Electrocortical Activity in Older Adults Is More Influenced by Cognitive Task Complexity Than Concurrent Walking

Human cognitive-motor performance largely depends on how brain resources are allocated during simultaneous tasks. Nonetheless, little is known regarding the age-related changes in electrocortical activity when dual-task during walking presents higher complexity levels. Thus, the aim of this study was to investigate whether there are distinct changes in walking performance and electrocortical activation between young and older adults performing simple and complex upper limb response time tasks. Physically active young (23 ± 3 years, n = 21) and older adults (69 ± 5 years, n = 19) were asked to respond as fast as possible to a single stimuli or a double stimuli appearing on a touch screen during standing and walking. Response time, step frequency, step frequency variability and electroencephalographic (EEG) N200 and P300 amplitudes and latencies from frontal central and parietal brain regions were recorded. The results demonstrated that older adults were 23% slower to respond to double stimuli, whereas younger adults were only 12% slower (p 0.05). More importantly, the P300 amplitude was significantly reduced for older adults when responding to double stimuli regardless of standing or walking tasks (p < 0.05), with no changes in younger participants. Therefore, physically active older adults can attenuate potential walking deficits experienced during dual-task walking in simple cognitive tasks. However, cognitive tasks involving decision making influence electrocortical activation due to reduced cognitive resources to cope with the task demands

Motor unit behavior during submaximal contractions following six weeks of either endurance or strength training

The study investigated changes in motor output and motor unit behavior following 6 weeks of either strength or endurance training programs commonly used in conditioning and rehabilitation. Twenty-eight sedentary healthy men (age, mean±SD, 26.1 ± 3.9 yrs) were randomly assigned to strength training (ST) (n = 9), endurance training (ET) (n = 10) or a control group (CT) (n = 8). Maximum voluntary contraction (MVC), time to task failure (isometric contraction at 30% MVC), and rate of force development (RFD) of the quadriceps, were measured before (week 0), during (week 3), and after a training program of 6 weeks. In each experimental session, surface and intramuscular EMG signals were recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during isometric knee extension at 10% and 30% MVC. After 6 weeks of training, MVC and RFD increased in the ST group (17.5±7.5 % and 33.3±15.9 %, respectively; P < 0.05) whereas time to task failure was prolonged in the ET group (29.7±13.4 %; P < 0.05). Despite surface EMG amplitude during 30% MVC contractions increased following both training programs, there were different changes in motor unit discharge rates between the training groups. After endurance training, the motor unit discharge rate at 30% MVC decreased from 11.3 ±1.3 pulses per second (pps) to 10.1 ± 1.1 pps (P < 0.05) in the vasti muscles, whereas after strength training it increased from 11.4 ± 1.2 pps to 12.7 ± 1.3 pps (P < 0.05). Finally, motor unit conduction velocity during the contractions at 30% MVC increased for both the ST and ET groups, but only after 6 weeks of training (P < 0.05). In conclusion, strength and endurance training programs elicit opposite adjustments in motor unit discharge rates but similar changes in muscle fiber conduction velocity.Fundação para a Ciência e a Tecnologia (FCT) of Portugal (Grant ID - SFRH / BD / 31796 / 2006). Danish Technical Research Counci

The effect of short-term endurance and strength training on motor unit conduction velocity

AIM: The aim of this study was to investigate the effect of strength and endurance training on the conduction velocity of vastus medialis obliquus and lateralis single motor units during voluntary sustained knee extensions. METHODS: Seventeen sedentary healthy men (age, mean ± SD, 26.3 ± 3.9 yr) were randomly assigned to one of 2 groups: strength training (ST, n= 8) or endurance training (ET, n= 9). Conventional endurance and strength training was performed three days per week, over a period of 6 weeks. Motor unit conduction velocity (MUCV), maximum voluntary force (MVC) and time-to-task failure at 30% MVC of the knee extensors were measured before and immediately following training. To assess MUCV, multi-channel surface and intramuscular EMG signals were concurrently recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during 60-s isometric knee extensions at 10% and 30% of MVC. RESULTS: After 6 weeks of training, MVC increased in the ST group (16.7 ± 7.4 %; P < 0.05) whereas time to task failure was prolonged in the ET group (33.3 ± 14.2 %; P < 0.05). Both training programs induced an increase in motor unit conduction velocity at both 10% and 30% MVC (P < 0.01). Furthermore after both training programs, the reduction in MUCV over time during the sustained contractions occurred at slower rates compared to baseline (P < 0.01). CONCLUSION: These results indicate that short-term endurance and strength training induce similar alterations of the electrophysiological membrane properties of the muscle fiber and in their changes during sustained contractionsGrant SFRH/BD/31796/2006 from Fundação para a Ciência e a Tecnologia (FCT) of Portuga

