Characteristic patterns of gait in the healthy old.

If the influences of aging processes on gait are to be understood, gerontologists must become better versed in experimental methodology appropriate to locomotion research. They must also begin to conduct experiments that move beyond mere description. Systematic research efforts that are interdisciplinary in nature and that incorporate several types of gait analyses will be needed to discover the causes of adaptations and impairments of gait in the aged. Certainly, this will not be easy to accomplish; however, we hope that the work reported here demonstrates this approach is possible and worthwhile.

Effects of age and physical activity status on the speed-aerobic demand relationship of walking.

Older adults tend to show lower preferred walking speeds and higher aerobic demands per distance walked than young adults. It has been suggested that a more sedentary life-style contributes to diminished musculoskeletal functioning, which in turn contributes to poorer economy of motion in the aged and sedentary adults. The purpose of this study was to quantify the speed-aerobic demand relationship during walking for old (greater than 65 yr of age) and young adults and to determine whether physical activity status affects this relationship. Aerobic demands for 30 young and 30 old individuals representing sedentary and physically active groups were measured as the subjects performed treadmill walking at seven speeds ranging from 0.67 to 2.01 m/s. All four age/physical activity groups displayed U-shaped speed-aerobic demand curves with minimum gross oxygen consumption per unit distance walked (ml.kg-1.km-1) at 1.34 m/s. A statistically significant age effect on walking aerobic demand was observed, with old subjects showing an 8% higher mean aerobic demand than the young subjects. This age-related effect was not associated with shifts in the speed at which aerobic demand was minimized or with the preferred walking speed of older individuals falling on a less economical portion of the speed-aerobic demand curve. Rather, it was speculated that declines in force-generating capacity of muscle in the aged may require recruitment of additional motor units and perhaps an additional proportion of less economical fast twitch muscle fibers to generate necessary forces. Physical activity status had no significant effect on walking aerobic demand.(ABSTRACT TRUNCATED AT 250 WORDS)

Manufacturing repetition effects- a reply to gentile and nemetz (1978).

Under the guise of repetition effects, Gentile and Nemetz (1978) vociferously attack the explanatory power and utility of short-term motor memory research. Such a criticism is based on the belief that treatment effects are confounded with learning effects in experiments which require subjects to constantly reproduce invariant target positions. In this note a systematic critique of Gentile and Nemetz's logic and experimental evidence illuminates the questionable status of their position. It is argued that the Gentile and Nemetz findings actually oppose the existence of the procedural artifact they would have us consider. On the basis of methodological and logical arguments presented, it is concluded that a properly designed experiment need not be confounded by repetition effects. Finally, guidelines on both the manufacture and avoidance of repetition effects are suggested.

Planning and preparing expected and unexpected movements: reexamining the relationships of arm, direction, and extent of movement.

Using variations of the movement precue method, this study sought to define the operational characteristics of motoric decisions that govern the planning and preparation of arm, direction, and extent of movement. Experiment 1 examined how these parameters are programmed when the precue method does not confound motoric and nonmotoric decision processes. Experiment 2 examined how an already planned and prepared response is modified (reprogrammed) when an unexpected response must be executed in its place. The collective results of both experiments demonstrated that (a) these parameters were planned and prepared in a specific order; knowledge about direction was necessary for the programming of arm or extent; (b) arm and extent were reprogrammed independently from direction but changes in direction caused all parameters to be reprogrammed, and (c) programming and reprogramming processes operated in a parallel mode when two or more parameters were involved. The results also showed that these parameters were organized within a hierarchical structure. The present findings were discussed in relation to those reported in previous precue studies and existing models of response programming.

Preprogramming, programming and reprogramming of aimed hand movements as a function of age.

The present experiments were conducted to investigate the relationship between age and the response programming operations underlying the execution of a ballistic motor act. In an initial experiment, two separate age groups of female subjects (mean ages of 21.9 and 69.1 years) performed aimed-movements of the right hand and arm in one of two movement directions (left or right), under preprogramming, programming, and reprogramming conditions. These operations were examined by providing advance information about the direction of an impending movement and manipulating the degree of correspondence between the advance information and a subsequent reaction signal. The results indicated that subjects in the older age group reacted and moved more slowly than subjects in the younger age group, however, there was no interaction between age and the three response programming conditions. Such findings indicated that the basic operational characteristics of these processes remain unaffected with advancing chronological age. Also, irrespective of age and response programming condition, responses to the right were initiated faster than responses to the left. This difference was especially accentuated for reprogramming. A second experiment, using a new stimulus-response mapping, replicated the left-right difference in initiation time; this difference was reversed when the left hand was used to execute the designated movement, indicating that this finding is indeed a response programming phenomenon. Further discussion focused on the possible operations underlying reprogramming.

An empirical note on attaining a spatial target after distorting the initial conditions of movement via muscle vibration.

Can one's limb be accurately positioned to a spatial location without a veridical estimate of the initial conditions of movement? The experiment reported here examined this question by distorting perception of a limb's starting position via muscle vibration. Subjects executed rapid flexion movements under no-vibration, contralateral arm vibration, and ipsilateral arm vibration conditions. Vibration was applied to the biceps for 10 sec prior to the start of a reproduction movement. The results showed that vibration on the ipsilateral arm caused a significant increase in reproduction error, relative to the no-vibration and contralateral-vibration conditions. This finding provides additional evidence that accurate knowledge about the initial conditions of movement is a necessary component in positioning a limb.