My ds could run 6km now can't even run 1km

[user1496341427]

Hi all
I would really appreciate it if you could help me. Three weeks ago my ds who is 13 was going on 6-8km runs by himself. In the last week though he has tried running twice and can't manage more than a Km without his legs almost buckling on him. He says it becomes too painful to run. I cannot think what has caused it, he has had no injuries or illness. If you have any ideas on what could be causing this please say
thank you

Is he having a big growth spurt? If so they can make the legs (knees particularly) very painful.

Does it hurt the rest of the time?

He needs to see a doctor, clearly. I hope everything's OK.

Shin splints, viral inflammation in the joints?

Plantar fascitis? Take him to the GP.

teenagers do this, ime. Their body parts fall apart with no notice & then work fine at some other point when they really want them to work fine. I'd need more evidence to be remotely worried.

Doctors. How is his breathing?

I have many questions for you and your son:
(1) What kind of pain does he have? Muscle pain, such as lactic acid or more bone/ heavy leg pain? Where in the leg? knee, ankle, hamstring ? The shin?
(2) What kind of shoes is he using. Very old and loved but cushioning is completely gone? Shoes should be replace regularly. Did he use the same shoes both on the 8k and last attempt? Running is a high stress sport on many of your bones, especially the tibia. It is equivalent to 4 times the body weight on the bones. You need good shoes.
(3) At what time of the day is he running and is it on an empty/full stomach?
(4) Does he or did he have asthma as a child? Does he have a runny nose, is he sniffing, or blowing his nose often? Muscle in the legs are the bigger of the body and use most oxygen. If he has problem breathing even without realising it, not enough oxygen gets to his legs. It's hay fever season, if he had asthma when he was younger, it should be worth having to do the peak flow test.
(5) Does he do a warm up or stretching (you should NEVER stretch before a workout but definitely warm up)
(6) Did he change his running path. Is it uphill or uneven ground? Had surface or grass?
(7) Is he a regular runner or was that 6-8 km race he did 3 weeks ago a one off?
(8) How is he sleeping now? Any chance he slept less , sneaky screen time instead of sleeping at night?
(9) Did he start too fast?

Anything related to the breathing even a runny nose with a history - even distant - of asthma would require a visit to the GP. Asthma is no joke.
Otherwise, have him rest, increase some muscle strength with squads and lunges and then start again with a less ambitious distance. Good shoes, no stretching , ideally no food or drinks 30 min before. A nice warm up, high knees, small jumps, lateral soft running, hops, ..

I had to stop running after I was diagnosed with Osgood Schlatters disease in my knees, OP.

Forgive the hairy knees but check for a bump like this below his knee, not sure if you can make it out from my terrible picture but if it's flaring up it may well be bigger and swollen. Painkillers and a knee brace are very helpful, encourage him to visit the GP and I hope it's nothing serious, probably just a growth spurt.