The origin of these strain related

After the day of arrival, the rats were handled for three days.
2.2. Experimental procedure
The experiment, which started after the last day of handling, lasted for 25 days and consisted of an initial screening phase and the subsequent exercise experiment, the latter being designed as a two-factor repeated measure. Here, experimental rats got access to a running wheel in order to perform exercise, whereas sedentary rats got access to a locked wheel hydrogen bond could not be turned but entered.