Stop jumping on the trampoline. Then take a few hops on a hard floor or hard cement surface to see if the back still hurts? Make sure there is someone beside you in case you fall.
If there is no back pain after jumping or hopping on a hard surface, then take several hot water showers.
If however, after hopping on a hard surface, the knees and legs give way and one falls, then the leg muscles and the lower back muscles are twisted. In this case, one should not be able to walk for more than a minute or two before the legs and lower back start hurting again. In this case, take hot water showers and do leg stretching exercises. One would also feel some pain when stretching the leg. However, leg stretching exercises are very important.