Schoolboy, 12, has carried his disabled best friend to class every day for SIX years come rain or shine

They say anything is possible when you have a good friend to support you through tough times. 

A disabled boy in China has been able to go to class for six years without a problem thanks to his classmate and best friend who piggybacks him every day.

Xu Bingyang, 12, carries Zhang Ze to school come rain or shine. The kind-hearted boy also helps his friend to fetch lunch and move between classrooms to attend different lessons. 

The beautiful friendship between the two children from Meishan city in south-western China's Sichuan Province was reported earlier this month by Chinese news outlets, including Sichuan Online and Xinhua.

Xu, who is much taller and stronger than Zhang, told reporters that it was his pleasure to be his friend's 'walking stick'. 

He added that it wasn't difficult to lift Zhang.

'I weigh more than 40kg (88 pounds) and Zhang Ze only weighs about 25kg (55 pounds), so it's okay for me to carry him,' Xu said. 

On the other hand, Zhang said he couldn't thank Xu enough for his benevolence. 

'Xu Bingyang is my best friend. Every day, he studies with me, chats with me and plays with me. [I] thank him to look after me like this every day,' Zhang told Sichuan Online.

Xu and Zhang are sixth-grade pupils at the Hebazi Town Central Primary School in the county of Qingshen. 

Zhang was diagnosed with a rare muscle condition, sometimes known as the rag doll disease, at the age of four.

The incurable condition, officially called myasthenia gravis, caused Zhang to lose all control of his voluntary muscles in his legs. He cannot walk on his own.

Fortunately, Zhang has been able to go to school like other children after Xu offered to help him as soon as they met in the first grade. 

WHAT IS MYASTHENIA GRAVIS? 

Myasthenia gravis is a rare long-term condition that causes certain muscles to become weak.

It mainly affects muscles that are controlled voluntarily –often those controlling eye and eyelid movement, facial expression, chewing, swallowing and talking.

Sometimes, the muscles that control breathing, neck and limb movements are also affected.

The muscle weakness associated with myasthenia gravis is usually worse during physical activity and improves with rest.

It is an autoimmune condition that affects the nerves and muscles. 

Autoimmune conditions are caused by the body's immune system mistakenly attacking healthy tissue.

In myasthenia gravis, the immune system produces antibodies (proteins) that block or damage muscle receptor cells.

This prevents messages being passed from the nerve endings to the muscles, which results in the muscles not contracting (tightening) and becoming weak.

It is not fully understood why some people's immune systems produce antibodies that attack the muscle receptor cells.

Speaking to Chengdu Economic Channel, Xu considered it his responsibility to help those in need. 

He said: 'I am bigger than him. I thought if I didn't help him, nobody else would.'

The journey for the pair hasn't been easy, however. 

For example, it would usually take the two boys three minutes to move from the classroom to the toilet, which are about 70 metres (230 feet) apart. 

To cover the short distance, Xu would gently hold Zhang by the hand or lift him up from the side as they slowly move forwards together. 

Whenever there are stairs, Xu would carry Zhang on his back. 

Xu also assists Zhang to refill his water bottle, hand in his homework and go to the bathroom.

Helping out friends day after day takes dedication, patience and perseverance.  

For about three years, Zhang was helped by Xu and another boy.

But the other pupil pulled out during the third grade because he said he didn't have spare time for himself to play or study, according to one teacher. 

'For so many years, [Xu] has continued doing good deeds and never complained in front of the teachers and classmates,' the teacher told Sichuan Online, adding that Xu is hardworking, down-to-earth and very mature. 

And apparently, not even Xu's mother knew about her son's selfless behaviour at the beginning. 

She said her shy son had never talked about his action in the family and she only found out about it from the other pupils. 

Talking about future, Xu said his biggest wish was to carry on helping others around him and volunteering for the society when he grows up.