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Episode 7: Unravelling the importance of the Straight Line Path

Unravelling the Importance of the ‘Straight Line Path’: Taming the Problem of Degrees of Freedom When Reaching for an Object

BBTA Tutors: Clare Fraser & Debbie Strang

The human body is an intricate machine with countless ‘degrees of freedom’ - an idea famously described by Nikolai Bernstein, a prominent neurophysiologist. The concept of degrees of freedom refers to the infinite ways, and choices, our limbs can move to achieve a goal. While this flexibility grants us a vast range of movements, it also presents a challenge for the brain to control and execute precise actions, such as reaching for a bottle of water in front of us. So, how does the brain manage this complexity?

In modern neuroscience, researchers have uncovered fascinating insights into how the brain navigates this problem. One crucial concept in achieving accurate reaching movements is the notion of the "straight line path."

Imagine reaching for the bottle of water on your desk - your brain calculates the most efficient and direct path from your starting position to the target. By prioritizing this optimal trajectory, the brain streamlines the movement and reduces the degrees of freedom, from all the multiple joints, which need to be controlled.

The "straight line path" is not just about moving in a straight line through space, however. It also involves taking into account various factors, such as the bottle's position, the starting position of your hand, and the angle of your arm, to optimize the movement. Think about how these influences are often critical in your analysis of your patient’s movement when you are working to rehabilitate their reaching function in a treatment session!

In addition, the ‘straight line path’ calculation also identifies what the task with the object is, following on from having picked it up. If you are picking up something that needs to be in a particular position to use it (such as pouring a drink into a glass, that happens to be resting upside down on a draining board) then you will most likely adapt your trajectory and style of grasp to make the following function most efficient and smooth (turning the glass over to allow you to pour your drink into it).

These calculations happen quickly and subconsciously, thanks to the brain's marvellous computational abilities.

On our recent Advanced Bobath Course, at Walkergate Park Hospital in Newcastle, we analysed the task of reaching for an object, and what interfering factors may be reducing the course participant’s efficiency in creating a straight-line path in this functional task, so that the process could be successfully applied to their patient analysis.

Furthermore, we know that the brain leverages proprioceptive feedback to refine the movement during the reach. Proprioception is the sense of the body's position and movement, and it plays a vital role in motor control. As your arm extends, proprioceptive signals continuously inform the brain about the arm's position and the distance remaining to the target. This feedback allows for real-time adjustments, ensuring that the movement stays on course and achieves the goal accurately.

Motor learning also comes into play, enabling the brain to fine-tune reaching movements through practice and experience. With repetition, the brain refines the motor commands needed for a precise and efficient reach, reducing the ‘problem’ of the degrees of freedom even further.

In conclusion, the brain is a masterful problem solver, deftly managing the challenge of ‘degrees of freedom’ when we reach for a bottle of water or perform any other movement. The concept of the "straight line path" is key to simplifying the complexity of movement control, allowing the brain to calculate optimal trajectories. Proprioceptive feedback and motor learning contribute to the brain's ability to achieve precise and accurate movements.

Are you keen to learn more neurophysiology science to provide the theoretical rationale for your treatment sessions with your patients? Do you want to know more about Human Movement Analysis and performance so you can develop your patient’s treatment programmes and practice tasks effectively?


If yes, then why not join one of our Bobath Courses and meet like minded therapists who are doing just that; www.bbta.org.uk.


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