Publications (7)20.41 Total impact
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Article: Grip strength in children: test-retest reliability using Grippit.
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ABSTRACT: To examine the reliability of peak and sustained grip strength in children using the Grippit. We compared the reliability of one trial, the best and mean of three trials and the reliability within 6-, 10- and 14-year-old groups. Test-retest study. Grip strength with the Grippit instrument was evaluated at two test occasions in 58 children. Intraclass correlation coefficient 2.1 (ICC), standard error of measurement (SEM) also expressed as a percentage value (SEM%), coefficient of repeatability and coefficient of variation were calculated. The test-retest reliability was good for both peak and sustained grip strength. The mean and best of three trials were equally reliable. Peak grip strength best of three trials, for example, was more reliable for the 6-year-olds (ICC 0.96, SEM% 6.3) and 14-year-olds (ICC 0.96, SEM% 5.2) compared to the 10-year-olds (ICC 0.78, SEM% 12.5). For peak grip strength in the whole sample, there was a systematic bias with better performance at the second measurement. Grip strength assessment in children with Grippit results in good relative and absolute reliability for peak and sustained grip strength. We recommend that three test trials are used. The mean of and the best of three trials are comparable.Acta Paediatrica 07/2008; 97(9):1226-31. · 2.07 Impact Factor -
Article: Quadriceps activity and movement reactions in response to unpredictable sagittal support-surface translations in women with patellofemoral pain.
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ABSTRACT: Patellofemoral pain (PFP) may be related to unfavorable knee joint loading. Delayed and/or reduced activity of vastus medialis obliquus (VMO) and different movement patterns have been identified in individuals with PFP in some studies, whereas other studies have failed to show a difference compared to non-affected controls. The discrepancy between study results may depend on the different tasks that have been investigated. No previous study has investigated these variables in postural responses to unpredictable perturbations in PFP. Whole body three dimensional kinematics and surface EMG of quadriceps muscles activation was studied in postural responses to unpredictable support surface translations in 17 women with PFP who were pain free at the time of testing, and 17 matched healthy controls. The results of the present study showed earlier onset of VMO activity and associated changes in kinematics to anterior platform translation in the PFP subjects. We suggest that the relative timing between the portions quadriceps muscles may be task specific and part of an adapted response in attempt to reduce knee joint loading. This learned response appears to remain even when the pain is no longer present.Journal of Electromyography and Kinesiology 05/2008; 18(2):298-307. · 1.97 Impact Factor -
Article: Norms for grip strength in children aged 4-16 years.
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ABSTRACT: The aim of this study was to provide norms for grip strength in children. A total of 530 Swedish 4-16-y-olds was tested with the instrument Grippit. The instrument estimates peak grip strength over a 10s period, and sustained grip strength averaged across the 10s. The increase in grip strength with age was approximately parallel for boys and girls until 10 y of age, after which boys were significantly stronger than girls. Strong correlations existed between grip strength and the anthropometric measures weight, height and, in particular, hand length. Right-handed children were significantly stronger in their dominant hand, while left-handers did not show any strength difference between the hands. It is therefore suggested that when evaluating grip strength in left-handed children both hands should be assumed to be about equally strong, while right-handed children are expected to be up to 10% stronger with their right hand. Sustained grip strength was consistently about 80-85% of peak grip strength, with somewhat lower values in younger children. The present normative data for peak grip strength were slightly lower than 1980s' data from the USA and Australia, probably because of divergences in age grouping and in instruments used. CONCLUSION: Norms for grip strength including estimates of variation were provided for children aged 4-16 y. These data will enable therapists and physicians to compare a patient's score with the scores of normally developed children according to age, gender, handedness and body measures.Acta Paediatrica 02/2002; 91(6):617-25. · 2.07 Impact Factor -
Article: Quantifying the independence of human finger movements: comparisons of digits, hands, and movement frequencies.
