendon degeneration. RESULTS: LE-injured upper extremities had lower rate of force development (50 lb/sec, confidence interval [CI]: 17, 84) and less grip strength (7.8 lb, CI: 3.3, 12.4) than nonnjured extremities. Participants in the LE group had a longer electromechanical delay (- 59% , CI: 29, 97) than controls. Peak rate of force development had a higher correlation (r = 0.56; p<0.05) with PRTEE function than grip strength (r = 0.47; p<0.05) and electromechanical delay (r = 0.30; p>0.05) for participants with LE. In addition to a reduction in grip strength, those with LE had a reduction in rate of force development and an increase in electromechanical delay. CONCLUSIONS: Collectively, these changes may contribute to an increase in reaction time, which may affect risk for recurrent symptoms. These findings suggest that therapists may need to address both strength and rapid force development deficits in patients with LE. LEVEL OF EVIDENCE: 3B.

Prolonged mechanical and physiological changes in the upper extremity following short-term simulated power hand tool use.

This study investigated in-vivo changes in upper limb dynamic mechanical properties and magnetic resonance imaging (MRI) parameters following short-term power hand tool operation. Previous studies have found reduction in mechanical properties following short-term power tool usage at long build-up times. This study advances that work by having participants operate a simulated pistol grip power hand tool and evaluating changes in mechanical properties, strength, discomfort level and MRI prior to tool operation and daily for 3 d after tool operation. Twenty-four participants were randomly assigned to operate a simulated power hand tool for either a high peak reaction force of 123 N (peak torque=8 Nm, build-up time=250 ms) or at a low peak reaction force of 5 N (peak torque=2 Nm, build-up time=50 ms). Subjects operated the tool for 60 min at the rate of six times per min. A reduction in stiffness (27%, p<0.05) was observed 24 h after tool operation for the high force group and this change persisted (26%, p<0.05) up to 72 h after tool operation. Similar changes were not observed for the low force group. No changes were observed in mass moment of inertia, damping, isometric strength and damping for either group (p>0.05). There was a signal intensity increase (12%, CI 19%, 5.06%) in the supinator muscle MRI for both groups 24 h after tool operation but only the high force group remained elevated (10%, CI 13.7%, 0.06%) 72 h after tool operation. Persistent short-term changes in mechanical and MRI parameters at high force levels could indicate increased strain on the upper limb and may negatively affect ability to react during rapid forceful loading of the upper limb. This research can ultimately lead to better ergonomic interventions through quantitative power hand tool design guidelines and work practices based on understanding the damaging effects of exposure to specific levels of reaction force, build-up time and repetition, as well as providing new outcome measures for epidemiological studies.

Mechanical and magnetic resonance imaging changes following eccentric or concentric exertions.

BACKGROUND: Prior work has shown that changes in mechanical parameters and magnetic resonance imaging parameters occur following submaximal eccentric activity but it is unclear whether similar changes occur following submaximal concentric activity. This study compared mechanical response parameters and MRI relaxation parameters following submaximal concentric or eccentric exertions. METHODS: This single site, randomized study investigated in vivo changes in human upper limb dynamic mechanical properties following exposure to short term repetitive submaximal eccentric or concentric exertions. Eighteen subjects were assigned to either an eccentric or concentric group and exercised for 30 min at 50% of isometric forearm maximum voluntary contraction. Changes in strength, symptom intensity, magnetic resonance imaging T2 relaxation measurements, which are indicative of edema, and dynamic mechanical parameters (stiffness, effective mass, and damping) were ascertained prior to exercise, 1h after, and 24h later. FINDINGS: Strength decreased following exercise (P<0.01), however only the eccentric exercise group exhibited a reduction in mechanical stiffness (55%, P<0.01) and damping (31%, P<0.05), and an increase (17%, P<0.05) in magnetic resonance imaging T2 relaxation time. INTERPRETATION: The changes in mechanical parameters and magnetic resonance imaging findings following repetitive submaximal eccentric activity could negatively impact the ability of the arm to react to rapid forceful loading during repetitive industrial work activities and may result in increased strain on the upper limb. Similar changes were not observed following concentric exercise.