The relationship between task difficulty and motor performance complexity

Difficult tasks are commonly equated with complex tasks across many behaviors. Motor task difficulty is traditionally defined via Fitts' law, using evaluation criteria based on spatial movement constraints. Complexity of data is typically evaluated using non-linear computational approaches. In this project, we investigate the potential to evaluate task difficulty via behavioral (motor performance) complexity in a Fitts-type task. Use of non-linear approaches allows for inclusion of many features of motor actions that are not currently included in the Fitts-type paradigm. Our results indicate that tasks defined as more difficult (using Fitts movement IDs) are not associated with complex motor behaviors; rather, an inverse relationship exists between these two concepts. Use of non-linear techniques allowed for the detection of behavioral differences in motor performance over the entire action trajectory in the presence of action errors and among neutrally co-constrained effectors not detected using traditional Fitts'-type analyses utilizing movement time measures. Our findings indicate that task difficulty may potentially be inferred using non-linear measures, particularly in ecological situations that do not obey the Fitts-type testing paradigm. While we are optimistic regarding these initial findings, further work is needed to assess the full potential of the approach.

Pilates instruction affects stability and muscle recruitment during the long stretch exercise

PURPOSE

To examine pelvic stability with and without instruction regarding the voluntary recruitment of the 'powerhouse' muscles during a long stretch exercise on the Pilates Reformer.

SCOPE

Evaluation of the muscle activity and pelvic stability during a Pilates exercise of 12 physically active volunteers. Volunteers performed five repetitions of the long stretch in sets of two, one with and one without instruction regarding the voluntary recruitment of the powerhouse muscles. Electromyography of the external oblique (EO), multifidus (MU), gluteus maximus (GM) and adductor longus (AL) muscles and pelvic angle stability were recorded.

CONCLUSION

When asked to perform the exercise with instruction regarding the voluntary recruitment of the powerhouse muscles, all muscles were more activated, with the exception of the EO. In the voluntary recruitment situation, lumbopelvic stability, as measured by the coefficient of variation of the pelvic angle, was higher than in instances without instruction. Lumbopelvic stability undergoes changes with and without instruction regarding the voluntary recruitment of the powerhouse muscles when the long stretch exercise is performed on a Reformer.

Wearing a Wetsuit Alters Upper Extremity Motion during Simulated Surfboard Paddling

Surfers often wear wetsuits while paddling in the ocean. This neoprene covering may be beneficial to upper extremity movement by helping to improve proprioceptive acuity, or it may be detrimental by providing increased resistance. The purpose of this study was to evaluate the effects of wearing a wetsuit on muscle activation, upper extremity motion, heart rate, and oxygen consumption during simulated surfboard paddling in the laboratory. Twelve male, recreational surfers performed two paddling trials at a constant workload on a swim bench ergometer both with and without a wetsuit. Kinematic data and EMG were acquired from the right arm via motion capture, and oxygen consumption and heart rate were recorded with a metabolic cart and heart rate monitor. Wearing a wetsuit had no significant effect on oxygen consumption or heart rate. A significant increase in EMG activation was observed for the middle deltoid but not for any of the other shoulder muscle evaluated. Finally, approximate entropy and estimates of the maximum Lyapunov exponent increased significantly for vertical trajectory of the right wrist (i.e. stroke height) when a wetsuit was worn. These results suggest that a 2mm wetsuit has little effect on the energy cost of paddling at lower workloads but does affect arm motion. These changes may be the result of enhanced proprioceptive acuity due to mechanical compression from the wetsuit.