Doctor of Philosophy / The aims of the Thesis were: to investigate and quantify the factors influencing the production of maximum isometric grip strength force in a sample of Australian teenagers when using JamarTM-like handgrip dynamometers; to determine the reliability of this measure over long and short retest intervals; to establish a database of anthropometric and strength values for this group and prediction equations for premorbid strengths to aid assessment of recovery in those with upper limb pathologies. The history of these handgrip dynamometers demonstrates that they have been employed in one form or another for over three hundred years and are still widely used today in hand rehabilitation and medical examinations. Many new types of dynamometers have been constructed subsequent to the ubiquitous JamarTM and have all been briefly reviewed here. Handedness (dominance) was thought to be a possible factor influencing grip strength performance and was later evaluated. But first, the Edinburgh Handedness Inventory was tested with 658 teenagers and 64 adults and confirmed to be a valid tool for assessing handedness. Its validity was improved by substituting the tasks of sweeping and opening the lid of a box for hammering and use of a screwdriver. Its excellent reliability (ICC = .78, p < 0.01) was confirmed with 45 teenagers and 45 adults. There were 235 teenagers who performed maximal isometric grip strength tests and from the results a local database was created. It was confirmed that the grip strength difference in males and females becomes significant after the age of 13 years, and that the average teenaged male is stronger than the average teenaged female by 11.2 Kg force (p < .01). Height, weight, BMI, hand dimensions, past upper limb injuries, degrees of handedness and exercise levels were measured and compared with known norms to establish that the grip strength tested sample of teenagers was representative of urban teenagers in Australia. The influence of handedness on maximal grip strength in dominant and non-dominant hands was unable to be completely ascertained due to the vast majority of the sample of teenagers being right-handed. Only 13 of the 235 teenagers used their left hand for most tasks, with another 20 using their left hands for a small majority of tasks. There was a grip strength bias towards the dominant hand of 2.63 kg force (p < .01). The most accurate way to predict the grip strength of one hand is by knowing the grip strength of the other hand. Prediction models found that 90% (R2 adj .902) and 70% (R2adj .702) of the variance in one hand could be accounted for by the grip strength of their other hand for male and female teenagers, respectively. Prediction equations were also created to assist in estimating the pre-morbid grip strength of teenagers suffering from bilateral hand injuries. If for the males, measurements for height and hand surface area were entered into these models, the grip strength of the dominant and non-dominant hands could be estimated with 62.6 and 63.5% of the variance between the real and predicted scores accounted for, respectively. For the females the prediction models using height and hand surface area could only account for 33.9 and 42.8% of the variances, with no other independent variables improving the prediction equations. The reliability of the maximal grip strength performance of 154 of these teenagers was retested after one or four weeks. A number of sub-group permutations were created for age, gender, retest time interval and handedness groups. The measures of grip strength for males were highly reliable with ICC (3,1) values ranging from .91 to .97. These measures were significantly higher than that obtained from the females, where reliability values ranged from .69 to .83. Handedness played a significant part in grip strength reliability. The dominant hand of right-handed teenagers achieved an ICC (3,1) of .97, as contrasted with the non-dominant hand of left-handers who attained a very poor ICC (3,1) of .27. The shape of the hands of the males did not influence their grip strength or their reliability values, which ranged from .954 to .973. The shape of female hands did not affect their ability to generate maximal grip strength, only its reliability. The females with hands shaped squarer-than-average had mean grip strength reliability values of ICC (3,1) at only .48, in contrast to those with longer-than-average hands who achieved a mean ICC (3,1) of .92. The handle shape of the dynamometer may disadvantage square-handed females, and this should be further investigated.