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ABSTRACT: To determine whether other digits move when normal humans attempt to move just one digit, we asked 10 right-handed subjects to move one finger at a time while we recorded the motion of all five digits simultaneously with both a video motion analysis system and an instrumented glove. We quantified the independence of the digits to compare (1) the different digits, (2) the right versus the left hand, and (3) movements at a self-paced frequency versus externally paced movements at 3 Hz. We also quantified the degree to which motion occurred at the proximal, middle, or distal joint of each digit. Even when asked to move just one finger, normal human subjects produced motion in other digits. Movements of the thumb, index finger, and little finger typically were more highly individuated than were movements of the middle or ring fingers. Fingers of the dominant hand were not more independent than were those of the nondominant hand. Self-paced movements made at approximately 2 Hz were more highly individuated than were externally paced movements at 3 Hz. Angular motion tended to be greatest at the middle joint of each digit, with increased angular motion at the proximal and distal joints during 3 Hz movements. Simultaneous motion of noninstructed digits may result in part from passive mechanical connections between the digits, in part from the organization of multitendoned finger muscles, and in part from distributed neural control of the hand.Journal of Neuroscience 12/2000; 20(22):8542-50. · 7.11 Impact Factor -
Article: Nondigital afferent input in reactive control of fingertip forces during precision grip.
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ABSTRACT: Sensory inputs from the digits are important in initiating and scaling automatic reactive grip responses that help prevent frictional slips when grasped objects are subjected to destabilizing load forces. In the present study we analyzed the contribution to grip-force control from mechanoreceptors located proximal to the digits when subjects held a small manipulandum between the tips of the thumb and index finger. Loads of various controlled amplitudes and rates were delivered tangential to the grip surfaces at unpredictable times. Grip forces (normal to the grip surfaces) and the position of the manipulandum were recorded. In addition, movements of hand and arm segments were assessed by recording the position of markers placed at critical points. Subjects performed test series during normal digital sensibility and during local anesthesia of the index finger and thumb. To grade the size of movements of tissues proximal to the digits caused by the loadings, three different conditions of arm and hand support were used; (1) in the hand-support condition the subjects used the three ulnar fingers to grasp a vertical dowel support and the forearm was supported in a vacuum cast; (2) in the forearm-support condition only the forearm was supported; finally, (3) in the no-support condition the arm was free. With normal digital sensibility the size of the movements proximal to the digits had small effects on the grip-force control. In contrast, the grip control was markedly influenced by the extent of such movements during digital anesthesia. The poorest control was observed in the hand-support condition, allowing essentially only digital movements. The grip responses were either absent or attenuated, with greatly prolonged onset latencies. In the forearm and no-support conditions, when marked wrist movements took place, both the frequency and the strength of grip-force responses were higher, and the grip response latencies were shorter. However, the performance never approached normal. It is concluded that sensory inputs from the digits are dominant in reactive grip control. However, nondigital sensory input may be used for some grip control during impaired digital sensibility. Furthermore, the quality of the control during impaired sensibility depends on the extent of movements evoked by the load in the distal, unanesthetized parts of the arm. The origin of these useful sensory signals is discussed.Experimental Brain Research 07/1996; 110(1):131-41. · 2.39 Impact Factor -
Article: Grip-force responses to unanticipated object loading: load direction reveals body- and gravity-referenced intrinsic task variables.
