5 Legs Dog My Dogs Legs Shake After He Has Been Running In The Garden For 5 -10 Mins?

My dogs legs shake after he has been running in the garden for 5 -10 mins? - 5 legs dog

we had our last dog in January, well above its weight. has lost half the weight. but if you play in the garden and runs for about 5-15 minutes walk to grab begin to tremble. What do you think it might?