Doctor of Philosophy / The aims of the Thesis were: to investigate and quantify the factors influencing the production of maximum isometric grip strength force in a sample of Australian teenagers when using JamarTM-like handgrip dynamometers; to determine the reliability of this measure over long and short retest intervals; to establish a database of anthropometric and strength values for this group and prediction equations for premorbid strengths to aid assessment of recovery in those with upper limb pathologies. The history of these handgrip dynamometers demonstrates that they have been employed in one form or another for over three hundred years and are still widely used today in hand rehabilitation and medical examinations. Many new types of dynamometers have been constructed subsequent to the ubiquitous JamarTM and have all been briefly reviewed here. Handedness (dominance) was thought to be a possible factor influencing grip strength performance and was later evaluated. But first, the Edinburgh Handedness Inventory was tested with 658 teenagers and 64 adults and confirmed to be a valid tool for assessing handedness. Its validity was improved by substituting the tasks of sweeping and opening the lid of a box for hammering and use of a screwdriver. Its excellent reliability (ICC = .78, p < 0.01) was confirmed with 45 teenagers and 45 adults. There were 235 teenagers who performed maximal isometric grip strength tests and from the results a local database was created. It was confirmed that the grip strength difference in males and females becomes significant after the age of 13 years, and that the average teenaged male is stronger than the average teenaged female by 11.2 Kg force (p < .01). Height, weight, BMI, hand dimensions, past upper limb injuries, degrees of handedness and exercise levels were measured and compared with known norms to establish that the grip strength tested sample of teenagers was representative of urban teenagers in Australia. The influence of handedness on maximal grip strength in dominant and non-dominant hands was unable to be completely ascertained due to the vast majority of the sample of teenagers being right-handed. Only 13 of the 235 teenagers used their left hand for most tasks, with another 20 using their left hands for a small majority of tasks. There was a grip strength bias towards the dominant hand of 2.63 kg force (p < .01). The most accurate way to predict the grip strength of one hand is by knowing the grip strength of the other hand. Prediction models found that 90% (R2 adj .902) and 70% (R2adj .702) of the variance in one hand could be accounted for by the grip strength of their other hand for male and female teenagers, respectively. Prediction equations were also created to assist in estimating the pre-morbid grip strength of teenagers suffering from bilateral hand injuries. If for the males, measurements for height and hand surface area were entered into these models, the grip strength of the dominant and non-dominant hands could be estimated with 62.6 and 63.5% of the variance between the real and predicted scores accounted for, respectively. For the females the prediction models using height and hand surface area could only account for 33.9 and 42.8% of the variances, with no other independent variables improving the prediction equations. The reliability of the maximal grip strength performance of 154 of these teenagers was retested after one or four weeks. A number of sub-group permutations were created for age, gender, retest time interval and handedness groups. The measures of grip strength for males were highly reliable with ICC (3,1) values ranging from .91 to .97. These measures were significantly higher than that obtained from the females, where reliability values ranged from .69 to .83. Handedness played a significant part in grip strength reliability. The dominant hand of right-handed teenagers achieved an ICC (3,1) of .97, as contrasted with the non-dominant hand of left-handers who attained a very poor ICC (3,1) of .27. The shape of the hands of the males did not influence their grip strength or their reliability values, which ranged from .954 to .973. The shape of female hands did not affect their ability to generate maximal grip strength, only its reliability. The females with hands shaped squarer-than-average had mean grip strength reliability values of ICC (3,1) at only .48, in contrast to those with longer-than-average hands who achieved a mean ICC (3,1) of .92. The handle shape of the dynamometer may disadvantage square-handed females, and this should be further investigated.

