Random walk: Random number generation during backward and forward walking- the role of aging.

Deficits in executive function, visuospatial abilities, and cognitive embodiment may impair gait performance. This study aimed to investigate the effect of age on random number generation (RNG) performance during forward and backward locomotion to assess cognitive flexibility and cognitive embodiment during walking. Another aim was to examine the effect of age on the associations of RNG performance during walking with stride time variability (STV), the percentage of double support (DS%), and visuospatial abilities as measured by a spatial orientation test (SOT). Twenty old (age 68.8 ± 5.3, 65% female) and 20 young (age 25.2 ± 2.2, 45% female) adults generated random numbers during backward walking (BW) and forward walking (FW) over-ground and over a treadmill with an internal focus of attention and visual-attentive distraction; six walking conditions in total. To assess cognitive flexibility, sample entropy was calculated for each RNG sequence. The average of the first 5 numbers in each RNG task was calculated to assess the relationship between small/large numbers and movement direction. STV and DS% were recorded using inertial measurement units, and spatial orientation was measured using a computerized test. The older subjects had less flexibility in generating random numbers in three of the six walking conditions. A negative correlation between RNG flexibility and STV was found in older adults during treadmill BW with visual-attentive distraction and forward over-ground walking, whereas no correlations were demonstrated in the young group. The spatial orientation score (a higher value means a worse outcome) correlated positively with RNG flexibility in the older group under all walking conditions, suggesting that older adults with better visuospatial orientation have lower cognitive flexibility, and vice versa. There was no correlation between small/large numbers and direction of motion in either group. The correlation between RNG flexibility and STV may indicate similar executive control of verbal and gait rhythmicity in old adults. Conversely, our results suggest that cognitive flexibility and visuospatial ability may decline differently.

Optimizing neuromuscular electrical stimulation for hand opening.

AIM: To investigate the effect of introducing an interphase interval to a biphasic pulse on force production and muscle fatigue, during stimulation of the wrist and finger extensors and to determine whether the IPI effect on force is dependent on electrode position. METHODS: Electrically-induced contraction forces of the wrist and finger extensors were measured in 15 healthy subjects undergoing stimulation. These forces were assessed with interphase interval settings at 0, 100, and 200µs, with both electrodes located just distal to common extensor origin (proximal placement) or with the distal electrode placed over the extensor and abductor policies longus muscles (distal placement). The degree of discomfort related to stimulation sensation was evaluated using a numeric rating scale. Muscle fatigue was measured during proximal placement. RESULTS: Under both electrode locations, introduction of 100 or 200 µs interphase interval enhanced force production; yet, only the 100µs interphase interval increased force without increasing discomfort. Additionally, stimulation sensation was more comfortable with proximal placement. Introducing interphase interval significantly increased the muscle force output during a repetitive stimulation fatigue protocol. CONCLUSIONS: When using neuromuscular electrical stimulation to activate the wrist and finger extensors, clinicians should consider locating both stimulating electrodes proximally over the extensor surface of the forearm and apply a 100 µs interphase interval to a biphasic pulse. Future research that should establish these findings in individuals with various pathologies, especially in patients with residual hand spasticity.

Effects of amplitude and phase-duration modification on electrically induced contraction force and discomfort.

BACKGROUND: Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation. However, the optimal combination of phase-duration and amplitude for enhancing motor output is not yet resolved. OBJECTIVE: To test the effects of increasing phase-duration and amplitude on isometric knee extension force and discomfort, while controlling the effects of electrode-skin resistance and body mass index (BMI). METHODS: Twenty-one healthy volunteers participated in the study. Stimulation was set at 250 µsec phase-duration and 45 Hz to evoke 10% of maximal voluntary isometric contraction of the quadriceps. Electrode-skin resistance was measured. Then, electrically induced contraction (EIC) forces and discomfort level were measured under four conditions: Moderate (25%) or substantial increase (50%) from baseline amplitude with constant phase-duration and moderate (25%) or substantial increase (50%) in phase-duration with amplitude constant. RESULTS: Compared with baseline, EIC force was significantly higher in all intensification conditions, while discomfort was significantly greater in all conditions except for moderate increase in phase-duration (p= 0.44). Amplitude intensification produced significantly higher force and greater discomfort than phase-duration. Electrode-skin resistance and BMI were not significant covariates. CONCLUSIONS: Greater force is elicited by increasing amplitude than by similar increase in phase-duration; however, the associated discomfort is also higher. Clinicians may use phase-duration while conditioning for NMES.