The later levels take concentration, fine control of your entire body, and a clear head.

It took real physical effort, and more concentration than she had ever put into anything in her life.

It took all his concentration to hold on to the Dream.

It took little concentration to keep his thought stream in the same level as father's.

It is like a dream, where running takes complete concentration.

Whatever they had done to get her into this body took enormous power and concentration.

It no longer took all her concentration just to stay in the saddle.

It took all her concentration just to stay at forty miles per hour.

It took all his concentration to come up with a reply.

Although it took total concentration, she was managing quite well.