A comparison of manual guidance and knowledge of results in the learning of a weight-bearing skill.

BACKGROUND AND PURPOSE: Patients with certain neurological or orthopedic conditions often present with asymmetrical weight-bearing in stance. In the treatment of such patients, physical therapists often use manual guidance to promote symmetrical weight-bearing. Research investigating the efficacy of manual guidance to effect a change in weight-bearing status however, is lacking. As a first step in assessing the utility of such guidance, the present study compared the effect of providing two frequencies of manual guidance and of knowledge of results (KR) in the learning of a weight-bearing skill in healthy subjects. SUBJECTS AND METHODS: Forty healthy subjects (20 males and 20 females) with a mean age of 21.8 years (SD = 4.9 years) were randomly assigned to one of four groups differentiated on the basis of the type and frequency of information provided for learning. Subjects were required to learn to distribute their weight on their feet at a 70:30 ratio. Following a pretest, one group of subjects was positioned by experimenter-provided manual guidance at the hips until 70% of their weight was on one foot, as determined by a bathroom scale. This guidance was provided on every trial for 10 blocks of 12 trials (GD100%). A second group was provided with guidance on every third trial (GD33%), with the other two trials being performed without any assistance. A third group was verbally provided with KR regarding the percentage of body weight on the test foot after every trial (KR100%) while the final group was given KR after every third trial (KR33%). Following acquisition, retention tests were performed 10 minutes, one day, and one week later during which no feedback or guidance was given. RESULTS: No difference between groups was found at the pretest, but an analysis of variance performed on the accuracy of achieving the 70% goal in retention revealed main effects for technique and frequency. These effects were overshadowed by a significant interaction of these variables with retention test. Analysis of this interaction revealed that the most accurate performance was exhibited by the KR33% group while the GD100% group consistently exhibited the poorest learning. The GD33% and KR100% groups showed a decrease in performance accuracy with time following practice. DISCUSSION AND CONCLUSION: These results indicate that infrequent KR was the most effective technique in learning to modify weight-bearing status and that frequent manual guidance during practice is ineffective for learning this task. The next step is to determine whether these findings hold in subjects with various orthopedic and neurological conditions.

Interactions of 1-methylimidazole with UO2(CH3CO2)2 and UO2(NO3)2: structural, spectroscopic, and theoretical evidence for imidazole binding to the uranyl ion.

The first definitive high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to UO2(Ac)2 (Ac = CH3CO2) is reported. The crystal structure evidence is confirmed by IR, Raman, and UV-vis spectroscopic data. Direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center is confirmed. Structural analysis at the DFT (B3LYP) level of theory showed a conformational difference of the Meimid ligand in the free gas-phase complex versus the solid state due to small energetic differences and crystal packing effects. Energetic analysis at the MP2 level in the gas phase supported stronger Meimid binding over H2O binding to both UO2(Ac)2 and UO2(NO3)2. In addition, self-consistent reaction field COSMO calculations were used to assess the aqueous phase energetics of combination and displacement reactions involving H2O and Meimid ligands to UO2R2 (R = Ac, NO3). For both UO2(NO3)2 and UO2(Ac)2, the displacement of H2O by Meimid was predicted to be energetically favorable, consistent with experimental results that suggest Meimid may bind uranyl at physiological pH. Also, log(Knitrate/KAc) calculations supported experimental evidence that the binding stoichiometry of the Meimid ligand is dependent upon the nature of the reactant uranyl complex. These results clearly demonstrate that imidazole binds to uranyl and suggest that binding of histidine residues to uranyl could occur under normal biological conditions.