The purpose of this study was to determine the correlation among three hand strength measurement methods: Hand dynamometer, MDD (Middle Digital Extension Isokinetic Dynamometer), and Cybex. Five students (2 males, 3 females) from Ball State University were asked to participate in this study. Both right and left lower arm data were collected from these subjects. A Cybex 340 (Lumax Cor.) was employed to determine wrist flexion and extension isokinetic peak torque, total work, and power at 30 degrees/second and 60 degrees/second. A MDD was used to determine third digit eccentric torque, work, and power. A hand dynamometer (Lafayette Instrument Co., Model 76618) was used to determine grip force. Pearson product moment correlation coefficients were used to determine correlation among these variables. Significant correlations were noted between isometric grip strength and isokinetic 30 and 60 degrees/second wrist flexion power, as well as between isometric grip strength and isokinetic 30 degrees/second wrist extensor power. The results of this study indicate there is very little relationship between the three clinically used measurement tools. / School of Physical Education

Children with unilateral spastic cerebral palsy (USCP) have impairments affecting upper limb function, particularly in grasping abilities. Specifically, children with USCP may display precision grip impairments, which can lead to activity limitations. The interplay between feedforward and feedback control is essential for successful grasping, requiring somatosensory information to be integrated with the motor output. This integration occurs through the transmission of somatosensory information through the dorsal column medial lemniscus (DCML) pathway, while independent finger movement to grasp an object is controlled by the motor cortex via the corticospinal tract (CST). While previous studies demonstrated the CST relates to anticipatory control of grasping, this may not explain all the variance of grasp impairments in children with USCP. Although studies have highlighted the importance of sensory information in grasping in typically developing (TD) adults, there are no studies examining the relationship between brain structure and function in terms of precision grip impairments in children with USCP. Additionally, sensorimotor integration plays an important role in precision grip. In some children with USCP, the lesion that occurs in the brain can cause the CST to reorganize to the contralesional hemisphere. This results in the sensory and motor tracts in different hemispheres, impacting motor impairments. When this sensory-motor dissociation occurs or when there are successive lifts of an object with each hand, it is thought that the information is transferred through the corpus callosum (CC). However, damage to the CC can restrict somatosensory processing, which can further impair grasping abilities. Previous studies have only looked at precision grip impairments in relation to the CST. Therefore, an integrative approach is necessary to fully understand the mechanisms of precision grip impairments in children with USCP. In this study our aim was to examine the neural basis of precision grip in children with USCP. Twenty-seven children participated in an MRI assessment. This included the acquisition of structural and diffusion-weighted images (DWI) to extract diffusion metrics of the CST, DCML pathway, and CC. Children also participated in clinical sensory measures, including the stereognosis test, grating orientation task, and the two-point discrimination task. Additionally, children performed precision grip lifts using a custom-made object. All children were asked to grasp an object with interchangeable surfaces (i.e., sandpaper and rayon) to measure adaptation of grip force (GF) to object texture. They were also asked to grasp the same object, hold it in the air and slowly release their grip so that the object gradually slips from their fingertips. Twenty-seven children performed these tasks with their less affected hand, and 16 with their more affected hand. Additionally, 17 participants grasped an object with various weights with each lifting sequence consisting of lifting an object in succession with the same hand and then one lift with the contralateral hand. The results demonstrate the greater reduction of integrity (more damage) of the DCML pathway, the poorer the grasp task performance, as indicated through the safety margin (the difference between the minimum amount of force needed to prevent slipping and the applied grip force). Regression analyses and cluster analyses display that CST integrity and organization may also contribute to safety margin. This suggests that diffusion metrics of multiple pathways and CST organization when considered together contribute to grasping impairments in children with USCP. To assess this further, we examined the relative difference in the peak rate of force between objects with various weights during successive lifts with each hand. Children with USCP did demonstrate anticipatory control within hands and a generalization of anticipatory control between hands. However, a loss of the transfer information was shown when first grasping the object with their less affected hand and then their more affected hand, in children with an absent contralateral CST. Therefore, the results suggest precision grip impairments may not exclusively be due to sensory impairments, but instead how the sensory information is integrated with the motor output of the same hand.

This investigation was conducted to explore the between trial variability of the measures of the isometric peak force, time to peak force, area to peak force, area under the curve, slope (20%-80%), and the average slope of subjects assigned to perform a series of four isometric grip strength contractions and to develop a discriminant function equation that would predict group membership. Forty-nine college students were instructed to perform either a series of four maximal voluntary contractions (sincere) or a series of four submaximal (deceptive) contractions. The subjects were retested 24-48 hours after the initial test session. Data from both test sessions were recorded, displayed, and analyzed using segmental curve analysis. The coefficients of variation were computed for each test variable. The grand mean coefficient of variation for the sincere condition was .31 ± .02 compared to the grand mean coefficient of variation for the deceptive condition which was .77 ± .11 (p < .01). Coefficients of variation were used to predict group membership. The prediction equation accurately classified 92% of the sincere condition and 64% of the deceptive condition. / Master of Science