Interpersonal and intrapersonal variance of exponent of power function observed in grip strength task.

For grip strength there is a power function with an exponent of 1.7 between the subjective magnitude and the actual force exerted by a subject, but large variabilities among and within individuals were found. We focused on these variabilities and investigated the relationship between them by conducting a ratio production procedure requiring trials of maximum effort and half of maximum effort. For 30 adults we conducted four measurement trials, two on the same day, and the remaining two trials on a day or two later. The mean value of the exponent, the standard deviation, and the coefficient of variation of the four trials for each subject were calculated. The mean value of the exponent of the power function for all subjects was 1.6. This value approximated the value of 1.7 reported by Stevens and Mack. The values ranged from .50 to 5.39. The correlation between subjects' mean exponent value and standard deviation was .90, and the correlation between the mean value of the exponent and the coefficient of variation was .50. There was a close relationship between interpersonal and intrapersonal variance.     

Anthropometric correlates of basketball free-throw shootings by young girls.

The purpose of this analysis of data from a larger investigation was to assess effects of anthropometric factors on free throw shooting performance of 15 girls from Michigan and 18 from Puerto Rico. Subjects performed 60 free throws (10 trials x 3 ball sizes x 2 basket heights). Correlations were low, with two exceptions, .53 between shooting performance at the low basket and grip strength (as measured by hand grip dynamometer) for girls from Michigan, and .49 for hand width and performance at the low basket for girls from Michigan.     

Lower extremity strength and hopping and jumping ground reaction forces in children with neurofibromatosis type 1

The purpose of this study was to (1) extend the research findings of decreased muscular force production in grip strength to the lower extremity strength of children with NF1 and (2) to determine if there was a relationship between isometric strength and functional activities in children with NF1. Force production was assessed using a hand held dynamometer (HHD) and a functional task (hopping and jumping) on a force plate. Data from twenty-six children with NF1 were compared to data from 48 typically developing children of similar sex, weight and height. Children with NF1 demonstrated statistically significant lower force production with HHD (p<0.01) during hip extension, but similar force production for knee extension and ankle plantar flexion compared to the control group. A relationship existed between the ground reaction forces at take-off from both hopping and jumping and the force generated from knee extensor strength in the NF1 group. The addition of a functional task to hand held dynamometry is useful for determining a relationship between common clinical measures and functional activities.     

Sugar proximity and human grip strength

In a double-blind experiment with 90 undergraduate students the hypothesis was tested that proximity to sugar reduces human grip strength. An earlier study indicated that sugar proximity does indeed significantly reduce human grip strength. When additional controls were added to this design to reduce random sampling error, the hypothesis was not supported.     

Grip strength and fatigue in junior college tennis players.

Change in grip strength over 30 trials was documented in two samples of junior college tennis players to assess possible fatigue. Eight men and eight women performed 30 maximum-grip strength tests with 25-sec. rests between trials. Significant positive correlations (.38 and .53 for men and women) were observed between grip strength and trials. In practical terms, grip strength did not change over 30 trials in these tennis players. The data suggested that the repetitive gripping patterns used by these players in tennis play resulted in consistent maximum-grip strengths across 30 trials.     

Anticipatory modulation of precision grip force with variations in limb velocity of a curvilinear movement

The authors examined the relationship between peak velocity of a discrete horizontal elbow flexion movement in which the hand path was curvilinear and premovement modulation of precision grip force. The velocity of the movements of 7 participants was varied from maximal velocity to a velocity that required several seconds to reach a target. An object instrumented with force transducers for the forefinger and thumb measured precision grip force. There was a positively accelerating quadratic relationship between grip force change before movement and peak velocity of the ensuing limb movement. On some low-velocity trials, premovement grip force modulation reflected a net decrease. In contrast, high-velocity trials were preceded by net increases in grip force. Using cluster analysis, the authors classified grip forces in low-velocity movements as an empirically distinct set of entities from grip forces in high-velocity movements. The cluster of high-value grip forces suggested an anticipatory strategy that allowed participants a large safety margin in grip force to avoid object slip on movement initiation. The cluster of low-value grip forces at movement initiation suggested a second anticipatory strategy in which participants changed grip force very little, perhaps to increase the ability of proprioceptors in the hand to sense force changes. Those findings suggest that modulation of grip force before initiation of movements in which the hand path is curvilinear may be governed by two distinct velocity-dependent anticipatory strategies.     

