I would surmise that "conditioned' refers to "practiced".
The emergency stop button might be ideally placed for the machine, but if the operator had not practiced (conditioned him/herself) to use it, the response time might be unacceptably long.
Also, the task could require strength and the party was "not conditioned" to accomplish this task;
See:
http://sydney.edu.au/whs/guidelines/ergonomics/ERGO1.shtml
- Fitness for work tasks should be gradually developed. To achieve any repetitive or forceful task requires the person to gradually train their muscles and joints for this specific task. It doesnβt matter if the activity is a game of squash or data entry. If the person is not "conditioned" to the task, pain is a common response.
(This is no much more than a guess and could be 100% wrong, but it makes some sense to me.)