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Water is an essential nutrient for all persons; thus, maintaining a chronic state of optimal hydration is recognized to provide health benefits. Fluid balance is maintained via thirst, a feedback-controlled variable, regulated acutely by central and peripheral mechanisms. However, voluntary drinking is also a behavior influenced by numerous social and psychological cues. Therefore, whether “thirst-guided” drinking maintains optimal hydration status is a multifactorial issue. Thirst perception is typically assessed by subjective ratings using either categorical or visual analog scales; however, which instrument yields greater sensitivity to change in hydration status has not been examined. Ratings of thirst perception do not always yield predictable patterns of voluntary drinking following dehydration; therefore, perceived thirst and ad libitum drinking are not equivalent measures of human thirst. The recommendation “drink to thirst” is frequently given to healthy individuals during daily life. However, factors and conditions (e.g., age, disease) that influence thirst should be recognized and probed further.

The extent to which therapeutic, exercise or robotic devices can maximize gait function is a major unresolved issue in neurorehabilitation. Several factors may influence gait outcomes such as similarity of the task to overground walking, degree of coordination within and across limbs, and cycle-to-cycle variability in each device. Our objective was to compare lower extremity kinematics, coordination and variability during four locomotor tasks: overground walking, treadmill walking, elliptical training and stationary cycling in 10 non-disabled adults (6 male; mean age 22.7±2.9 yrs, range 20-29). All first performed four overground walking trials at self-selected speed with mean temporal-spatial data used to pace the other conditions. Joint positions, excursions, and the Gait Deviation Index (GDI) were compared across conditions to evaluate kinematic similarity. Time-series data were correlated within and across limbs to evaluate intralimb and interlimb coordination, respectively. Variability in cadence was quantified to assess how constrained the locomotor rhythm was compared to overground walking. Treadmill walking most closely resembled overground with GDI values nearly overlapping, reinforcing its appropriateness for gait training. Cycling showed the largest GDI difference from overground, with elliptical closer but still a significant distance from all three. Cycling showed greater hip reciprocation Cycling and elliptical showed stronger intralimb synergism at the hip and knee than the other two. Based on kinematics, results suggest that elliptical training may have greater transfer to overground walking than cycling and cycling may be more useful for enhancing reciprocal coordination. Further evaluation of these devices in neurological gait disorders is needed.

The most common functional motor goal of lower extremity rehabilitation is to improve walking ability. For reasons of feasibility, safety or intensity, devices are frequently used to facilitate or augment gait training. The objective of this study was to compare the muscle activity patterns of the rectus femoris and semitendinosus muscles during four conditions: overground walking, treadmill walking, stationary cycling, and elliptical training. Ten healthy adults (six male, four female; mean age 22.7±2.9 years, range 20-29) participated and surface electromyographic data were recorded. Linear envelope curves were generated and time normalized from 0 to 100% cycle. The mean plus three standard deviations from a static trial was used as the threshold for muscle activity. Repeated measures analysis of variance procedures were used to detect differences between conditions. Elliptical training demonstrated greater rectus femoris activity and greater rectus femoris/semitendinosus coactivation than all other conditions. Consistent with previous work, treadmill walking demonstrated greater rectus femoris activity than overground walking. Minimal differences in semitendinosus activation were observed between conditions, limited to lower peak activity during cycling compared to treadmill walking. These results provide normative values for rectus femoris and semitendinosus activation for different locomotor training methods and may assist in selecting the most appropriate training device for specific patients. Clinicians and researchers should also consider the kinematic and kinetic differences between tasks, which cannot necessarily be inferred from muscle activation patterns.