Bimanual Lifting: Do Fingertip Forces Work Independently or Interactively?

Bimanual coordination is a commonplace activity, but the consequences of using both hands simultaneously are not well understood. The authors examined fingertip forces across 4 experiments in which participants undertook a range of bimanual tasks. They first measured fingertip forces during simultaneous lifts of 2 identical objects, noting that individuals held the objects with more force bimanually than unimanually. They then varied the mass of the objects held by each hand, noting that when both hands lifted together performance was equivalent to unimanual lifts. The authors next measured one hand's static grip force while the other hand lifted an object. They found a gradual reduction of grip force throughout the trial, but once again no evidence of one hand influencing the other. In the final experiment the authors tested whether tapping with one hand could influence the static grip force of its counterpart. Although the authors found no changes in static grip force as a direct consequence of the other hand's actions, they found clear differences from one task to the other, suggesting an effect of task instruction. Overall, these results suggest that fingertip forces are largely independent between hands in a bimanual lifting context, but are sensitive to different task requirements.     

Influences of hand posture and hand position on compatibility effects for up-down stimuli mapped to left-right responses: evidence for a hand referent hypothesis

Unimanual left-right responses to up-down stimuli show a stimulus-response compatibility (SRC) effect for which the preferred mapping varies as a function of response eccentricity. Responses made in the right hemispace and, to a lesser extent, at a midline position, are faster with the up-right/down-left mapping than with the up-left/down-right mapping, but responses made in the left hemispace are faster with the up-left/down-right mapping. Also, for responses at the midline position, the preferred mapping switches when the hand is placed in a supine posture instead of the more usual prone posture. The response eccentricity effect can be explained in terms of correspondence of asymmetrically coded stimulus and response features, but it is not obvious whether the hand posture effect can be explained in a similar manner. The present study tested the implications of a hypothesis that the body of the hand provides a frame of reference with respect to which the response switch is coded as left or right. As was predicted by this hand referent hypothesis, Experiment 1 showed that the influence of hand posture (prone and supine) on orthogonal SRC was additive with that of response location. In Experiment 2, the location of the switch relative to the hand was varied by having subjects use either a normal grip in which the switch was held between the thumb and the index finger or a grip in which it was held between the little and the ring fingers. The magnitudes of the mapping preferences varied as a function of the grip and hand posture in a manner consistent with the hand referent hypothesis.     

The influence of color and demand characteristics on muscle strength and affective ratings of the environment

Demand characteristics may influence claims that the color pink inhibits muscle strength whereas blue increases muscle strength. In Experiment 1, undergraduates (N = 59; 30 women, 29 men) were told either that the experimenters thought pink would increase and blue decrease strength or that blue would increase muscle strength and pink decrease muscle strength. A hand dynamometer assessed grip strength as subjects stared at each of 8 differently colored panels. Results indicated that men viewing the pink or orange panels had higher grip strength under pink-strengthen than under pink-weaken instructions. The reverse relationship was found for men viewing a green panel. For women, the pink-weaken instructions resulted in a higher grip strength than did the pink-strengthen instructions, regardless of actual color present. In Experiment 2, women in a no-instruction control condition had lower grip strength than women given the pink-weaken instructions. For men, the control (no-instruction) condition resulted in higher grip strength than the pink-weaken condition. Results of both studies suggest that men followed overt demand characteristics but that women reacted with increased intensity to any suggestion that a stereotypically feminine pink is associated with weakness.     

The Influence of Color and Demand Characteristics on Muscle Strength and Affective Ratings of the Environment

Demand characteristics may influence claims that the color pink inhibits muscle strength whereas blue increases muscle strength. In Experiment 1, undergraduates (N = 59; 30 women, 29 men) were told either that the experimenters thought pink would increase and blue decrease strength or that blue would increase muscle strength and pink decrease muscle strength. A hand dynamometer assessed grip strength as subjects stared at each of 8 differently colored panels. Results indicated that men viewing the pink or orange panels had higher grip strength under pink-strengthen than under pink-weaken instructions. The reverse relationship was found for men viewing a green panel. For women, the pink-weaken instructions resulted in a higher grip strength than did the pink-strengthen instructions, regardless of actual color present. In Experiment 2, women in a no-instruction control condition had lower grip strength than women given the pink-weaken instructions. For men, the control (no-instruction) condition resulted in higher grip strength than the pink-weaken condition. Results of both studies suggest that men followed overt demand characteristics but that women reacted with increased intensity to any suggestion that a stereotypically feminine pink is associated with weakness.     

