However, it's possible to get soft-tissue injuries through juggling. For example, repetitive strain injury or overload injuries because of a sudden increase in load or prolonged loading on the soft-tissues involved in juggling.
Generally, juggling comprises tossing and catching movements that are repeated many times during both practice and performance. These movements are made to overcome the masses of the juggler's anatomy and the juggled objects; and the force of gravity. In particular, the shoulder (rotator cuff) muscles are used heavily during juggling.
The four muscles of the rotator cuff work as a system to move the arm and stabilise the shoulder. Each muscle is connected to the scapula (shoulder blade) and the top of the humerus (upper arm bone). The muscles are:
- Subscapularis - this muscle is on the front aspect of the scapula
- Supraspinatus - this muscle is at the top of the scapula
- Infraspinatus - this muscle is on the rear aspect of the scapula
- Teres minor - this smaller muscle is also on the rear aspect of the scapula, and below the infraspinatus.
Here's an example of a rotator cuff injury. Over a period of time, my subscapularis developed trigger points that made the muscle fibres tighten. This resulted in pain in the shoulder area and a restriction to the range of juggling motion. One of the ways in which I treated my injury was to self-massage the subscapularis to release the trigger points. Currently, I strengthen (as well as lengthen) this muscle through specific exercises. I'm delighted to have found that there has been a significant improvement in the manner in which I juggle.
Plenty of information about strengthening and stretching the rotator cuff muscles can be found on the internet. It's insufficient to focus solely on the rotator cuff. Other muscles involved in juggling require maintenance too. For instance, the actions of juggling typically shorten the pectoral muscles (chest muscles) . Tight pectorals can make the upper back muscles work harder and can cause postural-related injuries. So it's important to stretch the pectoral muscles too.