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ABSTRACT: Humans preserve grasp stability by automatically regulating the grip forces when loads are applied tangentially to the grip surfaces of a manipulandum held in a precision grip. The effects of the direction of the load force in relation to the palm, trunk, and gravity were investigated in blindfolded subjects. Controlled, tangential load-forces were delivered in an unpredictable manner to the grip surface in contact with the index finger either in the distal and proximal directions (away from and toward the palm) or in the ulnar and radial directions (transverse to the palm). The hand was oriented in: (1) a standard position, with the forearm extended horizontally and anteriorly in intermediate pronosupination; (2) an inverted position, reversing the direction of radial and ulnar loads in relation to gravity; and (3) a horizontally rotated position, in which distal loads were directed toward the trunk. The amplitude of the grip-force responses (perpendicular to the grip surface) varied with the direction of load in a manner reflecting frictional anisotropies at the digit-object interface; that is, the subjects automatically scaled the grip responses to provide similar safety margins against frictional slips. For all hand positions, the time from onset of load increase to start of the grip-force increase was shorter for distal loads, which tended to pull the object out of the hand, than for proximal loads. Furthermore, this latency was shorter for loads in the direction of gravity, regardless of hand position. Thus, shorter latencies were observed when frictional forces alone opposed the load, while longer latencies occurred when gravity also opposed the load or when the more proximal parts of the digits and palm were positioned in the path of the load. These latency effects were due to different processing delays in the central nervous system and may reflect the preparation of a default response in certain critical directions. The response to loads in other directions would incur delays required to implement a new frictional scaling and a different muscle activation pattern to counteract the load forces. We conclude that load direction, referenced to gravity and to the hand's geometry, represents intrinsic task variables in the automatic processes that maintain a stable grasp on objects subjected to unpredictable load forces. In contrast, the grip-force safety margin against frictional slips did not vary systematically with respect to these task variables. Instead, the magnitude of the grip-force responses varied across load direction and hand orientation according to frictional differences providing similar safety margins supporting grasp stability.Experimental Brain Research 07/1996; 110(1):142-50. · 2.39 Impact Factor -
Article: Control of grip force during restraint of an object held between finger and thumb: responses of cutaneous afferents from the digits.
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ABSTRACT: Unexpected pulling and pushing loads exerted by an object held with a precision grip evoke automatic and graded increases in the grip force (normal to the grip surfaces) that prevent escape of the object; unloading elicits a decrease in grip force. Anesthesia of the digital nerves has shown that these grip reactions depend on sensory signals from the digits. In the present study we assessed the capacity of tactile afferents from the digits to trigger and scale the evoked grip responses. Using tungsten microelectrodes inserted percutaneously into the median nerve of awake human subjects, unitary recordings were made from ten FA I and 13 FA II rapidly adapting afferents, and 12 SA I and 18 SA II slowly adapting afferents. While the subject held a manipulandum between a finger and the thumb, tangential load forces were applied to the receptor-bearing digit (index, middle, or ring finger or thumb) as trapezoidal load-force profiles with a plateau amplitude of 0.5-2.0 N and rates of loading and unloading at 2-8 N/s, or as "step-loads" of 0.5 N delivered at 32 N/s. Such load trials were delivered in both the distal (pulling) and proximal (pushing) direction. FA I afferents responded consistently to the load forces, being recruited during the loading and unloading phases. During the loading ramp the ensemble discharge of the FA I afferents reflected the first time-derivative of the load force (i.e., the load-force rate). These afferents were relatively insensitive to the subject's grip force responses. However, high static finger forces appeared to suppress excitation of these afferents during the unloading phase. The FA II afferents were largely insensitive to the load trials: only with the step-loads did some afferents respond. Both classes of SA afferents were sensitive to load force and grip force, and discharge rates were graded by the rate of loading. The firing of the SA I afferents appeared to be relatively more influenced by the subject's grip-force response than the discharge of the SA II afferents, which were more influenced by the load-force stimulus. The direction in which the tangential load force was applied to the skin influenced the firing of most afferents and in particular the SA II afferents. Individual afferents within each class (except for the FA IIs) responded to the loading ramp before the onset of the subject's grip response and may thus be responsible for initiating the automatic increase in grip force. However, nearly half of the FA I afferents recruited by the load trials responded to the loading phase early enough to trigger the subject's grip-force response, whereas only ca. one-fifth of the SA Is and SA IIs did so. These observations, together with the high density of FA I receptors in the digits, might place the FA I afferents in a unique position to convey the information required to initiate and scale the reactive grip-force responses to the imposed load forces.Experimental Brain Research 03/1996; 108(1):155-71. · 2.39 Impact Factor
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Institutions
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1996–2008
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Umeå University
- • Department of Community Medicine and Rehabilitation
- • Department of Plant Physiology
Umeå, Vaesterbotten, Sweden
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