Attentionally splitting the mass distribution of hand-held rods

Two experiments on the length-perception capabilities of effortful or dynamic touch differed only in terms of what the subject intended to perceive, while experimental conditions and apparatus were held constant. In each trial, a visually occluded rod was held as still as possible by the subject at an intermediate position. For two thirds of the trials, a weight was attached to the rod above or below the hand. In Experiment 1, in which the subject's task was to perceive the distance reachable with the portion of the rod forward of the hand, perceived extent was a function of the first moment of the mass distribution associated with the forward portion of the rod, and indifferent to the first moment of the entire rod. In Experiment 2, in which the task was to perceive the distance reachable with the entire rod if it was held at an end, the pattern of results was reversed. These results indicate the capability of selective sensitivity to different aspects of a hand-held object's mass distribution, without the possibility of differential exploration specific to these two tasks. Results are discussed in relation to possible roles of differential information, intention, and self-organization in the explanations of selective perceptual abilities.     

Effects of Sensory Deficit on Phalanx Force Deviation During Power Grip Post Stroke

The effect of sensory deficits on power grip force from individual phalanges was examined. The authors found that stroke survivors with sensory deficits (determined by the Semmes-Weinstein monofilament test) gripped with phalanx force directed more tangential to the object surface, than those without, although both groups had similar motor deficits (Chedoke-McMaster and Fugl-Meyer), grip strength, and skin friction. Altered grip force direction elevates risk of finger slippage against the object thus grip loss/object dropping, hindering activities of daily living. Altered grip force direction was associated with altered muscle activation patterns. In summary, the motor impairment level alone may not describe hand motor control in detail. Information about sensory deficits helps elucidate patients' hand motor control with functional relevance.     

A possible proximity effect on human grip strength

A double-blind experiment with 58 adults tested the hypothesis that proximity to sugar reduces human grip strength. An analysis of variance supported the hypothesis.     

Conflict in object affordance revealed by grip force

Viewing objects can result in automatic, partial activation of motor plans associated with them-"object affordance". Here, we recorded grip force simultaneously from both hands in an object affordance task to investigate the effects of conflict between coactivated responses. Participants classified pictures of objects by squeezing force transducers with their left or right hand. Responses were faster on trials where the object afforded an action with the same hand that was required to make the response (congruent trials) compared to the opposite hand (incongruent trials). In addition, conflict between coactivated responses was reduced if it was experienced on the preceding trial, just like Gratton adaptation effects reported in "conflict" tasks (e.g., Eriksen flanker). This finding suggests that object affordance demonstrates conflict effects similar to those shown in other stimulus-response mapping tasks and thus could be integrated into the wider conceptual framework on overlearnt stimulus-response associations. Corrected erroneous responses occurred more frequently when there was conflict between the afforded response and the response required by the task, providing direct evidence that viewing an object activates motor plans appropriate for interacting with that object. Recording continuous grip force, as here, provides a sensitive way to measure coactivated responses in affordance tasks.     

Exteroception and exproprioception by dynamic touch are different functions of the inertia tensor

When an object is held and wielded, a time-invariant quantity of the wielding dynamics is the inertia tensorIij. The 3 × 3 quantityIij is composed of moments of inertia (on the diagonal) and products of inertia (off the diagonal). Examination ofIij as a function of different locations at which a cylindrical object is grasped revealed that the products related systematically to grip position (a direction), and both the products and moments taken together related systematically to the extent of the rod to one side of the hand (a magnitude in a direction). In two experiments, observers wielded an occluded rod that was held at an intermediate point along its length and reproduced both the felt grip position and partial rod length. In both experiments, perceived grip position was a function of the rod’s products of inertia and perceived partial rod length was a function of the moments and products. Discussion focuses on the specificity of exteroception and exproprioception toIij.     

