A growing number of youngsters, especially university students, are suffering "trigger finger" and other muscle-related problems as the time they spend on smartphones increases.

At risk are those who use phones for prolonged periods, bending their necks and elbows and tapping fingers on screens to text long messages. This can result in fingers, wrists, shoulders and even necks becoming "locked" in one position, with associated pain.

"We've found that the ages of our patients are getting lower, since [students] are spending more hours on smartphones and computers," Chutiphon Thammachari, a physiotherapist at Mahidol University's Faculty of Physical Therapy, said on Monday.

In a growing trend over the past two years, more young patients -- mostly students aged between 20 and 22 -- are seeking treatments for muscle and tendon inflammation at the university's Physical Therapy Centre.

In the past, the majority of patients were office workers in their 40s, Ms Chutiphon said.

Trigger finger is a disorder of the tendons with stiffness and a sensation of locking when a finger is straightened, she said.

Meanwhile, "texting thumb" is caused by inflammation of tendons controlling the thumb.

Frequent and prolonged use also puts phone users at risk of painful "tennis elbow", when tendons are overloaded by the need to hold the joint in a bent position.

The same problem can afflict tendons in the shoulder and neck.