The mid-line is an imaginary line down the centre of our body that divides us into left, and right.
Crossing the mid-line refers to the ability to reach across the middle of our body, with our arms and legs, allowing us to perform a task on the opposite side of our body. Difficulty crossing the mid-line of our body can also make visually tracking a moving object quite difficult. It links in with the right side of the brain controlling the left side of the body and vice-versa.
To keep it simple, it's a pretty critical developmental skill needed for success with a number of every day tasks from fine motor skills such as writing, to gross motor skills such as hitting a ball with a bat. Many individuals, with or without, a neurodevelopmental disability, developmental delay or learning difficulties, can have difficulty crossing their mid-line.
These difficulties can impact self-esteem & self-confidence, and lead to an avoidance of physical activity or structured exercise, impacting both physical and mental wellbeing.
From a gross-motor perspective, there are a number of obvious signs for difficulty crossing the mid-line:
Using the left hand for tasks on the left hand side of their body, and right hand for right side activities.
Avoiding crossing the mid-line by rotating through their trunk to the opposite side rather than reaching.
Have difficulty coordinating gross motor patterns such as jumping, skipping etc
The good news? It can be improved.
From an exercise therapy perspective, there are a number of ways we can develop an individual's ability to cross their mid-line during an exercise therapy session. Quite often we practice crossing the mid-line, or the underpinning skills unintentionally, however, there are some specific ways we can put greater emphasis on developing this skill. We need to develop the building blocks required for crossing the mid-line.
For example:
Bi-lateral coordination - using both the left and right side at the same time (eg - lift right knee and left arm). Before we can cross sides, the two sides need to work well together to do the same thing (think pushing, pulling, climbing, crawling etc).
Body awareness - develop our proprioceptive ability (the processing of information from our muscles and joints, telling us about our body's position in space
Core stability - strengthening the muscles of the trunk and back which allow stabilisation of the body to be able to move the arms and legs with control.
Planning and sequencing ability - developing the ability to process and execute instructions with multiple steps (e.g step through the agility ladder, jump onto the box, step down, catch the ball)
These are the skills underpinning our ability to cross our midline, allowing us to throw and catch, kick a ball, coordinate our way through various forms of structured, and unstructured, physical activity and exercise. If youth lack the confidence, or ability, they are more likely to avoid physical activity, and have preference for sedentary activities.
Building competence is vital for ongoing physical activity and structured exercise participation.