Effect of unaccustomed eccentric exercise on proprioception of the knee in weight and non-weight bearing tasks

The study investigates the effects of eccentric exercise of the quadriceps on proprioception of the knee in weight and non-weight bearing tasks. Proprioception of the exercised leg was assessed at 120 and 150 of knee extension in 15 healthy adults (age 25.0 ± 3.6 yrs) before, immediately after, and 24 h following eccentric exercise of the quadriceps. Three tests of proprioception were performed: 1. matching the position of the exercised leg (right leg) to the reference leg (left leg) in sitting (non-weight bearing matching task); 2. repositioning the exercised leg after active movement in sitting (non-weight bearing repositioning task); 3. repositioning the exercised leg after active movement in standing (weight bearing task). Maximum knee extension force was reduced by 77.0 ± 12.3 % immediately after the exercise, and by 82.7 ± 16.2% 24 h post exercise, with respect to baseline (P < 0.001). The absolute error in the non-weight bearing matching task at 120 of knee extension was greater immediately following eccentric exercise (12.3 ± 5.6, P < 0.001) and 24 h after exercise (8.1 ± 4.5, P < 0.05) compared to baseline (5.8 ± 2.7). Similarly, the absolute error in the non-weight bearing repositioning task at 120 was greater both immediately (5.9 ± 3.1 , P < 0.01) and 24 h post exercise (5.2 ± 3.0 , P < 0.05) compared to baseline (4.5 ± 2.6 ). Therefore, in both non-weight bearing tasks, the subjects matched the position of their leg after eccentric exercise by adopting a more extended knee position of the exercised limb. Furthermore, the subjects showed higher variability in their performance immediately post exercise (P < 0.05, compared to baseline) but not 24 h after. In contrast, eccentric exercise did not affect the repositioning errors in the weight bearing task. In conclusion, eccentric exercise of the quadriceps impairs proprioception of the knee both immediately after and 24 h post exercise, but only in non-weight bearing tasks

Immediate and delayed effects of eccentric exercise on proprioception of the knee

The study investigated the effects of eccentric exercise of the quadriceps on proprioception of the knee in open- and closed-chain tasks. Fifteen healthy adults (9 men; age 25.0 ± 3.6 yrs) participated. Proprioception of the right leg was assessed at 120º and 150º of knee extension before, immediately post, and 24h following eccentric exercise of the quadriceps with 3 tests: 1. matching the position of the right knee to the left knee; 2. repositioning of the right knee after active movement (open chain); 3. repositioning after active movement in standing. Immediately after the exercise and 24h post exercise, maximum knee extension force was reduced with respect to baseline (percent reduction, 77.0 ± 12.3 % and 82.7 ± 16.2%, respectively; P<0.001). For the position matching task at 120°, proprioceptive acuity of the right knee was reduced immediately following eccentric exercise (error, 12.3 ± 5.6˚) compared to baseline (5.8 ± 2.7˚) (P<0.001). 24h post exercise, the positioning error (8.1 ± 4.5˚) was lower than immediately after the exercise (P<0.05) but greater than in the baseline condition (P<0.05). Proprioception of knee extension was also impaired during the open-chain repositioning task, both immediately (error 120°, 5.9 ± 3.1˚, P<0.05) and 24h post exercise (5.2 ± 2.9˚, P<0.05). Conversely, the repositioning task in weight bearing was performed with similar error as in the baseline condition. In conclusion, eccentric exercise of the quadriceps impairs proprioception of the knee both immediately after and 24h after exercise, however this effect was not observed in the weight bearing task.Grant SFRH/BD/31796/2006 from Fundação para a Ciência e a Tecnologia (FCT) of Portuga

Analysis of Outcomes in Ischemic vs Nonischemic Cardiomyopathy in Patients With Atrial Fibrillation A Report From the GARFIELD-AF Registry

IMPORTANCE Congestive heart failure (CHF) is commonly associated with nonvalvular atrial fibrillation (AF), and their combination may affect treatment strategies and outcomes