Unimanual and Bimanual Weight Perception of Virtual Objects with a new Multi-finger Haptic Interface

Accurate weight perception is important particularly in tasks where the user has to apply vertical forces to ensure safe landing of a fragile object or precise penetration of a surface with a probe. Moreover, depending on physical properties of objects such as weight and size we may switch between unimanual and bimanual manipulation during a task. Research has shown that bimanual manipulation of real objects results in a misperception of their weight: they tend to feel lighter than similarly heavy objects which are handled with one hand only [8]. Effective simulation of bimanual manipulation with desktop haptic interfaces should be able to replicate this effect of bimanual manipulation on weight perception. Here, we present the MasterFinger-2, a new multi-finger haptic interface allowing bimanual manipulation of virtual objects with precision grip and we conduct weight discrimination experiments to evaluate its capacity to simulate unimanual and bimanual weight. We found that the bimanual ‘lighter’ bias is also observed with the MasterFinger-2 but the sensitivity to changes of virtual weights deteriorated

The Ceremony

In the beginning, it is easier (and often smarter) to play it safe. It’s better to say no, to walk away, to revert to what you know and what is comfortable. But that cannot be your whole experience. There are times where you have to say yes. Be smart about it. Think it over. Weigh your options. Use what you know

Short-Interval Cortical Inhibition and Intracortical Facilitation during Submaximal Voluntary Contractions Changes with Fatigue

This study determined whether short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) change during a sustained submaximal isometric contraction. On 2 days, 12 participants (6 men, 6 women) performed brief (7-s) elbow flexor contractions before and after a 10-min fatiguing contraction; all contractions were performed at the level of integrated electromyographic activity (EMG) which produced 25 % maximal unfatigued torque. During the brief 7-s and 10-min submaximal contractions, single (test) and paired (conditioning–test) transcranial magnetic stimuli were applied over the motor cortex (5 s apart) to elicit motor-evoked potentials (MEPs) in biceps brachii. SICI and ICF were elicited on separate days, with a conditioning–test interstimulus interval of 2.5 and 15 ms, respectively. On both days, integrated EMG remained constant while torque fell during the sustained contraction by ~51.5 % from control contractions, perceived effort increased threefold, and MVC declined by 21–22 %. For SICI, the conditioned MEP during control contractions (74.1 ± 2.5 % of unconditioned MEP) increased (less inhibition) during the sustained contraction (last 2.5 min: 86.0 ± 5.1 %; P \u3c 0.05). It remained elevated in recovery contractions at 2 min (82.0 ± 3.8 %; P \u3c 0.05) and returned toward control at 7-min recovery (76.3 ± 3.2 %). ICF during control contractions (conditioned MEP 129.7 ± 4.8 % of unconditioned MEP) decreased (less facilitation) during the sustained contraction (last 2.5 min: 107.6 ± 6.8 %; P \u3c 0.05) and recovered to 122.8 ± 4.3 % during contractions after 2 min of recovery. Both intracortical inhibitory and facilitatory circuits become less excitable with fatigue when assessed during voluntary activity, but their different time courses of recovery suggest different mechanisms for the fatigue-related changes of SICI and ICF

Muscle fatigue degrades force sense at the ankle joint

To investigate the effects of muscle fatigue on force sense at the ankle joint, 10 young healthy adults were asked to perform an isometric contra-lateral force ankle-matching task in two experimental conditions of: (1) no-fatigue and (2) fatigue of the plantar-flexor muscles. Measures of the overall accuracy and the variability of the force matching performances were determined using the absolute error and the variable error, respectively. Results showed less accurate and less consistent force matching performances in the fatigue than no fatigue condition, as indicated by decreased absolute and variable errors, respectively. The present findings evidence that muscle fatigue degrades force sense at the ankle joint

Signing up to motor signatures: a unique link to action

No abstract availabl

Effect of Level and Downhill Running on Breathing Efficiency

Ventilatory equivalents for oxygen and carbon dioxide are physiological measures of breathing efficiency, and are known to be affected by the intensity and mode of exercise. We examined the effect of level running (gradient 0%) and muscle-damaging downhill running (?12%), matched for oxygen uptake, on the ventilatory equivalents for oxygen () and carbon dioxide (). Nine men (27 ± 9 years, 179 ± 7 cm, 75 ± 12 kg, : 52.0 ± 7.7 mL·kg?1·min?1) completed two 40-min running bouts (5 × 8-min with 2-min inter-bout rest), one level and one downhill. Running intensity was matched at 60% of maximal metabolic equivalent. Maximal isometric force of m.quadriceps femoris was measured before and after the running bouts. Data was analyzed with 2-way ANOVA or paired samples t-tests. Running speed (downhill: 13.5 ± 3.2, level: 9.6 ± 2.2 km·h?1) and isometric force deficits (downhill: 17.2 ± 7.6%, level: 2.0 ± 6.9%) were higher for downhill running. Running bouts for level and downhill gradients had , heart rates and respiratory exchange ratio values that were not different indicating matched intensity and metabolic demands. During downhill running, the , (downhill: 29.7 ± 3.3, level: 27.2 ± 1.6) and (downhill: 33.3 ± 2.7, level: 30.4 ± 1.9) were 7.1% and 8.3% higher (p < 0.05) than level running. In conclusion, breathing efficiency appears lower during downhill running (i.e., muscle-damaging exercise) compared to level running at a similar moderate intensity