Effects of surface texture and grip force on the discrimination of hand-held loads

In this paper, we report the results from two experiments in which subjects were required to discriminate horizontal load forces applied to a manipulandum held with a precision grip. The roughness (and hence friction) of the grip surfaces and required grip force were manipulated. In the first experiment, subjects were instructed to judge the load while maintaining hand position and not letting the manipulandum slip. It was found that performance was influenced by surface texture; a given load was judged to be greater when the surface texture was smooth than when it was rough. This result is consistent with a previous study based on lifting objects and indicates that the effect of surface texture applies to loads in general and not just to gravitational loads (i.e., weight). To test whether the load acting on a smooth object is judged to be greater because the grip force required to prevent it from slipping is larger, a second experiment was carried out. Subjects used a visual feedback display to maintain the same grip force for smooth and rough manipulandum surfaces. In this case, there was no effect of surface texture on load perception. These results provide evidence that perceived load depends on the grip force used to resist the load. The implications of these results in terms of central and peripheral factors underlying load discrimination are considered.     

Conflict in object affordance revealed by grip force

Viewing objects can result in automatic, partial activation of motor plans associated with them—“object affordance”. Here, we recorded grip force simultaneously from both hands in an object affordance task to investigate the effects of conflict between coactivated responses. Participants classified pictures of objects by squeezing force transducers with their left or right hand. Responses were faster on trials where the object afforded an action with the same hand that was required to make the response (congruent trials) compared to the opposite hand (incongruent trials). In addition, conflict between coactivated responses was reduced if it was experienced on the preceding trial, just like Gratton adaptation effects reported in “conflict” tasks (e.g., Eriksen flanker). This finding suggests that object affordance demonstrates conflict effects similar to those shown in other stimulus–response mapping tasks and thus could be integrated into the wider conceptual framework on overlearnt stimulus–response associations. Corrected erroneous responses occurred more frequently when there was conflict between the afforded response and the response required by the task, providing direct evidence that viewing an object activates motor plans appropriate for interacting with that object. Recording continuous grip force, as here, provides a sensitive way to measure coactivated responses in affordance tasks.     

The effect of light color on muscular strength and power

The purpose of this study was to assess the effect of the color of light in a room on muscular strength and power. A convenience sample of 18 men (M age = 20.4 yr., SD = 1.2) performed a modified Wingate Anaerobic Cycle Test for muscular power and a hand grip strength test in each of the following conditions: red, blue, and white (neutral) ambient light. A repeated-measures multivariate analysis of variance indicated that average muscular power was significantly higher when performing the test in the room with red light compared to rooms lit with blue light or white light. The results also indicated that grip strength was significantly higher in the room lit with white light as compared to the room lit with blue light.     

Voluminous sucrose consumption in female rats: increased "nippiness" during periods of sucrose removal and possible oestrus periodicity

In a two-bottle paradigm in which water and 10% sucrose water were always available, female rats drank about 200 cc of the sugar water (about 65 g of sucrose/kg) per day for 4 wk. There were no significant decreases in consumption over this time. In Exp. 2 female rats singly housed were given two bottles containing water for 1 wk. and then a bottle containing water and a bottle containing 15% sucrose for the next week for 6 wk. When sucrose was available, the rats ate 33% more rat chow. When sucrose was removed, the rats displayed more episodes of biting a stimulus when the food cubes were being removed for daily measurements. Some females exhibited a marked 4- to 5-day periodicity in sucrose (7.5%) consumption. The persistent and voluminous consumption of sucrose water and enhanced agonistic-like behavior during periods of withdrawal suggests the presence of a robust phenomenon with potential dinical applications to the challenge of addiction.     

Provisional norms by age group for Japanese females on the controlled force-exertion test using a bar-chart display

This study examined age-group and individual differences on the controlled force-exertion test by bar-chart display and proposed a provisional norm in 249 females who were right-handed and ages 15 to 84 years. The subjects matched their submaximal grip strength to changing demand values, appearing as a bar chart on the display of a personal computer. The subjects performed the controlled force-exertion test three times with 1-min. intervals (single trials were 40 sec.), after one practice trial using the dominant hand. A total of the differences (%) between the demand value and the grip-exertion value for 25 sec. was used as an evaluation parameter. The measurements showed a right-skewed distribution, normalized after logarithmic transformation. Analysis of variance identified significant differences between means of each age group; test performance decreased after 40 years of age. Norms for each age group were presented.