In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The exercise - isoproterenol ( E - 1 ) and exercise control ( EC ) groups exercised daily for thirty days on a treadmill at 1 mph , 2 % grade while animals of the sedentary - isoproterenol ( S - I ) group remained sedentary .
### Output Text:
The exercise - <span class="chemical">isoproterenol</span> ( E - 1 ) and exercise control ( EC ) groups exercised daily for thirty days on a treadmill at 1 mph , 2 % grade while animals of the sedentary - <span class="chemical">isoproterenol</span> ( S - I ) group remained sedentary . 